Fred L. Delp

I have a 2005 MB SL 500. The car has Lowenhart LB 5 20 x 12 inch rims on rear. I had 295 x 30 x20 tires on rear. Tires were too wide and rubbed slightly on outside edge occasionally. Went two sizes smaller to 275 x 30 x 20. This size curred the rubbing problem but tires won't stay inflated when the car is driven. They will air up and hold air until the car is moved - then they go flat in a few minutes. I knew nothing about tires and rims until I bought this car and now only know what I have picked up on line. I have learned that local tire dealers seem to know nothing about tires and rims once you are outside the realm of what came on the car originally. I believe the rims are okay and that my problem is that the 275 x 30 x 20 is too narrow for the 12 inch rim to stay inflated when the car is driven. My question is would 285 x 30 x 20 tires be okay to put on the 12 inch rims. Will they stay inflated and would they be safe. I found a tire and rim size matching chart and it said a 285 x 30 x 20 tire worked with rim widths of 9.5 inches to 11 inches so that gives me some cause for concern. Any info would be much appreciated.

Fred Delp

amdeutsch

It appears that your rear rim is too wide for your application but it may also have the incorrect offset for your vehicle. There are several offset calculators links posted on MBWorld.

threeMBs

Even 295/30-20 you had are too narrow for 12" wide wheels (11" max), and obviously 12" wide wheels are too wide for SL/CLS - 11" max.

Even 305/25-20 are a bit narrow for 12" wheel (11.5" max). The correct size for those wheels - 315/25-20 - is of course too wide for the car.

If changing wheels is not an options, then try 305/25-20 - you will give up 1/2" per sidewall, but (if they'll fit correctly) should not rub (but this will depend on wheel's offset too).