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!