weight distribution?

[lock]

Hi,
Just trying to draw on the wealth of wisdom here to find out if there is a simple way to work out the percentage of weight distribution between the front and rear wheels of any bicycle; both during the design process and/or once the bike has been built?

[trikeman]

Hi,
Just trying to draw on the wealth of wisdom here to find out if there is a simple way to work out the percentage of weight distribution between the front and rear wheels of any bicycle; both during the design process and/or once the bike has been built?

Once the bike is built measuring the weight distribution is pretty easy. Just put each wheel on a scale (one at a time) and record the measurement.

Calculating what the weight distribution will be before a bike is built requires a bit more physics. What you would do is use the fact that if a body is at rest, in this case meaning the wheels are not sinking into the ground or jumping into the air, the sum of all the Moments about any point must be zero.

If we want to know the weight on the theoretical weight on the front wheel, we could sum the moments that gravity is creating on all the components by taking their weight at their center of gravity and multiplying this by their horizontal distance from the contact patch of the rear wheel. The sum of all those little moments must equal the opposite moment created by the ground pushing up on the front wheel times its horizontal distance from the rear wheel contact patch. You would do the rear wheel weight in the reverse manner. I hope that is not too muddy to follow. I may try to draw you a picture later today.

[lock]

Hi Trikeman,
Thanks for your repsonse and I appologize :oops:because my question was flawed. I meant the percentage of rider's weight on the front and back wheels but I just realized I did not state that.

[trikeman]

Ahh. That one is much easier. For the actual weight weigh the front and back wheels with you on it (you will probably need a helper) and convert the total to a percentage.

For the theoretical, guess where you think the riders center of gravity is and locate that along the wheelbase. The percentage of the distance of the riders COG from the rear is the percentage of weight on the rear, and vice versa. :wings:

For a vertical rider the COG is probably close to the center of the body. For a rider sitting down with his legs in front the COG is probably somewhere about mid-thigh. For a heavily leaned back rider, I would guess the COG might be near the butt.

Hope that helps.

[John Lewis]

The usual approximation is that your C of G is located about your belly button.

If weighing the bike as mentioned in a previous post with only one set of scales: Remember to place a piece of wood equal to the thickness of the scales under the other wheel or else you will be in error. Probably not a lot but an error none the less.

I know this from doing weight and balances on homebuilt planes to determine C of G. Believe me we don't want errors there.

John Lewis

[trikeman]

Good catch John. I am not sure my bathroom scale (which is all I have to weigh bicycles with) is accurate enough to pick up the minor error of the difference when the bike is slightly tilted (no blocks), but its an error nonetheless.

[lock]

Thanks trikeman and John! That is exactly the info I was looking for.