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· Opeler
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142 Posts
Best Tire Pressure

I know 3 guys who are in the tire business the run high-end / high-volume stores. They all have the same formula:

Identify the max tire pressure located on the tires you are running. Subtract 4~5 lbs. from that max tires pressure for normal every day driving.

Tweak from there!
 

· boomerang opeler
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5,661 Posts
oh boy do you guys run hard tyres
the pressures for uk/europe are 26psi front and back with normal tyres (29 if you are running for long times at 90 mph+ or a full load )
at 36 you are running on the centre of the tread and loosing half the footprint of the tyre , they must wander all over the road :eek:
 

· Member
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648 Posts
On my 205-50-15's I run 32F 30R on the street. When autoXing, to get to use all the tread I have to back down to 30F, 28R.
Jc
 

· Super Moderator
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15,258 Posts
Best bet is to experiment. It depends a lot of the brand of tire, and the tire width as related to the rim width. You basically want the tread to fully contact the ground with even pressure. A nice way to check is to roll through a puddle while on a freshly tarred parking lot, and check the tire pattern left on the ground by the water on the tread. It's a starting point.

Most of my Manta's had a 205/60-13 radial tires on a 7" rim, so the tire and wheel were well matched width-wise. I'd run 34 front and 30 rear to help balance the chassis and provide good steering feel.

Now on my Ascona I'd run 8" front and 9" rear wheels with 235 front/245 rear tires, but in a bias ply. If I ran anything over 26 psi they would ride on the center of the tire and wear like hell! Normally ran 24/23 on those. My racing slicks however (bias ply again), would be run at 21 front and 20 rear for track days. Due to the heat of driving at high speeds, these expanded to about 28 front and 30 rear (yes my car was set up to oversteer).

Point is, you need to take into account all the factors present. Around-town jaunts won't heat the tires like high speed highway runs.

HTH,
Bob
 

· Super Moderator
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15,258 Posts
jordan said:
I didn't know bias ply tires were made, necessary, or even wanted these days.
Most racing tires are still bias ply. Even the Hoosier road racing 'radials' are technically still a bias-ply tire, the only altered the belts by about 10 degrees to qualify as a 'radial' tire. And Goodyear NASCAR slicks are radials, again by description only, they're still very similar to bias construction.
 

· Registered
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197 Posts
Discussion Starter · #9 ·
Just a followup..I experimented a little, and found 30 front/28 back seem to be pretty good. I have always had/seen a little more in the front because of the engine weight,, but just out of curiosity, why does the door panel say 19 front/28 rear?? Thats alot less in the front!.
 

· Member 1000 Post Club
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1,521 Posts
Keep in mind that the pressures listed on the door were for tires constructed in the same era as the car. Fast forward 30+ years and those numbers are no longer valid. Second, with the lower air pressures biased toward the front, understeer will be increased.

You should run pressures that result in a relatively flat contact patch. Other factors that come into play are weight distribution, handling characteristic changes and comfort. Having higher pressures in the front vs the rear will help to reduce understeer. Lower pressures in the front vs the rear will increase understeer. There are exceptions to this rule, however. One can jack the rear pressures up so much more than the front that tire loses traction and begins to oversteer.

With the modern radial tires, pressures in the 32 to 36 range are pretty common. Running 32 psig vs 30 psig will make the turn in a bit more crisp and reduce rolling resistance.

HTH
 
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