[mvnbykes]

I just got a new bike as a backup. It's a 53 cm Raleigh, and my current ride is a 54 cm Trek. The lbs put a longer stem on the Raleigh and is going to get me a new seatpost (the clamp keeps slipping on the original). The Raleigh has 170 cranks and the Trek has 172.5. How much of a difference does crank length make, and do I need to adjust my saddel height for the shorter cranks? I took it on a ride last night and it felt pretty good while seated spinning or pushing harder gears, but out of the saddle sprinting felt unusual due to the shorter cranks. All my previous bikes had 172.5's on them. I don't know much about crank length's and their effect on spinning/pedaling except that shorter ones are recommended for shorter people (I'm 5' 91/2"). Anyway, thanks in advance for all replies.

Mark
"Those who say it cannot be done shouldn't interrupt those of us who are doing it."

 

[R.Rice]

I have 172.5's on one of my bikes and 170's on the other.Honestly,I can't really tell the difference.

If you are going to set up one based off the others center of BB to top of saddle then you will have to raise the saddle which will mean you have to move it foward too.

 

[Visitor302]

Longer cranks = more power. Good for jumping off a starting line, or pulling a hill
Srot cranks = speed. Shorter stokes for more RPM.

Like bore vs. stroke in a mucle car.....

 

[C-40]

torque not power...

Longer cranks = more power. Good for jumping off a starting line, or pulling a hill
Srot cranks = speed. Shorter stokes for more RPM.

Like bore vs. stroke in a mucle car.....

Longer cranks, provide more leverage or torque. Power is torque times cadence. In this case, the difference is a measly 1.4%. I'd be surprised if anyone could tell much difference, particularly out of the saddle. Too many other variables to credit the crank length for the difference.

As for saddle adjustments, trying to adjust two different saddles accurately enough to cover this minor difference is unlikley. How to adjust the saddle for this difference is also debatable. In theory there would be the need for a 2.5mm rearward movement of the saddle to maintain the same KOP, but it's not easy to measure KOP this accurately in the first place. Same goes for saddle height, unless you've got the same saddle on both bikes. There's a valid argumant for using the same saddle height to split the length difference equally between the up stroke and down stroke. Raising the saddle puts the entire difference at the top of the stroke.

 

[Mr. Versatile]

Longer cranks = more power. Good for jumping off a starting line, or pulling a hill
Srot cranks = speed. Shorter stokes for more RPM.

Like bore vs. stroke in a mucle car.....

That's technically correct, but I doubt very much if you'll be able to discern much, if any, difference with a 2.5 MM. difference.

 

[Kerry Irons]

Power source?

Longer cranks = more power. Good for jumping off a starting line, or pulling a hill.

So, just where does this extra power come from? In reality, longer cranks = lower cadence = higher gear = the same speed and the same power output from the rider.

 

[TurboTurtle]

Longer cranks = more power. Good for jumping off a starting line, or pulling a hill
Srot cranks = speed. Shorter stokes for more RPM.

Like bore vs. stroke in a mucle car.....

The analogy is good as long as you are only talking about the engine. The longer crank gives the engine more torque, the shorter gives the engine more rpm (cadence). Neither gives the car more power or speed. - TF