tire psi question, need help on recommended tire PSI - Ford Mustang Forum
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post #1 of 12 (permalink) Old 05-11-2018 Thread Starter
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Question tire psi question, need help on recommended tire PSI

So I replaced the 255/40r19 Pirellis with the 96w rating with Cooper 255/40r19 with the 100W XL tires, the tire shop i think overinflated the tires. one of the tires read 40 PSI. I know my stock tires were recommended at 32 PSI cold. Do you think the Cooper's being XL load range 100W that the correct tire pressure is 40 PSI, or is that too high? I can't get reliable information because the 96W and 100W XL would probably have different PSI recommendations, right ? Then I read, if you under-inflated the tires, they go bad fast, over-inflate them, they get punctures easier. Tires are turning out to be a headache, what is it with every tire shop putting the wrong pressure in every car tire?

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post #2 of 12 (permalink) Old 05-12-2018
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On a XL rated tire the full load capacity of the tire is reached 40psi where as a non XL tire it is 36 psi. A 100 rated tire can carry 1764 pounds a 96 tire can carry 1565 pounds.

I am quite happy with 32 psi for all around driving. I would start there and go up or down to suit your needs.

Dave

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post #3 of 12 (permalink) Old 05-12-2018 Thread Starter
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Originally Posted by dgc333 View Post
On a XL rated tire the full load capacity of the tire is reached 40psi where as a non XL tire it is 36 psi. A 100 rated tire can carry 1764 pounds a 96 tire can carry 1565 pounds.

I am quite happy with 32 psi for all around driving. I would start there and go up or down to suit your needs.

Dave

what load and are your tires? what size? I want to to drop the pressure to 36 all around to see how they handle. 32 wouldn't be underinflated?
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post #4 of 12 (permalink) Old 05-12-2018
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Use the vehicles recommended pressure, not the tires max.
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post #5 of 12 (permalink) Old 05-12-2018 Thread Starter
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Use the vehicles recommended pressure, not the tires max.

would the vehicle's recommended pressure apply to the same size tire with a higher load rating? I would never air a tire up to max pressure. Thanks.
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post #6 of 12 (permalink) Old 05-13-2018
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what load and are your tires? what size? I want to to drop the pressure to 36 all around to see how they handle. 32 wouldn't be underinflated?
My car came with 255/40-19 96Y P Zero summer tires and the door placard recommends 32 psi.

You are over thinking this. Put 32 psi in them. If the ride is to soft and squishy add a couple of psi until you are happy. Conversely if it's to harsh go down in pressure, keep in mind the low pressure warning will come on around 28 psi.

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post #7 of 12 (permalink) Old 05-13-2018
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You can always do the chalk test, too.

Start with a good alignment and a ballpark guess tire pressure. Use chalk (or paint, sharpie, whatever) to draw a line across the width of the tread. Drive it, and see how the chalk wears. Try different pressures until the chalk wears evenly. That's how your tires will wear.

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post #8 of 12 (permalink) Old 05-13-2018
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would the vehicle's recommended pressure apply to the same size tire with a higher load rating? I would never air a tire up to max pressure. Thanks.
Yes, the recommended pressure for the vehicle is just that, the recommended pressure for the vehicle.
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post #9 of 12 (permalink) Old 05-13-2018
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Originally Posted by Urambo Tauro View Post
. Use chalk (or paint, sharpie, whatever) to draw a line across the width of the tread. Drive it, and see how the chalk wears. Try different pressures until the chalk wears evenly. That's how your tires will wear.

Agree with above ....+ then check tire wear across the face of all 4 tires periodically (1,000 miles or so) and make fine adjustments, of course starting with Fords recommended psi settings.

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post #10 of 12 (permalink) Old 05-14-2018 Thread Starter
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Quote:
Originally Posted by Urambo Tauro View Post
You can always do the chalk test, too.

Start with a good alignment and a ballpark guess tire pressure. Use chalk (or paint, sharpie, whatever) to draw a line across the width of the tread. Drive it, and see how the chalk wears. Try different pressures until the chalk wears evenly. That's how your tires will wear.
had the alignment checked after the tires were installed. I went with the factory setting that Ford put on the door jamb sticker, 32 PSI. thanks
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post #11 of 12 (permalink) Old 05-14-2018 Thread Starter
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Yes, the recommended pressure for the vehicle is just that, the recommended pressure for the vehicle.
so I went ahead and evened every tire out to 32 PSI. Thanks
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would the vehicle's recommended pressure apply to the same size tire with a higher load rating? I would never air a tire up to max pressure. Thanks.
Yes, vehicle recommended is for all tires you put on no matter what the tires load rating is. Load rating is for when you are let's say moving out of an apartment and you put everything you own in the car, well now you have added excess weight and to ensure you don't damage the tires you would inflate them to their max tire pressure to handle the weight you added by packing it with all your stuff. Now if you are just tooling around you will just go by the manufacturers recommendation for ride comfort, control and gas mileage


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