Crank arm size

[Solanog]

Hi I just bought a new crankset and when I got it I was in a hurry and didn't notice that it is different from what i've been using in the past both in my MB and in my RB. The arms are 172.5mm and the old ones and the ones I've used for years are 175. I ride a 54 frame which is my right size, I may use a 55 or even a 56 with no problem.
So my question is, would I feel any difference using this shorter by 2.5mm cranks? Should I try to go and ask for a change for 175mm (if they are available)? Could this shorter ones could be better for me?
Is there a formula or something to estimate the crank length for a given cyclist?

Thanks for your help

 

[Peter@vecchios]

Hi I just bought a new crankset and when I got it I was in a hurry and didn't notice that it is different from what i've been using in the past both in my MB and in my RB. The arms are 172.5mm and the old ones and the ones I've used for years are 175. I ride a 54 frame which is my right size, I may use a 55 or even a 56 with no problem.
So my question is, would I feel any difference using this shorter by 2.5mm cranks? Should I try to go and ask for a change for 175mm (if they are available)? Could this shorter ones could be better for me?
Is there a formula or something to estimate the crank length for a given cyclist?

Thanks for your help

Put 3 people in a room and ask about crank length..get 4 opinions. If you are happy with 175 w/o any issues, I would go get a 175. BUT, If ya keep the 172.5, raise your saddle 2.5mm. I doubt you could tell a difference tho.

Difference in circumference, how far your foot travels in 1 revolution is 16mm, not much. Some other brainiac can tell you differences in leverage, etc for that 2.5mm.

We had a new customer who rode a DeRosa for YEARS with one crank 2.5mm longer than the other and never knew it until we pointed it out.

 

[Solanog]

Put 3 people in a room and ask about crank length..get 4 opinions. If you are happy with 175 w/o any issues, I would go get a 175. BUT, If ya keep the 172.5, raise your saddle 2.5mm. I doubt you could tell a difference tho.

Difference in circumference, how far your foot travels in 1 revolution is 16mm, not much. Some other brainiac can tell you differences in leverage, etc for that 2.5mm.

We had a new customer who rode a DeRosa for YEARS with one crank 2.5mm longer than the other and never knew it until we pointed it out.

Well, my thoughts are similar, I thought 2.5mm what the heck that's nothing but also asked myself, if they make them in all those different lengths then it might as well make a difference.
I supponse that the ideal length has to do with your leg length so is there a formula to calculate that arm length?

 

[swampy1970]

Well, my thoughts are similar, I thought 2.5mm what the heck that's nothing but also asked myself, if they make them in all those different lengths then it might as well make a difference.
I supponse that the ideal length has to do with your leg length so is there a formula to calculate that arm length?

Just because they make them doesn't mean that they're useful in those increments.

One would think by now that someone would have come up with a 'formula' for this but you'd be wrong. When you consider that someone the size of Pantani was reputed to have used 180mm cranks in the mountains and someone not much bigger (Marc Madiot) used 180mm cranks all year to great effect but taller riders like Jan Ulrich 'only' used 177.5s, it makes you wonder what the scoop really is.

Common 'lore' puts the small guys on 170mm and tall guys on 175mm or maybe even 177.5. I'm sure there's a little more than 1/4" increase in inside leg yet to use a crank much longer than that brings about talk bordering on heresey.

 

[Peter@vecchios]

Well, my thoughts are similar, I thought 2.5mm what the heck that's nothing but also asked myself, if they make them in all those different lengths then it might as well make a difference.
I supponse that the ideal length has to do with your leg length so is there a formula to calculate that arm length?

No formula. Like handlebar width, more personal preference than anything. Boardman used 38cm hbars, for instance. I used 170mm on my first real bike, a Ciocc, with Victory. Upgraded over time to SuperRecord, went with 172.5(I'm 6') but didn't really 'feel' a difference.

 

[Solanog]

No formula. Like handlebar width, more personal preference than anything. Boardman used 38cm hbars, for instance. I used 170mm on my first real bike, a Ciocc, with Victory. Upgraded over time to SuperRecord, went with 172.5(I'm 6') but didn't really 'feel' a difference.

I'm 5'10" and have used 175, now I'll be 175 on the MB and 172.5 on the RB, I may not even notice the difference. I may install this crankset this week so maybe I'll test it on the weekend, not much to do if I don't like it since I don't think the BShop will received a used one for a new one.

 

[dgregory57]

I accidentally put 175's on a bike for a short lady and she didn't notice.

I am 6' tall and use 172.5 because that is what the shop recommended based on my inseam. Most of my bikes in the past had 170's...

Some say that going shorter is good for spinning (less distance for your foot to travel per revolution) and longer is good if you are a masher (more leverage).

But, if you hadn't seen the number, the chances are you would have never noticed the difference other than thinking your seat post needed adjusting.