I use 172.5mm cranks on my road bike (5-10" tall, ~32" inseam). I’m wondering if longer a crank – which typically is a good idea for pure road TT – would make running off the bike harder. IOW, does a longer crank work the hamstrings more than a shorter crank? I’m not thinking about anything drastic here, just 175mm (convenient, since a friend has a spare crank with that length arms that I can use for the tri/TT bike I’m building).
If it’s a friend’s spare TT crank that you can use, I say use it. You might not be able to tell the difference.
Years ago, when I used to ride a lot, I could tell the difference between the two crank-lengths. An hour ago, I just got off some rollers switching back and forth between these two lengths by switching bikes, and I couldn’t tell the difference.
At least, not today on rollers on those two bikes.
180’s for me and I have not found them to overwork the muscles anymore than the shorter size cranks.
Some people may say that 180’s are too long but I like them.
Before you stress over these tiny differences in crank lenghths, you may want to be aware that much of the ‘traditional’ info out there on bicycle crank length is based on zero science and even less common sense.
There are a few good websites that try to point this out. Here is a good quote from one: “The major manufacturers create a false impression of the precision required by offering 2.5mm increments within a very small range. Although top riders often express a preference within that micro-range, performance gains from 2.5mm of adjustment will surely be psychological.”
Anyway, read a bit here, and then you will be able to decide the best options for yourself:
I say try it. I’m an inch shorter than you and I had a chance over the summer to ride a pair of Profile carbon cranks. I didn’t think going from a 172.5 to 175 was going to make a big difference…I was sorely mistaken. I ride at a higher cadence as I’m just not built to be a “masher” and for me it just really seemed to slow my cadence. I tried the 175’s over rides that I knew well over different days so I wouldn’t jump to a conclusion either way. For some I’m sure it’s not a big deal but for me it wasn’t worth it.
Miguel in the 'No…El Tribato
I found the opposite was true. I was riding 180’s and decided to ride 177.5 since I’m “getting-old” and changing to a shorter crank seemed like a good idea to “spin” faster. I figured it was harder to push the 180 so I opted for a shorter crank. Well…hell…that didnt work at all. So , now I’m back with the 180’s on both my tri bikes. The change never affected my run times but did affect my bike times. The 180’s were/are faster for my body type (really long legs at 37" inseam), and riding style. Over the past year I’ve concentrated on a slower cadence, probably about 90-95 or so. I was trying to hold just over 100 before then. The slower cadence appears to produce faster bike times for me
Longer cranks generally don’t work the muscles any more than shorter cranks because people are not using those muscles very much anyhow, unless they are using PowerCranks. With PC’s it can make a big difference and we recommend longer cranks for those primarily interested in running improvement. I predict it will hardly make any noticeable difference with regular cranks. Try it and report back.
I should add that I am definitely a masher by nature, preferring 80rpm over 100rpm anytime, given equal power output.
I’ll try it out and report back in a couple months after it’s all assembled and I’ve tested it.