TT Crank Length

Hi. I ride 172.5mm cranks on all my bikes, including TT. I’m looking at a sweet used TT bike upgrade that has 165mm cranks. The seller says he also rides 172.5mm on his road bike but went to 165mm for the TT bike due to tighter hip angle and wanting higher cadence. Anyone have experience with crank arm length as a function of road vs. TT? Thanks!

I ride 165’s on the TT bike and 172.5’s on the road but, more importantly I went from 172.5’s on the TT bike to 165’s. I’m probably going to oversimplify this…As far as cadence goes there is no magic. Just because they are shorter by 7.5mm doesn’t mean you will automatically spin faster and therefore generate more power. People seem to think this. You still have to push the torque. So, all they effectively did was cause me to ride a higher (harder) gear. Cadence is nearly the same and so is power at threshold. Maybe a little more with the 165’s but less than 5W and that could be due to a number of other factors.

The only possible benefit is being able to raise the saddle by 7.5mm to maybe open the hip angle, flatten the back more (maybe) and/or help breathing. I’m just not convinced they have helped in any appreciable or noticeable way for me.

I changed from 172.5 to 165.

The main reason was to reduce knee discomfort.

No difference noticeable in terms of speed either positive or negative, but I can get lower with less knee problems and so hopefully more aero and faster this year.

If anything, the hip angle should be more open, not tighter. Shorter cranks set off a cascade of changes:
Less distance from bottom bracket at the bottom of your pedal stroke means you can move up your saddle which means you can get a flatter back. That also means your legs don’t come up as high, hence the more open hip angle at TDC. More open hips mean a more forceful pedal stroke earlier in the rotation. There is no real effect on cadence to speak of.

I also ride 172.5 on my road bike but changed to 165s this year on my TT bike. It makes a big difference for me because I’m already short and getting my back flat is hard because stems only go so low. If the seat can go up 7.5 mm, that helps.

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p.s. you can use this app to find the difference when changing crank length (up or down):

So I want to revive this question…

I just got a fit for a new TT bike (looking at the discount P2/P3s since my race wheels are rim brakes) and my fitter is recommending I switch to shorter cranks. Right now I have 175mm cranks and I’m 193cm (6’4"). He said I could go as small as 155mm and has done the same thing with other athletes my size and it allows him to put them in more aero positions, and I would be a good candidate for that because I’m pretty flexible and generally comfortable in most positions.

Has anybody else had experience going small with their crank lengths to this much of an extreme?

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I’m 6’3" and have very long legs for my height.

I use 180mm road cranks and love them. I have used this length for 10+ years. I briefly went back to 175mm on the road after being talked into by forum posts elsewhere (lots of people want you to use short cranks). After a few months, I realized I just like the feel of longer cranks: I always felt a bit constrained in my range of motion on short cranks.

TT bikes, same thing for me minus 5 mm. I use 175mm on my Shiv TT. I use a Dash saddle that really allows me to rotate my hips forward so that my hip angle is about the same as my road position. 170mm cranks just don’t allow me to feel like I can power over short rollers in my tuck position very well. I can’t keep my speed up as well as the whole “bull rush the bottom of the hill” thing goes away a bit. You know when you drop into the little ring a little too early on a climb? It kind of always felt like I was having to spin too fast at the first part of any roller on the TT bike. That’s about the best way I can describe it. Also on descents in TT’s, I put it into a big ol’ gear, about 80-85 rpm on the descents while maintaining power target. Again, that felt easier on longer cranks.

I’m a huge fan of cranks that feel good and little short cranks just don’t feel good to me.

Here’s another test for you: do you skip step when climbing stairs? I have always skipped a step as it feels better and faster. I haven’t thought about it, I just do it. When I’m walking with my wife up steps and go one at a time, I feel like I’m slow and kind of uncomfortable.

Anyway, that’s my .02. Good luck!

I went from 175 to 165mm on my road bike with positive results in form improvement and no detriment in power. I’m 6’ but like @Otoman also have proportionally longer legs than average.

So YMMV. I don’t think there’s a right or wrong answer.

If it were me, I’d try the 155mm. Only issue is that I don’t think they’re very common. Who makes them and how much are they?

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I was thinking about this the other day, and I realized that a couple years ago I would be much more likely to take stairs 2 at a time, but then I went and re-worked my running cadence to be closer to 90 and now I take stairs 1 at a time pretty much exclusively.

I think I’ve settled on trying the shorter cranks, not sure if I’ll go all the way to 155, but maybe dip my toe in and go 165. Then if that works, go further.

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Cobb makes 155’s (and 145’s). I probably have the 155s sitting in my garage if you want to try them.

I experimented with shorter cranks on my road bike and TT bike for awhile. I had 155’s on the TT bike and 145 on the road bike. Now the 145’s are on the TT bike and I have 162.5’s on the road bike. Equipment drove the switch back - I was frustrated with pedal power meters and wanted a non hub based one (and evidently quarq makes 162.5 road crank, not a size I had heard of prior). It’s more noticeable in TT position. The only thing I noticed on the road over 165’s was not really thinking about clipping my pedal.

I’m 5’9" and averagely proportioned.