# Pvd-rad



## pvd (Jan 4, 2006)

Anyone interested in actually testing this out against your own designs?

I'd like to hear what others come up with for body angle and arm angles for a given front center and riding style.

I'm soooo RAD! | Peter Verdone Designs


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## scottzg (Sep 27, 2006)

Lol you're kinda kicking a midget here. 



Me-
190.5 cm * 4.47 magic number= RAD 851.5



Hardtail 1- This was supposed to be a big mountain/ vacation bike, but it kicks ass everywhere but switchbacks and flat terrain.

front center- 846mm
wheelbase- 1267mm
RAD- 975mm
angle- 54.6



Hardtail 2- General purpose trailbike.

front center- 782mm
wheelbase- 1208mm
RAD- 960mm
angle- 55.7




Hilariously longer and lower than RAAD suggestions. Both bikes are pretty beginner friendly, moreso than anything you might create with RAAD. Raising the bars any higher on ht2 aggravates one of my hands. Happens on HT1, too, but that bike works best with the bars lower anyway.


For me, his numbers aren't even in the ballpark. I don't know if it's cuz he's accustomed to bikes from 'the bad old days,' or because his formula falls apart as you deviate from median height.


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## pvd (Jan 4, 2006)

The point is that you use the methodology that I spell out, not LM's system.

My system corrects for arm and body differences, using the torso and arm angle as references.


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## dr.welby (Jan 6, 2004)

Is there supposed to be a diagram that goes with all the B numbers?

I'm getting similar RAAD numbers, longer and lower than the system suggests.


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## pvd (Jan 4, 2006)

I may make a diagram but the B values are for cell reference. Cut and paste into excell for your pleasure.


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## dr.welby (Jan 6, 2004)

Ok, just to confirm:

Body Angle from Ground (B1) = torso angle, i.e hips to shoulder joint, relative to horizon

Arm Angle from Body (B2) = straight arms, i.e. shoulder to wrist, relative to what?

Sole to Arm Socket (B3) = arm socket is shoulder joint? Vertical distance or straight line?

Arm Socket to Grip (B4) = straight arm?


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## pvd (Jan 4, 2006)

Straight arm. Straight body.
Tun the body onto a single hinge.


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## pvd (Jan 4, 2006)

Arm is socket to bar end holding bars.
Socket to floor.


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## scottzg (Sep 27, 2006)

pvd said:


> Straight arm. Straight body.
> Tun the body onto a single hinge.


Ah, got it. My attack position photo was not working at all.


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## pvd (Jan 4, 2006)

I just updated the page with more images:


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## pvd (Jan 4, 2006)




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## scottzg (Sep 27, 2006)

I gave this a solid effort using bikecad and google sheets.

Here's my results.








*Feel free to mess with the spreadsheet.* _<--- this spreadsheet is accessible to anyone, and removes almost all the work (edit)_

-It was difficult to guess where a straight line through the rider is, in order to get lean angle. I'm not sure i could guess within 5* of correct.

-I'm not sure how this is more valuable than RAAD's using a tape measure straight from the pedal to the grip. It seems like there's an 3rd dimension that RAAD captures that this doesn't.

-I don't like how we need to be <1* accurate over a several foot span. Lots of room for an error to stack up.

-I tried doing this with a photo, and that just added more room for error. _edit- I moved the saddle position forward to get my dude standing up, which i now see has dislocated his knee. So these results are trash and that method doesn't work because of how bikecad is designed.
_

It's almost certain i'm just not understanding/doing this correctly. ...But the spreadsheet works!


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## dr.welby (Jan 6, 2004)

Ok, now I get it.


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## pvd (Jan 4, 2006)

scottzg said:


> It's almost certain i'm just not understanding/doing this correctly. ...But the spreadsheet works!


With your existing bike, work from both directions. That will resolve the angles.
Once you see the utility, it beats SBH by a mile.


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## pvd (Jan 4, 2006)

dr.welby said:


> View attachment 1295423
> 
> 
> Ok, now I get it.


So, our bodies are 1.8 degrees apart. Very close despite the wide variance in the other dimensions and style differences. Pretty cool.


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## scottzg (Sep 27, 2006)

pvd said:


> With your existing bike, work from both directions. That will resolve the angles.
> Once you see the utility, it beats SBH by a mile.


Oh i totally see the utility; it's why i'm still fussing with it. It's a valuable measurement now that we've abandoned roadie fit rules.

Took another stab, using a bunch of trig to get the numbers i've never measured. Got a 29.8% angle for torso-arms. Reasonable, but the bike i'm measuring is more progressive than anything commercially available, so i'm skeptical/curious. Skepticurious? I'm gonna try it with a photo and see how the numbers diverge. I'd love to see this implemented in bikecad.


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## Cord (Dec 10, 2006)

Angles for Body from Ground and Arm from Torso. Am I correct in that you are photographing yourself and then drawing lines on? If so are you trying to align back with leg on 1 pedal at bottom of stroke? Heel or toe on pedal? 

Sorry, I think I’m not really getting this?


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## pvd (Jan 4, 2006)

Guys!
If you have a measurement of your current bike and the measures of your body, you don't need to get on the bike. Work the problem from both sides.
This is where the utility of this function comes from.


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## Cord (Dec 10, 2006)

See, I told you I wasn’t getting it! Ha ha! 

I was once taught that when delivering any technical information you should always assume your audience was completely inept. I have now proven this using myself. 

I shall get out my Zeus book and tape measure at the weekend.


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## dr.welby (Jan 6, 2004)

Here's another bike. This is an interesting way to think about fit but I'm not sure how I'd use it as a design tool yet.


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## pvd (Jan 4, 2006)

Cord said:


> See, I was once taught that when delivering any technical information you should always assume your audience was completely inept. I have now proven this using myself.


This points to several problems that I have. Almost all of the people in the motorcycle and bicycle industries and especially in the custom frame world have very little understanding of the bicycle, technology, or maths. Spelling everything out for them grows exhausting. Thus, I do my best to explain myself clearly and specifically. I have no interest in teaching kindergarten in every post.

Also, I'm not a poet. I'm an engineer. Much is written about bicycles by people that don't understand them and don't offer any insight. Their prose is elegant and very easy to read. It's also useless. Show me anyone (besides Foale and Cossalter) who is even attempting real technical content? So, you get what you get. Try to keep up.


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## pvd (Jan 4, 2006)

dr.welby said:


> Here's another bike. This is an interesting way to think about fit but I'm not sure how I'd use it as a design tool yet.


So, this second bike shows a near identical fit on the bike to what I have on my Warbird....but you are much taller than me. We wouldn't really see that using other methods.

What is the big difference between the two bikes you've posted?


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## dr.welby (Jan 6, 2004)

pvd said:


> So, this second bike shows a near identical fit on the bike to what I have on my Warbird....but you are much taller than me. We wouldn't really see that using other methods.
> 
> What is the big difference between the two bikes you've posted?


First bike is a stock Trance 29 in large, with a 70mm stem flipped at -6 and no spacers.

Second is a frame I built sort of around bikepacking. It has the sameish reach as the Trance at 460mm, but it has a taller stack. It uses a 90mm stem flipped to -17 and has bars with generous sweep.

Both bikes are too short, next frames will be at least 500 reach.

These hinge diagrams are definitely interesting as a condensed way to look at position and fit for trail MTBs.


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## Cord (Dec 10, 2006)

pvd said:


> This points to several problems that I have. Almost all of the people in the motorcycle and bicycle industries and especially in the custom frame world have very little understanding of the bicycle, technology, or maths. Spelling everything out for them grows exhausting. Thus, I do my best to explain myself clearly and specifically. I have no interest in teaching kindergarten in every post.
> 
> Also, I'm not a poet. I'm an engineer. Much is written about bicycles by people that don't understand them and don't offer any insight. Their prose is elegant and very easy to read. It's also useless. Show me anyone (besides Foale and Cossalter) who is even attempting real technical content? So, you get what you get. Try to keep up.


Wow, sorry for not understanding. No need to have a little temper tantrum.


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## pvd (Jan 4, 2006)

dr.welby said:


> Both bikes are too short, next frames will be at least 500 reach.
> 
> These hinge diagrams are definitely interesting as a condensed way to look at position and fit for trail MTBs.


Agreed.

Stack and reach have become almost totally irrelevant regarding bike design. I use them on my data plates but for a specific reason. I've dropped them from any other use.


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## VegasSingleSpeed (May 5, 2005)

Cord said:


> Wow, sorry for not understanding. No need to have a little temper tantrum.


It's just the state of the art in general. You've proven yourself no slouch with the technical side of frame-building, but nonetheless miss the point that this RAAD is strictly an exercise in geometry. Such is the problem communicating anything that is technically-challenging to others who may not be staring at the problem from the same point of reference, regardless of their general level of 'expertise'.

You don't have to measure your body or arm angles. Those angles can be calculated from the triangle resulting from your 'height' (height of shoulder joint, minus crank length + pedal height), arm length (shoulder to grip length), and the distance from the BB to the grips (a function of the bike's geometry and fit). Two sides of the triangle are based on your body's dimensions; one side of the triangle is based on the bicycle's dimensions. Once you have those three dimensions, you can calculate the body and arm angle that's needed for the remaining inputs of the model.


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## scottzg (Sep 27, 2006)

Hey pete, how are you getting your armpit measurement? I get a very low number doing it as you would with inseam, a higher number jamming a broom handle up there, and an even higher number by waving my arm around and guessing where the joint actually lives. Similar problem with reach- are you going from grip to cortacoid process (i think that's the name of the bump on the outside of the shoulder...?) like fitkit does, or some other method?

i guess it doesn't matter if you always do it the same way, but if you're gonna compare against others...

Cool, thanks!


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## Cord (Dec 10, 2006)

Scott, you’ll find it VERY hard to find a true instantaneous centre of rotation for the shoulder. As it rotates from 0° (hand at bottom) up towards 90° (hand horizontal in front of you) and onwards the humeral head both rotates, and slides. Also as you lift your arm your clavicle and scapula (the bit that actually contains the joint) are lifted via a selection of ligaments, one of them connected to the coracoid process you mention. The whole coracoclavicular ligament system just doesn’t allow the shoulder joint to rotate around a fixed centre. From 0° to 180° could be as much as 2” 3” depending on the amount of flexibility in the persons joint. If the joint has poor mobility in capsule, then the other ligaments will help by rising the entire joint. Probably overkill, but the best way to establish centre for the positions you need would be to draw a centre line lower on the bicep and then photograph at various positions and then extend these lines to find the centre. 

But then wot wood I no, Like pVD sed, I’m just a thiky that dun’t kno nuthin. And his fIrsT DeSCriptiOn woz So pERfict thAt qestIOns is nOT neEdEd


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## pvd (Jan 4, 2006)

scottzg said:


> Hey pete, how are you getting your armpit measurement?


It's not the armpit. It's the location of the pivot point of the joint that the arm pivots from the body. Think about it.


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## pvd (Jan 4, 2006)

Cord said:


> Scott, you'll find it VERY hard to find a true instantaneous centre of rotation for the shoulder.


Right. Just give it a try. This isn't rocket science. Why not make the measure with the arm at 90 degrees to the body as that's the general working angle of the arm when riding.


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## dr.welby (Jan 6, 2004)

scottzg said:


> Similar problem with reach- are you going from grip to cortacoid process (i think that's the name of the bump on the outside of the shoulder...?)


I used the bump (acramoid?), it's repeatable. I lined it up with the edge of the door trim and used a pencil in my fist to make a mark on the wall. And then rounded to the nearest centimeter.


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## scottzg (Sep 27, 2006)

dr.welby said:


> I used the bump (acramoid?), it's repeatable. I lined it up with the edge of the door trim and used a pencil in my fist to make a mark on the wall. And then rounded to the nearest centimeter.


acromion! That's it.

That makes the most sense to me. It's repeatable, you can use the same point for both measurements, and it's fairly immune to variance caused by the complexity of shoulders.

It's been a long time since i played with a fit kit, but i remember the distance not really changing if you moved your arm around.

The measurement is only useful (to me, at least) if you can compare across individuals, so that stuff is important.


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## pvd (Jan 4, 2006)

I'm not sure about the acromion. I'm going to need to look into that. The better we can approximate the point of pivot the better and it seems like the front of the acromion could be close.

https://en.wikipedia.org/wiki/Acromion

Also, below, I compare 3 very different bikes; The 180mm forked hardtail Warbird, the full rigid klunker Spitfire, and the flat bar all-road Airspeeder. It's interesting how close they are and what is changing just slightly on each.


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## Cord (Dec 10, 2006)

Heres some info for me and my current fave 160mm travel bike.


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## Golem builder (Jul 31, 2009)

Here's mine









Seems quite accurate.


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## dRjOn (Feb 18, 2004)

been thinking about the utility of this a bit.... a question- is thigh/lower leg /foot size not going to influence this significantly? the premise is to look at weight balance/position, but utilising a static postion of one foot down with crank at lowest point and standing straight. seems fair and relatively reproducible, so will help with the design process.

but in riding you would have hips and knees significantly bent. length of the levers and flexibility/style will influence where the weight is. even cleat postion relative to foot length and toe up or down could affect where your weight. 

is the difference between the static position and range in the dynamic enough to muddy the water too much for the static position to be highly useful? even when pedaling the bike is leaning and you never fully stand straight, so your weight is always going to be lower...some more than others...

very interesting to think about all this ~


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## pvd (Jan 4, 2006)

dRjOn said:


> Is the difference between the static position and range in the dynamic enough to muddy the water too much for the static position to be highly useful?


Of course, like any 'rule of thumb' this is not an accurate model. That would be impossible without trackside point tracking and rendering in 3D space. So what do we do? We look for something that works to help predict our needs as different rider bodies on different terrain with different strengths and skills....on different bike designs. That's a lot to pack in. Too complex and we get lost in the weeds. Too general (LLB-RAD) and it's completely useless.

I feel that this system does give a useful feed back based on the 4 inputs. The problem at this point is finding out how to generalize the two angular fields. More, the simple measure of just the arm socket location is proving to be difficult to produce accurately and repeatedly among folk. That is where my work on this is going now. I may have to visit some kinesiologists for some help.

This as a tool would be a boon for me as a designer, especially given my current te techniques. Necessity is the mother of invention and I need this tool.


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## dRjOn (Feb 18, 2004)

makes sense - i moonlight as a family doctor in the daytime and can attest to the complexity of the shoulder joint. I've been applying the drawings to some of my bikes and thinking how to try and use this in the future. I've also had a lot of interest in the effect of bar width and sweep recently - its good food for thought...


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## scottzg (Sep 27, 2006)

I forgot to post myself up. Here's my two hardtails-









It looks like i tend to have my bars lower and closer than the rest of you do, looking at hinge angles. Huh. I think i'm also several inches taller than anyone else whose posted, so it might be an indicator that i'm STILL riding bikes that are too small.


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## dr.welby (Jan 6, 2004)

scottzg said:


> Huh. I think i'm also several inches taller than anyone else whose posted, so it might be an indicator that i'm STILL riding bikes that are too small.


Darn, sounds like you need to build a new frame _for science._


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## scottzg (Sep 27, 2006)

dr.welby said:


> Darn, sounds like you need to build a new frame _for science._


Ah man i have a rack full of custom frame bikes. I love them and i'd feel horrible (and liable) if someone got hurt due to my amateur metalwork. I need to ride more so i wear them out and i need more bikes!

This is what i find so interesting with this measurement- it's an easy way to quantify how mountain bikes fit. It cuts through the bullshit of long/short arms, legs, and torso. And how we compromise fit and handling. >500mm reach seems crazy to me, but guess i'm still coming to terms with what being tall with long arms means. 20mm of reach doesn't mean much if forward lean/hinge angle is middle of the ballpark.

I think as more experts post up their stuff some real data will crystallize... which is why it's so important to standardize how this is measured.


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