Quote:
Originally Posted by vwnate1
Jeeze......
I know Bakersfield is a rough town but damn .
I find that tires usually age out and begin having sidewall leaks before I wear them out .
Of course, unlike most I take the time to properly inflate my tires and keep the vehicles in proper alignment .
Most manufacturer's suggested inflation pressure are far too low to give a soft & cushy ride .
|
The US DOT mandated TPMS was because people are bad about keeping air in their tires. TPMS costs several hundred dollars, and the sensors don't last life of the car, adding more to the total cost of ownership. In contrast, "flat tire monitor" (FTM) costs about $1/car (the cost of an indicator light and a reset button). The rest is using the existing ABS sensors and some software.
A lot of BMW's have a <100 MPH recommended pressures and >100 MPH pressures. For Frau Putzer's X3 <100 MPH, the recommended pressures are 32 PSI front and 35 PSI rear. For >100 MPH, they're 35 PSI front and 45 PSI rear.
The low recommended pressures keep the tires sticking to the pavement when there's a discontinuity in the pavement (expansion jointz, efc.) Also, BMW and M-B are trying to get the cars to ride better on those miserable run-flat tires.
I maintain the same pressures for an entire rotation stint. Then I measure the depths and calculate wear in the circumferential channels. Comparing the two side channels' wear to the two middle channels' assesses the pressures. Based on the wear patterns, I change then the pressures for the next rotation stint if necessary. For the X3, 39 PSI all around gives me almost perfectly equal side wear vs. middle wear. The front tires still wear a little more on the sides (under-inflation), and the rear tires wear a little more in the middle (over-inflation). But, with rotation it all evens out.
Comparing the inside channel's wear to the outside channel's wear assesses alignment. I can catch a misalignment before it causes real damage to the tires. Alignments are cheap compared to tires.
For all this to work, I need a high-resolution (0.001"), digital tread depth gauge. The old mechanical, plunger gauges don't cut it.
BMW passenger cars tend to wear the inner half of the rear tires more, due to a high negative camber of the rear wheels. BMW SUV's tend to wear the outer half of all four tires more, due to less rear camber, higher center of mass causing more body roll and more weight transfer to the outside tires in a turn, and higher aspect ratio tires causing more tire deformation in turns.
The X3's non-run-flat, all-season Bridgestone Dueler H/P Sport AS's are symmetric. After 29k miles, the two inner channels have worn down about 0.5/32" more than the two outer channels. So, at their half life (~32k miles) I'll have the tires flipped on the rims. That will make the tires last another ~7k miles or so.
I put protectant (Meguiar's Endurance) on the outside sidewalls when they start turning brown, and I put it on the inside sidewalls when I rotate the tires. I'm still on my second bottle of Endurance after maybe twenty years. I had to throw away the first bottle because the bottle cracked.