When you want to add upgrades to your vehicle after putting in a better sound system your car’s wheels and tires are usually next on the list.
There are a variety of reasons to upgrade your OEM Wheels and tires other then visual appearance most of the time its for better handling on or off road. You might also install aftermarket wheels if they are lighter then the OEM version to improve your ride and handling characteristics or if you are making upgrades to your disk brake rotors and need more room for the larger disks.
What ever reason you have it is important to understand what limitations will restrict your choice of tire and wheel combination and what measurements need to be taken so you can get the most out of your purchase.
To function properly the wheel needs to position the tire within the wheel well so no contact will occur during movement of the suspension. This includes up and down motion an turning. The wheel also needs to have enough offset from the brakes and suspension so it can rotate without contact.
The OEM specs are the best place to start if you haven’t made radical changes to the suspension and braking system.
If you have added larger rotors and calipers you will need to make measurements before and after the change to understand any position changes.
Wheels have 4 standard dimensions that need to be accounted for.
The first is the diameter – this is the circular width often referred to as the Height of the wheel often rated in standard inches 13 – 14- 15 … all the way up to truck wheels in the 30’s the measurement is actually taken from bead to bead where the tire will mount on the wheel because the lip of the bead could be longer for a number of reasons.
The second is Width– This is the depth of the wheel and will set the width of the tire that can be mounted. Again the dimension is taken from the inside of the Bead.
Centerline is the third measurement and this is the half way point of the width. If the wheel had an 8″ width the centerline would be 4 inches in from either bead. This measurement is not used for ordering but relates to the next measurement.
Centerline Offset – Once we know the width of the wheel and the centerline we reset the centerline to 0 and measure in and out from that center point
Face Side +4+3+2+1–0 -1-2-3-4 Brake Side
The Centerline offset is where the mounting pad is set This is the place behind the lug nuts where the wheel sits on the hub of the axle. The measurement can be a negative or positive value. The deeper you get towards the brakes is negative offset.
Centerline Offset is a very important measurement and is often the reason why wheels don’t fit or tires rub.
After you have the primary measurements you can worry about a handful of others which are somewhat cosmetic or application specific.
First is the hub height. This is the distance of offset built into the hub of the wheel. In some designs it is a straight line in others there is an arc that will allow break calipers to pass into the area of the hub.
Second is your lug pattern an although it can change between manufacturers its simply something you need to tell the parts person when you place your order.
Hub Diameter The opening in the center of the wheel to allow the hub to pass through is another factor that your parts person will need to know but it will be set when you tell them the make of your vehicle.
Lug patterns and Hub openings are measurements you may want to take if you are making radical alterations to your suspension such as swapping axles due to an engine or deferential swap.
Placing Your Order
When you finally get to the point that you are making your order many of the headaches of taking measurements will be accounted for by the Wheel manufacturer. There are only so many vehicle models that are made every year and information about standard distances are provided to the aftermarket by the car makers. The problem you run into is when you want to alter your suspension outside of normal clearances.
Lift Kits, Drop axles, altering springs, struts, shock mounts, brake sizes, control arms and a number of other things will push you out of OEM specs.
Starting from OEM measurements and then calculating new distances by taking before and after measurements when you think they are a factor will allow you to get the right wheel the first time.
If you make a mistake just find the specs of the wheel that you ordered and use those measurements to order new ones. If you have a wheel with a -2 inch centerline offset that is binding then you should be able to use that dimension to understand you need a -1 or -3 or whatever will fit your application.
Unfortunately Aftermarket manufacturers often only make wheels with one set of specs so you might find yourself using another brand and style wheel just to get one that fits.
The YouRepair Store sells a full line of Automotive Wheels and Parts