All the racers I know that run the M/T radails, regardless of weight, HP or suspensions, run between 18 and 22 lbs. Just remember that most air pressure gauges are not exactly the same on readings. Play around with your tires with your gauge only to find out what reading works the best on your tires and car. I run the 315x60x15 M?T ET Street Radails (on both ten inch and twelve rims) on my 3400 lb. Duster with ladder bars, it will spin the tires really bad the first run at the track (no matter what kind of burn out) after driving it on the street. That car runs mid tens at 128 MPH with a best 60 ft. time of 1.43 so far(518 stroker and 727 trans), I have tested 17 to 22 lbs so far and 18 lbs works the best on my guages(SP?)