Weight to Gearing maths

TheDrunkMonk

I've got a maths question for you guys n gals.

I'll try and keep the numbers round(ish) and I know there will be some other affecting factors, but if one of you could give me an idea of what to expect I'd be most pleased.

If I weigh 15 stone, and climb a very steady 10% hill with a compact chainset in 34-27 with a cadence of 100rpm what would the equivilent gear for the same amount of force/effort(???) at the same cadence, if I weighed 12 stone? (or 20% less if you like)

amaferanga

Are you sure that you climb 10% gradients in a 34-27 gear @100rpm? I make that >500 Watts and about 15km/h. If you were 12 stone, for the same power (500 Watts) your speed would be about 18-19km/h. But if you can hold 500 Watts for more than a minute or so when you get to 12 stone then you'll be winning races.

Have a look at this

jibberjim

amaferanga wrote:

Are you sure that you climb 10% gradients in a 34-27 gear @100rpm? I make that >500 Watts and about 15km/h. If you were 12 stone, for the same power (500 Watts) your speed would be about 18-19km/h. But if you can hold 500 Watts for more than a minute or so when you get to 12 stone then you'll be winning races

I can hold over 500 watts for 2 and half minutes up over 10% gradients - generally at close to 100rpm too, but I don't win races. I weigh just less than 12 stone.

amaferanga

I can hold over 500 watts for 2 and half minutes up over 10% gradients - generally at close to 100rpm too, but I don't win races. I weigh just less than 12 stone.

Okay, so maybe an exaggeration, but someone capable of holding >500 Watts for a few minutes without training to race would have quite some potential. I seem to recall you posting power figures up and with your figures you are certainly capable of winning races.

jibberjim

amaferanga wrote:

I can hold over 500 watts for 2 and half minutes up over 10% gradients - generally at close to 100rpm too, but I don't win races. I weigh just less than 12 stone.

Okay, so maybe an exaggeration, but someone capable of holding >500 Watts for a few minutes without training to race would have quite some potential.

Sure The numbers are still good!

bledington

As a rough answer:

34 - 27 is a 32.7 inch gear

Moving 15 stone over 32.7 inches requires the same energy as 12 stone over 40.8 inches
which is the same as 34 - 22 approximately.

touchy

bledington wrote:

As a rough answer:

34 - 27 is a 32.7 inch gear

Moving 15 stone over 32.7 inches requires the same energy as 12 stone over 40.8 inches
which is the same as 34 - 22 approximately.

thats not quite how gear inches work. A 34-27 (32.7 inch) gear will make a bike move 102.7 inches along the ground.

TheDrunkMonk

Does that mean the answer given wasn't correct? (Approximately)

touchy

TheDrunkMonk wrote:

Does that mean the answer given wasn't correct? (Approximately)

I expect the answer will still be the same, but im not sure as i dont know how it was calculated.