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

[KonaSS]

You will not notice the difference. If you road both back to back, maybe....but after 5 minutes your wouldn't. As long as your fit compensates for the change.

And as others have said, a lot of people are finding success moving to shorter cranks. At 5'11" I am moving all bikes to 170 (gravel, road, mtb). But only as I get a new bike. So still switch between cranks sizes with no problems.

[benb]

Depends on height and other things.

I've always had 175 as I'm 6'1" and basically any stock bike in my size will have 175s.

I ran 172.5 for a season once as an experiment.. in general I want to say it wasn't great. But no injuries or anything. I don't think I had great results that year and I partly blamed trying shorter cranks but it surely wasn't the only thing, probably changing jobs to a higher stress job was more significant.

It's 2.5mm, maybe we make too much of a big deal of it, but there are a bunch of knock on effects.

Did you move your saddle back 2.5mm to adjust? That's going to tighten your hip angles at the top of the pedal stroke enough to negate some of the more open angle from the shorter cranks. If you did that did you need to move your bars back 2.5mm or up some? Did you need to adjust your cleat position as a result of the cranks? For me I have big femurs and mostly my knees do not like being positioned forward of the pedal spindle when riding on flat ground. Shorter cranks mean my saddle goes back, and that shifts my CG back on the bike, lengthens the effective reach of the bike, and causes all kind of other issue. I can get a good fit a lot easier when the cranks are longer and my cleats are relatively far back on my shoes.

Do the super stiff road shoes which act as an extension of the lever arm negate some of all of this anyway? If the shoe is stiff enough you could be turning almost the same circle with your feet and it's just where the pedal is attached to your shoe that changes, at least for the power portion of the pedal stroke. It depends on what fit adjustments are made, and do you even have precise enough ability to adjust the bike? Lots of shops/riders probably don't have the ability to measure/adjust to down to 2-3mm accurately over and over.

I think I would greatly hate shorter cranks mountain biking. I have never tried shorter ones there. And when I go to the gym and hop on an exercise bike/spin bike I notice they usually have 165s or something and those feel absolutely ridiculous to me. But MTB has more low cadence stuff when navigating obstacles and ultra steep climbs and I think I would really notice it there.

There's the whole tri/TT argument about even if the shorter cranks reduce power it's worth it for the aero. But whether that is even meaningful for you depends on how your ride and where you ride. If there's lots of big climbs in the places you ride you're not going to be in an aero tuck all the time and maybe those shorter cranks are suddenly a net negative. It's gotta be more complicated than all the bike blogs make it out to be.

[XXtwindad]

Originally Posted by benb

Depends on height and other things.

I've always had 175 as I'm 6'1" and basically any stock bike in my size will have 175s.

I ran 172.5 for a season once as an experiment.. in general I want to say it wasn't great. But no injuries or anything. I don't think I had great results that year and I partly blamed trying shorter cranks but it surely wasn't the only thing, probably changing jobs to a higher stress job was more significant.

It's 2.5mm, maybe we make too much of a big deal of it, but there are a bunch of knock on effects.

Did you move your saddle back 2.5mm to adjust? That's going to tighten your hip angles at the top of the pedal stroke enough to negate some of the more open angle from the shorter cranks. If you did that did you need to move your bars back 2.5mm or up some? Did you need to adjust your cleat position as a result of the cranks? For me I have big femurs and mostly my knees do not like being positioned forward of the pedal spindle when riding on flat ground. Shorter cranks mean my saddle goes back, and that shifts my CG back on the bike, lengthens the effective reach of the bike, and causes all kind of other issue. I can get a good fit a lot easier when the cranks are longer and my cleats are relatively far back on my shoes.

Do the super stiff road shoes which act as an extension of the lever arm negate some of all of this anyway? If the shoe is stiff enough you could be turning almost the same circle with your feet and it's just where the pedal is attached to your shoe that changes, at least for the power portion of the pedal stroke. It depends on what fit adjustments are made, and do you even have precise enough ability to adjust the bike? Lots of shops/riders probably don't have the ability to measure/adjust to down to 2-3mm accurately over and over.

I think I would greatly hate shorter cranks mountain biking. I have never tried shorter ones there. And when I go to the gym and hop on an exercise bike/spin bike I notice they usually have 165s or something and those feel absolutely ridiculous to me. But MTB has more low cadence stuff when navigating obstacles and ultra steep climbs and I think I would really notice it there.

There's the whole tri/TT argument about even if the shorter cranks reduce power it's worth it for the aero. But whether that is even meaningful for you depends on how your ride and where you ride. If there's lots of big climbs in the places you ride you're not going to be in an aero tuck all the time and maybe those shorter cranks are suddenly a net negative. It's gotta be more complicated than all the bike blogs make it out to be.

Great answer. Lots to chew on there.

I guess the general consensus is that moving from a 175 to 172.5 isn’t going to be that big of a deal.

[Mark McM]

One thing that hasn't been mentioned yet is the affect of crank length on gearing. Moving from longer to shorter cranks will typically decrease the torque the rider generates, but will allow them to spin the cranks at a higher RPM. Power is a combination of both torque and RPM, so the power can remain the same as crank length changes. But, in order to spin the cranks faster at a lower torque, the drivetrain's gear ratio(s) have to be lowered. Or another way to put it, if a rider switches to shorter cranks without changing the gearing, to the rider it will feel as if the gear ratios have been increased.

I recently switched from 170mm cranks to 165mm cranks. After adjusting the saddle to account for the crank length difference, I could barely feel any difference most of the time. The two cranks felt "different", but most of the time they felt neither "better" or "worse" than each other. With the shorter cranks I could spin a little faster, and bend over a little more, but otherwise there there was hardly any noticeable change in performance. Well, except one. I found that when climbing the steepest slopes where I had to drop to my lowest gear, the gear felt a little bit harder with the shorter cranks, no doubt due to being able to generate less drive torque.

Sheldon Brown used to measure gear ratios not in gear inches (effective wheel diameter) or in development (distance traveled per revolution of the cranks), but in a system he called gain-ratio; this was a system that combined chainring/sprocket ratio with the crank length and wheel radius, to come up with a total gear ratio that accounted for wheel size and crank length. Gain-ratio is the ratio of the distance the pedals traveled to the distance the bicycle traveled. With shorter cranks the feet don't move as far for a given movement of the bicycle, resulting in a higher gain-ratio, which to the rider is effectively a higher gear ratio.

[Waldo62]

Originally Posted by XXtwindad

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.

Right, cyclocross and MTBs hadn't figured out clearance for pedal strikes, and gearing on dirt over the past 50 years (sarcasm). Also, with fatter tires and gravel-specific (eyeroll) frames, your bottom bracket is higher than on lower volume road tires. All that and the fact that every respectable crank manufacturer already makes 172.5s in 1x, double, and triple chainring configurations, points to the fact that there is no need for this "gravel-specific" crank. Praxis created a product for which a market should not exist. Also, last year I climbed Railroad Grade up Mt. Tam in 39-28 and 39-26, so someone is running that gear combo on dirt, albeit Tam isn't East Bay. You may also want to look up information on Jobst Brandt's dirt/mixed terrain rides and check out the gears those riders used.

[XXtwindad]

Originally Posted by Waldo62

Right, cyclocross and MTBs hadn't figured out clearance for pedal strikes, and gearing on dirt over the past 50 years (sarcasm). Also, with fatter tires and gravel-specific (eyeroll) frames, your bottom bracket is higher than on lower volume road tires. All that and the fact that every respectable crank manufacturer already makes 172.5s in 1x, double, and triple chainring configurations, points to the fact that there is no need for this "gravel-specific" crank. Praxis created a product for which a market should not exist. Also, last year I climbed Railroad Grade up Mt. Tam in 39-28 and 39-26, so someone is running that gear combo on dirt, albeit Tam isn't East Bay. You may also want to look up information on Jobst Brandt's dirt/mixed terrain rides.

This seems an odd topic for you to be litigating so fervently. Ascending Railroad Grade is practically road riding. Short version: I will happily follow you up Canyon/East Ridge while you run the aforementioned gearing. It should give us plenty of time to catch up.

Longer version: most modern gravel bikes have lower bottom brackets. Mine has a 75mm drop. My Cielo has a BB drop of 70mm, just for the sake of comparison.
All the major manufacturers have gravel specific cranks. (My current bike has the GRX) It might just be that you find the idea of “gravel bikes” superfluous. Which, of course, is an opinion you’re entitled to. But if you’re going to own a gravel bike, it’s helpful to have the accoutrements to accompany it.

[Waldo62]

Originally Posted by XXtwindad

This seems an odd topic for you to be litigating so fervently. Ascending Railroad Grade is practically road riding. Short version: I will happily follow you up Canyon/East Ridge while you run the aforementioned gearing. It should give us plenty of time to catch up.

Longer version: most modern gravel bikes have lower bottom brackets. Mine has a 75mm drop. My Cielo has a BB drop of 70mm, just for the sake of comparison.
All the major manufacturers have gravel specific cranks. (My current bike has the GRX) It might just be that you find the idea of “gravel bikes” superfluous. Which, of course, is an opinion you’re entitled to. But if you’re going to own a gravel bike, it’s helpful to have the accoutrements to accompany it.

You'll find plenty of articles discussing the superfluosity (yes, I just made that up) of gravel bikes and gravel components. They're marketing ploys pure and simple, and the buying public is eating it up because shopping and more shopping cures all ills.

[Jaybee]

Non-racers should have been on 48-32 or 46-30 the whole time. It makes more of the cassette more usable more often without spending so much time cross-chained. I mean, sure, I could probably make due with an old-school 46-39 CX crank, but I'm not MVDP and my rides aren't CX courses - they have climbs of 30 minutes to an hour on loose surfaces where I don't really want to turn 39/28 out of the saddle at 40rpm.

Back to the original topic, if you want an in-depth discussion of crank length, have you read Appleman's stuff yet?

[2000m2]

I had significant knee pain with 175mm cranks. To the point where after one ride, it hurt quite a bit to walk up the stairs from my garage. My other bike at that time had 172.5mm cranks and no knee pain there, so I now stick to 172.5mm cranks. Maybe I should explore 170's.

[Mark McM]

Originally Posted by Jaybee

Non-racers should have been on 48-32 or 46-30 the whole time. It makes more of the cassette more usable more often without spending so much time cross-chained. I mean, sure, I could probably make due with an old-school 46-39 CX crank, but I'm not MVDP and my rides aren't CX courses - they have climbs of 30 minutes to an hour on loose surfaces where I don't really want to turn 39/28 out of the saddle at 40rpm

This really depends on what you mean by "the whole time". Keep in mind that years ago the top (small) sprocket on freewheels/cassettes were larger than they are today. In the freewheel era, the smallest sprockets on freewheels were typically 13 or 14 teeth. Only a few special freewheels even had 12 tooth sprockets. With a 13 or 14 tooth small sprocket, a 52 chainring is quite manageable for a non-racer. When cassette freehubs first became available, the smallest sprocket available was 12 tooth, and most cassettes still started with 13 tooth sprockets. Even in the '00s, most cassettes started with a 12 tooth or smaller. It is only in the last 15 years or so that cassettes with 11 tooth sprockets have become common (remember that Shimano had to modify their Hyperglide freehubs to even take an 11 tooth sprocket, and the new freehubs were called Hyperglide-C).

Long story short, over the years, the smallest sprocket on drivetrains have gotten smaller, and only as the small sprocket got smaller has there been a need and desire for smaller chainrings. Sure, a crank with a 46 tooth big chainring might be fine today with a cassette with 11 tooth sprocket, but that's a gear that is still bigger than years ago when many bikes had 52 tooth big chainrings and 14 tooth small sprockets.

[unterhausen]

I used to think 172.5mm cranks felt a lot slower. Years later, I rode an entire randonneuring series on 175's. I switch back and forth between 170 and 175 all the time and really don't notice the difference.

I blame it on cognitive bias.

[XXtwindad]

Originally Posted by Jaybee

Non-racers should have been on 48-32 or 46-30 the whole time. It makes more of the cassette more usable more often without spending so much time cross-chained. I mean, sure, I could probably make due with an old-school 46-39 CX crank, but I'm not MVDP and my rides aren't CX courses - they have climbs of 30 minutes to an hour on loose surfaces where I don't really want to turn 39/28 out of the saddle at 40rpm.

Back to the original topic, if you want an in-depth discussion of crank length, have you read Appleman's stuff yet?

I'll read the article. I've seen his cranks. Total eye candy.

[mhespenheide]

To the original question, some people can tell a difference immediately and some people really can't. And they don't mind switching between crank lengths on different bikes.

I'm taller than average and prefer 177.5mm cranks. I have one bike that has 175's and I can feel the difference. It's quite noticeable to me in the first 10-15 minutes, and then a minor (but still noticeable) difference over the rest of the ride.

[Ozz]

I rode my Seven for a year+ thinking it had 175 cranks...went to a fitter, and he said they were 172.5...sure enough, stamped right there on the back...

I guess I was not discerning enough to notice.....ymmv

[wgp]

Just adding this article I just finished on Rouleur regarding the benefits of shorter crank arm length ...

link: https://www.rouleur.cc/blogs/rouleur...en-your-cranks

I usually ride 175, but my latest addition has 172.5 arms on the crank - I for the life of me cannot feel the difference!