markwebb

172 vs 175. Where does the 3mm make a difference?

At top the 175 is 3mm closer, but at bottom 3mm farther away. Does that mean you get more leverage pushing and a slightly longer stroke for additional power?

How do you determine fit 172 vs 175?

When should you choose longer vs shorter cranks?

AEO

it goes closer to the top, further forward, further backward and lower.

yes, more leverage, but at the cost of being able to spin smoothly.
crank length is usually decided by your leg length, but there's no solid formula. as a quick guideline complete bikes are already equipped with what the manufacturer deems you should use.

johnny99

Lennard Zinn was one of the tallest pro cyclists of his day. Today, he's an expert bike mechanic. Here are some of his thoughts on crank arm length (especially for tall people):
https://www.zinncycles.com/cranks.aspx

AnthonyG

The difference 3 mm makes isn't much if that's about the right length for you in the first place but if those lengths are a bit long or bit short for you then the 3 mm difference is quite noticeable.

The extra length gives you more leverage ONLY at the 9-3 o'clock position. At the 6-12 o'clock position it accentuates the dead spot. Visa-versa for shorter cranks so you even out your power delivery with shorter cranks. I think one of the important aspects of crank length that isn't discussed much is the impact they play on your aerodynamic position. Longer cranks have your knee's rising higher at the top of the stroke and this can make it harder to get into and maintain an aerodynamic position. Short cranks make it EASY to adopt an aerodynamic position. One of the things they achieve on TT bikes by steepening the seat tube angle is that by moving you forward on top of the cranks your knees don't rise as high anymore.

I'm a fan of shorter cranks rather than longer cranks for general use and one important factor to take into account is that you usually need to move the saddle rearwards when using shorter cranks in relation to longer cranks and when you do this everything is fine. Sitting forward with short cranks doesn't feel powerful in my experience.

Mind you if you have long legs then use long cranks.

Regards, Anthony

rizz

I went from 175 to 170 and can't tell any seat-of-the-pants difference.

Mr. Beanz

I think it's 172.5 which means only 2.5 mm which is .097 of an inch. So if I remove the insoles from my cycling shoes, I'll have a more powerful stroke and more leverage?:roflma2:

merlin55

Come on you guys....think about this....For a given rider longer cranks arms mean that your knee and hip joint moves through a slightly larger range of motion. Assuming you DO NOT change your seat height, the longer cranks would have your leg a little straighter at the bottom of the stroke and a little more bent at the top.

I rode 172.5 for about 15 years, and 175 mm for the last 20 years or so on my road bike, after finding that I like the longer cranks on my mountain bike. The difference is very subtle, it mainly depends on your leg length and pedaling style which you prefer. FYI I'm 6' and ride a 58 cm with plenty of seat post extension

Richard_Rides

You'll have blisters. But you'll save precious grams...

rmwkokomo

Going from 172.5 to 175 gives about a 1.4 percent longer lever - so yes more leverage.

Removing your insole only changes the relative height of your foot - no change in leverage.

531Aussie

(They're more than likely 172.5mm cranks, but....). This means that due to them being 3mm further away at the bottom, you have to lower your seat 3mm, which effectively doubles the length at the top (making them 6mm closer at the top), which is, in my opinion, the main conundrum with long cranks: you get more leverage, but they're harder to push for most of the downstroke because your knees come up much higher.

I'm 6ft with long-ish legs (35.25"/89.5cm inseam) and size 43 shoes. I used 180mm cranks for a year, but in the end I hated them coz I felt I couldn't "get on top of the pedals" to really pound them. I went back to 175s for a month, but now I use 172.5s. I prefer the relatively higher position I get over the pedals with 172.5s. In my opinion, crank length is mostly about position, not so much spin, unless you're a sprinter

The increased knee flexion could also cause injuries

531Aussie

ha! No, removing your insoles won't move the pedal further forward at the 3 o'clock position.