172.5 or 175? Is there any benefit either way?

[BRad704]

I need to decide today which crankset gets Powerbeats glued on. I have the following sets, but not sure which way to go. I'm 6'1", 58cm frame; if it matters.

105 5800 172.5
Or
Ultegra 6700 175

I've always ridden the 172.5 until this week and only swapped to the 175 to test out a friend's stages PM. I don't know that I can tell a difference between the two.


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[Meisen]

I think it ultimately is about comfort and perhaps position. Some people notice, others don’t. I use a 165 on my TT bike to reduce hip angle impingement in aero, a 172.5 on my road bikes and 175 on the fat bike because that’s what it came with. There is of course some math on the impact of the length but ultimately it seems like it doesn’t make a big difference at least in my n=1

[grognaak]

Crank length affects your bike fit, mechanical advantage, and cornering clearance. Many cyclists will not notice any significant difference between those common lengths you mention.


Sheldon's two cents:

https://www.sheldonbrown.com/cranks.html

[earlfoss]

I ran 175 for many years and it worked great for me. Last season I decided to give 172.5 a try, and I perceive no great difference at all. I think the slightly shorter crank allows me to stay in the drops for longer. That alone makes the switch worth it in my eyes.

[BRad704]

Thanks guys. Good info and thanks for the link to the SB page.

Seems there's no advantage either way, both sets are within 50g of each other so weight isn't even a consideration.

Looks like I'll stick with it the 105 set to keep my group consistent.


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[tculbreath]

I am 6'1" and used to ride 175's, now on 172.5 exclusively. What I have noticed is they spin up faster requiring less leverage to turn over. I have enjoyed them more for Crits, climbing hills, and my cadence has increased a bit. If you appreciate mashing your pedals on flat land, I'd stay with a 175. Otherwise, the 172.5 is a nice change. Just my $.02

[Davist]

I ran 175s since I got "back in" as they came on the bike (58cm), my gravel and new bike came with 172s, not a huge difference but I can keep cadence better on the 172s..

[mhespenheide]

6'4" here. I ran 175's for over a decade, then decided that I wanted to try 180's. It took me over a year of riding not to notice them. I rode them for a couple years, then tried 177.5's; the 177.5's were almost instantly comfortable. So now I use 177.5 for almost everything, 180's for mountain biking.

If you can't tell a difference yourself, don't worry about it.

[benb]

I'm 6'1" and have pretty much always rode 175s. Most bikes in my size historically were coming with them over the time I've been riding. As I've moved on to building up frames I kept with it. I ride a 56 now mostly, and that would be annoying if I buy a complete bike as most 56s seem to come with 172.5mm cranks.

I did ride 172.5 one year. My perception was that it wasn't as good for me but I didn't know as much about fit then and it wasn't a great year anyway.

I have seen issues with hip angle at the top of the pedal stroke limiting how much drop I can run. IIRC I would be raising my saddle 2.5mm if I put 172.5s on, which would produce a 5mm drop in the top of the pedal stroke and open up my hips, which would probably allow me to drop my bars.

But the flip side is I think I'd have to increase my setback by a few mm as well to stay balanced with shorter cranks, which would decrease the hip angle at the top of the pedal stroke and negate any advantage. Cleat position might come into effect too though.

It's an expensive experiment if you have PMs.

My guess is it has to do with lots of things including ratio of femur:lower leg as well.

[Mark McM]

As far as the effect of crank length on power or efficiency: Despite a lot of hypotheses, theories, and multiple experiments and tests, no one has yet come up with a solid, repeatable correlation between crank length and power or efficiency. So instead, it comes down to other factors (fit, aerodynamics, pedal clearance, etc.) and natural preference (which may be related to individual physiology, types of riding done, or simply what a rider has become used to). So, I don't know that anyone can give any strong guidance as to which is better for you.

[dddd]

I find that saddle height is less of a sensitive issue when using shorter cranks, and that I can get in higher-effort workouts more safely (without knee discomfort) with shorter cranks when I have been off the bike for any length of time.

I've done serious training on 165's and was happy with them, my inseam is about 32", in my 50's now.