Under Pressure: Tire Inflation In The Real World
Tuesday July 31, 2007
Hi, I recently changed the tires on my car to Goodyear 185/70R14. These are bigger than the skinny tires my car came with and I have more control of the vehicle. Since the recommended pressure sticker on the door panel doesn't apply for this new set, can you recommend an ideal pressure for this size? Thanks in advance.
Regards, Rajiv
Rajiv, there's nothing wrong with putting a twist on what tires you're running. Drivers upgrade their tire performance all the time using what's called Plus Size Tire Sizing. As far as the pressure goes, you're right that the pressure sticker on your door jamb will no longer be accurate. In fact, I would recommend that anybody driving a used car use the tire markings rather than the door sticker.
Comments
I would like to expand on the comment of using the tire marking on the tire instead of the door sticker. You are correct in saying that the pressure on the sticker no longer applies, but I feel that the answer of using the tire marking is by far the “short answer”.
The marking on the tire as I’m sure you know is there to indicate the maximum tire pressure allowed for that tire, and it is intended to be used to carry the maximum amount of weight the tire can handle (also marked on the tire in the same spot).
However, since the vehicle weight and rim size has not changed, the driver will be giving up handling, braking, ride, acceleration and perhaps milage for the sake of a simple and quick fix to his upgrade.
The correct answer requires a fair amount of experiment to see what is the best all round tire presure for the current combination.
I saw a print add (I think for B.F. Goodrich tires) that described how to test tire contact with a piece of chalk, a empty parking lot and a tire pressure gauge. The basic idea is to increase the tire contact with the road under normal driving situations by laying out a simple road course that includes left and right turns, an acceleration area and hard braking area. Changing the tire pressure until an optimum tire contact patch is obtained.
I would recommend starting with the max pressure on the tire and working down until the best patch is observed.
This would problably take the better part of the day, because you would want to stabilize tire temperature between practice runs, but in the end it could improve the performance of the vehicle by optimizing the tire contact, and after all isn’t that why you would change the size or type of tires on a vehicle.
Thanks for listening.
I agree. Using the maximum tire pressure on the sidewall will amount to overinflation except when carrying maximum weight loads. But, I don’t have a whole day or a lot to go thru the elaborate procedure recommended. Is there a simpler way to do it?
Thanks for your informative response.