170mm vs 175mm Crank - Will I notice much difference?

[cyberknight]

That's what I felt when changing from 150 to 170 (but only for a short while).
It would be interesting to do a lab study on same bikes with different lengths of crank and measuring the rider's power output. My suspicion is that it would make little difference if at all, and of course may change once the rider is accustomed to a particular length. Replicating the conditions is nigh-on impossible. A test the next day on different cranks would be inconclusive, as would changing on the day having already done minutes on one crank and then changing to another. Mike Burrows had some interesting thoughts on crank length. My own thought is that 200mm would be much too long, and 50mm would be much too short - somewhere between these extremes is everyone's ideal crank length

i guess it depends on leg length too, im a short ass i have been told i should be running shorter than 170s

 

[Fastpedaller]

i guess it depends on leg length too, im a short ass i have been told i should be running shorter than 170s

That's a popular assumption (and an understandable one) but who knows for certain?

 

[Tom B]

Cheers all...

I did start to ponder and work out the changes in force / leverage as well as the circumference, I briefly started to work out how much less my cleat would travel over the 1300 or so revolutions to work. But then the missus asked me what I was doing and I remembered that my A level physics and maths was a long time ago and that I had a beer open.

I'll report back when I get them. Interestingly is seems that 170mm is usually cheaper than 175mm that's probably why I was magnetically drawn to them .

 

[Fastpedaller]

Cheers all...

I did start to ponder and work out the changes in force / leverage as well as the circumference, I briefly started to work out how much less my cleat would travel over the 1300 or so revolutions to work. But then the missus asked me what I was doing and I remembered that my A level physics and maths was a long time ago and that I had a beer open.

I'll report back when I get them. Interestingly is seems that 170mm is usually cheaper than 175mm that's probably why I was magnetically drawn to them .

Spa cycles have a good range of square taper cranks in various lengths (IIRC the price is the same for all lengths of the same model)

 

[cyclintom]

Team;

Time has come to replace the crankset, chain and cassette on my everyday commuting / everything weapon.

It has needed doing for a few months and I bought he bits before Christmas. Given the grotty weather I decided to just give up maintaining the old set and run it to oblivion with nothing to lose.

It appears that I have inadvertently clicked the 170mm crank option instead of my usual 175mm crank option - I usually buy the 175mm for no better reason than because that's what I always buy and that's what it came with.

Looking online and being 5'9" it seems 170mm cranks arn't an outrageous choice.

Has anyone any experience of changing crank lengths and how much would or will I notice ?

Actually the 170's are probably the best idea you could come up with. The older you get the more strain 175's put on your knees. Atr first you notice it as taking longer to "warm up" before you can spin the cranks out. With the smaller cranks there's no warm up period on the cranks though your hips begin taking the strain sooner or later.

At 5'9" you might even feel better at 167.5. Most of the pros who ride so much faster than a normal rider it isn't funny are changing over to 165's. I was having knee problems and changed down to the 172.5 (I'm 6'4" with a 34" inseam) and I made a mistake and installed an old set of 175's on the normal riding bike. And now my knees hurt walking up stairs.

 

[Jameshow]

Actually the 170's are probably the best idea you could come up with. The older you get the more strain 175's put on your knees. Atr first you notice it as taking longer to "warm up" before you can spin the cranks out. With the smaller cranks there's no warm up period on the cranks though your hips begin taking the strain sooner or later.

At 5'9" you might even feel better at 167.5. Most of the pros who ride so much faster than a normal rider it isn't funny are changing over to 165's. I was having knee problems and changed down to the 172.5 (I'm 6'4" with a 34" inseam) and I made a mistake and installed an old set of 175's on the normal riding bike. And now my knees hurt walking up stairs.

I'd read that but couldn't put my finger on it can you?

 

[a.twiddler]

This is all beginning to sound like the fable of the Princess and the Pea. A true princess will be unable to sleep if there is a dried pea under her matress no matter how many mattresses are piled up, particularly if she knows about it.

A troglodyte commoner such as myself can sleep on anything. So if you tell people that there's an advantage to be had from having a crank of x length when you've been happily trundling around for years on one of y length, the amount of stress and anxiety that causes is unbelievable. So perhaps someone will try one, and convince themselves that it makes a difference, while another will try one and find that it makes no difference. It's all a matter of perception.

Now if someone were to suggest that if you were to paint your frame red, you'd go faster...?

 

[Jody]

i guess it depends on leg length too, im a short ass i have been told i should be running shorter than 170s

Same here with height. 175-170 makes a massive difference with the feel

 

[bobzmyunkle]

I run 165 and 170.
I don't notice the difference. If I was buying new it would be 165 but it wouldn't be a deal breaker. The 170s are on a bike with seized seat post so may not change anytime soon.
I had 175 on my turbo bike which started to cause hip pain. Sorted with a cheap 165 crank set. I suspect the onset of the hip pain correlates with ageing.

 

[wafter]

Aren't pro cyclists going to smaller cranks irrc?

It will be the next big thing in cycling ...

You heard it here first!!

Yes; it's been the next big thing for the past couple of years now

That's what I felt when changing from 150 to 170 (but only for a short while).
It would be interesting to do a lab study on same bikes with different lengths of crank and measuring the rider's power output. My suspicion is that it would make little difference if at all, and of course may change once the rider is accustomed to a particular length. Replicating the conditions is nigh-on impossible. A test the next day on different cranks would be inconclusive, as would changing on the day having already done minutes on one crank and then changing to another. Mike Burrows had some interesting thoughts on crank length. My own thought is that 200mm would be much too long, and 50mm would be much too short - somewhere between these extremes is everyone's ideal crank length

If you look online you'll see the results of numerous studies that largely corroborate what you're suggesting - i.e. power output is largely constant over a wide-ish mid range of lengths and only really starts to be affected at the extremes. That said there are potentially other bio-mechanical advantages outside of raw power output..


For the record I switched from 175 to 170mm on my Fuji. I needed a new crank anyway for reasons covered in the thread and used this as an opportunity to go shorter for a number of reasons:

- Reduced hip angle / associated loads
- Reduced knee angle /associated loads
- Reduced knee / belly impingement
- Improved mudgard clearance / reduction in toe strikes


It's only something like a 3% difference in length, and while it maybe felt slightly nicer / smoother, I'm not sure as I'd have picked up the difference in a blind test.

For the record I'm a similar height (5' 9.5" ish) but with fairly long legs (84cm / 33" inseam) and have no problems with 170mm cranks, so I'd certainly not see an issue with going shorter than 175mm if you have shorter legs.

Ideally 170mm is my default; I'd certainly avoid going longer again but wouldn't be shy of going a bit shorter - my Routier has 165mm cranks and feels "different" in a nice way (maybe smoother in terms of pedal stroke), but I can't say for certain that this is 100% down to the crank length.