I’ve read all the theory, mainly what I know is that one of my XTRs is 170mm and the other is 175mm and I have no idea which is which, certainly can’t tell when riding.

165 for the cool kids !

(and me)

I reckon I might notice less pedal strikes, since the hemlock can drag its arse a little bit sometimes, but I can’t feel it in the pedalling action. Switching to thinner pedals has much the same effect but few people talk about choosing the right pedal thickness for their leg length after all.

I was never comfortable with 170s on one bike (CX) with 175 on everything else – just felt wrong and gave me sore hips.

I guess my legs are used to 175s and everything had settled into that diameter – the mechanical “advantages” of 170s and 175s were clearly overcome by sheer pain and misery on long rides.

I certainly notice it on the roadie, less so on the mtb

As said, less gives better ground clearance.

How long are your legs?
Do you spin or grind?

If yours are short like mine & prefer to spin then 170’s are perfect.

Like Amplebrew I used to get very sore knees afterlong rides or when using the big ring alot.

They are also better if you are recovering from any knee surgery.
I had a new ligament.

I only made the change this year after a conversation with another rider
who said that 170’s might be better for a shortarse like me.
Big difference .No knee pain.

Small con is changing the cranks on all your bikes.
i took a full suss abroad for a week and forgot to change from 175 to 170.
No problems whilst there , but my knees where vvv bad the week after.
J.

Van Nicholas have a size of everything calculator on their website