175mm rather than 172.5mm cranks ... will I notice the difference?

C3PO

I'm trying to source a new groupset and the lead times are crazy - 12+ weeks in most cases! I can get SRAM Force within a couple of weeks but with either 170mm or 175mm cranks - 172.5mm is 14-15 weeks! My road bikes all have 172.5 cranks but my MTBs are 175mm. I'm 180cm in height. I assume I would be better going with 175mm rather than 170mm? Will I notice any difference as long as I reset my saddle height correctly?

fat bloke

I've often gone shorter on cranks - 170,165 & not really noticed any difference, but I've never gone longer than 172.5. A cycling buddy of mine used to have chronic knee trouble and he blamed a too-long crank for it.

If they're any use to you I have two sram cranks for sale, a 170 rival and a 172.5 red.

Lumen

Shorter is better on the road.

https://www.youtube.com/watch?v=S0SpYdxg1UY

C3PO

Thanks guys - any research I've done seems to suggest that cranks that are too long are more likely to cause issues than shorter ones so I might be better going with 170mm?

fat bloke

C3PO wrote: »

Thanks guys - any research I've done seems to suggest that cranks that are too long are more likely to cause issues than shorter ones so I might be better going with 170mm?

Gosh yeah, if there's 170 available go for that!

MojoMaker

Definitely go short. Most of us are riding cranks that are too long for us anyway.

C3PO

As an aside, the lack of availability of Shimano parts seems crazy - 5 or 6 months delivery time on an Ultegra Groupset! :eek:

fat bloke

What are you looking for? In an online world one can forget to try an old school shop. Got r8000 supplied and fitted by a bricks'n mortar establishment before Christmas for a good deal.

P2C

I have different sizes on bikes. I use 165 on the tt as I find the hip angle less severe. Getting old. I have 175 on the hardtail and I find I am constantly clipping the pedals of rocks and the ground when cornering.

cletus

I can understand a 10mm difference causing issue, but 2.5mm?

fat bloke

cletus wrote: »

I can understand a 10mm difference causing issue, but 2.5mm?

Well, that's the increment by which they vary so it must have a significance I suppose.
Perhaps it's because you're describing a circle with the cranks, therefore a 2.5mm radial increase is a 5mm diameter increase in rotation?

cletus

fat bloke wrote: »

Well, that's the increment by which they vary so it must have a significance I suppose.
Perhaps it's because you're describing a circle with the cranks, therefore a 2.5mm radial increase is a 5mm diameter increase in rotation?

Maybe, I'd have to think about that one, but my gut feeling is that you're only 2.5mm closer at the top, or 2.5mm farther at the bottom, you're never combining both at the same time. If you lifted your saddle by 2.5mm, I'd be surprised if anyone on here would notice it.

Most of us walk around on a daily basis with a greater than 2.5mm differential in leg length, and we don't notice it.

triggermortis

I bought a new bike in October and it has 175 cranks on it. I definitely can’t get as comfortable as my other bikes that all have 172.5 cranks on. I’ll be swapping to 172.5 as soon as I can (be bothered to get around to doing it - I have the parts but don’t know if they’ll fit yet..)
Definitely feel it more in my knees after riding the new bike

C3PO

fat bloke wrote: »

What are you looking for? In an online world one can forget to try an old school shop. Got r8000 supplied and fitted by a bricks'n mortar establishment before Christmas for a good deal.

That was my first port of call but my LBS who have sourced groupsets for me in the past can get nothing from their suppliers at the moment!

dom_1000

At 181cm I always go for 175mm, the bikes for my size are always specced at 175mm anyway.

Longer cranks give you easer gearing for climbing.

Though shorter cranks are more aero for tt bikes

Lumen

dom_1000 wrote: »

Longer cranks give you easer gearing for climbing.

Longer cranks close the hip angle which reduces power...for climbing.

If you need lower gears, fit a wider range cassette.

Eamonnator

Will longer cranks not give greater leverage on climbs?

Lumen

Eamonnator wrote: »

Will longer cranks not give greater leverage on climbs?

If you're riding a single speed, maybe. Otherwise, gears provide leverage.

dom_1000

Longer cranks and gearing can both positively affect climbing.
Hip angle is negligible unless you are going for an extreme aero position.

dancecatz2000

2.5mm you shouldn't notice much difference, just make sure your saddle is at the same height on each bike, iv different if 170mm on my hacker, 172.5 on my good bike,

Eamonnator

Chris Froome, who is 1s 1.86 metres, rides 175mm cranks.

Seweryn

Eamonnator wrote: »

Will longer cranks not give greater leverage on climbs?

Yes and no.

The longer cranks will give higher peak torque by about 1.5 %, but it will "available" for shorter portion of the pedal stroke due to the more compromised knee angle.

Eamonnator

Seweryn wrote: »

Yes and no.

The longer cranks will give higher peak torque by about 1.5 %, but it will "available" for shorter portion of the pedal stroke due to the more compromised knee angle.

I think I understand that.
But, why does Froome not use shorter cranks?

C3PO

Eamonnator wrote: »

I think I understand that.
But, why does Froome not use shorter cranks?

Well, I suppose given that he’s 6cms taller than me it stands to reason that he would use a longer crank?

Lumen

C3PO wrote: »

Well, I suppose given that he’s 6cms taller than me it stands to reason that he would use a longer crank?

Also Froome uses osymetric chainrings so it's not directly comparable.

And he's Froome.

Seweryn

Eamonnator wrote: »

I think I understand that.
But, why does Froome not use shorter cranks?

Maybe he hasn't tried other sizes? Maybe he get used to the size he has been using? It takes time to adopt to a new crank size. My first bike came with 175 mm, which I changed to 170 mm and for the last few years I have been on 165 mm.

Eamonnator

https://www.cyclingnews.com/features/chris-froomes-factor-ostro-vam-gallery/

This article is about Froome's Factor Bike.
The rings don't appear to be asymmetric, but it may not be Froome's actual bike

Edit:
Although that seems to be Froome's race number.

Mr. Cats

Eamonnator wrote: »

https://www.cyclingnews.com/features/chris-froomes-factor-ostro-vam-gallery/

This article is about Froome's Factor Bike.
The rings don't appear to be asymmetric, but it may not be Froome's actual bike

Heard him say in an interview that medics asked him to switch to regular set-up during his recovery and he plans to switch back to asymmetric later.

LollipopJimmy

Chatting in a LBS and they've said it's near impossible to source Shimano parts at the moment. As for the question in the OP... I don't think it makes a massive difference unless you're looking for marginal gains

CramCycle

Basically for most people, shorter is better, but the differences are so small that I wouldn't be stressed unless you have a want for marginal gains or have medical issues. Longer crank take longer to wind up a sprint and affects your cadence but again, really no difference. If you force consistent cadence, there are differences but if you let people ride to their preferred cadence (which changes with crank length), again, minimal difference.

dom_1000 wrote: »

At 181cm I always go for 175mm, the bikes for my size are always specced at 175mm anyway.

Longer cranks give you easer gearing for climbing.

Though shorter cranks are more aero for tt bikes

Longer cranks aren't easier for climbing, I think that's just law of the lever being stuck in peoples head, gear availability makes the difference here, you aren't pushing the power through the same angle and there is far more than one thing changing when you look at the overall picture. As for the Aeroness for TT bikes, that's more to do with ability to flatten your back more.

Long story short, if it feels comfy, then you will be fine, unless you plan on becoming Sam Bennett, in which case, go for shorter cranks but for everyone else, whatever your bike comes with is fine.

I ride 165mm and do notice the difference going up but you adapt really quickly, and overall, minimal difference.

C3PO

LollipopJimmy wrote: »

Chatting in a LBS and they've said it's near impossible to source Shimano parts at the moment. As for the question in the OP... I don't think it makes a massive difference unless you're looking for marginal gains

Not a bit concerned about marginal gains ... my 60 year old knees are a far bigger worry!

C3PO

LollipopJimmy wrote: »

Chatting in a LBS and they've said it's near impossible to source Shimano parts at the moment. As for the question in the OP... I don't think it makes a massive difference unless you're looking for marginal gains

Yep - my LBS told me to source what I can and he’d fit it for me as he can get nothing! Ordered a SRAM Force groupset today rather than wait for 4-5 months for Shimano. 2 weeks delivery for 170mm .... 14-15 weeks for 172.5!

fat bloke

I have two mint cranks for sale for ages and no interest whatsoever in them!

theunforgiven

My good bike has 170mm cranks and I upgraded my winter bike about a year and a half ago to 105 but all I could get were 172.5mm cranks, (was a great deal from Merlin) and to be honest I can't tell any difference.
I'm a short arse, 5"6, and the 2.5mm is not noticeable.
You should be fine.

C3PO

fat bloke wrote: »

I have two mint cranks for sale for ages and no interest whatsoever in them!

Brand new build so keen to use new parts ... while since I’ve had a new bike!

grogi

C3PO wrote: »

Thanks guys - any research I've done seems to suggest that cranks that are too long are more likely to cause issues than shorter ones so I might be better going with 170mm?

Yes, it's safer to go shorter than longer.

There is hardly any downside to too short cranks, while too long cause many issues. I currently rife 170mm and I'm 194cm...

grogi

dom_1000 wrote: »

Longer cranks and gearing can both positively affect climbing.
Hip angle is negligible unless you are going for an extreme aero position.

The difference in angles is certainly not negligible, especially in the knee angle.

cletus

I've been looking at some studies and websites discussing crank length, hip and knee angle etc.

None of them discuss length changes of 2.5mm. the norm seems to be 7.5 to 10mm. Last page I looked at suggested that a 7.5mm reduction could reduce maximum knee flexion by 3-4°, and if the saddle is raised by the same amount, another 3-4° can be gained, leading to less pain at the knee, for a total of between 6 and 8°

If we assume that the correlation of figures is linear (which would give the 'best' possible score for a 2.5mm crank difference), shortening your crank by 2.5mm would gain you between 1° and 1.3°. Combining this with a 2.5mm saddle height adjustment would double this for a 2-2.6° reduction in flexion of the knee.

I would strongly argue that it would be next to impossible to notice a difference in knee flexion of between 1 and 2.6°

Lumen

The video I posted near the beginning of this thread deals with the dynamic effects. It's not all about angles.

I get the impression almost nobody has watched it. :pac:

velo.2010

Lumen wrote: »

The video I posted near the beginning of this thread deals with the dynamic effects. It's not all about angles.

I get the impression almost nobody has watched it. :pac:

I did! Even downloaded a free CAD package from the internet.;)

Eamonnator

Lumen wrote: »

The video I posted near the beginning of this thread deals with the dynamic effects. It's not all about angles.

I get the impression almost nobody has watched it. :pac:

I did and have been worrying about it ever since.

cletus

Lumen wrote: »

The video I posted near the beginning of this thread deals with the dynamic effects. It's not all about angles.

I get the impression almost nobody has watched it. :pac:

I watched it, but didn't refer to it in the last post I made, because it doesn't support the idea that a 2.5mm change in crank length would be noticeable.

It's an interesting video, but the crank length change he makes to his 4 bar linkage is 15mm, from 175 to 160.

This change causes a reduction in hip flexion of 2°. I didn't bother downloading a free cad package, but we can extrapolate these figures like I did above.

2.5mm decrease in crank length gives a 0.167° reduction of hip flexion, albeit for his particular setup. You'd have to put your own numbers into the cad drawing to see how inconsequential it would be for you

Lumen is right to point out that there is much more going on than just crank length, but a lot of the time you'd need to be an actual engineer to work it out.

Having said that, nothing so far presented, or that I've read, convinces me that anyone other than maybe the top riders in the world, could detect, in a double blind test, a crank length difference of 2.5mm

Lumen

velo.2010 wrote: »

I did! Even downloaded a free CAD package from the internet.;)

Bravo! You win the internet.

Eamonnator wrote: »

I did and have been worrying about it ever since.

Me too, and I was hoping to inflict that misery on as many people as possible. :pac:

cletus wrote: »

that there is much more going on than just crank length, but a lot of the time you'd need to be an actual engineer to work it out.

That video is interesting to me because he focuses on the kinematics, which is (I think) exactly where the good bike fitters and physios focus also.

Pedalling dynamics has been a particular concern for me recently as my return to cycling has seen a steady ramp up in intensity accompanied by various niggles around the knee, and I'm trying to figure out some combination of strength & conditioning, bike/cleat fit and intensity to fix them.

As I sit on the turbo for interminable hours I look down at my knees and think "are they tracking properly?". And where I detect a bit of a wobble is at the top of the stroke.

Obviously it is possible to fit a bike well with various different crank lengths, but if by choosing shorter cranks I could (for instance) get another 10rpm in cadence without my form going to crap (and risking attendant injury) that would be worth it, if I was in a position to buy various lengths and so the choice didn't cost anything.

FWIW I'm 183cm with short legs and use 172.5mm cranks, and I have no particular desire to spend a load of money on shorter cranks, but I think it's an interesting area of discussion nonethless, and I very definitely would not go longer in order to "get more leverage".

Large bottle small glass

Eamonnator wrote: »

I did and have been worrying about it ever since.

You'll be grand, to quote a rather hardy Australian miner I met one time "if you don't wear out you'll rust out"

CramCycle

Long story short, saddle height is of far more concern than crank length for 99.9% of posters here, if you have a choice, go shorter but if you have to adjust your saddle height to accommodation your cranks, it most likely means your seat post was at the wrong height regardless.

sbs2010

I think the video guy has made a couple of errors in his analysis,

He mentions ankle angle but says it's pretty much constant for most people and he sets it as 90 in his CAD. I don't think that's right at all. Ankle angle changes all the way through the pedal stroke. >90 at the down stroke and <90 at the up stroke. There's no one cycling with a constant 90 deg. shin to foot angle.
And by my reckoning it only takes 0.5deg difference in ankle angle at the upstroke to allow you keep the same hip and knee angles if you change your crank by 2.5mm

And secondly, he has the ankle pivot in the same plane as the pedal axle. But your ankle is maybe 8-10cm above your heel. Thats got to make a difference to all the angles he's worked out.

So I reckon it makes damn all difference, except to give you maybe a tiny bit more leverage, essentially you're riding a light gear if you've longer cranks. But I have 177.5 cranks so what would I know

CramCycle

There are studies out there that show differences that don't go into the reasons why, just what the hard data says. Long story short, evidence indicates that shorter is better in regards the lengths supplied by most manufacturers but that difference is small, so small in fact that most of us will never notice. Also, as said before, a saddle height being off by the same difference as a crank length change would make a far greater difference (+/-).

Eamonnator

CramCycle wrote: »

Long story short, saddle height is of far more concern than crank length for 99.9% of posters here, if you have a choice, go shorter but if you have to adjust your saddle height to accommodation your cranks, it most likely means your seat post was at the wrong height regardless.

I'm gonna go with this.
I'm 186cms with long legs. I have 175mm cranks on all 4 of my bikes. I have been using 175mm cranks since records began about 35 years ago.
I'm not going to switch at this stage and I'm going to try and stop thinking about it.

grogi

CramCycle wrote: »

There are studies out there that show differences that don't go into the reasons why, just what the hard data says. Long story short, evidence indicates that shorter is better in regards the lengths supplied by most manufacturers but that difference is small, so small in fact that most of us will never notice. Also, as said before, a saddle height being off by the same difference as a crank length change would make a far greater difference (+/-).

One won't notice performance difference between 2,5mm or even 5,0mm. I didn't see feel any difference when I jumped from 175mm to 170mm.

However, even 2,5mm might make the difference for injuries - I don't get knee pains anymore.

harringtonp

Lumen wrote: »

Bravo! You win the internet.



Me too, and I was hoping to inflict that misery on as many people as possible. :pac:



That video is interesting to me because he focuses on the kinematics, which is (I think) exactly where the good bike fitters and physios focus also.

Pedalling dynamics has been a particular concern for me recently as my return to cycling has seen a steady ramp up in intensity accompanied by various niggles around the knee, and I'm trying to figure out some combination of strength & conditioning, bike/cleat fit and intensity to fix them.

As I sit on the turbo for interminable hours I look down at my knees and think "are they tracking properly?". And where I detect a bit of a wobble is at the top of the stroke.

Obviously it is possible to fit a bike well with various different crank lengths, but if by choosing shorter cranks I could (for instance) get another 10rpm in cadence without my form going to crap (and risking attendant injury) that would be worth it, if I was in a position to buy various lengths and so the choice didn't cost anything.

FWIW I'm 183cm with short legs and use 172.5mm cranks, and I have no particular desire to spend a load of money on shorter cranks, but I think it's an interesting area of discussion nonethless, and I very definitely would not go longer in order to "get more leverage".

Welcome back to boards. Was wondering where you had been.