Instructions1. Use a set of calipers that measure to the nearest .001". Please follow directions on using your calipers.
2. Measure the diameter of the stud, making sure the calipers measure the outer edge (major diameter) of the threads, and not the inner diameter of the threads. Enter this in the first box.
3. Measure the distance between two adjacent studs. Make sure you measure from the outside of each stud, again using the outer diameter of the threads. Enter this reading into the second box.
4. Hit the "Calculate" button!
The calculator works, as long as accurate measurements have been entered. If you do not feel comfortable making measurements, please find someone that can.
If you want to measure from centerline to centerline, enter 0 for the stud diameter.
If you want to measure the inside distance between the two adjacent studs, enter a negative number for stud diameter.
If you want to measure the bolt circle for your rims, the same instructions apply, just measure to the edge of the lugnut hole.
1. Measure from the center of a stud to the center of the opposite stud.
|Actual Bolt Circle vs Measured Distance Center to Center of Opposite Stud
3.937" (100mm) vs 3.744"
4" (101.6mm) vs 3.804"
4.25" (108mm) vs 4.042"
4.409" (112mm) vs 4.193"
4.5" (114.3mm) vs 4.280"
4.528" (115mm) vs 4.306"
4.724" (120mm) vs 4.493"
4.75" (120.6mm) vs 4.518"
5" (127mm) vs 4.755"
5.118" (130mm) vs 4.868"
5.5" (139.7mm) vs 5.231"
We will use an '82-92 Camaro as the example.
It can also be calculated, as shown below. Don't forget to add for the rim's lip and tire bulging past the rim (I use about .25"). Our 16x8" 0mm offset front rims would have 4.25" of backspacing. The positive 16mm rear rims (16mm/25.4 = 0.63") have about 4.9" of backspacing
Measuring Maximum Backspacing
Measuring Bolt Circles
/ 2 + 50mm / 25.4 Offset + 0.25" Lip = 6.97" Backspacing
Ideally, you would want some clearance on the inside of the rim to compensate for suspension movement, etc. In this case, we recommend 2" adapters for the front and rear. You can run the 2" adapters in the rear, even though you only need an extra 1.12" backspacing. This will move the wheel further out in the wheelwell, matching the front, and the wider track will help cornering as well. The only time to not match the front adapters is when you have wider wheels in the back (17x11 ZR1's for example). In that case, the wheel will fit in the wheelwell if the 1.25" adapter is used, but will protrude past the fender lip if you have a wider than necessary adapter.
For all fourth-gen rims - 2" adapters front and rear should be used on a third-gen. Some folks prefer having a thinner adapter in the rear. This will fit fine, but the rim will be inside a bit compared to the front. The same thickness on the front and rear gives a more balanced look than using thinner adapters in the rear (with the same size rims f&r) For C5 and 17x11 ZR1 rims, please do the math!
Using a 4th Gen Rear
There are two ways of bolting the adapters to your hub. One uses a lugnut with a long shank and washers. The clearance needed for the holes ends up as a slight bit of slop when they are bolted on. This isn't usually noticeable when driving. The other method is to use acorned lugnuts to bolt on the adapters, just like for the rims. The lugnuts center the adapter when they are tightened. This is a significantly more precise way to bolt on the adapters, and is how we make them.
Various Rim Dimensions
Disclaimer - These dimensions have been gotten from
and are not verified. Use at your own risk. If you see an incorrect
number, please let me know by mail: firstname.lastname@example.org.