Using 172.5 and 175 crank

[Dambha]

Morning all

 

Is it advisable to use a 172.5 left arm crank with a 175 right crank...got a left arm power metre.

 

In theory could you increase the stack height between your cleats and cycling shoes by using something to make up that 2.5?

 

Any advice would be highly appreciated

[Butterbean]

While a jimmied system might work in theory, just don't do it.

 

Swap the crank arm or buy a new crank to match...

['Dale]

Morning all

 

Is it advisable to use a 172.5 left arm crank with a 175 right crank...got a left arm power metre.

 

In theory could you increase the stack height between your cleats and cycling shoes by using something to make up that 2.5?

 

Any advice would be highly appreciated

 

Not advisable.

It's one of the peculiar things in bike fitment where a millimetre becomes a mile and can create injury issues.

[bertusras]

Does stacking it not actually exacerbate the issue though?

 

Let's say you add 2.5mm under your right shoe to the 175mm crank side to 'shorten' it. At the bottom of the stroke you'll be at a relative 172.5mm, spot on, but when you're at the top of the stroke, you will actually be at a relative 177.5mm.

 

Right?

 

Edit: Math is hard.

Edited June 19, 2020 by bertusras

[Vetplant]

While a jimmied system might work in theory, just don't do it.

 

Swap the crank arm or buy a new crank to match...

Please listen to Guy.

 

Replacing the Crank is much cheaper than the repair cost from the physio/bio.

 

https://bikehub.co.za/classifieds/item/cranksets/408359/shimano-fc-rs510-11-speed-compact-crankset

[Chris_]

Morning all

 

Is it advisable to use a 172.5 left arm crank with a 175 right crank...got a left arm power metre.

 

In theory could you increase the stack height between your cleats and cycling shoes by using something to make up that 2.5?

 

Any advice would be highly appreciated

 

Then you'll be 5mm out at the top of the pedal stroke...

[DieselnDust]

Does stacking it not actually exacerbate the issue though?

 

Let's say you add 2.5mm under your right shoe to the 175mm crank side to 'shorten' it. At the bottom of the stroke you'll be at a relative 172.5mm, spot on, but when you're at the top of the stroke, you will actually be at a relative 177.5mm.

 

Right?

 

Edit: Math is hard.

 

 

 

That's why you add the 2.5 spacer to the 175mm side.

The effect will always be to have that side 2.5mm higher when the leg is at full extension. its not so much an issue when the leg is under compression

Edited June 19, 2020 by DieselnDust

[100Tours]

That's why you add the 2.5 spacer to the 172.5mm side.....

 

 

Nope - Bertus is right here.

 

The bigger impact of changing crank length (imho) is how high you have to lift your leg at the top of your stroke to get it over the hump. if you have built up the shoe your foot is going to have to clear a higher hump to get around the loop - the bottom of the stroke is less of an issue (you fix that with seat height).

[DieselnDust]

Morning all

 

Is it advisable to use a 172.5 left arm crank with a 175 right crank...got a left arm power metre.

 

In theory could you increase the stack height between your cleats and cycling shoes by using something to make up that 2.5?

 

Any advice would be highly appreciated

 

 

2.5mm is within a normal leg length discrepancy. Technically you can get away with it if you fit a spacer under the shoe connected to the 175mm crank arm. However.........

 

 What if the other leg is the one that requires correction and you now exaggerate the leg length discrepancy?

[DieselnDust]

Nope - Bertus is right here.

 

The bigger impact of changing crank length (imho) is how high you have to lift your leg at the top of your stroke to get it over the hump. if you have built up the shoe your foot is going to have to clear a higher hump to get around the loop - the bottom of the stroke is less of an issue (you fix that with seat height).

 

 

ya sorry was thinking about the 175mm crankarm and typed 172.5mm. Corrected post

[LuckyLuke]

Go for a bike fit, usually your left leg is bit shorter than the right, then it probably wont be an issue and my fitter agreed, i was going the same direction but got a powertap wheel for cheap

Edited June 19, 2020 by devilliers

[Long Wheel Base]

So if you do the 2.5mm spacer thing on the shoe, when at 90deg(crank), you are 172.5mm away from the centre but you a small amount above or below 90deg(foot) in reality?

 

Waiting for all the biopace/Qring/sqaushed chainring guys to start with how this can improve power or pedal stroke or whatever it is these things do.

[Quagga]

That's why you add the 2.5 spacer to the 175mm side.

The effect will always be to have that side 2.5mm higher when the leg is at full extension. its not so much an issue when the leg is under compression

Disagree, the angle of the hip will be less putting strain on lower back and Glute

[Kalahari Vegmot]

Seems like a decent idea mind you.

 

2.5mm is really nothing; just bend the saddle to even the legs out that little bit and you'll be golden????????

[thebob]

Sounds like a shortcut to a world of pain

[Wayne pudding Mol]

Do it and report back in 1000kms and we can publish a paper

 

Disclaimer - I am in no way responsible for any medical bills