Tire Sizes & Squish for design

[yoshi]

Originally Posted by Engineer

On paddle tire sizing, are they measuring just the carcass, or are they measuring including the paddles?

Thanks,
Carl

You don't count the paddles for the height when setting things up, they sit below the surface.....

[plkracer]

I was running car tires at moses lake at 15 or so psi and the back of the chassis would tag the ground over rough whoop when the shocks bottomed out. Wasn't bad, I didn't feel it, but my uncle said a small amount of sand would spray out.I have 1.5 inches of gc, so the tires soak up quite a bit, and they sink a bit in the sand. It should be better when I go to 27 inch tires.

[Engineer]

Originally Posted by yoshi

You don't count the paddles for the height when setting things up, they sit below the surface.....

Thanks..... Now I just need the numbers for the tires to use this information.

[K-fab]

Just speculation on my part, but from many pix I've seen of cars in the bottomed out position, it appears that the tires generally use about half the thickness of the side wall in flex.

I would imagine using this as a basis would cover your needs.

Don't design using the bottomed out aspect for geometry - design using the full diameter.

Use the flexed position for the fully bottomed out position of suspension travel.

[punkur67]

I think the sand tires unlimited website has some of the info you are looking for.

[LiveWire]

Originally Posted by yoshi

You don't count the paddles for the height when setting things up, they sit below the surface.....

This may seem long winded, but this relates to an argument I got into recently and thoroughly investigated. I thought some here might find the info useful.

It would not matter if they were on top, say on asphalt. Even on regular car tires, the rolling circumference is less than measuring around the tire. Most people assume it is because of the flat spot on the bottom of the tire. Therefore, it is a very common misconception that you measure from the center of the wheel to the ground to get the 'rolling radius'. Some people will even go so far as to say you can run two different size tires and inflate them differently to compensate. The second part would be true is the first part were. Neither are.

If you were to look at a radial tire because less things come into play there, the outer carcass of the tire is a fixed circumference. The radial belts do not change in length significantly with a change in air pressure or a weight on the vehicle. Those belts, however, are not at the outer surface of the tire. The tread blocks compress together as they go into the flat spot on the bottom. At the point of contact, they do not move in an arc to the center of the wheel, but rather linear and parallel to the flat spot in the tire's belt. This is why tire manufactures list revolutions per mile without qualifying the weight of the vehicle or tire pressure. That would only come into play at extreme over or under inflation. The same would apply to the paddles as it would to the tread blocks. With bias ply tires, there is some tire growth with air pressure.