Wheel size, backspace, learn me!

[Baron Von Crowder]

Ive been eyeing some different options on wheels for the 69. Help me out if you can:
I had 17" x 10.5" deep dish bullet wheels on it with a 315, and it was on the bare ragged edge of fitting. There was room on both sides, but just enough.

Per American Muscle's website, they are
Back Spacing: 6.8" (174mm) Offset: +28mm (1.10")

I put a set of FR500's on that were 18 x 10, and AM's site shows:
Back Spacing: 6.3" (161mm) Offset: +22mm (0.9")

So to me, that looks like the difference of the 1/2" in width of the wheel is split in half, and that's the 6mm difference in the offset.

I see a lot of 10" wheels that show +20. Does that mean that they will be 2mm twards the outside of the car? I dont think that would be a problem, but I wanted to make sure before I went crazy.

[NoClassic]

[BMCSean]

Welp, there you go.

[Baron Von Crowder]

yeah, I can google that too.

it still doesnt help me with figuring out if this would fit or not
Wheel Size
18x10
Color
Hyper Silver
Bolt Pattern
5-114.3
Offset
+12
Backspacing
5.97

[DON SVO]

I see a lot of 10" wheels that show +20. Does that mean that they will be 2mm twards the outside of the car? I dont think that would be a problem, but I wanted to make sure before I went crazy.

First, 25.4mm = 1"

+20 would indicate 20mm on the positive side of center. 20mm is just over 3/4", which means that the bolting surface is 3/4" outside of centerline... so if you had a 10" wide wheel that would mean that 5 3/4" of the rim width was toward the inner fender and 4 1/4" was toward the outer fender.

As a rule of thumb, it's easy to remember that more positive offset moves the wheel in, negative moves the wheel out. This is all countered by rim width: A 9" wide rim with +15 offset will sit damn close to a 10" wide rim with +40 offset.

[Baron Von Crowder]

First, 25.4mm = 1"

+20 would indicate 20mm on the positive side of center. 20mm is just over 3/4", which means that the bolting surface is 3/4" outside of centerline... so if you had a 10" wide wheel that would mean that 5 3/4" of the rim width was toward the inner fender and 4 1/4" was toward the outer fender.

As a rule of thumb, it's easy to remember that more positive offset moves the wheel in, negative moves the wheel out. This is all countered by rim width: A 9" wide rim with +15 offset will sit damn close to a 10" wide rim with +40 offset.

Thank you Don, that was what I was looking for.

[DON SVO]

Thank you Don, that was what I was looking for.

Realize of course all wheels pretty much have offset. if you wanted a wheel that was more flush with the fenders, you have to do some rough math. If you needed a wheel that sat 1" closer to the fender than the current wheel it would be something like this:

Stock/current: 9" wheel, +35 offset (roughly 3.65" of rim sit outboard)

New wheel: 10" wheel, +10 offset, (roughly 4.60" sit outboard with no change to inner depth)

or

11" wheel, +20 offset (4.75" outer but 6.25" inner)

[CWO]

http://www.1010tires.com/Tools/Wheel-Offset-Calculator

[Baron Von Crowder]

considering something like this

[CWO]

http://www.rimsntires.com/specspro.jsp

[CWO]

http://kgm.tiwing.com/calcs/offsetcalc.htm

[CWO]

http://www.tyresizecalculator.com/tyre-wheel-calculators/wheel-offset-backspace-calculator

[CWO]

my favorite

http://www.willtheyfit.com/

[Sleeper]

you can make a cheap fitment checker out of a yard stick and a couple rubber bands.

[Baron Von Crowder]

you can make a cheap fitment checker out of a yard stick and a couple rubber bands.

Im kinda lucky, I've already had about the biggest wheel/tire that will fit, so I know what that dimension is to base what I can fit off of.