I have a 2007 SL550. I replaced the original wheels and tires with new, larger ones. The newer tires have shorter sidewalls as well. What tire pressure should I use? Should I go with the car's recommended 30/33psi front/rear, or something else? I already hit a pothole and pinched the sidewall on one of the front tires which I need to replace. Could this be due to tire pressure that was too low?

Original tires
front 255/40-18
rear 285/35-18

New Tires
front 245/35-20
rear 275/30-20

 

The air pressure will not change. With the load indexes 97 and 95 the same, the air pressure remains the same.

 

Not sure how the Load Index relates to tire pressure. I didn't know if the fact that the new tires have a larger diameter and a smaller sidewall might mean that they should have a different pressure. Also, if the automobile specifies 30psi and the tire has a maximum psi of 51psi, am I OK with any pressure in between the two?

 

The load index refers to the amount of weight a given tire can carry at different air pressures.




As long as the tire you went from is P metric to P metric tire or European metric to European metric the air pressure, in theory, will remain the same when the load indexes haven’t changed. I’m pretty sure that you have Euro-metric sized tires.

P metric tire starts with a P, for example P255/70R16, and the European metric doesn’t have the P at the beginning of the tire size (255/70R16).

 

Hmmm, those didn;t turn out the same when I posted them before, lets try those again!

Load Index 26 27 28 29 30 31
95 1235lbs 1272lbs 1290lbs 1345lbs 1400lbs 1455lbs

32 33 34 35 36
1510lbs 1530 lbs 1530lbs 1554lbs 1609lbs


hopefully it works this time!

 

well, its just not working to post that stuff here. Sorry!