High RPM Poster
Jul 6, 2012
none right now.
Trying to figure out what tire pressure to run in my recently purchased '75 coupe. The decal on the door says 20 psi front and rear which seems quite low to me. I'm running 245/60/15 B.F Goodrich T/A's vs the GR70-15 listed on the door. 255 would be closer in diameter to the old G70 size but the 245's aren't too far off. The previous owner of the car said he ran 32 psi in them. I found this to be too harsh and rather darty on the highway. I've reduced them to 30 psi and the car still wanders a bit sometimes if the surface is less than ideal. I'm wondering if I should go lower still? What are you guys running your tires at?
Good question! I think I pretty much run everything I own at 30psi..or what the decal says on the car.

One option I've always wanted to do was to take one of those infrared thermometers and take the temperatures of the tires on the inside, middle and outside of the tread face after a good straight line drive on the highway. My theory is that I would like to see an even temperature across the tread face. If the middle is hotter, then I have too much air and if the outsides are hotter, I need more air. The only problem I see with this is with camber angles and stuff, the inside may always be hotter than other areas of the tire so I'm not sure. However, if you have access to one of these devices, it may be worth a shot.

30psi sounds good. If it's darty, would your car need an alignment? Hopefully some other C3 guys can help out.
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My 76 also enjoys taking in as much of the road as possible, I chalk it up to being almost 40 years old and like 5 feet wide (and Saskatchewan highways). My 2010 also darts at times due to the grooves pushed into the highways by heavy trucks, and the tires on it are half foot wider than the C3. I run the suggested psi that is stamped on the tire, that is the pressure at which the manufacturer designed it to run.
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