Crank arm length

[Mountain Bru]

Just now, Nicomrs said:

but my logic tells me that say i keep my cadence in a specific gear the same, do i have to put down a lot more power on shorter cranks? 

Read this :

11 hours ago, Mountain Bru said:

I get what you mean, but your understanding of the relationship between power and crank arm length is slightly off. 250w is 250w regardless of crank length.
However....
Power=Torque x Angular Velocity     (Angular Velocity would be cadence in our world)
And 
Torque = Force x radius  (Radius here would be crank arm length, Force is how hard you're pushing the pedal around the BB)

So if power is the same, cadence is the same, and you reduce the crank arm length from 175mm to 165mm, that's roughly a 6% reduction, so you'll need roughly 6% more force on the pedals to produce the same power (not exactly, but roughly). 
 

 

[Nicomrs]

1 minute ago, Mountain Bru said:

Read this :

 

6% doesnt sound like a lot but certainly feels

[Jewbacca]

33 minutes ago, Mountain Bru said:

Never heard of 150mm cranks... is that even a thing? 

Sounds like it could be pretty harsh on the knees though.... Gonna need to put some proper force on those cranks to produce watts, and I think the deadspot at the top/bottom of the stroke gets bigger with shorter cranks too. 

I have a 42 tooth Direct Mount chainring on the Lyne cranks I want to run on this..... Take the 20 inch Bike to Around the Pot, Swartberg, CTCT and a host of other cool things and try to raise some money for the SPCA

[Chadvdw67]

1 hour ago, Mountain Bru said:

Lifting your pedal up 5mm should theoretically make pedal strikes happen less, but in all honesty I think it's bad technique if you pedal strike a lot, not a crank length problem. Ride over the rocky stuff with level pedals. If you must pedal, judge the rocks nicely so you pass them with your "impacting pedal" at 12 o clock when you pass it, even if you've gotta free wheel a bit.

 

 

You are 100% correct, it is/was poor technique, it happens in pedaly sections because of poor judgement, I was getting better in any case, after I rode with the shorter cranks I made a conscious effort and improved a lot, but the shorter cranks just felt nicer anyway, and it didn't cost me anything extra, so......

My knees would sometimes get irritated, I wouldn't really say sore, but I could feel a niggle in my knees on some rides, since having the shorter cranks it hasn't happened, so bonus there as well

[justinafrika]

5 hours ago, Eldron said:

there are a few paper that measure power, oxygen consumption etc and the scientific consensus is that crank length is largely irrelevant (even at the ridiculous extremes).

 

7 hours ago, buckstopper said:

Just received, as a gift of course, a 165cm 105 set

Does this count as a ridiculous extreme? Wouldn’t mind seeing that, but it'll need a rider on each side of the crank. Could be fun.

Edited August 9, 2021 by justinafrika

[Eldron]

1 hour ago, justinafrika said:

 

Does this count as a ridiculous extreme? Wouldn’t mind seeing that, but it'll need a rider on each side of the crank. Could be fun.

Not at all - I fitted a rider this morning with 165mm cranks. An asian lady to be fair. On the lower end of the normal distribution - uncommon but not rare.

Most track riders use 165-170mm cranks.

[ChrisF]

15 minutes ago, Eldron said:

Not at all - I fitted a rider this morning with 165mm cranks. An asian lady to be fair. On the lower end of the normal distribution - uncommon but not rare.

Most track riders use 165-170mm cranks.

mm vs cm .... 

[Eldron]

24 minutes ago, ChrisF said:

mm vs cm .... 

Ah. Too much work today for a sense of humour ????

Edit: Can we re-institute the comic sans thing for when you make a funny? It will make dishing out advice so much easier....

Edited August 9, 2021 by Eldron

[ChrisF]

6 minutes ago, Eldron said:

Ah. Too much work today for a sense of humour ????

Edit: Can we re-institute the comic sans thing for when you make a funny? It will make dishing out advice so much easier....

We REALLY need CS font for Android ....

 

Even worse ... cant properly add emojis from the phone...

[justinafrika]

3 hours ago, justinafrika said:

 

.

Edited August 9, 2021 by justinafrika

[Parker66]

I have a 175 mm crank (bb30) that I'd be willing to trade for 165's.

My new bike is so low and get pedal strikes on the daily.

Let me know

[Mountain Bru]

While we're trading cranks..... I have 175mm M8100 XT cranks in really good condition. If anyone has a 170mm M8100 crankset, I'd love to swap. 

Also.....

pink font is a good sub for comic sans.

(Serious about the cranks though)