Quote:
Originally Posted by Frank Lee
What I have found is, there is quite a difference from the hypothetical calculations and the real world experiment results. All my calculations showed that a 155 series tire would have a square patch at 50 psi on the front; but then my experiment showed that airing up my 185 series tire to 50 psi STILL wasn't enough to achieve a square patch.
"Could someone verify how you calculate the psi needed for a square contact patch?"
I'd go by axle weight rather than total weight/4. Most cars, being FWD, carry about 2/3 of their mass on the front axle unless really loaded. Then once you have a sq in value for the front and rear patches, you need to know how wide the tread is THAT IS CONTACTING THE GROUND.
|
Good point about the weight distribution. I hadn't though of that. I wonder how much of the tire actually lifts from the sides, but I figured it would be small. I didn't notice any appreciable change when I pumped up my tires, but you are right, contact patch is smaller then tire width and should be noted.
I'm wondering if the psi issue has something to do with the tire being a flexible toroid rather than an impermeable cylinder. The only thing I can come up with is that a tire is flexible, so it is subject to differential stress. Like a rolling pin pushing on dough, some of the force is being redistributed to the sides rather then straight down.
An impermeable cylinder would allow the entire air pressure to support the axle while the toroid must share that pressure with the axle
and the further compression of the rest of the air in the tire (plus wheel bulging).
I might be getting a little too deep and lost into all of this, so feel free to set me straight.
If anyone has been able to achieve a square contact patch, would they mind posting vehicle weight, tire width, and psi? Now that I think of it...I should probably perform my own test.
- LostCause