As I was putting my SA 15" wheels and 215/75 tires on the GoldBrick this previous weekend, I got to thinking about tire pressures. Since I recall some questions on this in the past, I figured I'd post my own meanderings.... First off, I've only got Syncros. Non-syncro pressures might be slightly different (though I don't believe that is the case.) With 185/80R14 tires, the recommended pressures are 40 psi in the front and 48 psi in the rear. With 205/70R14 the recommended pressures are 36 psi in front and 40 psi in the rear. Now for some simple math and analysis. Based on the weight of the vehicle we can figure out the AREA that each tire covers on the road when loaded...because we know the pressure the tire exerts. However, if we simply glance at the above numbers a simpler pattern emerges. 36 psi is about 10% less than 40 psi (the front tires). the 185 (remembering that this number is the WIDTH of the tires) is about 10% less than 205. Or to reverse this...the 205 is about 10% wider than the 185 tires...which is a nice correlation to the pressure. Onto the rears...and the math isn't quite as close, but is still similar. 40 psi is about 18% less than 48, but the width is still only about 10% wider. Going for Kentucky windage and I guesstimate that another 5% wider tire will allow for about a 5% decrease in tire pressure... So on my 215s I went for 35 psi in front, and 37 psi in the rear. The ride feels just about right (perhaps a trifle stiffer, but reasonable). |
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