Chevy Bolt Pattern Guide - Vehicle Lug Reference
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H = High Positive or FWD (Front Wheel Drive) typically +45,40,35 offsets
M = Medium Offset or RWD (Rear Wheel Drive) Typically +20 offset
L = Low Offset or RWD (Rear Wheel Drive) Typically 0 offset
Plus sizing your wheel & tire combination was designed to enhance vehicle performance and looks by allowing fitment of larger diameter rims and lower profile tires. The theory is that while making these changes, you keep the overall tire diameter within 3% of the original equipment tires. This is important because larger variances can cause problems with transmission shift points which can decrease fuel mileage. It can also confuse braking system computers which can even lead to brake failure.
Here's the rule of thumb for "plus sizing":
Plus 1: Increase section width by 10mm Decrease aspect ratio by 10 points Increase rim diameter by 1 inch
Plus 2: Increase section width by 20mm Decrease aspect ratio by 20 points Increase rim diameter by 2 inches.
This is not exact, but it will usually get you in the right ballpark. We always recommend consulting with the people you are purchasing the wheels and tires from to ensure fitment.
Centerbore relates to the center hole in the wheel that centers the wheel on the hub of the car. Since most wheels are mass produced, they have a large center bore to accommodate several different vehicles. If this is the case, it is recommended that you use a hub ring. Hub rings are hard plastic or metal ring that fits between the wheel and the vehicle. This centers the wheel perfectly on the hub ensuring that there is no run out when the wheel is installed on to the vehicle. Without hub rings it is possible to get vibrations even if the wheel / tire assembly is perfectly balanced.
Torque: All alloy wheels should be installed using a torque wrench. This ensures that the wheels are not too tight or too loose. Check your vehicle's manual for correct settings. When you install wheels for the first time, you should re-torque wheels after about 100km to 150km (60 to 90 miles). Always refer to Owner's Manual for proper factory specifications that take precedence over the listed recommendations. 12mm = 70~80, 7/16" = 55~65, 1/2" = 75~85, 14mm = 85~95, 9/16" = 95~115, 5/8" =135~145.