Offsets and Rims

[Andrew1990]

Hey guys, how's it going? I have a 1999 Mustang V6, and I am looking to buy a pair of rims. The sizes of these rims are 18 x 9 in. +24 mm offset (for front) and 18 x 10 in. +22 mm offset (for rear). I am new to buying rims, I haven't purchased them before, and I was wondering if there is any possibility of these rims rubbing on the wheel well. I would appreciate any advice anyone could give me, thank you for your time.

[SpectorV]

25.4 mm = 1 inch so the front are offset right at an inch, so you say the center line of the wheel 9/2 = 4.5 since its a positive offset you add 1 inch to 4.5 to get the back spacing, so its 5.5 back spacing. This means that 3.5 inches of the rim is out from the rotor in the front. Those will stick out a bit, 3-3.25 is about perfect.

For the rear its nearly an inch as well, so 10/2 = 5.0 + 1(offset) = 6inch meaning 4 inches of the rim is from the mounting surface out.

Thats about right on, if your car is lowered the rear may hit the fender lip a little. I have a set set of 18x10s coming with the same setup as those you mentioned its close.. roll the fenders a tad if they hit and your ok. To keep save you need to take it back about half an inch to 3.5.

[Andrew1990]

Thank you very much for the help. However, I do have a question; what do you mean by "take it back half an inch to 3.5"?

[SpectorV]

the offset is how far the mounting surface of the rim is away from the center line of the wheel.

if its a positive offset that means that the mounting is outward to ward the rim off the center line, and a negative offset is it is pushed in toward the back off the rim past the center line.

So if you have a 9 inch wide rim the center line is 9/2 or 4.5 inches.

since its a positive offset nearly an inch (25.4mm = 1in) so its toward the outside 1 inch. So you add 1 to 4.5 to get 5.5 inches. That means 5.5 inches from the back of the rim to the mounting point on the rim. thats the back spacing number.

so what is left? 9 inch rim - 5.5 back spacing = 3.5in

3.5in is the amount of the rim that is from the mounting surface to the outside of the rim (front of the rim) that magic number says how much of the rim will stick out. On a 94-04 mustang you should not go much over 3 inches.

My 03 cobra rims are 6.11 inch back spacing on a 9 wide rim, so 9-6.11= 2.89~ and my rims are right on the edge of the fender, much more and they would stick out under the front fender. So 3 inches would be about my personal limit.

another wrench to throw at you... as you lower the car the A Arm pushes up and inward (how its designed) so... the wheel will actually pull inward depending on how much you lower the car, this can make up for a wheel that sticks out more~ its not a big huge thing but they do tuck in.. this is the whole reason caster/camber plates are needed to align the car once its droped, there is no stock adjustment so when the wheel tucks in and pulls in you mess up the wheel alignment and it wears on the inside.

[Andrew1990]

thank you very much for all your advice. I appreciate it