Crankset length?

[d_douglas]

I know there’s been a million threads on this, but what is the current whizzdome of what length cranks to run? I am moving from 175 to 172.5mm on road type bikes these days.

My MTBs are both 175mm but I know common wisdom has dictated I should use 170mm (got deals on 175mm, so I went cheap)!

If I was to get a new CX crankset is 170mm a bad idea? I am curious because I see lots of deals in this size, but don’t want to throw $$$ away just st because they’re cheap.

172.5mm? 170mm?

[weisan]

the cranks on my bikes are all over the map, 175, 172.5, 170. Couldn't tell a difference. That's just me and how I roll.

[oldpotatoe]

I know there’s been a million threads on this, but what is the current whizzdome of what length cranks to run? I am moving from 175 to 172.5mm on road type bikes these days.

My MTBs are both 175mm but I know common wisdom has dictated I should use 170mm (got deals on 175mm, so I went cheap)!

If I was to get a new CX crankset is 170mm a bad idea? I am curious because I see lots of deals in this size, but don’t want to throw $$$ away just st because they’re cheap.

172.5mm? 170mm?

Put 3 people in a room and ask about crank length and get 4 opinions..Really no 'common' wisdom, it's whatever 'feels' right. Remember that a foot travels further with a longer crank arm(the circle) but it's only 1.6cm bigger circle(170mm vs 172.5mm) plus there are issues with leverage, femur length, etc. So no rules or rules of thumb..remember BIG guys use 165mm cranks on the track..

True story..lady at Vecchio's with really nice Derosa, pink, Super Record group(older type)..in for overhaul..take cranks off..RH crank arm 170, left crank arm 172.5,,she didn't even know it was that way...

170 for cross 'may' be a good idea as shorter means faster spinup cuz it's shorter but differences really lost in the noise. Remember, shorter crank, raise seat..if height correct...

[Mark McM]

Over the years, several groups have done studies and tests to find the best crank length(s) for power and efficiency, and all of them have found that their results are inconclusive - people can pedal efficiently with a wide range of crank lengths (after given some time to get used to them). Riders often have a preferred crank length - but this generally turns out to be the ones they are most used to. Also keep in mind that cranks are generally available only in a small range of sizes. For example, where a given model of bike might come in a size range of 49 - 62 cm (+/- 12%) to fit a range of riders from 4' 10" to 6' 4" (+/- 13%), most models of cranks are only available in a range of lengths from 165mm to 180mm (+/- 4%).

Instead, cranks lengths are usually selected for a combination of personal preference and practical reasons. Keep in mind that crank length has an impact on other bicycle/frame dimensions, including BB height and pedal clearance, toe overlap, saddle setback and seat tube angle, etc., which is a large part of the reason that there are only a narrow range of crank lengths made. Since riders can easily adapt to different crank lengths, the geometry implications of crank length probably plays the largest role in crank length selection.

All that being said, the trend in recent years has been toward shorter crank lengths. The reasons are two fold; for racing, it has been found that shorter cranks allow a more acute hip angle, which allows a lower torso angle for aerodynamics; shorter cranks also reduce knee articulation angle, which can reduce knee strain for those with knee issues.

[velofinds]

I've found this (https://www.trainingpeaks.com/blog/the-benefits-of-reducing-your-crank-length/) to be a useful/reasonable bottom-line recommendation for me:

Trying to decide between a 165 and 170mm crank is a waste of time as there is too small of a difference to matter. An athlete should pick the length that allows them to most comfortably apply force to the pedals without restriction. This is why in the future, I think manufacturers will start making crank lengths in 5 to 10mm increments. Based on tradition, I think the 170, 172.5, and 175mm will stick around, but we are splitting hairs moving in 2.5mm increments.

If you are a taller individual (say, 6' and up) 172.5 or 175 are probably ok and, unless you are highly sensitive and attuned to your bike, you will probably not be able to tell the difference. I'm 5'8" and am happy on both 170 and 165 (and can't tell the difference switching between those two despite putting lots of miles on both). I can tell the difference between 170 and 175, however, and am happier on the former.

YMMV.

[LouDeeter]

I've experimented for 35 years between 170-175. I'm 5'7". I found that the longer cranks tended to cause more knee and hip pain when riding hard. Sheldon Brown and I had a conversation about the "leverage" of crank length and he convinced me that while seated, the chainring teeth number are the leverage, not the crank length, which comes into play more when riding out of the saddle. Since I live in Florida now, I rarely encounter a hill that requires me to rise out of the saddle so I have gravitated toward 170 more so to protect my aging knee and hip joints. I would tend to use the crank length more to get my knee over pedal position correct than anything else. This is just my unscientific opinion of course, but it makes sense to me.

[shortwaveradio]

You're going to get all kinds of opinions on the subject, but just to add another answer to your sample size of anecdotes, I'm 6'0 with a 31" inseam, and I run 172.5 on my road bikes, and 170 on my cross bike.

[d_douglas]

I've experimented for 35 years between 170-175. I'm 5'7". I found that the longer cranks tended to cause more knee and hip pain when riding hard. Sheldon Brown and I had a conversation about the "leverage" of crank length and he convinced me that while seated, the chainring teeth number are the leverage, not the crank length, which comes into play more when riding out of the saddle. Since I live in Florida now, I rarely encounter a hill that requires me to rise out of the saddle so I have gravitated toward 170 more so to protect my aging knee and hip joints. I would tend to use the crank length more to get my knee over pedal position correct than anything else. This is just my unscientific opinion of course, but it makes sense to me.

Thanks to all. Well, as I have a bum hip (ohhhh, I sound old saying that!), the shorter the crank might be the better one to choose.

I don't care about going fast, I just care about doing it for as long as possible - 25 more years?

[rnhood]

If you're 6' or taller, and not in an aggressive position, 175 is fine. 172 is also. If you are in an aggressive position with hip issues, a 170 is likely the better size especially if most of your riding is on flatter terrain. Otherwise, 172. Its a good compromise....even though I have not known anyone who could tell the difference.

[d_douglas]

Well, I tend to ride singletrack (MTB type stuff) on my CX bike. I don't race, but use that bike to do kind of stupid things :).

If I use an MTB 1x crank, I don't have a 172.5mm option - its 170 or 175mm for me...

[Jimbo]

THIS. Check studies with J. C. Martin as first or senior author. Other first authors will include Elmer, McDaniel, and Barratt. No significant effect on max power or efficiency in the range of 145-195. No effect on how power is produced during maximal sprinting (muscles spanning the ankle, knee, and hip). Minor changes in how power is produced during submaximal cycling.
Pick the length you like. Shorter may help you get more aero. Longer may help you work on your flexibility. Shorter may be easier on your joints as you get older.
Cheers,
Jim

Over the years, several groups have done studies and tests to find the best crank length(s) for power and efficiency, and all of them have found that their results are inconclusive - people can pedal efficiently with a wide range of crank lengths (after given some time to get used to them). Riders often have a preferred crank length - but this generally turns out to be the ones they are most used to. Also keep in mind that cranks are generally available only in a small range of sizes. For example, where a given model of bike might come in a size range of 49 - 62 cm (+/- 12%) to fit a range of riders from 4' 10" to 6' 4" (+/- 13%), most models of cranks are only available in a range of lengths from 165mm to 180mm (+/- 4%).

Instead, cranks lengths are usually selected for a combination of personal preference and practical reasons. Keep in mind that crank length has an impact on other bicycle/frame dimensions, including BB height and pedal clearance, toe overlap, saddle setback and seat tube angle, etc., which is a large part of the reason that there are only a narrow range of crank lengths made. Since riders can easily adapt to different crank lengths, the geometry implications of crank length probably plays the largest role in crank length selection.

All that being said, the trend in recent years has been toward shorter crank lengths. The reasons are two fold; for racing, it has been found that shorter cranks allow a more acute hip angle, which allows a lower torso angle for aerodynamics; shorter cranks also reduce knee articulation angle, which can reduce knee strain for those with knee issues.

[d_douglas]

jeez, what kind of answer is that :)?? You are basically saying to choose whatever you like - they all have pluses and minuses?

Joking of course - I know there is no right answer to this question - only opinions.

[Jimbo]

Uh, there are many opinions, but what I wrote was not opinion. It was the result of several carefully done studies.
Just ride!
Cheers,
Jim

jeez, what kind of answer is that :)?? You are basically saying to choose whatever you like - they all have pluses and minuses?

Joking of course - I know there is no right answer to this question - only opinions.

[Ronsonic]

I'm 6'1 and think I could pass a blindfold test between 175 cranks and 172.5.

I think.

I am certain that I don't much care.

[oldguy00]

I'm 5'10 and always used to use 175's just because. I've since switched mostly to triathlon and have switched to 165's. Easier on the hip restriction. I have hip issues too, CAM/FAI in one hip. After two years on them, 165's feel natural.

[mattsurf]

I've found this (https://www.trainingpeaks.com/blog/the-benefits-of-reducing-your-crank-length/) to be a useful/reasonable bottom-line recommendation for me:



If you are a taller individual (say, 6' and up) 172.5 or 175 are probably ok and, unless you are highly sensitive and attuned to your bike, you will probably not be able to tell the difference. I'm 5'8" and am happy on both 170 and 165 (and can't tell the difference switching between those two despite putting lots of miles on both). I can tell the difference between 170 and 175, however, and am happier on the former.

YMMV.

Exactly the same, 5'8'' tall, I cant tell difference between 165 and 170, however, 175 feel horrible.

I use 170 on all my bikes now

[93KgBike]

I bought a CL bike that had a 172.5/175 l/r setup that I thought would be terrible, intolerable, unrideable. It wasn't any of those things. It was more like, hmm, non-optimal. Still I changed it like the next morning and then sage smoked the whole frame, rinsed it in holy water and got a tarot reading.

I like 165s for track and technical single track. And for sitting up high.

[Mark McM]

When I switched from 170mm to 172.5mm cranks on my road bike, I noticed right away, and found I preferred the shorter crank. But I didn't notice the difference in my legs (not exactly anyway); I ride with a fairly acute hip angle, and the longer cranks caused my legs to come up higher, and squeeze my abdomen a bit (making it a little harder to breathe).

On my MTB, where I have more upright riding position, switching between 170mm and 175mm cranks is barely noticeable.

[timenoway]

The take home message seems to be that because we can get more aero these days on our bikes, shorter cranks are the way to go without sacraficing too much of the leverage onto the pedals?

[bironi]

It all depends on your choice of saddle and the color of your bike.

[oldpotatoe]

The take home message seems to be that because we can get more aero these days on our bikes, shorter cranks are the way to go without sacraficing too much of the leverage onto the pedals?

2.5 or 5mm in crank length makes no difference in aero-ness or not.
Put 3 people in a room and ask about crank length, get 4 opinions. Overall feel and injury prevention is what is important but again..a 6 foot person using 170/172.5/175 really makes little difference in leverage, aeroness, 'power'..

l..l<-that's about 2.5mm:eek:

Had a lady customer, really pretty pink DeRosa..doin' an overhaul..cranks come off(SuperRecord..old stuff)..right crank was 172.5, left crank 170..she didn't even know it..

[zmalwo]

the truth is if the UCI frame geometry regulation was based on a 190mm crank, we would be now arguing how 185mm, 190mm, 192.5mm, 195mm, etc...... fits 5'2, 6'4 etc...... I personally think it makes no difference whatsoever.

[Ralph]

I've experimented for 35 years between 170-175. I'm 5'7". I found that the longer cranks tended to cause more knee and hip pain when riding hard. Sheldon Brown and I had a conversation about the "leverage" of crank length and he convinced me that while seated, the chainring teeth number are the leverage, not the crank length, which comes into play more when riding out of the saddle. Since I live in Florida now, I rarely encounter a hill that requires me to rise out of the saddle so I have gravitated toward 170 more so to protect my aging knee and hip joints. I would tend to use the crank length more to get my knee over pedal position correct than anything else. This is just my unscientific opinion of course, but it makes sense to me.

For my 5' 10" height....above is how I look at it also. If I wanted more mechanical advantage from longer crank, instead of going longer, just use a ring with fewer teeth. 53 on 172's like 52 on 170's, about same percentage difference etc. (or 50, 51) And it's directly proportional. This is basic stuff we learned in high school physics studying pulleys and levers. On my Dad's old farm....he had a well......with a bucket attached to a rope, that went up over a pulley, then back down to a large piece of round wood, with a handle stuck/driven in the side to wrap up the rope when you turned the crank. There was always a lot of discussion about whether to use two pulleys at top or one....sacrifice distance for advantage, and how big the piece of wood need to be, and the length of the crank, where the rope wrapped up. We could make it easy or hard, slow or fast...depending on those factors. Same principles.