kumquat wrote:MrWhoopee wrote:kumquat wrote:Probably because there's more weight over the front wheels than the rear wheels. In between the front wheels is the entire engine and transmission. In between the rear wheels is, usually, an empty metal box.
That would explain it generally (both FWD and AWD), but why only for the AWD? The weight of the differential offsets the transfer-case and the drive-line is more or less balanced. Why.........?
Matters less for FWD because there's no drive power to the rear wheels. In slippery conditions where you're going to be transferring power to the rear wheels with some frequency, you want to make sure they have as much traction as the fronts. If they're overinflated and have significantly less contact patch and traction, then they're just going to spin as well and not help you out. The driveline is not even remotely balanced. The rear differential weighs, what, 50-100 lbs max? How much do you think the engine and transmission weigh?
Also, besides traction, as you mention is diameter. At the same pressure, the front tires will have a smaller effective diameter. The computer could become confused and have less opportunity to provide optimal traction if it sees the rear wheels turning more slowly than the front.
It's all about the weight distribution, and there's a lot more weight in the front than back.
When I said that the driveline was more or less balanced, I meant that it's weight was equally distributed front to rear.
The computer does not factor into this, the AWD system is strictly mechanical and I don't have traction control.
You have given me a likely explanation. The extra pressure in the front compensates for the extra weight, giving the front and rear wheels an
equal effective diameter, keeping rotational speeds equal front to rear and eliminating any preload on the VC. It's not necessary to do this with FWD, so the tire pressures can be equal, giving a little softer ride.
I've been driving with equal pressure front to rear (having only just discovered the AWD specs) and have noticed a tendency to wander a little on slick roads at higher speeds (with studded snow tires). I will adjust the pressure today and see if it makes a difference.
Thanks for playing.