Slippy

Hi, not sure if this is the best forum for this Q but here goes...
how does one go about calculating the mass/load that the rear wheel is taking (ie rider+bike?)

KBentley57

Easy if you have two scales. Place one under your front tire, one under the back. Assume riding position, and record the weight on each scale. This will tell you the "net weight" on each wheel.

dabac

You don't even need two scales. Stack some phone books or whatever you have available until you have another platform the height of the scale to rest the other wheel on. Get on, record value, switch places for stack & scale, get on, record value.

Not that this will tell you anything particularly useful. You'll get the static load, but a bike in motion sees a lot of dynamic loads, bumps, potholes, rider moving around etc.

BCRider

What the guys have suggested above is the MEASUREMENT of the wheel loads. And really that's the only way to go. A rider's mass can be known but their actual center of mass is just way too convoluted and position sensitive to try to manage. So it's just easier and more accurate to use a bathroom scale and measure the wheel loadings.

Keep in mind you need to be in your actual normal riding position. Or try it with various "attack" and "sight seeing" riding positions for a range of wheel loadings depending on riding position. The trick will be to balance. LIkely this whole thing is best done near a wall so you can lightly lean an elbow or shoulder against the wall for balance.

davidad

You can use this chart for ballpark figures. https://www.adventurecycling.org/res...SIRX_Heine.pdf

FBinNY 

Weighing is the best method for getting the static axle weight. As another person pointed out dynamic weight is far greater and more complex but that's for the engineers to worry about. Static load is the starting place for comparison.

You can also estimate the weight distribution between front and rear wheels fairly simply. Assume the bike itself places half it's weight on each axle (as you'll see next, a pound or two won't matter). Now since most of place very little weight on our hands, assume all of the rider's weight is in the saddle. Measure the wheelbase and use a plumb & ruler to measure the horizontal distance from the center of the saddle to either axle.

The weight distribution can now be calculated as follows:

Weight on rear axle = total weight times the distance to the front axle divided by the wheelbase.

Reverse front and rear for the weight on the front axle, then check your math by adding both axle weights and checking that they add up to the riders weight.

Don't forget to add 1/2 the bikes weight when finished.

BCRider

But "most" riders other than perhaps racers DO put some weight on their hands. And then there's the weight put on a rider's feet while pedalling. Add to this that as you change from riding in the drops, to the hoods, to the cross portion of a bike with drop bars that you're radically altering the angle of your back and shifting your weight to the rear with each change and any single figure quickly becomes meaningless. Even with flat bars which limit the rider's hand positioning just leaning forward with a bend to the elbows or sitting up straight with locked elbows is going to alter the weight distribution a lot. Then there's the tendency to slide forward during climbing a hill and to slide back during a descent and braking.

So even without bumps and other things just how the rider positions themself from moment to moment is going to cause a sizeable range of weight distribution. Riding a bike is typicaly quite a dynamic exercise.

All of which comes back to wondering why the OP wants this information.

FBinNY 

The operative word is estimate. Even if one were to use the "more accurate" method of actually weighing the axle loads, there will still be changes as he rides.

Certainly working with an estimate, one can fudge it a bit for where he sits, or how much weight he thinks he transfers to his hands. Almost all riding weight transfer will be forward and tending to equalize axle load anyway.

And as I said earlier, static load is the starting place for all considerations of weight distribution, whether bicycle or automotive.

BTW- the Op might want axle weight info to use as a guide to choosing tire cross section. Ours is not to reason why..... He asked how to calculate, so that's what I answered.

Scrockern8r

I found 65/35 to be a reasonable ballpark to get me started as well.
-Tally up the weight of you, bike, and anything else going with you.
-Rear = .65 x total weight
-Front = .35 x total weight

Mark Kelly 

That this cannot be so is seen by simply looking at a typical rider on the bike - the saddle is the rearmost point on the rider. This proves that the riders Centre of Mass must be forward of the saddle.

A more reasonable approximation is that the riders weight is roughly over the bottom bracket. That makes the rear weight estimation easier too - it's roughly total weight x (wheelbase - chainstay length) / wheel base

Road Fan

Weigh yourself holding the bike. Multiply that by some number between 0.55 and 0.65. That's an estimate of rear axle loading. If you need a better number, do the rear-wheel weighing thing.

Or,

Assume all the rider weight is over the BB. Measure the rider weight, bike weight, wheelbase and the chainstay length and divide chainstay by wheelbase (long division or calculator), then subtract that from 1. Multiply that fraction times the sum of the bike plus rider weights. Unless your touring load is similar ot the bike weight, this will also be a decent estimate.

I just put the rear wheel on a scale, with me on the bike.

Slippy

Thanks everyone!