cadence

[GrasB]

Correct me if I am wrong here, but the length of crank length is irrelevant, in term of r.p.m. in a given gear, one r.p.m. of the crank for example a 52th front and 13th rear gives a 4:1 ratio so a 110mm crank length will turn the rear 4 times as will a 170mm crank length, the longer crank will lower the overall gearing because you have a greater circumference to travel, giving more leverage. if my understanding is correct.

I don't want to go here but....
Apply 10Kgf on 175mm cranks with a 4:1 gear & you'll generate 4.29Nm of force at the rear wheel.
Apply 10Kgf on 150mm cranks with a 4:1 gear & you'll generate 3.68Nm of force at the rear wheel.
So under the same conditions at 90rpm the 150mm cranks will feel like you're riding on a 16.7% higher gear while your drive train gearing is the same.

I think so too, but the greater leverage on the longer cranks needs your foot to move further per rotation so at a higher footspeed. I think GrasB's post would imply that with much longer cranks, you'd pedal a slower rpm, with the same footspeed, but presumably a harder gear ratio (with the higher leverage), so it would appear more grindy in cadence terms, but its the same output... i think

The boy did good

 

[black'n'yellow]

So under the same conditions at 90rpm the 150mm cranks will feel like you're riding on a 16.7% higher gear while your drive train gearing is the same.

I've often thought to myself while riding along, "hmmm this gear feels 16.7% more difficult than the previous one.."

 

[simmi]

1.8m/s foot speed... that puts you in a nice striking distance of your maximum power (which is produced around 2.25m/s +/-0.1 m/s) under most conditions.

I didn't know that. so in simple terms for sprints if one rev of your crank is 1.0m your optimum spinning speed would be 2.25 revs per second or a cadence 135?

So for my 170mm crank 1 rev = 1.07m so cadence would be 126?

 

[GrasB]

I've often thought to myself while riding along, "hmmm this gear feels 16.7% more difficult than the previous one.."

No but I be you've often thought "this gear is a little too high I should change down.". Consider that 2t sprocket jumps tend to be in the 9-13% range.

I didn't know that. so in simple terms for sprints if one rev of your crank is 1.0m your optimum spinning speed would be 2.25 revs per second or a cadence 135?

Somewhere between 2.15m/s & 2.35m/s is where you'll produce maximum power for short duration sprints (10s sprints, maybe as long as 30s maximal effort sprints). That's mostly independent of crank length, you'll simply produce that power at higher rpms on shorter cranks. BTW you don't think about this on the road, you'll get a feel for the right gear to be in for sprinting. As a general rule you'll actually find the best sprinters go beyond peek power by 10 rpm or so, this means they put the most power into acceleration before it falls off as they get to terminal velocity.

 

[black'n'yellow]

No but I be you've often thought "this gear is a little too high I should change down.".

Absolutely - and then I do. Change down, that is. Problem solved. I can't help thinking this is all a bit over-complex when it needn't be...

 

[GrasB]

Absolutely - and then I do. Change down, that is. Problem solved. I can't help thinking this is all a bit over-complex when it needn't be...

The basic take home from foot speed is when making radical crank length changes you do need to consider the impact it'll have on your gearing. Both the top & bottom ends.