# Must have SHORTER CRANKS!



## NukeDOC (Nov 11, 2011)

ok so i have jumped on the shorter crank bandwagon, and i am a true believer. i already have a 155mm on my single speed, and a 150mm on my triathlon bike, with both showing noticeable improvements in speed, aerodynamics, and most importantly... knee pain. 

so... 
i have a jamis xenith race with a BB30 bottom bracket and 170mm gossamers. this is my favorite bike... but now i refuse to ride her because of the fact that i do not yet have short cranks on her.

i have two options, and though money is a definite factor, overall longterm satisfaction bears a little bit more weight. so now my question is out of my options which would be "smarter"?

option 1: BB30 to threaded 68mm adapter. permanent solution as far as i know, so no turning back, but at least i could sell my old crank set with the bottom bracket which would make it an easier sell. from what i understand, the bearings and the "cups" would need to be removed, then the adapter press fit into the frame and sealed in with loctite... FOREVER. not sure about any warranty voids yet. but this would give me the ability to install a square taper BB to which i have a whole bunch of options of brand and length of cranks to install. total conversion shouldnt cost me no more than $200 with installation (i would rather pay someone to make sure its done right and possible avoid warranty violation, though i can do it myself).

option 2: 150mm RotoR 3D+ crankset for BB30. flat out swap. easy peasy. just not on the wallet at about $700 shipped. and selling my gossamer crank arms for about $15 (if that) isnt even making a dent in that. but the swap would be easier, i can do it myself. i dont have to worry about press fitting anything into a carbon frame (always scary to me). and i for sure am not voiding any warranty by doing a basic bolt on swap. but SEVEN HUNDRED BONES!

opinions?


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## cda 455 (Aug 9, 2010)

NukeDOC said:


> ok so i have jumped on the shorter crank bandwagon, and i am a true believer. i already have a 155mm on my single speed, and a 150mm on my triathlon bike, with both showing noticeable improvements in speed, aerodynamics, and most importantly... knee pain.
> 
> so...
> i have a jamis xenith race with a BB30 bottom bracket and 170mm gossamers. this is my favorite bike... but now i refuse to ride her because of the fact that i do not yet have short cranks on her.
> ...


I'll throw this out: 

Have you tried looking at BMX cranks for tapered-square axles? I bought a 180mm BMX crankset for tapered square axle to experiment much like what you have done. I believe they sell crank length that you're looking for. The problem is that they only hold single chainrings. Here's the website where I bought my crankset:

United Squad BMX Seat Post Clamp 1 1 8 28.6mm Black items in BMXGuru store on eBay!



Are the noticeable improvements logged/charted via cycle computer? 

What is your inseam/sit bone length?


I'm the exact opposite of you: I went with longer cranks, 180mm.

I have 170mm on my HT MTB and 175mm on my FS MTB. Bought a BMX 180mm crankset and swapped it onto the HT to see if I like them. So far I love the longer cranks! But I haven't gone on a ride longer than 20 miles, though.

My inseam/sit bone length is 33".


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## NukeDOC (Nov 11, 2011)

BMX cranks are what i am using on my single speed and my tri bike. but those both have square taper bottom brackets. thus my dilemma, because my jamis has a BB30 bottom bracket.


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## milkbaby (Aug 14, 2009)

I was intrigued by your problem and did a little googling... and I found this:
Short Triple Chainring Cranks

Which reminded me of a custom crankset that was machined by a local rider that owns a high tech machine shop. Another rider needed two different crank lengths to adjust for an anatomical anomaly and had one crank arm machined down to a shorter length. You could just have the same done to your Gossamer crank arms. If you could find a shop locally, that might be the cheapest and easiest way to go. It doesn't seem like it would be expensive, since the upcharge over retail seems to be only about $50 from the bikesmith guy in the link above...


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## cda 455 (Aug 9, 2010)

milkbaby said:


> I was intrigued by your problem and did a little googling... and I found this:
> Short Triple Chainring Cranks
> 
> Which reminded me of a custom crankset that was machined by a local rider that owns a high tech machine shop. Another rider needed two different crank lengths to adjust for an anatomical anomaly and had one crank arm machined down to a shorter length. You could just have the same done to your Gossamer crank arms. If you could find a shop locally, that might be the cheapest and easiest way to go. It doesn't seem like it would be expensive, since the upcharge over retail seems to be only about $50 from the bikesmith guy in the link above...



Bingo!!


It looks like that's your answer :thumbsup: !


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## CamW (Mar 25, 2011)

I had a threaded adaptor loctited into my frame which I just had removed to install BB30 cranks so it can be done. Shop had to order a special tool to remove it but it is doable, just not 100% sure what adaptor you want.


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## milkbaby (Aug 14, 2009)

CamW said:


> I had a threaded adaptor loctited into my frame which I just had removed to install BB30 cranks so it can be done. Shop had to order a special tool to remove it but it is doable, just not 100% sure what adaptor you want.


Does your BB shell have an aluminum sleeve or is it just carbon composite? It seems like it would be scary to break out the loctited adapter directly from carbon...?


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## BicyclePhD (Apr 24, 2006)

NukeDOC said:


> so...
> i have a jamis xenith race with a BB30 bottom bracket and 170mm gossamers. this is my favorite bike... but now i refuse to ride her because of the fact that i do not yet have short cranks on her.
> 
> i have two options, and though money is a definite factor, overall longterm satisfaction bears a little bit more weight. so now my question is out of my options which would be "smarter"?
> ...


The adapter can be pressed out even with the loctite on it. The 2009 Xenith SL had a 2 piece adapter that had to be epoxied in, which is permanent. As for voiding the warranty by having an adapter installed, it will not void it.


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## CamW (Mar 25, 2011)

milkbaby said:


> Does your BB shell have an aluminum sleeve or is it just carbon composite? It seems like it would be scary to break out the loctited adapter directly from carbon...?


Mine is an all aluminium frame. I may be mistaken but I was under the impression all BB30 frames had aluminium sleeves of some sort. PFBB30 definitely has the potential for composite shells though.


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## nickt30 (Nov 29, 2008)

i have short femurs which makes my knee travel up and down further to allow my tibia and foot to travel from the top of the circle to the bottom. This is where i though my pain was coming from.....to much bent knee angle at the top......so i put on some short cranks to see if that would help. 

I put on a 155mm crank length. I had to apply too much force to get the bike rolling and the hill required much more effort.........my knees where killing me.

I went longer to 175mm and the forces on my knees were reduced......maybe that is why my knees do not bother me on my mtn bikes (each with 175mm).

From what i can tell the longer lever of the crank arm had more leverage and required less force to spin it.

Most of my problem solved.....i do have the right leg shorted then the other so a thick shim is between my cleat and show with the cleat pushed a bit forward to allow the same hip flex angle as the longer one......also changing the normal set back seatpost to a straight thomson got the arc of my knee movement over the pedal....(ofcourse i had to lengthen the stem to fit)

I am obviously not built for cycling.

I do want to try a Rotor set up.


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## rook (Apr 5, 2009)

NukeDOC said:


> ok so i have jumped on the shorter crank bandwagon, and i am a true believer. i already have a 155mm on my single speed, and a 150mm on my triathlon bike, with both showing noticeable improvements in speed, aerodynamics, and most importantly... knee pain.
> 
> so...
> i have a jamis xenith race with a BB30 bottom bracket and 170mm gossamers. this is my favorite bike... but now i refuse to ride her because of the fact that i do not yet have short cranks on her.
> ...





Are you sure you aren't going too short? Maybe, there are some 165mm cranks that you might like. Just curious, but how tall are you?


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