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Old 07-01-2019, 08:23 AM   #23
CapriRacer
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Join Date: May 2003
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Re: For Anyone Who Owns a Digital Tire Gauge

Quote:
Originally Posted by RidingOnRailz View Post
See my 'Railz' responses, within:

Railz: My 1996 GL had 205/60R15 tires on it. At this point I don't recall the speed rating, but I replaced them with H-rated, same size. ..
That would seem to confirm that it is the 15" option that has the pressure split


Quote:
Originally Posted by RidingOnRailz View Post
Railz: So the max cold stamped on a tire(35, 44, 51psi) is based on that speed rating? ..
Oh, if it were just that simple. The tire manufacturer is the one who decides what max pressure is to be imprinted and he is constrained to use those 3 pressures, and by the speed rating. You will find S and T rated tires with a max pressure of 44 or 51 psi, even though the speed rating test is performed at 35 psi.

Quote:
Originally Posted by RidingOnRailz View Post
Railz: Communists!
No, this is the height of capitalism. Making money off of selling information.

Quote:
Originally Posted by RidingOnRailz View Post
Railz: I will have to look at the size section on her sidewall again for that load index and speed letter, IE: '89T', 91V' or which ever hers might be. BTW on my Contour, the replacement tires did have the H embedded inside the size, and they were in fact H-rated tires.


So Capri: Would you consider it just happy coincidence that the formula I shared here worked for mine and my wife's cars and tires, yielding as it did a perfect split just above and below the equal recommended tire pressure on our door placards? Because we both really like how our cars drive after setting them to the values I derived.
No, the formula you shared is tantalizingly close. It just uses some faulty assumptions. The result it provides will be within shouting distance of what it would get if it hadn't made those assumptions.

Then there is the issue of what people like in the way of vehicle handling. When I was calling on Ford, I talked to the ride engineers - the ones the specify the spring, shock, and sway bar settings. Their job was to ignore their own preferences and delivery a product that met the goals as determined by the management team. But one of the items NOT on the agenda was tire pressure. That had been predetermined based on a procedure the company had loads of experience with.

However, that result of tire pressure, spring rate, sway bar size, and shock damping didn't always appeal to every driver and it is common for folks to tune their car by using a tire pressure different than what is on the vehicle tire placard. The danger is not using enough tire pressure - which increases the risk of a structural tire failure - or using too much that wet traction is significantly reduced.
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