Crank arm length: 172.5 vs 175. Is there an appreciable difference?

[XXtwindad]

I’m curious. I usually use a 175mm length crank. Most people I know that worry about these things (and that might be the operative word) prefer a 172.5.

The reason I ask is that I’m really intrigued by the new Praxis Zayante gravel crank and that only comes in a 172.5 length (or shorter).

[Turkle]

I switched from 175 to 172.5 because I was much more comfortable when riding in the drops with the shorter cranks. My fitter actually wanted me to go to 170 but that was too drastic a change for me.

I have one bike still on 175 cranks and it's really noticeably uncomfortable when I'm trying to get aero... Which reminds me I have to swap those out. Hmm.

I think that something like crank length really matters when you're at the extreme end of your position, up against the limits of your flexibility. At that point, I really notice small differences like 2.5 mm!

[dcama5]

Interesting question for sure. I have 3 road bikes (and no other bikes) 2 have 175mm cranks and 1 has 177.5 cranks. However, I cannot feel any difference between the 3. If the difference is 5mm, I can feel it, but if the difference is 2.5mm, I cannot.

[Ewiser]

A friend who is a bike fitter has found Linder cranks cause knee issues over time. An recommends shorter cranks.

https://youtu.be/pubilU2QAaA

[madcow]

If the studies I read are valid, which I believe they are, then there is no downside to going shorter. Personally I'd say skip the 172.5 and go down to 170 or even 165...

Here's a snippet from our deflection testing some years ago where we touched on crank length:

Over the years a lot of different arguments have been made about the benefits of longer/shorter cranks. None of which has really been thoroughly tested until Jim Martins study. Martin showed that length didn’t statistically matter when it came to power, once power was averaged around the entire pedal circle and not just in the forward position, it turns out that shorter cranks (down to 145mm) produced more average power than a longer crank. This conclusion however considers only average power and not other factors which definitely have a bearing on real world use. Damon Rinard followed up the Martin study with some of his own testing comparing the aerodynamic differences in crank length. In almost every case there was an aerodynamic improvement with the shorter crank and without a loss in power. So the power advantage and aerodynamic advantage, combined with shorter cranks generally allowing for a more aggressive or more comfortable position on the bike and less chance of repetitive motion injury we feel that shorter cranks are something most people should consider. We’re not saying they’re right for everyone, but if you’re on the fence as to which size is best for you, we suggest that you go for the shorter. If you’re interested in more on crank length we suggest reading the above articles as well as this article written by Frank Day for USA Cycling.

[Ken Robb]

We have had quite a few discussions on this topic that can probably be found in the archives. I can discern a 5mm. difference but not 2.5. When I went from 175 to 180 I was thrilled by how the extra leverage allowed me to muscle up hills in taller gears----until my knees started to object. I find it easier to spin 170mm cranks. 172.5 might be best for me but-------I don't remember ever owning a bike with cranks that length. I do fine with 175.

[rustychisel]

When I was super-fit and cycling a lot I could discern the difference between 172.5 and 170mm, but not now. Most of my current riding is done on 165mm fixed gear, but I'm a spinner anyway.

To the question: it matters if a) there are ground clearance issues with the longer cranks or b) there are hip angle issues with longer cranks and you're in TT mode or trying to get aero.

At present that second aspect is an issue to me, flexibility at 60 is not what it was at 40. Otherwise, ride what is comfortable to you.

[mstateglfr]

6'5.

Main road bike- 175mm praxis zayante
Backup road bike- 175mm praxis alba
Another road bike- 170mm shimano crank
Gravel bike- 172.5mm praxis zayante
Commute bike- 180mm Sakae triple crank from the 80s

I really can't tell the difference. Or maybe I can and don't care, but the end result of those two things is the same- I can happily use them all.

My geavel crank is 172.5mm because I got a good deal on it and partly justified that it makes sense to have it be slightly shorter to help reduce the chance of pedal strike since the bb drop is more. That justification is likely quite worthless though.

[pinoymamba]

5'8 on 172.5

[Waldo62]

Cranks on my bikes range from 175 to 185, and I can tell the difference. I like 175s the least. I rode 190s for a while and enjoyed them quite a bit.
What manufacturer in its right mind only offers cranks 172.5 or shorter?

[Tandem Rider]

I have rode 177.5s back in the day for road races and training. I rode 180s in TTs and 175s in crits. I have ridden 175s for everything for the last 25 years. I bought a new gravel bike last year, it has 172.5s on it, my knees have started hurting riding it the last couple of weeks. I would say it matters to some people, but it's an individual situation, unfortunately, it's a little costly to experiment.

[XXtwindad]

Originally Posted by Waldo62

Cranks on my bikes range from 175 to 185, and I can tell the difference. I like the 175 the least. I rode 190s for a while and enjoyed them quite a bit.
What manufacturer in its right mind only offers cranks 172.5 or shorter?

They’re gravel cranks, so the concern is for pedal strike. Praxis road cranks come in longer lengths.

[Waldo62]

Originally Posted by XXtwindad

They’re gravel cranks, so the concern is for pedal strike. Praxis road cranks come in longer lengths.

I find the idea of "gravel cranks" to be laughable.

[XXtwindad]

Originally Posted by Waldo62

I find the idea of "gravel cranks" to be laughable.

Not really. You’re dealing with larger volume tires, so chain stays, derailleurs, and cranks have to correlate. I’m far from a tech wiz, but there’s nobody who’s running a 53/39 and 11-28 on the East Bay dirt.

[Tychom]

I've been on 175mm for years on two road bikes, one gravel and one mountain bike. With a further road bike having 172.5mm cranks mounted.

Having noticed no obvious difference previously with the one bike with 172.5mm cranks, and having a bit of a knee issue in recent years at the top of the pedal stroke, I've now moved from 175mm to 172.5mm on my road and gravel bikes and from 175mm to 170mm cranks on the MTB in order to reduce the range of motion and the angle at the top of the knee.

The 2.5mm change is not noticeable at all to me I have to say, not in terms of perceived power (or perhaps that's torque) nor cadence.

The 5mm switch on the MTB is far more noticeable - cadence has picked up, pedal stroke is smoother, less pedal strike, but I feel like I've lost a gear (it has be now thinking of getting a 12s groupset and a 50/51t cassette over the current 46t).

The knee is certainly no worse for the changes so zero regrets.