Quote:
Originally Posted by RidingOnRailz
^This^ flys squarely in the face of everything I've ever been told, by automotive technicians, mechanics, and have read on-line, about tire pressure and tires in general.
Inflation pressures are secondary only to where, and how, one drives, and how much one hauls regularly.
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Indeed this does fly in the face of what is generally accepted. On the other hand, what you have cited as experts aren't tire engineers - and even then there is disagreement. Allow me to tell you where I developed this.
For about 10 years in my career I was a development tire engineer - I designed them! I had access to a lot of data - and one of those was detailed tread measurements of wear tests being performed. Because of all the data available, I was able to see that position on the vehicle had a major effect on how even the tires wore. Because these tests were done at the GAWR for each axle, loading was even for the vehicles in question.
As it happened, I chose some test data that involved a full sized RWD sedan. The data from that test showed that the front tires slowly developed shoulder wear, while the rears slowly developed center wear. (Mind you, the loading and the pressures on the tires was the same.) That meant that there was a wear effect independent of the load/pressure.
We also used to perform a city driving test - where a vehicle was driven around a simulated downtown area. The tires wore extremely fast. In some cases, we had tires wear out in 5K miles!! Here the test called for empty vehicles (curb weight) and placard pressures, and since we were using SUV's, one would expect the tires to be worn in the centers due to the lack of loading. That was not the case. Just like the other tests, the front tires wore in the shoulders and the rears wore in the center.
Later in my career, I was working in field testing (regular vehicles in service), I noted the same sorts of things - EXCEPT, many of the vehicles were small FWD cars, and there, the front tires wore fairly evenly as did the rears. This flies in the face of the conventional wisdom you cited above.
So why? Because the fronts on a FWD do both the drive (torque) and the cornering, where these functions were separate on a RWD. In other words, the position effect (drive vs cornering) cancelled each other on a FWD.
But that does not explain why the rear tires on a FWD wear evenly - and that's because the affect load/pressure has on tires is small compared to the effect torque and cornering have on wear.
But all of what I said above applies to steel belted radial tires. Bias ply tires don't behave that way because they don't have that reinforcing belt under the tread. That belt stiffens the tire which results in much longer wear life (among other things.)
And here's where it starts to make sense. The conventional wisdom was based on bias ply tires. For some reason that I don't quite understand, these sorts of "wisdom" don't seem to change over time, even when they should. For steel belted radial tires, this "wisdom" is hard to refute because there are enough examples where it is true, and even more where it is hard to sort out all the effects going on.
Take for example the rears on an empty pickup wearing in the center. Conventional wisdom would say that the uneven wear would be caused by the light load/ high pressure thing - and since very few people know about the drive tire/steer tire thing, they would conclude that the wear is 100% the result of load/pressure mismatch. Ergo, it reinforces the faulty convectional wisdom.
So I hope that explains things. I have spent the last 20 years trying to get people to realize that not everything one hears about tires on the internet is true - and this is just one of many.