Should I use the same length cranks on both road and tri bikes?

Triathlon Forum
1

I recently moved to shorter to cranks (165mm) on my tri bike to improve my position (which BTW was the best advice ever). Should I keep the same length cranks on my road bike or would 167.5mm cranks make much of a difference? I am 5’8" with 81.5cm leg length.

Thanks,
Joe

2

You are very, very unlikely to feel the difference. You should adjust your seat height accordingly though, even though it’s only a few mm.

3

Don’t worry about it…I rountinely go from 170’s on my Tri bike to 172.5 on my road and 175 on my MTB with no problems at all (as do MANY others I know).

Scott

4

I switch cranks on my road bike for crits (very tight turny courses) where i use 172.5 while I use 175mm for hilly races and TTs.
For training, I always go with the shorter cranks. Easier to spin.

5

I am 5’8" with 81.5mm leg length.

Can you give us a few more significant figures on leg length? Seriously, how do you measure to the nearest .5mm!?

Choosing thin socks or thick socks would be about the same as your crank length question.

6

I jump back and forth between 190 and 180. I agree that you probably won’t notice 2.5 mm.

7

Changed the post to reflect cm not mm. I am a pediatric dentist and work in 0.5mm increments daily. What other significant figures would you like for leg length?

I ride sockless…always.

8

I will be moving from 172.5mm to either 165mm or 167.5mm on the road bike. I moved from 172.5mm to 165mm on the tri bike and the difference was significant in comfort and performance. I guess I am trying to decide whether or not the exact same cranks are a necessity or at all beneficial if I am changing them anyway.

9

I would hold off before buying a new crankset to replace the 172.5 unless you already have one. When climbing on the road bike I find I like the extra leverage of the longer crankset, especially on steep climbs when I run out of gear and drop to a lower rpm, or when riding out of the saddle. I can still spin the longer crankset just fine at high rmp, but I needed the extra clearance of the shorter cranks in the aero position where I’m a little scrunched.

I’m sure some of the benefit of the shorter cranks in the tri position had to do with spinning a higher cadence and more clearance with your chest. That’s not really an issue on the road bike.

Chad

10

I would hold off before buying a new crankset to replace the 172.5 unless you already have one. When climbing on the road bike I find I like the extra leverage of the longer crankset, especially on steep climbs when I run out of gear and drop to a lower rpm, or when riding out of the saddle. I can still spin the longer crankset just fine at high rmp, but I needed the extra clearance of the shorter cranks in the aero position where I’m a little scrunched.

I’m sure some of the benefit of the shorter cranks in the tri position had to do with spinning a higher cadence and more clearance with your chest. That’s not really an issue on the road bike.

Chad

Totally agree with this. As you sit more upright, or have less drop, longer cranks tend to feel better.

11

So do you think muscle recruitment or “firing patterns” or muscle memory plays much of a role in performance when switching between lengths?

12

I notice the difference for about 10 pedal revolutions and then it sort of disappears. I suspect that 5-10 mm is just not that big of a difference when compared with the length of your leg and foot put together. 5-10 mm of seat height difference is something you notice but if you maintain the seat height then the crank length difference is negligible.
Chad

13

+1 to this.
I significantly doubt that anyone would have muscle memory thrown off by the matter of two mm at the end of any exercise (such as pedaling, running, swimming, etc)

Take running for example, the change in surface material is a lot more than 2mm as you run over it, but we all seem to do alright with that. Even streets as opposed to a track- not any significant difference after the first couple 100m.

I notice the difference for about 10 pedal revolutions and then it sort of disappears. I suspect that 5-10 mm is just not that big of a difference when compared with the length of your leg and foot put together. 5-10 mm of seat height difference is something you notice but if you maintain the seat height then the crank length difference is negligible.
Chad