Crank length

captain_tiara

Hello all.

I'm in the process of buying a lovely new shiny bike. Absolute bargain. My only worry is that it comes [no chance of changing them] 172.5 cranks. I'm 177 tall, have had cartilage/meniscus/ACL surgery 20 years ago and have always ridden 170 cranks, in the belief that they load my knees less. I do quite a lot of riding, have a sports science degree [so I'm probably over thinking this?] and I'm wondering what people's experience of riding slightly longer cranks is?

I could sell the crankset brand new unused & buy another set at 170 length. I could give them a go. How much difference is there?

imposter2.0

2.5mm - I seriously doubt if you will notice any difference at all. I used to switch between road and MTB where my cranks had a 5mm difference and still couldn't detect anything.

StillGoing

It's much more than just 2.5mm difference. Think about it; when your foot is at the bottom of the stroke, your seat needs to be lowered so you aren't over extending. As a consequence, the other leg at the top of the stroke is going to be over compressed because the seat will be closer to the top of the stroke reducing your potential to get maximum power out and risking injury to your already troublesome knees. You will never convince some people that crank length matters, but then it took a while for some to accept the world wasn't flat.

imposter2.0

philthy3 wrote:

It's much more than just 2.5mm difference. Think about it; when your foot is at the bottom of the stroke, your seat needs to be lowered so you aren't over extending. As a consequence, the other leg at the top of the stroke is going to be over compressed because the seat will be closer to the top of the stroke reducing your potential to get maximum power out and risking injury to your already troublesome knees. You will never convince some people that crank length matters, but then it took a while for some to accept the world wasn't flat.

So he needs to set his saddle height correctly on the new bike then? I never said that crank length didn't matter, by the way.

Grill

You won't notice. I rode 175 cranks on one of my bikes as I could have sworn they were 172.5 like the rest and had no idea.

Wheelspinner

I've not noticed a real difference between 175 (my usual sets) and 172.5 I had on one bike, but I *did* notice going down to a set at 170 I fitted to something a while back, and didn't like it.

Try it and see. If they are no good for you, the difference in price you'd get selling them with a couple hundred km on them is minimal anyway.

diamonddog

I ride cranks that are 5mm too long according to various measurements but have had no problems at all.

maddog 2

I can notice straight away.

I'd get the bike you want. Takes very little effort to remove an sell something these days. Any other solution is a bodge IMO.

cougie

I think you're overthinking it. Look at how long your legs and feet are. 2.5mm is a piffling amount.

I rode a bike with different length cranks for a few months. I couldn't tell on that even.

MichaelW

Either of those cranks would rate as a med size for a rider of your size.
There is 5mm diff in the leg vertical action but both are within bounds.
The crank length problems come from riders who are 4'10" or 6"6" and riding your size crank.

StillGoing

Imposter wrote:

philthy3 wrote:

It's much more than just 2.5mm difference. Think about it; when your foot is at the bottom of the stroke, your seat needs to be lowered so you aren't over extending. As a consequence, the other leg at the top of the stroke is going to be over compressed because the seat will be closer to the top of the stroke reducing your potential to get maximum power out and risking injury to your already troublesome knees. You will never convince some people that crank length matters, but then it took a while for some to accept the world wasn't flat.

So he needs to set his saddle height correctly on the new bike then? I never said that crank length didn't matter, by the way.

It was a reply to the original post and not you. However, if he sets his saddle height correct for his leg extension at the bottom of the stroke, it will be too low when at the top of his pedal stroke causing the over compression of the leg angle. If he sets it right for the angles at the top of his stroke, it will be too high when he's at the bottom of his stroke.

I'm a firm believer in crank length making a difference having tested on power meters to see what I achieved with different crank lengths at a given cadence and gearing.

MichaelW wrote:

Either of those cranks would rate as a med size for a rider of your size.
There is 5mm diff in the leg vertical action but both are within bounds.
The crank length problems come from riders who are 4'10" or 6"6" and riding your size crank.

Overall height has nothing to do with it. I'm 5' 7" long bodied with short legs and use 165mm cranks when I previously used standard 170mm ones. I can instantly tell the difference when I switch from my summer bike to the winter one that still has 170mm cranks fitted. Your theory may be right if someone is correctly proportioned, but not everyone is.

earth

If its a shiny new bike can't you ask the seller to swap the cranks for the 170mm ones you really want? If you explain the reason to them, they will be sympathetic. The only question is if they can do it without loosing out themselves.

captain_tiara

I'm afraid it's a take it or leave it deal. And it's too good to leave.

http://www.wiggle.co.uk/verenti-sense-dura-ace-2013/, which is a Ridley Helium really.

Especially when your friend works there, , & if he can't get them swapped then no-one can....

After talking to people & reading the posts, thanks, I think there are 3 possible outcome, A) I don't notice, It feels better, C) It feels bad & I swap them for something else.

Anyway I'll be taking delivery in the near future, & once I've done some mileage I'll try & remember to update this post.
Thanks for your thoughts.

StillGoing

You won't necessarily feel it. You need to compare performance with a power reading to gauge whether shorter cranks benefit you. If you're not interested in maximising your power output, then stick with the standard length cranks and save your money.

blackhands

Well I used gas analysis looking at efficiency and found absolutely no difference in 2.5mm crank length change.

sloppyschleckonds

blackhands wrote:

Well I used gas analysis looking at efficiency and found absolutely no difference in 2.5mm crank length change.

Pneumotach or ventilomete?

napoleond

I can barely notice going between road 175mm and track 165mm.
Bearing in mind there can be more than 2.5mm difference between chamois thickness in shorts, you won't notice 2.5mm. Just adjust your saddle the corresponding amount (if going up 2.5 mm crank, lower the saddle 2.5mm)

jotko

Just wear thinner socks

blackhands

SloppySchleckonds wrote:

blackhands wrote:

Well I used gas analysis looking at efficiency and found absolutely no difference in 2.5mm crank length change.

Pneumotach or ventilomete?

These do not do gas analysis - they are merely flow meters, and flow can vary for a number of reasons.

I used an Oxycon Pro to determine O2 consumption and CO2 production to look for a change in efficiency at various power outputs and cadence rates. Admittedly I was only testing myself so not a robust statistical sample.

wishitwasallflat

After a recent fit I was advised to go down to 170mm cranks but money it tight and I haven't done so yet. I too suffer knee problems so would appreciate if you would update if you do try them.

I suspect that like most things in this world there are people to whom it will make a difference and some for whom it won't. AFAIK there is only one published peer reviewed paper on this subject and they reported that it did make a difference to power. Not sure if there was any qualitative outcomes recorded in that study though.

buckles

Pretty good deal that bike!

captain_tiara

And after logging up over 2000KM on my lovely new bike my conclusions are.....

Once I got used to a bike that isn't my faithful old Condor Squadra that I've been riding around on for, oh my gosh, nine or ten years, I can safely say that the crank length difference was swallowed up by how much it feels the same but different.

What I mean is I'm happily suprised how tight & responsive the Squadra still is in comparison, but the Sense/Helium [esp after sticking some flipping bargain early unused Kryserium SLR's on & a new cockpit & saddle] just winds up & climbs better & soaks up road chatter & so points downhill like a rocket with stabilisers.....Amidst the way the bike handles I really don't feel affected by the 2.5mm crank length increase .

I'll be back on the Squadra now for winter. So glad I got some of the last Open Pro Ceramic rims, on the second set of bearings & they really don't care about winter grime! Happy happy me!