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forum
crank arms
hello people,
I was wondering if anyone has ever switched form a 172.5mm arm to a 170mm arm and if you noticed any difference? The groupo I want to buy has a 170mm arm and not the 172.5mm/ I think I will get the groupset with the 170mm and I can always buy 172.5mm if needed, but want to ask you.
Thanks,
If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.
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27 comments
Shot me lazer beam,
that best describes how to work a team.
Eg 1 man 1 bike. Yikes seeing the mechanical advantage on hikes,
rolling them hills
to achieve our thrills.
Bike fit comfort is as is per each man,
some prefer torque yet some prefer to spin across land.
Longer arms increase torque but the increase in the knee bend might be too much.
. Too short means no drive, imagine standing on axle, no luck
Hence fit to prefer Watt
And just spin 'em up.
Damage to my hip joint has left me with one leg a little over an inch short. Physiotherapist prescribed a 5/8" rise in one shoe, which I soon did not bother with. In any case, it lifted the heel but made much less difference at the arch, where one pedals.
I took up cycling for mobility and incidentally fitness and discovered a whole new world of freedom and exhilaration.
That is not directly relevant to crank lengths ("arm" is redundant) for the rest of you, but I mention it because I have never paid the slightest attention to my discrepancy in leg length, when cycling. I have never found any particular problem. My hip damage also makes my knee move outwards as it rises. This never seemed to hamper me either.
I did once think about getting cranks of different length (to each other), but there seemed to be no need to go to the hassle.
From my own peculiar case I conclude that our bodies are quite adaptable, and crank length makes very little difference, at least within 25mm.
Does anyone here actually understand what happens when you change the length of your crank arms?
It isn't necessarily about power, or spinning, or any of that. It's about making the bike fit your body. If you have shorter legs, shorter cranks can help. Remember, when you adjust saddle height you're doing that to get the correct amount of leg extension at the bottom of the pedal stroke. But crank length is how you also get the correct amount of extension at the top of the pedal stroke. If the crank arms are too long, you can still get the correct extension at the bottom of the pedal stroke by lowering your saddle - but then you risk knee pain at the top of the pedal stroke, because your leg is bent too far up into your body, just as you're using your quads to push down again.
Yes, there is a difference to be had in crank lengths, and it's a lot to do with ensuring you don't injure yourself while riding.
It's very unlikely you will notice any measurable difference. However, we are all built differently, so YMMV
What groupset? If SRAM Red by any chance then I'll swap you! A new bike arrived with 172.5mm which I'm sure will be fine but I'd probably have gone for 170mm.
I once bought a new chainset and was riding along thinking the bike seemed a bit off. Just couldn't seem to get away with it. A couple of hundred miles later, by chance, I noticed that one crank arm was 175mm the other 165mm! I mainly ride 165mm cranks to replicate my track setup, but one bike has 172.5mm, I wouldn't notice the difference if I didn't know - assuming both sides were the same!
I think it comes down to the person though. I'm easy going when it comes to bike fit, some people I know are extremely fussy and notice everything!
Measure your inseam in inches then multiply the inseam inches x 5.48 to give you crank arm length. I'm 5-7" with an inseam of 31.25 inches which puts at a 171.25 crank length. I rode with 172.5's for a number of years but for the past 5 have been on 170's, I feel that's my crank length. If you're close or in-between 170-172.5 fit your saddle height/fore/aft for the 170's go ride. It will at first feel a bit different than 172.5's but after a few humdred km's you'll know which length is best suited to your style of riding.
Got my vote Wellsprop. Whatever YOUR comfort prefers. They are near much same. If it didn't cost me anything I'd try 180 4 4 seasons such that my legs could bend more but it really good cycling with any good cranks. Every person is different
The Ride Far website has some great information on this:
https://ridefar.info/rider/comfort/position/#Crank_Length
It's all about hip rotation!
No I didn't.
I have bikes with 175mm cranks and bikes with 170mm no difference to feel. You must set seat height the same to measured from pedal spindle not the centre of crank.
i use 175 on all my bikes. I bought a bike with 172.5 and it just felt odd compared to the 175 cranks i was used to. It might only be a small difference but when folk are being being convinced to part with money for bikefits, i think its worth getting the size you want and like. Im sure someone will take your money and tell you you need shorter cranks...
I switched to a 180 crankset (ss if that matters) and it just felt too big. so have stuck with 175 as that works for me.
Get a pen, ruler and paper. Draw a vertical line about 1 cm in height. Now draw another 1cm vertical line exactly 2.5mm to the right of the first. Look at the size of the gap between the two vertical lines and tell yourself you could tell the difference when riding.
You can notice it.
Set your seat post at height. Can't reach pedal if risen 25mm but who cares if lowered 25mm.
Really depends upon your range of motion and like Kev indicates; most the time it wouldn't matter.
Longer stroke gives more torque, eg turns wheel using strength
Shorter stroke revs easier, eg rhythm development of horsepower.
Trucks have long stroke. Race cars have fast stroke. Each develop the equal horsepower yet each horsepower is different .
If too easy too pedal then torque it with longer arms or if too fast when spinning, shorten.
I'm lost too bro.. I'd use 165-185 and learn with what I'm given. I'd like longer cranks but that's because I don't climb, I'm tall cogged and the freewheel freewheels.
25mm is a factor of TEN greater than 2.5mm, you really need to recheck what's written and how mm/cm are different.
Raising your saddle 2.5mm would not make a difference as to whether you can reach the pedals or not, to suggest so is simply bogus.
the difference in crank length between a 170 to a 172.5 is going to produce such an infintessimally small change in torque that you would not know, it's in your head.
"Too easy to pedal" is down to the gearing, it's virtually nada to do with the crank arm length, you even state yourself that you "learn with what I'm given", you change your gear ratio to whatever you find best for the conditions, the crank length is not relevant to this and is more historical incorrect thinking repeated time and again.
Just typing.. Not much difference until the useable range is breached. Crank is relavent. Truck makes same bHp as race car but truck parts big.. Why? Torque. Both reliant upon weight issues as truck is fare per tare.
Longer cranks will give more torque, more torque means bigger chains to cope with strength.
Maybe some day 3 foot cranks on ratchet from near axle can be used with hub gears and really monster some strength. . As per now, if it's comfortable, ride it, you won.
What a load of cr@p.
Use that line as the radius of a circle, that is the distance your foot travels every revolution. Now multilpy that by 100 rpm to get some idea of the difference every minute you are riding. The difference is huge.
I don't notice much between a 172.5 and a 175 mm crank.
The 175 is on a fixie though and I like that feeling that while resting the leg will is cycling although not sure if because of the larger circle or the consent spin.
There is a difference but they're both fun and doing their job.
but will 2.5mm really make a difference?
I noticed 170mm is a lot more spinny than the larger sizes.
I have chainsets in 170, 172.5 and 175.
Technically, a shorter crank should be better for spinning lower gears and longer ones better at lower cadence with higher gears.
In reality, I dont notice the difference.
so, going from 172.5 to 170 wouldn't really make a difference. I guessing if I switched from 172.5 to 170 that I would soon forget about it. So with a shorter arm, my trunover would be quicker perhaps, than that of the 172.5 and good for climbing long hills.
You *might* notice a slight difference in crank length (I did when I switched from between bikes with 175 and 170mm cranks - but as I said, it's all in your head really).
There will be absolutely no difference in performance or power. Using a shorter crank will reduce the torque you produce (at the crank), however, that's irrelevant because the bike has gears anyway to give you a mechanical advantage.
Fundamentally, it comes down to whatever size you want/feel comfortable with. Bradley Wiggins is 6'3", he had 177.5mm cranks on his TT bike a few years back. He then had 170mm cranks on his later bikes (IIRC, a load of the BC track team switched to short cranks for some reason or another - Ned Boulting was chatting about it when commentating on a race a couple years ago).
I think using a 170mm crank would be ok for me if I switch from 172.5mm. I'm looking at going from 53/39 crank, with 11-28 cassette to a 52/36 crank with an 11-32 cassette . I live in rocky mountains and I do lots of climbing, which I'm strong at. I think the 170mm would benefit my aching knees and lower back
I went from 175 to 165 and you soon forget about it.
I don't think there would be much difference between the 172.5mm and the 170mm. I can definitely see there being a difference between 175 and 170. I think it wouldn't feel right like you said. I'm wondering if I would have to adjust my seat height up a little to accomodate the 170mm
I used to have 175mm cranks and bought a bike with 170s, it just didn't feel right. Can't put my finger on it but it didn't feel right.
I switched to 172.5 cranks and stuck with them. They feel right.
I think it's just in my head though.