Superman09

iTrader: (65)

I'm looking to get some rear wheels widened and need to know which would be the best base to start off with. Looking to go to an 18x10 bare minimum out back, preferably 18x10.5 if possible.

I have 3 choices to start off with.

18x8 with a 20 offset
18x9 with a 20 offset
18x9 with a 40 offset

Just need to get this in perspective of where each wheel will sit in my well and which of the 3 sets up the best to widen it out to 18x10 or 10.5 . Thank you very much!

Superman09

iTrader: (65)

i have no idea if i am even calculating this right but here is what i think it would be.

1"=25.4mm

Add 2" to the 18x8s with 20mm offset making them 18x10's with a 51+20=71mm offset
(This one seems out!)

Add 1.5" to the 18x9's with 20mm offset making them 18x10.5's with a 38.1+20=58.1mm offset
(Just a little outside of the range in the stickey)

Add 1" to the 18x9's with 20mm offset making them 18x10's with a 25.4+20=45.4mm offset
(Right in the middle of the range)

Add 1" to the 18x9's with 40mm offset making them 18x10's with a 25.4+40=65.4mm offset.
(Outside range)

Seems my only plausible option here is the 18x9's with a 20mm offset and add just 1 inch to them making them an 18x10 with a 45.4mm offset

Am i doing this right?

ZFSix

iTrader: (14)

You need to start out with a wheel that has a somewhat low offset. Widening the wheel is only going to make the inner barrel closer to the inner fender.

Thus: If you get a wheel that is already a high offset, it will bring the wheel closer to the inner fender and rub.

If you start out with a wheel that has a high offset you will need spacers once you get them widened to bring it back out to the outside of the fender and have the proper clearance.

BTW, I don't think you are calculating things right because:
Offset is the distance from the center of the wheel to the mounting surface. Therefore you won't be adding one complete inch to the offset. You will to the backspacing, so if you calculate the backspacing on the wheels, then you can use that.

Does that make any sense at all?

ZFSix

iTrader: (14)

Ok I think I got it to where it makes sense.

The backspacing on the 9" wheel with a 20mm offset is about 5.3"

Adding 1" to that will give you a 6.3" backspace and that will stick out.

If you use the 18x9 with a 40mm offset, you start off with a 6.1" backspace.

Adding 1" to that nets you a 7.1" backspace, and that is perfect!




Moral of the story, get the 18x9s with 40mm offest and get them widened 1" which results in a 51mm offset.

99Bluz28

iTrader: (35)

If you have a +40mm offset and add 1" (25.4mm) you get a +65.4 0ffset , not +51 . All so , IMO the the 9" with a +20mm offset would be your best bet! If you add 1"(25.4mm) to it you would have a 10" rim with a +45.6mm offset perfect!

All so, Backspacing and offset are not the same thing! There measured to a different point on the rim.

ZFSix

iTrader: (14)

You have one line that's right and the rest is wrong.

You are correct about backspacing and offset being measured in different places, but they result in the same information.

Offset is measured from the center of the rim barrel to the mounting surface.
Backspace is measured from the inside edge of the rim to the mounting surface.

Adding 1" to the width of the rim does NOT mean you add 1" to the offset, it means you add it to the backspacing.

The center of the rim on a 9" wheel is 4.5" obviously, and a 10" wheel is 5" we all know that.

Widening your wheel changes where the offset is measured from because the direct center of the wheel has changed.

Draw a picture of a rim and think about it for a while, then get back to me.

Oh and don't try to argue with me when you're wrong.

99Bluz28

iTrader: (35)

Yeah, your right!..lol..lol! Instead of adding the whole 1" to the offset I should have only added 1/2 of the amount that the wheel is widened, which would be 1/2" (12.7mm) .So yes, your wheel choice (9" +40mm offset) is the best offset for him to start with, not the 9" +20mm offset I suggested!

But, Your offset is still wrong.

The Correct offset is +52.7mm, not +51mm!

By the way, thanks for the correction!

ZFSix

iTrader: (14)

My offset was calculated in my head, not mathmatically, so it was a rough but educated estimate.

Superman09

iTrader: (65)

Ok, looking to get something that will work now and will have the ability to be widened down the road with no issues.....

How about an 18x9.5 with a 45mm offset? Should be pretty solid i would think.

And for clarification on the front would i want 18x8 with a 20mm or 35mm offset? Thanks!

ZFSix

iTrader: (14)

35 for the front, my head will explode if I do any more calculations right now. I'll get back to you later in the day.

Xsta Z 28

iTrader: (2)

For the rear the 18" x 9" with the 20 mm offset will work . . .

You are adding 1.5" or 38.1 mm . . . for offset take 1/2 the amout or 19.05 mm add that to the 20 mm you get and offset of 39.05 mm . . . I rum 38 mm offset 10.5" wide Fikses on the convertible. Fills the wheel well out nicely.

The others:

18" x 8" with a 20 mm offset . . . you are adding 2.5" or 63.5 mm to the wheel. Take half of that, 31.75 mm + 20 mm nets you 51.75 mm. This will also fit, but will be tucked into the wheel well a bit. Not as bad as the Z06 replicas, since they are 58 mm offset.

The 18" x 9" with a 40 mm offset will fit really nicely up front with not modifications.

Superman09

iTrader: (65)

thank you very much. Looks like an 18x9 with the 20mm offset is the ticket. Will i have to roll my lips for these or no?

There are also 18x9.5 wheels for the rear, they come in 20mm or 45mm offset. So therefore i would have to add 1" or 25.4mm/2=12.7mm to the offset. That brings 32.7 or 57.7.
-Either of these work?

I could also bump these out to 11" adding 1.5" meaning 38.1mm offset/2=19.05mm. So i could have 18x11's with either 39.05mm or 64.05mm.
-How about these?




As for the fronts. I will be running an 18x8 and have choice of either 20mm or 35mm offset, which will be the ticket for up front? Thank you very much!

Superman09

iTrader: (65)

Xsta Z 28

iTrader: (2)

I had to do some very minro rolling on the passenger side of my convertible.

The work to add 1" of materila or 2" of material is the same so the cost diff of adding less material would be pretty minor . . . . the 32.7 will not work at all . . . the 57.7 will be tucked in.

at 11" width neither of those work.



Front 35 mm on a 8" wheel