Does size really matter?

I switched off to my road bike for a couple or shorter easy rides during the week. My road bike has 172.5’s and my TT bike has 175’s for the cranks. I know I need a longer seatpost on my road bike due to fit issues, but do you really notice 2.5mm in crank arm legnth?

Secondly, is switching off between the two a bad thing?

You might not notice 2.5 mm but you *will *notice 5 mm difference which is actually the real difference from 172.5 mm cranks to 175’s- remember- there are *two *crankarms, opposing one another, each 2.5 mm longer. Big difference.

I have the opposite situation. 172.5’s on my TT bike and 175’s on my new road bike.

Just starting to get some mileage on the road bike and I can tell the difference. So far, I prefer the longer length…but its hard for me to determine if thats a function of the overall fit of the bike vs. the crank length alone.

Tom, as someone in the biz you may be able to answer this question: In another thread I’m looking for a compact crank with 177.5mm arms (currently have 175 because that’s what a new bike comes with). I’m reading some Zinn, and I think I may need to even go with 180s. My question is, why do only the highest end cranks offer crank arms in this length? I would think and Ultegra SL would at least offer such, but I’m just seeing cranks the like of the 09 DA or SRAM red. Is there no such think as a middle (or upper middle) tier crankset with longer arms?

I don’t notice it initially just pedaling along, but having different road bikes w/ 175s and 172.5s, I think the longer cranks give a little more pop climbing out of the saddle, but in turn seem to wear my legs out faster as the rides get longer (don’t really compare w/ 175s on my TT/Tri bike, since the type of riding is apples vs oranges). I think the extra leverage lends itself to pushing bigger gears, which can be nice in some situations like hammering with a group, but the juice comes at a cost vs spinning more conservatively.

Yes. In the past I’ve used 175s on my road bike (now 172.5s on my newest ride). I initially went with 175s on my TT bike, but due to the very aggressive position, my knees were bowing out. Going to shorter cranks helped to increase the thigh-torso angle and improve my power. So yes, size does matter.

There are likely a couple reasons why only the high end cranks come in a range of sizes. It’s also a bit of a chicken-and-the-egg affair. A big part of what makes a crank high-end is that it does come in a full range of sizes, whereas the value priced stuff is only available in limited sizes.

At the manufacturer level I think there has been some decision made that if a person wants very specific crank sizing they are a high end customer.

To more directly answer your question I do know the SRAM Red crankset is available in 177.5 mm crank arm length with 50/34 chainrings. I don’t see any 180 mm cranks listed at our favorite SRAM distributor though, although such a thing may exist elsewhere.

Thanks Tom. I may just keep my eyes open then and see if a deal pops up. I’ve only raced on 175s, but my fitter thinks that with my femur length I would have a mechanical advantage with the longer cranks, and he’s never steered me wrong. I’ll stick with what I know until I see something at a price that makes the experiment more bearable if the longer arms don’t pan out.