# A Geometry Exercise: Free Radicalizing a Buzz Bomb



## Speedub.Nate (Dec 31, 2003)

Hey everyone - I'm sharing this anal-retentive exercise with everybody partially under the guise of soliciting feedback, but mainly just to kill time and post some pictures and number crunching I've been doing before ordering a bunch of parts for an Xtracycle conversion I'm doing. (By all means, if you make it through this drivel and see something I screwed up, tell me!) I hope it makes some fine bathroom reading! 

I chose the Frame Building forum since this is dealing with steering angles and bottom bracket drop geometry, and because there's no appropriate forum on MTBR for cargo bikes. I'm posting a link to this as a continuation of some posts I made on the RootsRadicals Xtracycle users group on Yahoo! Groups - I can't post any pics over there.

If you're not familiar with Xtracycle's Free Radical, or want to know more about how it installs on a frame, they recently posted this *video* titled _Xtracycle FreeRadical Assembly_ on FB (I don't think you need an account to view it):  https://www.facebook.com/video/video.php?v=575270451252 

*Anatomy of an Xtracycle*









Drawing lifted from Xtracycle's Flickr page

*The Project:* Add an Xtracycle Free Radical extension to my Van Dessel Buzz Bomb (29"er) frame; figure out what the resulting geometry is going to look like so I can order the proper fork, and choose the right size wheels & tires.

*The Problem:* The Free Radical is straight-forward, but it's got the potential to install differently on every bike.

It mounts into the donor frame's existing dropouts, but the tongue - the forward attachment point - mounts to the chainstay bridge. Depending on how much bottom bracket drop a particular frame has (i.e. 29"er frames generally have quite a bit more than 26"), this can leave the NEW Xtracycle dropouts in any number of positions in an arc 15" behind the donor frame's dropouts.

*FreeRadical tongue @ the chainstay bridge, just behind the bottom bracket:*










*The Real Problem:* Head Tube Angle. Imagine the donor frame held in a work stand, the rear dropouts lined up on the same horizontal plane as the fork's dropouts (let's call it the _*O*riginal *A*xle *P*lane_ - the geometry the frame builder originally intended). The greater the amount of bottom bracket drop, the higher above the _*O*riginal *A*xle *P*lane_ the Free Radical dropouts for the NEW rear wheel are rotated.

At some point, the bike is going to be set back down on the ground - at which point the _*O*riginal *A*xle *P*lane_ disappears, and a _*R*eal *A*xle *P*lane_ is defined between the axle of the new wheel location (the _original frame's dropout_ is sitting somewhere below the _*R*eal *A*xle *P*lane_). The implication is a Slacker Head Tube Angle.

*The Fix:* I can either *(a)* play with fork axle-crown height (A-C) and wheel & tire size selection , or *(b)* come up with a technique to space the Free Radical's tongue higher off of the chainstay bridge to "lower" the new wheel.

For now, I'm going with Method *(a)* - adjusting the A-C.

*My first step* was to select a rainy Sunday afternoon to take a break from working on the house, and put some of my nifty tools to bicycle use. I installed the Free Radical onto the Buzz Bomb and set up shop with a PLS180 leveling laser, a Craftsman digital angle finder, a tripod, ruler, tape measure and a bunch of crap I could use as shims.

*Horizontal laser line represents my Reference Axle Plane*










The frame needed to be set to a reference point, so I chose to level it so that the Buzz Bomb's dropouts were on the same horizontal plane as the Free Radical's dropouts - the _*R*eference *A*xle *P*lane_. Not that I want to ride the bike this way, but it's a known point from which I can make measurements.

*Laser projects through frame and FreeRadical's dropouts*










*It wasn't lined up absolutely perfectly, but pretty damn close for what I'm doing*









From here, I'm interested in two measurements:

First, the head tube angle. Using my digital level, the _*R*eference *H*ead *A*ngle_ is at 70° - a little too slack for this 29"er. The stock Buzz Bomb, being a 29" frame, is designed with a 72 to 72.5° head tube angle. Initially, that's what I'll be aiming for with the Xtracycle kit installed.

*Measuring Reference Head Angle*










The second measurement is what I'm calling the _*R*eference *A*xle-to-*C*rown *H*eight_. This is the difference between 22 5/8" and 42 7/16" (from the bottom of the headset cup, to the laser beam that marks the _*R*eference *A*xle *P*lane_). This works out to 19 13/16", or 503mm.

Note that I've got the fat-stack Cane Creek headset cup on there, designed to lift the front end by a few millimeters.

That's something I can switch out for a slightly lower stack height if the need arises.
*Reference Axle-to-Crown Height, from below the headset cup&#8230;










&#8230;to the laser line representing the Reference Axle Plane*









Now I'm out of pictures to show, and get to do some math.

Using the reference measurements, a 503mm A-C fork _and_ similar front & rear wheel sizes would get me the 70° head angle, if I wanted that. But I want to shoot for 72° _and_ I want to run 29" on the front, if possible (the biggest _rear_ tire I can stuff into the Free Radical is a 26x2.35 Big Apple).

A solo bike with a typical wheelbase requires about 20mm change in axle-crown height to affect the head tube angle by 1°. But because the Free Radical stretches my wheel base by 15" - extending my wheelbase by about 38%, it now requires 27mm of A-C adjustment to dial in that same 1°.

(You can either trust me on that, or double check that the SIN of 1° x a 1473mm wheelbase and adjusted for a 70° head angle is 27mm - but it's easier just to trust me. Trust me.)
Great. If I want to steepen the head tube by 2°, I multiply 27mm x 2 and see that I need to lose 54mm from my _*R*eference *A*xle-to-*C*rown *H*eight_: 503-54=449mm.

So I need a fork with a 449 A-C height? No, wait, there's more!

The 29" wheel is going to raise the front axle, slackening my steering, and I need to account for that. Rather than measure actual tire dimensions (which I haven't yet purchased), I visited Schwalbe's website:

*Schwalbe Big Apple maximum dimensions*










Table lifted from https://www.schwalbetires.com/tech_info/tire_dimensions 
Taking the max diameters listed for the 26" and 29" versions of the 2.35 Big Apple, I note a 62mm difference (745-683=62). But only half of that is below the axle, so I cut it in half to 31mm. Yikes! That's a whole 'nother degree I need to account for in my axle-to-crown length. 449mm-31=418mm.

Hmmm, a 418mm A-C height 29er fork&#8230; Surly has two 26" suspension-corrected forks I can choose, both of which will accommodate 29" tires.

The Surly 1x1 rigid fork has a *413mm axle-crown height*, which is pretty close to what I'm looking for, but the clearance will be close - or non-existent - for the 2.35 Big Apple.
*WTB's Exiwolf 29x2.4 barely clears a Surly 1x1 fork designed for 26" wheels*










Photo lifted from Singlespeed Pimp on Flickr

Surly's 26" Big Dummy fork ought to clear the 29x2.35 Big Apple with a more comfortable margin, and the *425mm A-C height* is only 8mm taller (0.3° slacker) than what I'm aiming for.

BUT! Surly's two forks I identified have 45 and 43mm of forward offset. The original White Brother's CX-1 fork this frame was designed around had 38mm of forward offset - 7 and 5mm differences. For every millimeter of increased forward offset, I can slacken the head tube angle by 0.1°.

*Looks like the Big Dummy fork is it!*










Image lifted from UniversalCycles.com

Alternatively, I could plug in 650B or 26" front wheel sizes, but I'd need to adjust my aiming points for slacker head tube angles - likely involving swaps to longer 29"er suspension-corrected forks - weird, huh?

Oh&#8230; one last item to check out: bottom bracket drop - or in this case, how low is it going to be to the ground?

This is what I started with at _*R*eference *A*xle *P*lane_ - about 2" (52mm) of drop. If I were to run 26" x 2.35 Big Apples front and rear at this reference setting, I'd have a bottom bracket height off the ground of about 11.4" (~289mm). Maybe a little high for a pounding pavement cargo bike.

*Reference BB Drop *










But, with a shorter fork and a bigger front wheel/tire, it's going to be lower. How low?
+ 503mm _*R*eference *A*xle-to-*C*rown *H*eight_
- 425mm Surly Big Dummy Fork A-C height
+ 031mm Difference in tire height below the axle, 26" vs 29" Big Apples
= * 47mm * (actually, it's *42mm* after accounting for the effect the ~70° head angle has on the fork measurement).

This is the measurement at the front wheel. An adjustment is required because the bottom bracket is about half the distance from the rear axle as the front axle is, and everything is pivoting around the rear axle.

So, just for shits and giggles:

1093mm=Buzz Bomb original wheelbase 
450mm=original Buzz Bomb Chainstay
381mm=Free Radical additional length (~15")

I just need to calculate the ratio of the _*N*ew *C*hainstay *L*ength_ (CS + Free Rad) to the _*N*ew *W*heelbase_ (Buzz + Free Rad). This is: 
(450 + 381) / (1093 + 381)=831 / 1473=*0.56*

My 42mm front end adjustment x 0.56=a 24mm change in bottom bracket height, bringing it down to 76mm (compared to the laser-line _*R*eference *A*xle *P*lane_ in the previous photo*) - about in line with many road bikes.

*Net effect:* ~10.3" (~262mm) BB height off of the ground. That's maybe a touch low, but not too bad for hauling groceries and a baby around town.

*Anybody got any comments before I order my gear?* It's going to be interesting to see how close my calcs are to reality once I gather the parts and have a working bike to measure.

_* BB drop is actually greater, because it's measured from a line drawn between the two axles. On most bikes with similar sized wheels front and rear, this wouldn't be a factor (i.e. MY *R*eal *A*xle *L*ine stops being horizontal, because of the 69er combo). I'm actually not sure of the implications with the bigger front wheel on this build, but I think BB drop measured in the traditional manner should be around 96mm - nearly 4"!_


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## Walt (Jan 23, 2004)

*I doubt it matters*

Cargo bikes ride like... cargo bikes. The HTA, within a few degrees, isn't even noticeable, IMO, once you add a couple of feet to the wheelbase and load it up. It's not like you're going to be ripping up the singletrack on it. I would just leave it alone and ride it as-is.

If you insist on modifying things, I'd modify the tongue to raise the dropouts/bb to their correct height. Having a BB that is way too low can suck a lot, though to be pair it will almost certainly be fine in this case, since I'd be amazed if you could get the bike leaned over far enough to hit a pedal anyway.

-Walt


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## Speedub.Nate (Dec 31, 2003)

Walt said:


> Cargo bikes ride like... cargo bikes. The HTA, within a few degrees, isn't even noticeable, IMO, once you add a couple of feet to the wheelbase and load it up. It's not like you're going to be ripping up the singletrack on it. I would just leave it alone and ride it as-is.
> 
> If you insist on modifying things, I'd modify the tongue to raise the dropouts/bb to their correct height. Having a BB that is way too low can suck a lot, though to be pair it will almost certainly be fine in this case, since I'd be amazed if you could get the bike leaned over far enough to hit a pedal anyway.
> 
> -Walt


We'll see -- with the tandem I own, and compared others I've ridden, some are dogs and some are spritely. My C-Dale is somewhere in the middle, and I think it's directly attributable to too slack a head angle due to the suspension fork it wasn't originally designed for causing sluggish steering (Cannondale was apparently pretty non-discriminate with their tandem geometries, not making any changes for the introduction of suspension forks).

I have a GT Peace fork which would slacken the steering by another 1.5 degrees. Perhaps I'll swap between the Big Dummy fork and the GT fork to gauge the difference. Maybe I'll end up liking the slacker steering better?!? We'll see...

The funny thing is it took me just a few minutes to rig everything up and make the calcs; it tooks more hours than I care to admit to put together this post.  At this point, I think I just need to place my order and get my build on!


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## themanmonkey (Nov 1, 2005)

OK, I've been taking a hiatus from MTBR, but your post has pulled me out.

JUST BUILD THE BIKE. Stop trying to second guess what would be better and build and ride the bike. There are so many different parameters you're getting into that you won't know until the bike is being ridden. Cargo bikes are weird creatures and they all work differently with and without load.

Build the bike ride it and the decide what you like and don't like and then make the changes. I've been playing with cargo bikes for what feels like forever. My mechanical mentor Val Kleitz who I spent 8 years working with is a freak about cargo bikes. We spent many years designing and building and modding them and the key thing is to just build them and ride them. You can watch Val talk about cargo bikes here


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## Speedub.Nate (Dec 31, 2003)

themanmonkey said:


> OK, I've been taking a hiatus from MTBR, but your post has pulled me out.
> 
> JUST BUILD THE BIKE. Stop trying to second guess what would be better and build and ride the bike. There are so many different parameters you're getting into that you won't know until the bike is being ridden. Cargo bikes are weird creatures and they all work differently with and without load.
> 
> Build the bike ride it and the decide what you like and don't like and then make the changes. I've been playing with cargo bikes for what feels like forever. My mechanical mentor Val Kleitz who I spent 8 years working with is a freak about cargo bikes. We spent many years designing and building and modding them and the key thing is to just build them and ride them. You can watch Val talk about cargo bikes here


What'd be a really valuable contribution from you is some input on Val's thoughts on steering angles. Am I right trying to stick with my original Buzz Bomb geometry, which I really liked? I couldn't find any geometry data on Xtracycles Radish bike, so I'm using tandems as an example, which seem mirror solo-bike steering geometries.

There's no chance I'm doing anything custom with this build -- it's all off the shelf. And against your advice, I just want to make my best attempt at getting the setup close to right at the start, mainly to avoid monkeying around with multiple forks. I have no problem thinking out something before jumping in!

BTW, welcome back to MTBR. I, like you, have been on a LONG hiatus and this is a REALLY enjoyable way to get back on.


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## eMcK (Aug 22, 2007)

Wow. I've had at least 4 frames on my Xtracycle, about to install a fifth. I've also spent a good deal of time on a Big Dummy.

Build the bike and ride it. you are Way over-thinking this. Really. It will be a pig no matter what you do. The inherent flex to the system will be a bigger component of overall handling than head tube angle. Get it close to stock and forget about it.

Also, Walt, you might be surprised at how capable these things are in singletrack.


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## themanmonkey (Nov 1, 2005)

Speedub.Nate said:


> What'd be a really valuable contribution from you is some input on Val's thoughts on steering angles. Am I right trying to stick with my original Buzz Bomb geometry, which I really liked?


There are no original thoughts on steering angles it's just trial and affect for each bike and rider. Say you change your bars that will effect the front end more than 90% of the fork variations. If you're trying to stay with the original geometry just imitate it and go from there. Build the bike and then correct the things you don't like.

The problem is that worrying about the small details on paper doesn't tell you anything about how the bike actually rides. A Buzzbomb with the Xtracycle add-on will never ride just like the Buzzbomb. If you start with a known quality (Buzzbomb original stock) and add a single known change (Xtracycle rear) you can then have an idea of what needs to be changed to give you the ride you want.

This is the same kind of advice I give to first time builders. If you make as few changes as possible to a known quantity you then have an idea of what the changes affected. Good luck with the project. Cargo bikes are awesome fun and quite useful.


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## Speedub.Nate (Dec 31, 2003)

themanmonkey said:


> There are no original thoughts on steering angles it's just trial and affect for each bike and rider. Say you change your bars that will effect the front end more than 90% of the fork variations. If you're trying to stay with the original geometry just imitate it and go from there. Build the bike and then correct the things you don't like.
> 
> The problem is that worrying about the small details on paper doesn't tell you anything about how the bike actually rides. A Buzzbomb with the Xtracycle add-on will never ride just like the Buzzbomb. If you start with a known quality (Buzzbomb original stock) and add a single known change (Xtracycle rear) you can then have an idea of what needs to be changed to give you the ride you want.
> 
> This is the same kind of advice I give to first time builders. If you make as few changes as possible to a known quantity you then have an idea of what the changes affected. Good luck with the project. Cargo bikes are awesome fun and quite useful.


Ah! The hangup for me was I had no fork to use. I found myself having to choose between A-Cs of 410 to 500mm, plus the unknown of the smaller rear wheel (since a 29" won't fit). That's what spawned my measurements.

Got my starting point, I'm diving it! Thanks for the added info.


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## Speedub.Nate (Dec 31, 2003)

eMcK said:


> Build the bike and ride it. you are Way over-thinking this ... Get it close to stock and forget about it.


I think you guys are either scared of lasers or math. ;p Just kiddin' -- the best way for me to get this "close to stock and forgetting about it" was to think through it, short of having all the needed materials on-hand. I can't imagine how you're not seeing the fun of working through this exercise, putting some tools to a bike-related use, taking some fun pics and posting about it.

Anyway -- I hope somebody somewhere finds something useful in this post. Otherwise, keep spitting on my beautiful art *sob* 

I'll update in another week or two when I get 'er built. I'm super curious how close my numbers are.


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## smudge (Jan 12, 2004)

Speedub.Nate said:


> I think you guys are either scared of lasers or math. ;p Just kiddin' -- the best way for me to get this "close to stock and forgetting about it" was to think through it, short of having all the needed materials on-hand. I can't imagine how you're not seeing the fun of working through this exercise, putting some tools to a bike-related use, taking some fun pics and posting about it.
> 
> Anyway -- I hope somebody somewhere finds something useful in this post. Otherwise, keep spitting on my beautiful art *sob*
> 
> I'll update in another week or two when I get 'er built. I'm super curious how close my numbers are.


Nate, just do what feels best for you. I, like you, tend to calculate and think about every option I can conceive before moving forward with a given project. It can be a fun exercise and it can certainly uncover potential sticking points before you actually hit them but the reality is you won't know until you know. So keep doing what you're doing and calculate and theorize all you want but keep an open mind when you actually get this thing together. It may not ride how you expect and then you'll have to make practical changes.


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## themanmonkey (Nov 1, 2005)

Speedub.Nate said:


> Ah! The hangup for me was I had no fork to use. I found myself having to choose between A-Cs of 410 to 500mm, plus the unknown of the smaller rear wheel (since a 29" won't fit). That's what spawned my measurements.


That's actually even better for a cargo bike. Figure out the trail of the stock bike and imitate it with a 26" for and wheel in the front, no lasers needed. . . or sharks for that matter either. Basically this will end up just lowering the BB and a lower BB is better for stability on cargo bikes.


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## Speedub.Nate (Dec 31, 2003)

themanmonkey said:


> That's actually even better for a cargo bike. Figure out the trail of the stock bike and imitate it with a 26" for and wheel in the front, no lasers needed. . . or sharks for that matter either. Basically this will end up just lowering the BB and a lower BB is better for stability on cargo bikes.


You'd go lower than 10"? I'll admit that has me a little concerned, but as been said already, I probably won't be railing any berm shots on this bike. Numbers just didn't look friendly for a 26" front wheel, not without jacking up the front end.

Anyhow -- fork, wheels & rubber all ordered; should have it all on Monday. Gonna have some fun with the hubs, too.


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## themanmonkey (Nov 1, 2005)

I've ridden cargo bikes with really low BBs. If you're carrying cargo you're not really laying it down and you'll almost never pedal through a corner. You don't lean into turns as much as actually turning into them and getting the cargo weight as low as possible is better for control and general stability. Riding a cargo bike is totally different than riding a tandem.

I was a messenger on a long-john style cargo bike for 6 months and had to basically relearn how to ride a bike. Long-tail designs are a similar kind of change. What is good traditional design for a "standard" bike doesn't apply to cargo bikes. It just the same as if you were designing a recumbent, you take the book of normal parameters and throw it out the window. You build for the purpose.


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## fanzy4 (Aug 19, 2004)

A question a little bit off-topic: I thought the FreeRadical kit was not compatible with 29er wheels. How are you managing this ?

http://www.xtracycle.com/longtailtech/index.php/29er_compatible_Longtail
http://www.xtracycle.com/forums/viewtopic.php?t=1350


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## Speedub.Nate (Dec 31, 2003)

fanzy4 said:


> I thought the FreeRadical kit was not compatible with 29er wheels. How are you managing this ?


The rear wheel is going to be a 26" with a 2.35 Big Apple -- about the biggest tire the Free Radical is reported to clear (and even that is marginal).

It'll take a 700c x 35-37, and that's as close to a 29" tire as it'll get.

But you can see from my photo of the Free Rad's tongue across the Buzz Bomb's chainstay bridge that even 29" frames may require an extra little bit of attention. In my case, the chainstays are long enough that the tongue doesn't rest solidly on the chainstay bridge, and the bolt is going to end up behind the bridge rather than in front of it. I've got to make up a custom attachment plate to address this.


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## Schmitty (Sep 7, 2008)

I think the cargo bike team just pulled ahead of team recumbent.


-Schmitty-


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## derby (Jan 12, 2004)

Hey Nate! Just my SOP perspective, purely anecdotal. I think you are smart (as usual) to be concerned with the head angle with the slackening of the frame. I've found from going to slacker steering that using a shorter stem with wider bars gives more leverage to fight the increased steering flop without slowing steering feel. Plus you gain stability and leverage while standing to accelerate or climb.

Your weight distribution will be far more forward with the rear wheel extended so far back and exaggerate a steering flop problem, even if the head angle remained unchanged. Due to the added weight on the front wheel and longer wheelbase turning circle, going to a little less than original steering trail would probably be desirable. 

You knew all this already, I'm sure. I like your ambition to experiment and share the experience with everyone!


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## Speedub.Nate (Dec 31, 2003)

Heya, Derby. It's been a while!

Yeah, I hear ya -- I hedged my bet and added a couple of extra items to my order, to get my head angle another degree steeper, if need be: a lower stack headset, the shorter 1x1 fork, and a 2.0 front Big Apple. I'll have some options to play with.

I was looking at the Big Dummy specs and noted the 72 degree HA, which is steep for a 26" bike, but was done for exactly the reason you cited. I'll bet, when all is said and done, I'm going to end up happiest with a 73-74 angle. Some blog posts I read at Clever Cycles reinforced this.

Too bad there are no off-the-shelf 26" rigid forks with 51-52mm forward offsets in the A2C heights I need. That would have made my selection easier.

There's a big box gonna land on my doorstep next week that's going to make me busy!

I hope you're wrong about the wide bars -- I'm looking forward to steeling my wife's Marys.


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## ong (Jun 26, 2006)

Hi, Nate --

I moved from an Xtracycle on a light steel racing frame to a Big Dummy, and it was a huge improvement (mainly by eliminating flex). But, when I was using the original version, I used to get really bad speed shimmy. What fixed it for me was finding a fork with really low rake, for higher overall trail (a special Kona dirt jump fork). That ended up being much more important than head angle for me.

A couple of other notes -- the 2.35 doesn't really work well in the back. It's *barely* OK, but a real problem with a fender, and the chain hits the tire in certain positions. Schwalbe makes a 2.15" version of the same tire which works much better. I also ended up using Mary-like bars (actually a knockoff by Origin8), and getting a *very* upright position with lots of spacers.

- Jeff


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## Speedub.Nate (Dec 31, 2003)

Thanks, Jeff. I forgot to consider my handlebar height -- I'm glad you mentioned it. Every bit I lower the front end is going to require extra handlebar height, and it's also going to steepen the seat tube. I may need a seatpost with a healthy amount of setback.

The Buzz Bomb frame is pretty stiff aluminum. Not as stiff as a Big Dummy, but probably a good bit stiffer than steel.

I'll be running a gear hub with a 50mm chainline, so the chain/tire clearance shouldn't be an issue. Not sure about the fender fit. I'll be running an Eco Deck on top. Is that going to help or hurt matters?

A big attraction to me doing this project was reusing the Buzz Bomb frame, which has been sitting in a box and would have ended up on eBay. There are some killer closeout deals on the Big Dummy frames right now that would have saved me all the fun of this conversion and probably cost me around the same amount of money, but there was no excitement in that for me. I hope it works out to be something I'm happy with.


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## ong (Jun 26, 2006)

If the Eco Deck is that thinner aluminum one, then it should give you more clearance up top. The problem I've had with fenders isn't so much with clearing the snapdeck as with the back end -- I had to cut my fender short, since it couldn't fit inside the tailpiece of the bike.

I'm sure you'll be happy with the resulting bike -- I went to the Big Dummy because I carry passengers and really heavy loads a lot (and I'm over 200 lbs. myself!). With ~400 lbs on the bike, it was getting pretty flexy -- but it was definitely still rideable, and nothing ever snapped.

I got one of those crazy deals on the Big Dummy -- I think it was $550 before shipping, and even the shipping got negotiated down a bit. I'm happy with it, aside from some component issues (it was a major nightmare getting my hydraulic brakes working with 2m of hose, but that's not the frame's fault -- mostly my lame wrenching). 

Good luck!


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## Speedub.Nate (Dec 31, 2003)

ong said:


> If the Eco Deck is that thinner aluminum one, then it should give you more clearance up top. The problem I've had with fenders isn't so much with clearing the snapdeck as with the back end -- I had to cut my fender short, since it couldn't fit inside the tailpiece of the bike.
> 
> I got one of those crazy deals on the Big Dummy -- I think it was $550 before shipping,


Wow! What an amazing price! Is Surly clearing inventory to make way for a Bigger Dummy? I digress...

The Eco Deck is made of recycled plastics and has a series of mounting holes in it, resembling a cribbage board. It sits fully above the V-rack rails, for max tire clearance. I don't know how concerned I'll be with extending a fender all the way down at the rear.


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## Speedub.Nate (Dec 31, 2003)

Project update!

I ran into a small hurdle with the Buzz Bomb sliding dropouts interfering with the Free 
Radical, causing me to look around for options. I found something, and it's damn fine...

...an https://www.osbikes.com/bikes.htmlOS Bikes BLACKBUCK.

Justin at Bike-n-Bean near China Camp had this frame hanging on the wall, built once and 
used just long enough for the original owner to notice a slight frame alignment issue. 
Score!

It's not lost on me that I'm replacing one 'BB' with another. The geometries are very similar. 
The Van Dessel sliders are replaced by a pinch bolt EBB. Aluminum is replaced by steel 
(this, I hope, is not too much of a compromise).

Coolest of all: the curved seatstays nicely "fill in" the funky gap between the main frame 
and the Xtracycle, and the BB's color scheme looks like it was painted with a Free Radical 
in mind.

Here are a couple of fuzzy cell phone pics -- apologies for the quality. Time is short these 
days so the build is progressing slowly; I finished the wheels last week and won't have 
time to work on it again until next week -- hopefully to completion!


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## Val Kleitz (Feb 4, 2009)

Nate: Since you asked, a few thoughts:

Having fun with lasers is cool; I was smiling and chuckling as I looked through your pictures - hightly amusing, thank you for that.
The amusement factor comes from the knowledge that, try as you might, you will never factor in all the variables. It's fun to try, and even more fun to watch, but, really, riding it will be the test.
As far as bottom bracket height and head angle are concerned, you can do a lot by experimenting with the tongue height at the Freeradical/parent frame interface. The two immediate choices are above the chainstay bridge or below it - try both, and see what you can discover. If you do wind up mounting the tongue on top of the bridge, be sure to put a radius (or arc, as they are sometimes called) washer between the tongue and the bridge to keep the bridge from being destroyed. of course, custom plates would eliminate this problem, as well.
As far as front end geometry is concerned, I tend to favor low trail with fat tires, as this generates very little "wheel flop" and handles well at speed, too. Mine has a trail value of 39mm with Big Apple 2.35s, and I love the way it handles. The Radish has a trail value much higher than this (I forget, but I think it is somewhere in the neighborhood of 70mm), and while it is obviously not horrible to ride (at least, I have seen pictures of people smiling while they ride them), I would probably not recommend emulating its geometry. Really, anything between 35 and 50mm will work fine - I like low trail because I load up teh front end, but if you have no wieght on the front, a higher trail will be more appropriate.
With the NuVinci hub, your chain clearance will be lovely - I run the same hub with two chainrings and 2.35s, and have had no problems at all - even with full fenders. Hve fun with it - it's a very cool hub!


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## Speedub.Nate (Dec 31, 2003)

Val and others, this is water under the bridge as the necessary parts are now in my possession, but your comments confuse me: what am I missing?

If I haven't got a fork to start with, then I've got to start somewhere. A quick alignment exercise will at least get me a fork in the ballpark of what I want. What exactly would you have done without a fork on hand to start with?

A few of you have said that trail, not head angle, is what really matters. Given that my choice of off-the-shelf forks all come with approximately the same rake, exactly how is trail NOT tied directly to head angle? I see the two as completely dependent on one another, short of ordering a custom fork with rake of my choice. So again, I ask...


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## Speedub.Nate (Dec 31, 2003)

Val Kleitz said:


> With the NuVinci hub, your chain clearance will be lovely - I run the same hub with two chainrings and 2.35s, and have had no problems at all - even with full fenders. Hve fun with it - it's a very cool hub!


Val, are you also running Xtracycle's center kickstand with your Nuvinci? If so, how is the chain clearance in the stowed position?


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## Val Kleitz (Feb 4, 2009)

Nate: Granted that most forks are available in a very limited range of rakes, the trail is, indeed, dependent on the head angle. It would be nice to be able to order the same fork in, say, five different rake values, thus allowing the fine tuning of front end geometry. Since the bike industry does not work this way, I think that most of us would have chosen a fork based on tire clearance, similarity to the original, and aesthetics (not necessarily in that order), and then proceeded to tweak the geometry by altering the Freeradical attachment point, with many test rides. There is nothing wrong with your method, it just amuses those of us who approach it another way.

The stand I am using is a Rolling Jackass centerstand (go figure). I believe that it offers a bit more chain clearance than the Kickback, but not a lot more. I have no interference problems because I am using a two pulley chain tensioner, which lowers the lower run of the chain. I realize that you do not need such a device to tension your chain, but you may want to consider one anyway. Many riders have found that the Xtracycle system flexes enough vertically to make it very difficult to keep a simple cog and chainring style of drivetrain adjusted. A spring loaded tensioner will be forgiving of this type of flex, and a two pulley style will allow the use of multiple chainrings, if you wish. For pictures of the stand, see here: http://tinyurl.com/aqxfvx and for pictures of the chain tensioner(s), see here: http://tinyurl.com/das6m7

Really, the important thing is that you are having some serious fun putting it all together, learning a lot, and will have even more fun once it rolls. Ride on!


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## Speedub.Nate (Dec 31, 2003)

A couple more...

Still a little more work to go, but together enough to check my geometry. I hit my HTA 
target with 73.5-74° using the 413mm 26" Surly 1x1 fork, 29x2.0 Big Apple, and a Crank 
Bros directset headset with a 10mm lower stack height. The BB height off the ground is 
about where I expected it would be with the Buzz Bomb, except that this being an EBB it 
"in the 10-inch range". The rear deck is within a degree or so of level.










Good tire clearance with the fork. Again, Surly 26" 1x1 fork and a Schwalbe 29er Big 
Apple, 2.0" width.










Homemade chainstay plate. I made this up because the longer chainstay length of the 
29" frame meant there was no bridge for the Freeradical tongue to rest on. This plate 
consists of two pieces of 1/8" steel, sandwiching the stays, and a piece of 1x1 square 
steel tube inbetween. I'll be painting this up to keep it from rusting. I've yet to add another
bolt or two to keep it aligned and tidy looking.


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## Speedub.Nate (Dec 31, 2003)

Here's a dilemma I'm up against:










That first photo is of the chain on its way back to the rear wheel, threading neatly between 
the Freeradical frame member and the Kickback kickstand. Gearing in this mock-up is 
38x16, but ultimately I'll need something closer to 2:1.

Given the EBB adjustment, I've got a few chainring/cog options for snaking the chain 
through this gap.

But as soon as the kickstand is deployed...










...Kaboom!

I ordered up a smaller chainring to try to deal with this, but it can only move the chain so 
close to the Freeradical frame, so the Kickback will always impact it when extended.

A posted on the Rootsradical forum on Yahoo! Groups suggested a bigger ring and cog to 
try to get under the kickstand (over, as oriented in the photo where the bike is being held 
upside down). But to do so I think I'd need a 60T chainring and a 30T freewheel.


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## themanmonkey (Nov 1, 2005)

Damn, Nate that's a tough break. If I was in your spot I'd just toss a chain tensioner on and that should give you the clearance. Once it's built and you're riding it you'll most likely want to change something else. I know you're trying to go for that clean chainline.

I note that at Aaron's gallery all of the bikes seem to have rear deraileurs except Aaron's fixed version which has a standard kickstand.


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## Speedub.Nate (Dec 31, 2003)

themanmonkey said:


> Damn, Nate that's a tough break. If I was in your spot I'd just toss a chain tensioner on and that should give you the clearance. Once it's built and you're riding it you'll most likely want to change something else. I know you're trying to go for that clean chainline.


I can't cave in just yet.

I ran the numbers for a 60x30T chainring/freewheel combo, and it would drop (raise) the chain by about 1.5" at the location of the conflict. I think that, plus the EBB adjustment, would allow me to clear the centerstand by going underneath it.

But I only found one 30T freewheel option, which is a red flag because it might no longer be available when it comes time for replacement.

Circle A Cycles - Home









At $75, it's about $50 more expensive than a conventionally sized Shimano freewheel.


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## yourdaguy (Dec 20, 2008)

If the cranks would clear it (& I think they might) you could put the stand on backwards to move the problem closer to the front and facilitate smaller gears.


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## Speedub.Nate (Dec 31, 2003)

Another collection of pictures of the build.

I hastily got my hands on a 31T chainring (and after the fact realized the cranks I had
were 110, so had to run around to find a 94 - geez).










The chain threads nicely between the FreeRad and the Kickback. It harmonizes at a very
slow pedaling cadence, vibrating enough to rattle against the front bridge. At normal
speeds, it's smooth sailing, even over rough pavement. PVC tape over a small strip of
rubber will be my band-aid.

I have yet to solve my Kickback/chain clearance issue, so for the time being I won't be
able to deploy it.










Pedal clearance is very low. Bottom bracket height is roughly 10", right about where I 
estimated with the original Buzz Bomb frame. I'm getting some pedal strikes during very
slow speed maneuvering (turning around in driveways or at tops of hills, where I have to
pedal a little to keep forward momentum); smaller pedals may help, but I'll have to ratchet
the cranks as if I rolling through a rock garden or narrow rain rut off road.

On the plus side, the low BB height will keep my center of gravity lower when I have a
load. The small chainring certainly leaves me with plenty of clearance.










Something I failed to anticipate was how low the head tube would end up in relation to
saddle height, due to the short fork. Spacerpalooza! The handlebar, as pictured, is a bit
high. I've already taken a liking to my obscene spacer stack so will switch to a flat or
negative rise stem before removing any.










As was discussed in https://groups.yahoo.com/group/rootsradicals/message/10984 a current post in the Roots Radicals Yahoo! group, I notice flex in this setup when I'm mashing or standing on the pedals, but it's not bad -- just not as stiff as an aluminum frame might be. We'll see how that feels with a load attached.

Steering feels spot on. 73.6° is the final number I've come up with, which is maybe ½ to 1
degree steeper than what I normally run on my other 29er frames, although shy of the 74°
angle called for by this frame's designer.

The Nuvinci hub is a mixed bag. I've done a lot to get it to work with this frame. While
torquing the wheel nuts to the values called out, the main wheel nut stripped well below
the target torque. I hope it's just the nut, not the axle threads. To mount / dismount the
wheel, a 5mm allen wrench, 15mm and 11mm wrench, and a 21mm open-ended wrench
are all required! Once out on the street, the hub is smooth as butter. Despite its weight, I
quickly forget it's there.


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## NHpug (Mar 30, 2007)

Nate, I'm missing something about the kickstand. Is it made to work on an xtracycle? If so, why the interference?


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## Speedub.Nate (Dec 31, 2003)

NHpug said:


> Nate, I'm missing something about the kickstand. Is it made to work on an xtracycle? If so, why the interference?


Yes, it's made by Xtracycle, but with a rear derailleur or tensioner in mind (so the chain would run lower, and underneath the kickstand).

A bit of a shame it's resulted in so much trouble for me, but it's not necessarily a shortcoming of the FreeRadical design. Designing a "universal fit" component such as this is bound to result in these types of compromises.


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