# The extra mile.



## pvd (Jan 4, 2006)

Do you go the extra mile. Making sure you're right. Knowing the facts. Knowing why.

Me too.










https://www.pvdwiki.com/index.php?title=Head_Angle_Change_With_Suspension_Travel


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## G-reg (Jan 12, 2004)

SOH CAH TOA FTW!!! The High School Geometry is not really that impressive. How are you actually applying this? Seems like unless you are using a really short wheelbase or a long travel fork that frame/fork flex and wheel deflection would make a bigger difference.


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## pvd (Jan 4, 2006)

G-reg said:


> How are you actually applying this?


It's use for designing mountain bikes well.



G-reg said:


> The High School Geometry is not really that impressive.


That's funny, I asked two physics graduate students to solve this and neither of them could figure it out. I had to roll up my sleeves and figure it out when they couldn't

Could you show me the easy way of solving this?


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## G-reg (Jan 12, 2004)

pvd said:


> It's use for designing mountain bikes well.


How? You are determined to show how much you know, spill it. Previous sarcasm about the geometry aside, what does this really do for you? Are you really adjusting chain stay lengths, bb height, and head tube angles based on this? All the math is really just describing an arc, I'm not an engineer by any means, but what am I missing here. The complication I see is the varying rake/trail of a fork and the shortening of the wheel base due to a telescoping fork, but that is most likely canceled out by flex when you are really compressing a fork that much. So the question remains: how are you using this to adjust your frame geometry?


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## pvd (Jan 4, 2006)

It's used for predicting frame geometry at full extention and full compression so that the frame design doens't fail in climbing or decending situations. You can know if your pedals get too close to the ground in hard landings. It is critical for long travel forks and can optimize short travel forks.


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## chequamagon (Oct 4, 2006)

any arse can figure out how far pedals will be from the ground on full compression.

and head angle at full compression is useless knowledge. How much time is actually spent at full compression? probably less than 1% of ride time, and that is generous.


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## pvd (Jan 4, 2006)

chequamagon said:


> probably less than 1% of ride time


I'd say your estimate is high by several thousand percent. But here's the thing, I can ride my bike for hours with horiffic geometry going up a hill at slow speed, but it's that instant in a ride that the bike is pushed as hard as it can be that I really need it to not let me down.



chequamagon said:


> any arse can figure out how far pedals will be from the ground on full compression. and head angle at full compression is useless knowledge.


Really! Tell us more.


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## scottzg (Sep 27, 2006)

all that information would be a lot more useful if the bike had never been designed before and its geometry had to be pretty good on the first try. Fortunately, bikes have been around a long time and we have actual ride experience to rely on rather than just having to guess using math.

I'd rather buy a bike from someone reknowned for making good handling bikes and couldn't use a multiplication table than from a doofus with a math degree.


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## chequamagon (Oct 4, 2006)

give it up with your graphs and charts and formulas already. only german mags care about that crap. if you are steering when your fork is at full compression, you are gonna crash. And anyone can tell you that your head angle is gonna steepen through compression. Woohoo! Good discovery!

As far as pedal height. Measure them now. Subtract travel. Close fricken enough. If you need to be more exact than that, well you are just too much of a geek and not enough of a rider. I know my pedals are too low when they go bang. I know they are just right when they dont hit things.


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## pvd (Jan 4, 2006)

scottzg said:


> all that information would be a lot more useful if the bike had never been designed before and its geometry had to be pretty good on the first try. Fortunately, bikes have been around a long time and we have actual ride experience to rely on rather than just having to guess using math.


I build frames. I design the ones I build. Then I ride them. I know that I'm a far better rider than you. This 'math' stuff is what separates a bike from a very good bike.


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## dr.wierd (Aug 10, 2007)

pvd said:


> I build frames. I design the ones I build. Then I ride them. I know that I'm a far better rider than you. This 'math' stuff is what separates a bike from a very good bike.


I guess thats why PVD bikes are the most sought after bikes in the world and are considered the benchmark that all bikes are compared to......


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## NEPMTBA (Apr 7, 2007)

pvd said:


> I build frames. I design the ones I build. Then I ride them. I know that I'm a far better rider than you. This 'math' stuff is what separates a bike from a very good bike.


pvd:

I don't want to be in on a bash fest. Just asking questions.

May I ask did you ever consider building something like Ribi did for Roger De Coster on his factory Suzuki. The leading or trailing link front end has just disappeared, Amp and Girvin had great forks. You show you are very meticulous about dimensions and I feel you could push the envelope on this subject.
Telescopic forks have many drawbacks. Stiction, Flex. One good thing though is as they compress they aid in turning. I see the motorcycle world going to Elf or RADD non telescopic type designs. Do you think this type of design would benefit the Mt Bike industry?

Thanks
LC
:thumbsup:


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## MMcG (Jul 7, 2003)

wow - i was excited to see this forum emerge - but now........not so much.


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## CougarTrek (Jan 27, 2007)

pvd said:


> That's funny, I asked two physics graduate students to solve this and neither of them could figure it out. I had to roll up my sleeves and figure it out when they couldn't


I call bullsh*t. I have an undergraduate degree in physics and math and could simplify that expression significantly. All it is is high school trig (and a rather unimpressive example of it at that). Fixing all the typo's, incorrect information, and needless redundancies (it doesn't matter if you put radians or degrees into a trig function, unless you are too stupid to know how to set your calculator...) would do wonders to simplify it right off the bat! Then there's simply typing it in using an equation editor (even Microsoft word has one, so no excuses, especially if you are trying to market/sell this crap.) which would do wonders again for making it look much less complicated (not to mention legible). It's much easier than some equations I've dealt with as an undergraduate; that's not to say that you'll get anything out of simplifying it or that it will reduce that much. Chances are it's smarter to throw it in a computer program and plug in the variables.

Could it be that the graduate physics students just had better things to do and weren't stupid enough to want to play around with a poorly written high school problem when they could throw it in a computer if they cared?


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## Joules (Oct 12, 2005)

CougarTrek said:


> I call bullsh*t. (it doesn't matter if you put radians or degrees into a trig function, unless you are too stupid to know how to set your calculator...)


I concur with the BS. That looks suspiciously like an excel function. Not usually my tool of choice when doing heavy lifting.

And I promise you, every big bike company (the ones that actually have engineers designing their bikes) have figured this out - it's not that difficult a problem.


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## G-reg (Jan 12, 2004)

pvd said:


> It's used for predicting frame geometry at full extention and full compression so that the frame design doens't fail in climbing or decending situations. You can know if your pedals get too close to the ground in hard landings. It is critical for long travel forks and can optimize short travel forks.


Are you building slacker head tube angles and increasing wheelbase to make your bottomed out geometry better? How much steering are you doing at full compression anyways. If I'm hard on the brakes, or in big G-out, or landing a jump, pedaling or turning at that moment doesn't work out to well for me. I cant think that a degree or two of ht angle would help.


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## pvd (Jan 4, 2006)

G-reg said:


> Are you building slacker head tube angles and increasing wheelbase to make your bottomed out geometry better?


Yes, in a way. Slacker heads and steep seat tubes, short chainstays and longer front centers. My bikes are trail bikes, so by my design the rear is designed around climbing and the front around decending. With very long travel forks on hardtails, while decending, the head will get much steeper and the bb much lower, leading to some serious t-bones, capsises, and pedal snags. Slack the head out too much and the bike climbs really bad and the bike gets quite tippy if the bb is too high. This formula makes it possible to see how the bike will be climbing, JRA, and decending. That way I can optimize the good or minimize the bad in each case.


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## pvd (Jan 4, 2006)

CougarTrek said:


> I call bullsh*t. I have an undergraduate degree in physics and math and could simplify that expression significantly.


Waiting....


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## pvd (Jan 4, 2006)

NEPMTBA said:


> The leading or trailing link front end has just disappeared, Amp and Girvin had great forks.


I don't know if they were great, but they were interesting. My favorite is the Lawill Leader. That is what most people remember as being the best example of the leading link for bicycles.

Alternative front end designs are always a hot topic in motorcycles. Most people in motorcycling debate wether or not Britten would have been able to work out the bugs of his design if he had lived, or if he would have had to give in to a telescope. One of your bigger debates in the motorcycle building world.

While telescoping forks have some serious drawbacks, they are the best that we have. but by best, we are including durability, reliablity, servicablity, and strength in addition to pure function. The linkage types really start 'cracking' under pressure. too much service, easy to break, lots of parts, etc.

BMW's telelever is probably one of the most succesful alternatives, but it is really a hybrid.

With improved electronics we may still see a new Tesi or Omega swingarm front pop up again. But product liabilty may prevent this.


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## pvd (Jan 4, 2006)

dr.wierd said:


> I guess thats why PVD bikes are the most sought after bikes in the world


My bikes are not for sale. I make them for friends, family, and truely special projects. You may be lucky enough to one day test ride one though.


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## pvd (Jan 4, 2006)

*It's a pity.*

None of our 'math experts' can ever do anything but proclaim. They never show or prove anything. They bash my work but have none of their own to show. They claim the work is easy, but can't say why.

Here's a bone. I simplified the formula for you. Why don't you explain my work?


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## ~martini~ (Dec 20, 2003)

Is this going the extra mile, or being OCD? Or incredibly bored?

Seriously, petey, if you weren't such an ass about this stuff, we just _might_ be willing to give it all a fair shake. Posting a link with some kind of cryptic statement really doesn't get far. I got far more out your response to NEPMTBA than all of your other posts combined.

Designing a bike around a position it'll spend .001% of its time in seems fool hardy to me. But I'm just a regular joe that only rides bikes.


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## Francis Buxton (Apr 2, 2004)

I honestly don't give a rat's ass about a friggin' Excel line graph showing how my head angle changes with compression. I know that it increases as I eat into my travel, and I don't even have my MENSA card yet.

You wanna know how I choose my bb height? I've ridden bikes with 11.5", and I get a billion pedal strikes, especially fixed. I've ridden bikes with 12.5", and I feel tippy and too high. Like Goldilocks said, 12" is just right, and I didn't have to sit down and crunch out a formula I don't give a **** about.

Dude, we get it, you're smart. Guess what? We don't give a ****. Some of us here are smart too, and some of us know people smarter than you. It doesn't matter though. You're missing the forest for the trees. You're bogging yourself down in the minute details and not realizing that a)it's pretty hard to notice a millimeter or half a degree here or there and b)you can't build a frame to within a millimeter, no matter who you are.

Stop beating us over the head with your nerd stick and go ride your bike.


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## CougarTrek (Jan 27, 2007)

*Don't hold your breath*



pvd said:


> Waiting....


I'm not bored or stupid enough to work with such poorly printed full of typo's crap. I thought I'd made that quite clear. What's it equal to initially anyway? Thin air? 0?

All it is is manipulating trig functions and equations. If you honestly can't figure out how to do that it's not my problem and I can't explain it to you on an internet forum. Telling a mathematician "by manipulation of trig identities ____ simplifies to _____" is MORE than enough. I shouldn't need to hold your hand through it, and I certainly don't need to prove to you I can do it! I have much better things to do than do your high school math for you just to "prove" I can do it 

I've already "proved" I can do it to much more knowledgeable mathematicians and physicists than you, and earned the "privilege" of using software to do it! Heck, I have a CALCULATOR that would probably simplify it if I felt the need to enter it in!

There you go.... step 1) remove typos and needless redundancies 2) enter into good calculator 3) choose "simplify" function 4) wait and write down answer 5) Double check calculator/easy manipulation into form you wish. That was SOOO DIFFICULT! NOT.... (yes, I'm still convinced I could do it by hand if I wanted to, but I'm not that bored. I'm not even bored enough to try to decipher the random mess that is your image to put it into a calculator.)


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## pvd (Jan 4, 2006)

CougarTrek said:


> ...


Nothing? You've got nothing. I thought you said this was all so easy? I've given you almost everything and you still can't even connect the dots. Let me guess, do you use your degree in math to serve at Starbucks? Good coffee, bro.


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## Ptor (Jan 29, 2004)

pvd said:


> You've got nothing.


This is like watching a train wreck...it's horrible and ugly, but I can't stop watching. For the sake of my soul, as soon as I click "Submit Reply", I'm going off to "my account" and learn how to set up the "ignore" function for PVD...


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## Walt (Jan 23, 2004)

*Jeez, tough crowd.*

So let's take it as a given that the math is right, and that PVD did a good job with it. Ok? No need to posture about how clever we all are or aren't - we're all here wasting our time on an internet forum like a bunch of giggling Japanese teenagers, so clearly nobody here is quite ready to start preparing a nobel acceptance speech.

Heck, I might BE a giggling Japanese teenage, for all you know. 

To me, the question is now this (and, to be fair to PVD, it's the question he initially asked) - does crossing every t and calculating *everything* down to the last millimeter matter much? Or have 120+ years of hands-on engineering experience with the safety bicycle (and 20+ with suspension-equipped varieties) made work like this unimportant?

I guess I'd say that the engineering work for bicycles is pretty much done. When I build a custom frame, I don't worry much about the final head tube angle at full compression, for exactly the reasons that have been pointed out here, namely:
1) I've ridden dozens of bikes with similar enough configurations that I know through experience what works.
2) I find that the angle is irrelevant in such situations, for exactly the reasons (essentially: you're screwed anyway if you try to do anything but hang on) mentioned by other posters. 
3) The angles vary so little with wheelbase that one might just as well assume that a 100mm travel fork will compress to steepen the head angle by "about 4 degrees" and be done with it. This kind of rough estimate could be arrived at with a $2 angle finder, a tape measure, and any old mountain bike frame. Or some very simple trigonometry involving quite a bit less math.

Bottom line, in my opinion, is that while the math is right and in fact useful, the level of precision and the technique being used are a waste of time. But then again, I just wasted 10 minutes typing this up.

In any case, there are a lot of ways to skin a cat and I think PVD's works too - it's just a difference of style. Some people aren't interested in his level of precision, and that's fine. But mathematically precise information never hurt anybody, and as always, I've learned something from this thread.

Goodnight!

-Walt


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## TortugaTonta (Jun 14, 2004)

Walt said:


> Heck, I might BE a giggling Japanese teenage, for all you know.
> 
> Bottom line, in my opinion, is that while the math is right and in fact useful, the level of precision and the technique being used are a waste of time. But then again, I just wasted 10 minutes typing this up.
> 
> ...


I agree

1st I love it when people are so eager to claim they are "Better than you" at whatever. It brings to mind what my mommy allways taught me "its better to be silent and thought a fool than to speak and remove all doubt" How could anybody believe they are a better rider than me if they don't know who I am?

When I first built some frames I had all these crazy ideas about geometry, I built some bikes with short rear ends and long front ends. When I first rode them I thought they were awsome. After about a year I rode some bikes with a more conventional geometery and realized the bikes I built were not that great. The bikes I build this year will not be so far out of the ordinary.

I learned when you stray from what we know to be a good all around bike you end up with a bike that might be really good at one thing and horrible at another. It becomes quite clear why we have dh bikes, road bikes, bmx bikes and so on.

At this point I know that I am more sensitive to my attachment points on the bike, Handle bar width and bend, handle bar to pedal relationship. This is the difference between really putting power down on a sprint or feeling like I am riding a beach cruiser.

The bikes I build this year will be close to a classic xc bike with a slightly shorter rear end and slightly slacker head angle. I will ride them at the bmx track, dirt jumps and rip tight twisty smooth single track and ride them down to the diner with my sandls on. When I go out for some silly fast dh stuff I will be on a 8" travel bike because thats what they are made for :thumbsup:


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## Francis Buxton (Apr 2, 2004)

I think Walt and TT hit the nail on the head. PVD, you simply need to learn a few things about presentation. If your presentation isn't good, no one will believe your idea is any good, and I'm sorry, but your presentation sucks. You come off as a giant know-it-all, and in my experience, know it alls generally don't (know it all).

I'm not saying that your work is completely unimportant, but I could figure out your solution in Autocad in about 5 minutes. It's not so much a direct part of every frame design as a piece of background information to simply be aware of. Design for the best case (no compression) and simply be mindful of the worst case (full compression).

As Walt eluded to, I don't think there's a bike frame out there that's actually been built to within 1mm or less of the "design" top tube length and/or head tube angle, and I don't think any of us are sensitive enough to notice.


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## chequamagon (Oct 4, 2006)

Walt said:


> In any case, there are a lot of ways to skin a cat and I think PVD's works too - it's just a difference of style. Some people aren't interested in his level of precision......


Thats the comedy! Did you see his miter gaps pre-weld for his frames on his website? Precision, I think not.

Ive gotten closer with a bench grinder and a hand file.

(Disclaimer: Then again, Ive never TIG welded, only fillet and lug brazed. Maybe close tolerance isnt needed for welds? I just know that gap with a braze would fail miserably.)


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## pvd (Jan 4, 2006)

Good engineering gets the job done with loose tolerances, cheap materials, and a minimum of skilled labor.

I'm glad you can spend a few days on my site and eventually find a picture of a quick and dirty build to crack on. Too bad your work isn't up for critique.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> I'm glad you can spend a few days on my site and eventually find a picture of a quick and dirty build to crack on. Too bad your work isn't up for critique.


Did we ask you to put your work on here for critique. You apparently have a big ego. I would want to figure out that excel mess you posted......ever heard of MathCAD?

It is better to keep your mouth shut and appear stupid, than to open it and remove all doubt. - Mark Twain


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> It is better to keep your mouth shut and appear stupid, than to open it and remove all doubt.


Yup. You removed all doubt. MathCAD would only be usable if you actually understood the reasons behind the simple trig I used.


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## chequamagon (Oct 4, 2006)

pvd said:


> Good engineering gets the job done with loose tolerances, cheap materials, and a minimum of skilled labor.
> 
> I'm glad you can spend a few days on my site and eventually find a picture of a quick and dirty build to crack on. Too bad your work isn't up for critique.


I spent only about a half hour there. If you werent so full of yourself already, I would praise a few of the items I thought were truly unique, but being what this thread has become, you simply deserve the bashing.

And my "pièce de résistance" will be up for critique in March. Bash all you want then, but I dont have a "look at me, I am cool" website.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> Yup. You removed all doubt. MathCAD would only be usable if you actually understood the reasons behind the simple trig I used.


Dude, I don't have to prove anything to you or respond to your drivel. I earned my BS in Mechanical Engineering.....and do very well in my day job. But would never need to prove anything to this forum or anyother forum for that matter. It's apparent by your first post you are trying to jerk your own chain.....keep jerking and maybe you will amount to something.


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## TortugaTonta (Jun 14, 2004)

In the spirit of the thread...


I dropped out of high school and my dad can beat up your dad. :thumbsup:


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> I earned my BS in Mechanical Engineering.


What school did you get that degree from that didn't require simple trig? School doesn't teach you how to think, it gives you the tools to use if you ever figure out how to think. Sadly, many people never learn to think.

All this hate for me for using math? And mostly by "mathamaticians" and "engineers". I've brought something to the table, they have not. I've challenged them to show me that I'm wrong or that I'm stupid, they have not.


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## chequamagon (Oct 4, 2006)

pvd said:


> What school did you get that degree from that didn't require simple trig? School doesn't teach you how to think, it gives you the tools to use if you ever figure out how to think. Sadly, many people never learn to think.
> 
> All this hate for me for using math? And mostly by "mathamaticians" and "engineers". I've brought something to the table, they have not. I've challenged them to show me that I'm wrong or that I'm stupid, they have not.


oh trust me, you've already shown us all that we needed to know.


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## pvd (Jan 4, 2006)

chequamagon said:


> ...but being what this thread has become, you simply deserve the bashing.


What a horrible attitude. Bashing is such a juvinile way of responding to people. Resorting to personal attacks to restore your own sense of self worth. If you were smart (imagine), you would 'criticise' me. Criticism involves pointing out problems and flaws in someones work and providing possible solutions. At the very least PROVING someone is wrong.

And really, "pièce de résistance". Ouch! I could work you over with just that all day long. How about a preview? You know, some detailed construction process shots like you pointed out of mine. I bet all we'll ever see is $200 worth of raw materials and $1800 worth of paint and bondo. Pony up homeboy.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> What school did you get that degree from that didn't require simple trig? School doesn't teach you how to think, it gives you the tools to use if you ever figure out how to think. Sadly, many people never learn to think.
> 
> All this hate for me for using math? And mostly by "mathamaticians" and "engineers". I've brought something to the table, they have not. I've challenged them to show me that I'm wrong or that I'm stupid, they have not.


The only reason there is hate for you is the way you presented this material. Go back to your original post and study it with the same "passion" you're asking this forum to study your equation. If this is the way you submit material in your day job.......either you own your own company or you're soon to be unemployed.....In my years of engineering I have found that delivery of my ideas and solutions to problems is critical to getting other people signed......it has nothing to do with us solving your little equation.


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## D.F.L. (Jan 3, 2004)

Maybe a Mikesee time-out would help us all?


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> ..it has nothing to do with us solving your little equation.


Ha, ha! You're an engineer and you can't solve this problem. I give you two different solutions to the problem and you still have no idea where the numbers even come from.

Really, show everyone that you are, in fact, the smart one. It should take you about 3 minutes (if you really are an engineer).


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> Ha, ha! You're an engineer and you can't solve this problem. I give you two different solutions to the problem and you still have no idea where the numbers even come from.
> 
> Really, show everyone that you are, in fact, the smart one. It should take you about 3 minutes (if you really are an engineer).


First off you don't know me so don't jump to conclusions regarding my technical skills. All we are asking is that you cool it with calling everyone out on this board. I'm personally not going to waste my time on your excel dump.....right the equation in standard math notation and then I will show you a solution. Then get out your heat transfer, thermodynamics, and fluid dynamics books because I am going to hit you with a question that will rock your little narrow minded world


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> right the equation in standard math notation and then I will show you a solution.


I gave the reduced version quite a while ago:










Now, explain it. You have the full version to help you.

Also, I was the one called out in this thread.


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## Walt (Jan 23, 2004)

*Who cares?*

This has gone so far beyond relevance to bicycles that I'm tempted to move it elsewhere. If we had an "Intellectual posturing" forum it would already be gone.

Anyone care to discuss the actual original subject matter; regarding whether or not this level of precision is important when the rubber hits the dirt?

-Walt


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## Guest (Dec 18, 2007)

pvd said:


> That's funny, I asked two physics graduate students to solve this and neither of them could figure it out. I had to roll up my sleeves and figure it out when they couldn't





pvd said:


> ...you actually understood the reasons behind the simple trig I used.


So which is it? Harder than grad students can solve??? or simple trig??????


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## pvd (Jan 4, 2006)

indigosky said:


> So which is it? Harder than grad students can solve??? or simple trig??????


both, actually.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> I gave the reduced version quite a while ago:
> 
> 
> 
> ...


Okay, I need an explaination of your equation.....displacement is that fork traveled + sag...whereas the initial set up with 30% sag the fork was displaced 42mm.


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## pvd (Jan 4, 2006)

Walt said:


> This has gone so far beyond relevance to bicycles that I'm tempted to move it elsewhere. If we had an "Intellectual posturing" forum it would already be gone.
> 
> Anyone care to discuss the actual original subject matter; regarding whether or not this level of precision is important when the rubber hits the dirt?
> 
> -Walt


Actually, this is very much relevant to bicycles and framebuilding. It involves the willingness to do predictive anylisis on a bike design while in varying states. Some people see a bike as a fixed system and others as dynamic and changing. What tools do we use to understand how our bikes work while climbing or decending? How does all of this effect design? Are our tools accurate? What works?

This thread should not be moved or closed. It will die if nobody posts in it. People that do post in it obviously feel that it is valid for discussion. If people don't like it they don't have to read it or post in it. simple darwinian logic.

Questions of mathmatical accuracy and validity have been brought up. They are being discussed. People have said that I am wrong, I ask that they prove it. This is not posturing. This is how facts are weeded from fiction.


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> Okay, I need an explaination of your equation...


displacement is the distance moved from JRA equalibriam (sagged), positive is compression, negative is extention. 0 is sagged.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> Actually, this is very much relevant to bicycles and framebuilding. It involves the willingness to do predictive anylisis on a bike design while in varying states. Some people see a bike as a fixed system and others as dynamic and changing. What tools do we use to understand how our bikes work while climbing or decending? How does all of this effect design? Are our tools accurate? What works?
> 
> This thread should not be moved or closed. It will die if nobody posts in it. People that do post in it obviously feel that it is valid for discussion. If people don't like it they don't have to read it or post in it. simple darwinian logic.
> 
> Questions of mathmatical accuracy and validity have been brought up. They are being discussed. People have said that I am wrong, I ask that they prove it. This is not posturing. This is how facts are weeded from fiction.


I actually think this is very relevant to frame design. The bike industry doesn't have the best track record with regards to putting out well thought out designs...just look at the GF HiFi that had the over-center shock failure......it's better today then it was ten years ago when all the cottege industries were spitting out Gee Whiz products. My only beef with pvd is his provocation....but that's a personal difference in approach.


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## chequamagon (Oct 4, 2006)

pvd said:


> What a horrible attitude. Bashing is such a juvinile way of responding to people. Resorting to personal attacks to restore your own sense of self worth. If you were smart (imagine), you would 'criticise' me. Criticism involves pointing out problems and flaws in someones work and providing possible solutions. At the very least PROVING someone is wrong.
> 
> And really, "pièce de résistance". Ouch! I could work you over with just that all day long. How about a preview? You know, some detailed construction process shots like you pointed out of mine. I bet all we'll ever see is $200 worth of raw materials and $1800 worth of paint and bondo. Pony up homeboy.


Oh buddy, we have to work on this ego issue.

"pièce de résistance" is in quotes because it is sarcasm. I can admit that making a few frames does not make me anywhere close to an expert. Its probably gonna suck. The entire post is a jab at your supposed "expertise". Nobody is an expert after a few frames, probably not even after 100, no matter how good the math is. I betcha Walt doesnt even call himself an expert. And something tells me he has made a few more frames than either of us.

I am pointing out the main problem here! Its ego, and we are all involved.


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## greyspoke (Apr 30, 2007)

Some figures for Oranges:

224 200mm 64 degrees
Sub Zero 160mm 67 degrees (Patriot similar)
P7 140 mm 69 degrees
Evo8 100mm 71 degrees
All apparently measured with no sag.

Adopting the rough and ready 20mm = 1 degree figure, this would give figures at full travel of 74, 75, 76 and 76mm respectively.

I always assumed that one reason longer travel bikes had slacker angles was because of the need to avoid things getting too steep at full compression. But it's not surprising the 224 and Sub Zero are slacker even by this measure given what they are for.

So, full compression head angle is useful, but not a magic number.


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## jmoote (Aug 31, 2007)

pvd said:


> None of our 'math experts' can ever do anything but proclaim. They never show or prove anything. They bash my work but have none of their own to show. They claim the work is easy, but can't say why.
> 
> Here's a bone. I simplified the formula for you. Why don't you explain my work?


Your equation simply shows that the bike is modeled as a right triangle with the wheelbase as the hypotenuse. The fixed dimension is the distance from rear axle to the intersection with projected headtube angle. What do you want us to explain? This _is_ highschool geometry, and the only catch to the problem is realizing that wheelbase is a dynamic quantity as the fork compresses. The rest is obvious.

I agree with the others: your analysis is valid, but you're not impressing anyone with the way you present it. Just because you bothered to do the work does not make it a grand accomplishment.


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## Baulz (Sep 16, 2005)

pvd said:


> Yes, in a way. Slacker heads and steep seat tubes, short chainstays and longer front centers. My bikes are trail bikes, so by my design the rear is designed around climbing and the front around decending. With very long travel forks on hardtails, while decending, the head will get much steeper and the bb much lower, leading to some serious t-bones, capsises, and pedal snags. Slack the head out too much and the bike climbs really bad and the bike gets quite tippy if the bb is too high. This formula makes it possible to see how the bike will be climbing, JRA, and decending. That way I can optimize the good or minimize the bad in each case.


Do you calculate how much your tire will compress at full travel as well? That must alter the geo a bit.


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## scottzg (Sep 27, 2006)

pvd said:


> I build frames. I design the ones I build. Then I ride them. I know that I'm a far better rider than you. This 'math' stuff is what separates a bike from a very good bike.


THAT'S AWESOME! Oh man, i would be giggling for days after putting up a post like that.

How about this: I don't care if your bikes crank themselves up hills and float down boulder fields like riding on a kitten, I wouldn't buy one from you because you're a douche.

Honestly, you're embarrassing yourself! shut up!


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## pvd (Jan 4, 2006)

Baulz said:


> Do you calculate how much your tire will compress at full travel as well? That must alter the geo a bit.


I wouldn't dare try to calculate that. too many variables. i do mention that this will happen on the wiki, as well as chasis flex.


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## pvd (Jan 4, 2006)

scottzg said:


> I don't care if your bikes crank themselves up hills and float down boulder fields like riding on a kitten, I wouldn't buy one from you because you're a douche.


Again, I don't sell bikes.

Have a nice day!


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## Walt (Jan 23, 2004)

*Read my original reply...*

Maybe I wasn't clear. My question was whether this level of precision is important when there are quick and dirty ways to calculate this that I would consider "good enough". So in answer to PVD's original question, no, I do not "go the extra mile", at least wrt this question. I imagine one could spend days calculating and modeling every possible frame design in every possible situation. I just don't think it's necessary.

-Walt



mtnbiker4life said:


> I actually think this is very relevant to frame design. The bike industry doesn't have the best track record with regards to putting out well thought out designs...just look at the GF HiFi that had the over-center shock failure......it's better today then it was ten years ago when all the cottege industries were spitting out Gee Whiz products. My only beef with pvd is his provocation....but that's a personal difference in approach.


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## pvd (Jan 4, 2006)

jmoote said:


> Your equation simply shows that the bike is modeled as a right triangle with the wheelbase as the hypotenuse. The fixed dimension is the distance from rear axle to the intersection with projected headtube angle. What do you want us to explain? This _is_ highschool geometry, and the only catch to the problem is realizing that wheelbase is a dynamic quantity as the fork compresses. The rest is obvious.


Almost. What about the fork offset? Why is that not a factor?


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## NEPMTBA (Apr 7, 2007)

pvd said:


> I build frames. I design the ones I build. Then I ride them. I know that I'm a far better rider than you. This 'math' stuff is what separates a bike from a very good bike.


pvd:

I don't want to be in on a bash fest. Just asking questions.

May I ask did you ever consider building something like Ribi did for Roger De Coster on his factory Suzuki. The leading or trailing link front end has just disappeared, Amp and Girvin had great forks. You show you are very meticulous about dimensions and I feel you could push the envelope on this subject.
Telescopic forks have many drawbacks. Stiction, Flex. One good thing though is as they compress they aid in turning. I see the motorcycle world going to Elf or RADD non telescopic type designs. Do you think this type of design would benefit the Mt Bike industry?

Thanks
LC
:thumbsup:


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## TortugaTonta (Jun 14, 2004)

Walt said:


> Maybe I wasn't clear. My question was whether this level of precision is important when there are quick and dirty ways to calculate this that I would consider "good enough". So in answer to PVD's original question, no, I do not "go the extra mile", at least wrt this question. I imagine one could spend days calculating and modeling every possible frame design in every possible situation. I just don't think it's necessary.
> 
> -Walt


Walt, No, one degree of head angle or one mm of chainstay length is not the difference between winning or second place. A broken bike can be though.

Sam hill and I could trade dh bikes and he would still kick my ass in a race. Lance and I could trade road bikes and he would still kick my ass in a race. I could put pegs on my bike and I still couldn't feeble grind a rail. All the bling in the world will not make the difference between being a good rider and one that sucks.

At the same time liking a certain feel or look for your bike can make the ride a little more pleasurable. Thats why we have different colors different tread patterns and the like.

Just remember different isn't allways better.


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## Walt (Jan 23, 2004)

*Not sure I understand...*

What do you mean? My point was that you can calculate the HTA under compression in 30 seconds using a simple trig formula and only end up with maybe a few hundredths, or at worst a tenth of a degree error. I'm pretty sure I can't build a frame to 1/10 degree accuracy anyway. Why make things this complicated?

I never said I *don't* care about HTA at full compression. Obviously it matters. I just am saying that there's no need to calculate it with this level of precision.

-Walt



TortugaTonta said:


> Walt, No, one degree of head angle or one mm of chainstay length is not the difference between winning or second place. A broken bike can be though.
> 
> Sam hill and I could trade dh bikes and he would still kick my ass in a race. Lance and I could trade road bikes and he would still kick my ass in a race. I could put pegs on my bike and I still couldn't feeble grind a rail. All the bling in the world will not make the difference between being a good rider and one that sucks.
> 
> ...


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## TortugaTonta (Jun 14, 2004)

I agree with you. I was just giving examples of how a small difference in bikes will make no difference in my skill level or fitness level and that is the determining factor in how I ride my bike. I saw two occasions of kids riding 20" bikes with the front fork on basically backwards. One kids aunt had bought him a "next" bike from Dicks sporting goods. The aunt put the bike together herself and had the fork rotated 180 degrees. The 13 year old kid still hit the dirt jumps on the bike. I really don't think he was concerned about his fork offset, he was stoked to get a new bike for christmas.


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> displacement is the distance moved from JRA equalibriam (sagged), positive is compression, negative is extention. 0 is sagged.


I have to admit this thread has rekindled my interest in something I started working on a year ago. I am going to start working on the same analysis but with a FS bike and I hope to do it graphically through CosmosMotion. I know the FS analysis will be alot more complex due to added variables like rider weight, and linkage ratios


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## pvd (Jan 4, 2006)

Walt said:


> Why make things this complicated?


I don't really think that it is more complicated. Once the initial work is done, the formula is simple enough to use. But, the numbers do mean a lot more.

This number, wheelbase * cos(head angle), actually means something to the builder. So does, (wheelbase * sin(head angle))+MT. The tell us something about how the bike works, how it will ride. (hint)

Sure, going past the second decimal place is a total waste of time, but it's the perspective that really means something.

Also, the formula is a tool. it does a lot more than we have discussed so far. something that 20=1 will not ever do.

Hydraulic disc brakes are the simplest form of brakes we can use for what is on the market right now, but some people insist that mechanicals are more simple. A simple look at how the system works shows that hydros are in fact as simple a choice that we have.


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## pvd (Jan 4, 2006)

mtnbiker4life said:


> I have to admit this thread has rekindled my interest in something I started working on a year ago....


Awsome!

You should really take a look at Foale's work. It may help you out. Tony is the king of bike geeks. Nobody else even comes close. (except for Sharp, but he is long dead)

http://www.tonyfoale.com/suskin/MC_setup.htm


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## mtnbiker4life (Sep 19, 2005)

pvd said:


> Awsome!
> 
> You should really take a look at Foale's work. It may help you out. Tony is the king of bike geeks. Nobody else even comes close. (except for Sharp, but he is long dead)
> 
> http://www.tonyfoale.com/suskin/MC_setup.htm


It was this article in Desktop Engineering that started me on this analysis of a FS bike. I use Pro/E and SolidWorks along with a couple of highend anaylsis tools in my day job so I decided to start tinkering with frame geometry.

http://www.deskeng.com/articles/aaaabf.htm


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## pvd (Jan 4, 2006)

i'm stuck with just solid works and excel. BikeCAD makes framebuilding quick and easy.

I haven't messed much with the VPP stuff design wise, but I doubt that it is as complicated as that artical says. It would be good to talk to CarbonMike about this. (I do own a Intense 5.5 and it climbs much better than my older SLX. the SLX is much, much nicer going down though)


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## eMcK (Aug 22, 2007)

I don't get this thread at all. If you are attempting to enlighten us PVD, just come out and say what it is you mean. Some far you've come up with equations that when solved give you numbers, but you've never come close to saying how those numbers affect how you build bikes, or how using those equations would be better than the simple and quick equations Walt and others described.

In other words, quit asking questions that you have the answers to, or claim to. IMO it is a transparent attempt to boost your ego rather than share your knowledge.


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## jmoote (Aug 31, 2007)

pvd said:


> Almost. What about the fork offset? Why is that not a factor?


That is because this quantity is built into the dimension from the rear actual to a line projected from the front axle at the head tube angle ( =wheelbase(i) x sin(head(i)) in your notation)


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## TortugaTonta (Jun 14, 2004)

eMcK said:


> I don't get this thread at all. If you are attempting to enlighten us PVD, just come out and say what it is you mean. Some far you've come up with equations that when solved give you numbers, but you've never come close to saying how those numbers affect how you build bikes, or how using those equations would be better than the simple and quick equations Walt and others described.
> 
> In other words, quit asking questions that you have the answers to, or claim to. IMO it is a transparent attempt to boost your ego rather than share your knowledge.


On first glance I would agree with you, however.....

Sometimes the journey is as interesting as the destination. I think pvd is making his journey and he is excited. That is a good thing. However some of us have made the drive and we are bored by it.

If you are entertained by sitting down in front of the wood stove with your abaccus designing what you believe to be the perfect bike that is great. If you ride down the trail thinking you are going so fast because you solved the equation for perfect fork offset thats great. I personaly tend to be thinking I wish I could sprint harder or sprint longer or whatever my goal is at that time.

I would say most of us build frames for a certain level of accomplishment and entertainment. I am more entertained by the riding part than I am about fileing in the mitres at the seatstay to seat tube junction.

I think most would agree that it is foolish to claim that the route you chose for your destination is a more noble one. Especially since most of us have a different destination.

That being said I would like to hear about some journeys, just don't claim to be Neo and you just solved the Matrix, they are just stupid bicycles after all


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## pvd (Jan 4, 2006)

jmoote said:


> That is because this quantity is built into the dimension from the rear actual to a line projected from the front axle at the head tube angle ( =wheelbase(i) x sin(head(i)) in your notation)


while you are correct about the quanties, the thing is though, wheelbase(i) x sin(head(i) is a handling characteristic. it means something and has little to do with the hub axles. Numbers can be arrived at the way you say, but a diffent explanation would tell ua a lot more about the bikes handling.


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## Pooh Bear (May 25, 2006)

pvd said:


> People have said that I am wrong, I ask that they prove it. This is not posturing. This is how facts are weeded from fiction.


Prove that you're right!

As far as accuracy is concerned: It is not needed to this degree I think. You said you have some thoughts about tire compression and flex on your site, but there were too many variables. Well, you like calculating so much, why not figure this out as well?! Might give the desired number...

Well, what do the numbers tell you about the _feel _of the bike in that very short moment when your front suspension is fully compressed? Nothing!

*Hint* Front compresses fully means: Move your a$$ backwards and have the cranks flat so as not to hit the ground. Survive! :thumbsup:


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## double0b (Aug 8, 2005)

I guess that PVD is working towards getting banned from another forum. Great attitude...


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## Thylacine (Feb 29, 2004)

You crack me up, Pete. Keep up the good work!


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## mtnbiker4life (Sep 19, 2005)

Although, I don't agree with his posting style.....his equations are valid. I've worked through the equations posted on his website and I have to give merit because merit is due.

His original website has a lot of great technical information.


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