Many questions arise in regards to the two or three digit number located just beyond the tire size on the sidewall. This is the load rating. For passenger cars, it typically falls in the 80 to low 100 range. The number is followed by a letter which indicates the speed rating. The number/letter combination is referred to as the service description.
When purchasing a new tire, you're going to need a load rating very close to what was on the car from the factory. There may be plenty of sizes of tires that fit your car, but the number one priority of your tires is to support the weight of your vehicle. If you want to run 17" Honda Civic tires and wheels and the car had 14" wheels and tires from the factory, no problem. Your new setup will be closely matched to the original on volume of air between the wheel and tire, which means the tires will most likely be wider. The load rating number on a 185/65R14 is 85, while on a 205/40R17 it's 84 (85 translates to 1,135 lbs. per tire, where as 84 is 1,102 lbs.).
The same principle will apply for your 2008 BMW 3 Series, going from the stock setup of 16" BMW rims and tires to an 18" or 19" setup. You can usually verify the load requirements by finding the GAWR on the door placard of your vehicle. After locating the number, divide it by two to find your absolute minimum load rating. When you search by vehicle, we factor all of this in. Search results will only show tires that will be the correct load rating for your vehicle - very helpful when plus sizing.
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