Crank length questions

Hi all

A few questions I’d appreciate your help with!

I’m 5’11 and ride a 58cm bike with 175mm cranks.

I’ve kind of always had knee pain issues every now and then but its gone away with rest. I recently bought a TT bike and had a fit. 170mm cranks were used on this build and since i;ve used this bike on the trainer my cadence is higher and i swear my knees feel better.

So I’m thinking of replacing cranks on my road bike, from 175mm to 170mm.

Do you think i will notice a difference on the road bike or should i go down to 165mm? I could potentially get another fit but this will be expensive and i already know i want shorter cranks.

Finally, my bike is equipped with 105 r7000. ULtegra cranksets are cheap atm but will they be compatible?

You’re absolutely on the correct path here. I went from 175 to 172.5 on the same bike and much less to no knee pain. My would go away as well on rest days.

I still ride 175 on my mtb but don’t have as many issues, probably because there’s more standing and generally just less revolutions then when I’m on my road bike. I’ll be switching to shorter cranks on my mtb whenever I need a new crankset.

I would say you would def notice a difference on your road bike.

Personally I would go for shorter cranks on a TT bike, more so than on a road bike. The benefit is that you can have a slightly more open hip angle when you are really tucked up. Having said that you are quite tall so 165mm wouldn’t be that typical for someone of your height. I ride 165mm cranks and am 5’7. I would say it’s worth giving it a go, 165mm cranks are quite rare to come up second-hand so if it doesn’t work you should be able to sell it on to someone experimenting like you.

This. If you don’t mind losing a small bit of money (or maybe not with shortages of stock due to COVID) go ahead and try 165mm. If you don’t like it 170s are easier to get and so less resale value. You will also have less doubt about if you went far enough.

Some people swear by long cranks, some short. I think really it has much more to do with flexibility, inseam and femur lengths than your overall height. Sizing a bike by height isn’t a great method.

Note that the reduced crank length will affect other parts of your fit. Make sure that you record the current measurements of your bike for the distance from the seat to the pedal cleat surface with the crank at 6 o’clock, because your seat height will have to change a bit. Also get the seat sit bone surface to steer tube distance, because you might have to slide the seat forward slightly with the seat height adjustment. Those tweaks will give you an identical fit again.

That said, most cyclists and even many fitters, put the seat too high. The first thing most people with fit issues should try is lowering the seat 10 or 20 mm. Look up @bikefitjames on Instagram and scroll to the videos showing before and after fitting riders. Almost every time he has to significantly lower the seat.

Shorter crank

But there is podcast that’s a good listen to about this

Thanks for all the replies!

Great ideas on trying the 165 second hand, I’ll see if I can find any second hand.

Can’t understand why I’ve been riding the same crank length as people who are 6 ft 3…

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I am 5 feet 6 inches (167 cm) and I ride 160 mm cranks. Started with 172.5 went to 165 and wanted to try 160. switching from 172.5 to 165 instantly allowed me to use the drops when previously I could only stay there for a couple of minutes. Felt like I was hitting my belly with the long crank. I am now very happy with the 160’s.

I have another bike that is 165 which I sometimes use. the difference is that if my quads are tight, its quite noticeable on the slightly longer crank. it gets sore a little bit sore faster then on the 160’s.

My advice would be try to go as short as possible just to experiment. if it solves your problems then good for you, if not, there are many people that would buy that 165 mm crank off you. provided, you are able to find one in the first place.

hope it helps.

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