The width of the wheel is one of the key factors in selecting a wheel.
Go wider than stock?
Stay the same width?
Go narrower than stock?
These are a few questions that must be asked and answered before selecting a wheel. Not all wheels are available in all sizes.
The width of a wheel is measured from the inside bead to the outside bead.
The wheel width determines backspacing, forward spacing, offset selection and tire sizes.
Offset as said earlier is measured from the center of the wheel to mounting face.
Backspacing is the distance from the mounting face to the back of the wheel.
Forward spacing is the distance from the mounting face to the front of the wheel.
With knowing this only looking at offset when selecting wheels can be a very bad thing. Changing forward spacing and backspacing (by increasing wheel width) while maintaining the same offset can lead to potential rubbing issues.
the width of a wheel also dictates the size of tire that can safely be run.
is it possible to run a 275 series tire on an 8″ wheel? Yes, I ran it for part of the 2006/2007 season Solo2.
Is 275 on an 8″ wheel ideal? No, ultimately grip will be increased compared to a properly sized tire but there will be some side effects such as slower turn in, and “squirmy” sidewalls.
Why run an over sized tire for autox? Rules, in stock class changing wheel width is illegal, but tire width is unlimited. I will go into more detail about autox classing later.
Back to wheel width and tire width, each manufacture has listed the range of wheel widths any given tire can fit on. This is a good starting point for what is “ideal” although they do tend to lean towards a slight stretching of the tire. Some people prefer to have a little extra tire to help protect the wheel and increase grip. This can be accomplished by using a wheel width that is on the narrower side of the listed range.
Wheel width is a large contributor to wheel weight. When increasing wheel width it is a good idea to also upgrade to a better construction wheel either a high quality cast wheel or forged. Upgrading to a better construction usually means the overall weight of the wheels will be less.
Wheel weight will be discussed in further detail in a future article.
Wheel width is only one of the many aspects of selecting a wheel.
The other aspects of Diameter, Offset, Desired Tire Width, Acceptable Camber, Desired Usage, and Current and Future Suspension setups all need to be consider as well. Blindly saying “I want a 9″ wheel” can get you in loads of trouble if you’re not careful and don’t do your research.
I am buying 18×8 inch rims and what tyres are the best for that dimensions?225/40 or maybe 235/40 or maybe something else…
assuming the offset is correct for the car they are going on.
both the 225/40/18 and 235/40/18 are both excellent size tires for an 18×8, assuming the vehicle it’s going on requires a 25″ diameter tire.
What’s the offset and what car are they going on?
Hi,
I really appreciate the time spent on getting this information out. Here’s my situation. I have an ’05 STi. I recently bought a set of Volk Seibon Edition TE37’s in an 8.5″ width and a +50 offset. I want to use a 255/35/18″ tire but do not wish to use spacers or fender rolling in order to have them. I am running Cusco Zero 2R coilovers. I am not opposed to added camber adjustments as the car is mainly used as a DD with an occasional day at the track. What do you think? Thanks again for your time.
Jeff