Solution for cranks that are too long

Joerend92

Hi there,

Just looking for some advise please.

I’ve recently bought a new bike and have kept all the measurements the same as my old bike which caused me no problems. The only difference is the length of cranks, my new bike has 175mm and my old had 172.5. I have started to get left knee pain and cramping in calf’s after riding for longer than say 50 miles. This pain is still evident after dropping my saddle by 5mm.

I know the ideal solution is to buy new cranks but im not in the financial situation to do so. My partner is 24 weeks pregnant and have already got in the neck for buying another bike!

I was thinking of moving my cleats backwards a centimetre or two and wondered if this may help situation as it would decrease the angle of the knee and put less strain on the calf’s?

I’m just over 6ft1 and have a inseam of 34inch 1/2 so theoretically should be able to ride with 175mm cranks?

Thanks very much in advance for any advise,

Joe

timothyw

It isn't possible, is the short answer. If you move the cleat back then you are still making circles with 175mm radius, only now you have the cleats in the wrong position....

Could you look at transferring the cranks from your old bike? That would be the easiest way to test and confirm that this is what is causing the issue.

Frankly I find it hard to believe that a measly 2.5mm difference (seriously, get out a pencil and a ruler and try to draw a 2.5mm line... see how long it is) is responsible for the problem.

It's more likely to be some other aspect of the fit on the new bike.

mugensi

I seriously doubt that your cranks are the problem. You may have transferred all your measurements from the last bike to the new one but that only works when the frames are identical in every single way. A slacker seat tube or head-tube angle can throw all your measurements out by more than 4 or 5mm or more. Just because the frame sizes are the same doesn't mean you simply set everything up as on your last bike as stack/reach can vary drastically between different frames (of the same size) If the seat tube angle on your new bike is less than the old bike, then it sits you further behind the BB which will mean you are using different muscles pedalling compared to with the old bike. Just because you have set the distance from the saddle to the bars and saddle height etc as on the previous bike doesn't mean you are in the same position as before.

2.5mm is tiny and a thicker pair of socks could make up that difference quite easily.

You need a bike bit fit.

Joerend92

TimothyW wrote:

It isn't possible, is the short answer. If you move the cleat back then you are still making circles with 175mm radius, only now you have the cleats in the wrong position....

Could you look at transferring the cranks from your old bike? That would be the easiest way to test and confirm that this is what is causing the issue.

Frankly I find it hard to believe that a measly 2.5mm difference (seriously, get out a pencil and a ruler and try to draw a 2.5mm line... see how long it is) is responsible for the problem.

It's more likely to be some other aspect of the fit on the new bike.

Yep my thoughts exactly. I don’t see how such a small increase would cause a problem. It’s just that I had a professional bike fit previously which my old bike so have all the measurements to hand which are all exactly the same except crank length. Maybe a measurement is slightly out somewhere. If I’m gonna pay for another bike fit then I might as well buy a new crank.

You’ve suggested a good idea in regards to cranks. I have sold my old bike but have a bike on a turbo with 172.5 cranks so could swap cranks over for a week or two and see if any difference is seen.

Cheers

Joerend92

MugenSi wrote:

I seriously doubt that your cranks are the problem. You may have transferred all your measurements from the last bike to the new one but that only works when the frames are identical in every single way. A slacker seat tube or head-tube angle can throw all your measurements out by more than 4 or 5mm or more. Just because the frame sizes are the same doesn't mean you simply set everything up as on your last bike as stack/reach can vary drastically between different frames (of the same size) If the seat tube angle on your new bike is less than the old bike, then it sits you further behind the BB which will mean you are using different muscles pedalling compared to with the old bike. Just because you have set the distance from the saddle to the bars and saddle height etc as on the previous bike doesn't mean you are in the same position as before.

2.5mm is tiny and a thicker pair of socks could make up that difference quite easily.

You need a bike bit fit.

Thanks for advise. Yes a see where you are coming from. Ive gone from a Tarmac Sl4 to a Tarmac sl6 so probably not a massive difference in geometry but maybe enough to cause an issue. I will try to find a professional bike fit in my area for a reasonable price.

Thanks again

imposter2.0

If the only variable is the crank length, then try dropping your saddle by 2.5mm - not 5mm. I'm assuming the SL4/6 have the same geometry - if they have, and you have adjusted the saddle correctly, then crank length cannot be the cause.

Wearing thicker/thinner socks has no material effect on pedalling dynamics, btw.

fenix

2.5mm is nothing. Your legs won't even be the same length as each other.

Where you sit on the saddle, how you bend your ankle - all makes a difference. 2.5mm on the length from your hip to the pedal isn't going to make the difference.

StillGoing

The extra length of the crank may be causing the issue. The additional 2.5mm drop means that your hip angle at the top of the pedal stroke has tightened by 5mm. I'd expect the discomfort to materialise elsewhere than your calves though.

sungod

as above, can't see the crank length being the real issue for what you describe

as it's a new bike, any chance you suddenly increased duration/intensity of riding out of enthusiasm?

rather than paying for a bike fit, try going through 2-3 of the articles on this site... https://www.stevehoggbikefitting.com/bi ... can-it-be/
...and see if it helps you get the saddle height and position right for you

Joerend92

philthy3 wrote:

The extra length of the crank may be causing the issue. The additional 2.5mm drop means that your hip angle at the top of the pedal stroke has tightened by 5mm. I'd expect the discomfort to materialise elsewhere than your calves though.

This is what I was thinking. As I was getting knee pain I thought it may be due to the increased hip angle as that is the only thing I can think of which has changed. That’s why I was thinking of bringing cleats back a little bit because in my head that would reduced hip angle but I’m no expert so maybe wrong!

Cheers

Joerend92

sungod wrote:

as above, can't see the crank length being the real issue for what you describe

as it's a new bike, any chance you suddenly increased duration/intensity of riding out of enthusiasm?

rather than paying for a bike fit, try going through 2-3 of the articles on this site... https://www.stevehoggbikefitting.com/bi ... can-it-be/
...and see if it helps you get the saddle height and position right for you

No not particularly, not raced on it yet so haven’t done any particularly long hard efforts.

Great , thanks for info! Will go through these articles first and see if I can find the answer

Thanks again

bompington

I ran 175 cranks for a while at one time, mainly 'cos I got them cheap when I needed a new crankset.

Couldn't really tell the difference.

I'm 5'8 and built like a gorilla - inseam closer to 30 than 34½.

+1 for "it's not about the cranks"

DeVlaeminck

2.5mm isn't much but it's a change and with the thousands of revolutions they make I think it's possible that is causing the problem - not likely maybe but at some point increasing cranks will potentially cause injury so maybe that small increase is that point for you.

Fwiw I don't like 175mm cranks - I "think" I can tell the difference in that 2.5mm increase - I can't swear to it as it's always been on a different bike rather than swopping the cranks on the same bike but there you go.

That said for the cost of a new set of cranks I'd certainly be giving it a bit longer and seeing if the problem went away.

zefs

Moving the cleat further back would make the calves work less which could work so you could try that (1cm is enough if the current position is spot on from your bike fit).

What cadence do you usually ride at? based on your inseam it wouldn't be wrong to ride 175mm cranks.