Mismatched crank lengths

[dexterdent]

So, I think I know the answer to this one, but might as well ask as the few online answers I found differ.

How bad of an idea would it be to install a 172.5mm crank arm power meter on a 175mm crankset? Resulting in one side being 2.5mm shorter than the other. And you can't fix it with a shim as that both "shortens" and "lengthens" the crank depending on where you are in the pedal stroke.

Answers typically vary from "You won't even feel it" to "You will walk like an 90-year old within a week". I'm leaning towards bad idea?

[Sid the Sloth]

My advice would be to look for the same crankset in 172.5 or the same power meter in 175 instead of risking injury and asymmetries that could affect your performance permanently. You should be able to come out even. What cranks do you have? I might even be able to help. 

[Pure Savage]

29 minutes ago, dexterdent said:

So, I think I know the answer to this one, but might as well ask as the few online answers I found differ.

How bad of an idea would it be to install a 172.5mm crank arm power meter on a 175mm crankset? Resulting in one side being 2.5mm shorter than the other. And you can't fix it with a shim as that both "shortens" and "lengthens" the crank depending on where you are in the pedal stroke.

Answers typically vary from "You won't even feel it" to "You will walk like an 90-year old within a week". I'm leaning towards bad idea?

I guess you could add a 2.5mm shim under your cleat if you are hell bent, otherwise, go matchy matchy

[dexterdent]

Thanks for the inputs - It's an Ultegra 6800 series, compact.

I think I kindoff know that you are both right and that's definitely the correct plan. I guess it's a bit of an academic question - genuinely interested if I would feel the difference.

[TNT1]

33 minutes ago, dexterdent said:

So, I think I know the answer to this one, but might as well ask as the few online answers I found differ.

How bad of an idea would it be to install a 172.5mm crank arm power meter on a 175mm crankset? Resulting in one side being 2.5mm shorter than the other. And you can't fix it with a shim as that both "shortens" and "lengthens" the crank depending on where you are in the pedal stroke.

Answers typically vary from "You won't even feel it" to "You will walk like an 90-year old within a week". I'm leaning towards bad idea?

As long as you don't particularly like your knees, go for it.

[BaGearA]

i don't think you will feel it , i ha d a friend ride with mismatched crank arms for almost 3years unknowingly 

 

it took almost that same time with A physio to get his knees right again.

[TheoG]

Maybe you lucky and the one leg is 2.5mm longer than the other, hopefully on the matching side .... 😂

[dexterdent]

1 hour ago, BaGearA said:

i don't think you will feel it , i ha d a friend ride with mismatched crank arms for almost 3years unknowingly 

 

it took almost that same time with A physio to get his knees right again.

Thanks - this is what I was looking for! Figured it would be hard to feel the difference (which is what comes up a little when you google it) but might have long-term consequences.

Case closed for me. Hopefully this thread comes up when someone else googles this stupid idea.

Anyone want to buy a 2-month old 4iiii 105 172.5mm power meter?

[Eldron]

Mathematics versus Emotion!

You can do it - Stack the cleat on the 175mm crank using a 2.5m spacer. Job done.

I wouldn't do it though 😁😁😁

The only practical thing I can think of is that it would change your foot position over the pedal axle as you pedal.

The Engineer in me says goes for it. The Bikefitter is screaming NOOOOO!

[Furbz]

I know of a local prominent racer who road for a couple years without noticing he had a 172.5 on the left and a 175 on the right.

we are talking top top local rider from a number of years back.

never noticed. never had any issues. 

he did of course change it when we found it. 

[Jbr]

When I received my new bike it was supposed to come with 172.5 ultegra, unfortunately it was 170. I found on the hub a 172.5 and bought it the same day, sold the 170 the following day and lost R50 in the process.

 

I don't know what part we're talking about in this case, but I wouldn't be able to bear knowing that I'm riding mismatched crank lengths 🤣 (Although I probably wouldn't notice it if I didn't know.. I used to ride three bikes all three with different cranklength and it all felt normal to me)

[Shebeen]

are you legs the even same length to start with?

[The Ouzo]

1 minute ago, Shebeen said:

are you legs the even same length to start with?

My mom used to always have a slight limp, never concerned her until she got older and it started to cause pain, so she had it checked out. She always just thought her legs were unusually mismatched, turns out the reason they were mismatched in length was because at some point in her childhood years her one hip was dislocated and eventually created its own socket on her pelvis.

Now having been born and living in rural greece until her teenage years she doesnt know if she was born that way, or it happened after being born, but she does not recall ever dislocating her hip.

[PeterF]

4 hours ago, Eldron said:

Mathematics versus Emotion!

You can do it - Stack the cleat on the 175mm crank using a 2.5m spacer. Job done.

I wouldn't do it though 😁😁😁

The only practical thing I can think of is that it would change your foot position over the pedal axle as you pedal.

The Engineer in me says goes for it. The Bikefitter is screaming NOOOOO!

This will maybe solve the problem at the bottom of the pedal stroke but won't it compound the problem at the top of the pedal stroke?

[dexterdent]

10 minutes ago, PeterF said:

This will maybe solve the problem at the bottom of the pedal stroke but won't it compound the problem at the top of the pedal stroke?

That's how I understand it as well, as my horrible powerpoint drawing hopefully shows:

 

 

[lechatnoir]

3 minutes ago, dexterdent said:

That's how I understand it as well, as my horrible powerpoint drawing hopefully shows:

 

 

makes sense to my analytical brain. my spidey sense was tingling when this was first mentioned.