Hi guys,

I have another wheels question....again lol

so as you guys may know, I have been looking to get a set of 17x11 wheels with 3.75" BS rear and 4" BS front on 315-35-17 tires which gives me a tire width of roughly 12.5".

Since I already have a set of 295-40-18 in my garage and my car guy said they should fit no problem as long as the backspacing is correct, I am looking at the Rocket Racing Attack in 18x10 with 4.5" BS, they have 1.95" caliper clearance as well.

Now my question is, with the 315-35-17 setup I was getting 3.75" BS rear and 4" BS front. Now with the 18x10 at 4.5 BS I would need a 0.75" adapter rear and a 0.50" adapter front to get the same backspacing.

However, since the 295-40-18 are about 11.6 wide as opposed to the 12.5" wide 315-35-17, would I need to add that 1" of width to my front and rear adapters to achieve the same stance? So the tires come out as far as they would have if they were 315 instead of 295?

 

I'm not sure you fully understand back spacing of a wheel. The larger the bs, the more the wheel will go inboard. Less bs and the wheel moves outboard.

 

11" wide wheel @ 3.75" BS:
- The inner face of the wheel is 3.75" inside of the hub face.
- The inner edge the tire bead mounts against is 3.25" inwards from the hub face.
- The outer face of the wheel is 8.25" outside of the hub face.
- The outer edge the tire bead mounts against is 7.75" outwards from the hub face.

10" wide wheel @ 3.75" BS:
- The inner face of the wheel is 3.75" inside of the hub face.
- The inner edge the tire bead mounts against is 3.25" inwards from the hub face.
- The outer face of the wheel is 7.25" outside of the hub face.
- The outer edge the tire bead mounts against is 6.75" outwards from the hub face.

So, yes you'd have to add another inch to the spacers to put the wheels in the same outer position. If you want the tires in the same spot then you'd could adjust this figure by comparing the tire widths. Your 295-40-18 tires would be about 0.05" further out with 1" spacers.

Your 2nd last paragraph is correct. If the target wheel dimension has 3.75" of BS and the wheel you pick has 4.5" of BS then you do need a 0.75" spacer/adapter to turn the 4.5" BS wheel into a 3.75" BS wheel.

The trick as you properly asked is what happens to the outer location of the wheel when changing wheel widths but keeping the same backspacing.

 

I understand the concept of backspace.

Basically what Im asking is, originally the wheels were 17x11 with 3.75BS rear and 4"BS front. I know that since the 18x10 wheels are 4.5"BS I will need 0.75" spacer rear and 0.5" spacer front to get them to have the same 3.75/4" BS that the 17x11 would have.

So would I add 10mm to each spacer to compensate for the 10mm difference between the 295 and 315 tire in order to have it come out as far as the 315 setup would have.

 

The answer is in my post, but let me word it a different way.

Think of the tire width relative to the rim width. Between the combos, the 285 tire is 0.1" wider relatively to the rim width (it is 0.9" narrower but the rim you're putting it on is 1" narrower). This is 0.05" per side, meaning the 285 tire on a 10" rim sticks out 0.05" further past the wheel lip on each side compared to the 315 tire on a 11" rim.

So, adding 1" more to the spacer would put the wheel lip in the same position. Adding 0.95" to the spacers would put the sidewall in the same location. In theory anyways.

 

With that width of wheel and bs, your wheel/tire will stick out past the fender lip. Is that the look you want?

 

 

Didn't realise you had flares.

 

did you study the sticky

Share Your C3 Upgraded Wheel/Tire Combo's

running a tire calculator, stock tires are 27 inch tall which fills the wheel well the best, so the 295x40x18 tires are 27.3 tall, do you own the rims? what I did was laid my stock 255x60x15 on the floor, and the new 285x40x18 mounted on the rims next to each other and used a ruler and straight edge to determine the hubcentric spacers needed. research, research, research. you have to get it right to look good

 

I have been in that thread countless times lol

I had no luck selling the 295 40 18s so im just going to use them

the wheels I decided on are the American racing VN327 rally wheel in 18x11 with 4.00 back space

spacers/adapters I will figure out once I have the wheels and tires mounted on the car

by looking at the numbers, im thinking I will probably have to do a 3/4" - 1" spacer on the rear. The front might be okay as is with the 11" wheel and 4" BS