Offset is killing me.

359 Views 3 Replies 3 Participants Last post by Matthew Huffman, 14 d ago

Matthew Huffman

Discussion Starter · 1 mo ago

So my understanding is if you use an adapter, you SUBTRACT that width from the ET of the wheel.

For example, 35 ET with a 20 spacer, results in an ET of 15. Am I correct?

I for some reason thought we had a 35 ET on our cars (I guess it is 55).

I picked up some wheels. 18x10 ET 35 and 18x8 ET 35 (for them on a trade, so no money out of pocket) They are 5x100, so I figured a 20mm adapter would be fine.

Calculated out, the numbers come out:

Front:
Inner changes 40mm more.
Outer changes 40mm more.
ET becomes 15.

Rear:
Inner changes 15mm more.
Outer changes 65mm more.
ET becomes 15.

So a few questions based off this:

1. How much clearance is there on the inner measurement to begin with? How far in can we go before we have significant issues?

2. Obviously the rears will poke out more, which I'm okay with to an extent, but do the fenders have the clearance to accommodate? Note I do not have it lowered.

3. Has anyone ever just modified the wheel hubs themselves with a different bolt pattern and knocked out the studs from the factory position? Or does this compromise the hub integrity too much?

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peachferrari

· #2 · 1 mo ago

Yes you are correct in subtracting the spacer width from the offset--it's going to push the wheels out farther, which is effectively a lower offset number.

Keep in mind too that with the wider wheels (10" vs 8") the offset is measured from the centerline of the wheels--so those are going to have an extra inch on each side of the mounting surface.

Hopefully someone else can chime in on the potential clearance with the fenders.

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Joe Crockett

· #3 · 18 d ago

So I'm in the same boat. Been trying to fit as much tire in the back as possible. From what I have read, and concluded is that there is tons of space up front. The rear is the limiting factor. You can actually fit more tire in the back if you're willing to go up in rim size. The upper control arm will hit the rim with full unload when you start going much higher than et45 when you're at a 18x10" width in the rear. If you have a 20" rim you can go to a full et55 and have zero issues. I actually have the same problem. Trying to get as much tire/ traction in the back as possible and it's been a solid journey researching what fits and what doesn't. There just isn't much available for our cars and the offsets these cars like.

I finally settled on Forgestar F14 because they are affordable and have the offsets I can use. They still aren't ideal. The highest offset they offer in 18x10 is a et42. Which is fine for inner clearance, but I'm certain there will be some poke, but everything I've seen and read is it should clear without issue. I've still rolled the rear fenders and have them a gentle tug. Will see in a couple months when they come in and I'll let you know first hand what a 285 width tire on a 10" rim et42 will look like and clearance. Text if you wanna talk more about it.

Ps. Charge pipes and engine cover came in. Thanks a bunch, and I should know more about what I need for smog on that car which will determine what can come off it. Perhaps we can work something out regarding that intercooler. Drop a line if you find an oem turbo, I might have to swap that too.

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Matthew Huffman

Discussion Starter · #4 · 14 d ago

Joe Crockett said:
So I'm in the same boat. Been trying to fit as much tire in the back as possible. From what I have read, and concluded is that there is tons of space up front. The rear is the limiting factor. You can actually fit more tire in the back if you're willing to go up in rim size. The upper control arm will hit the rim with full unload when you start going much higher than et45 when you're at a 18x10" width in the rear. If you have a 20" rim you can go to a full et55 and have zero issues. I actually have the same problem. Trying to get as much tire/ traction in the back as possible and it's been a solid journey researching what fits and what doesn't. There just isn't much available for our cars and the offsets these cars like.

I finally settled on Forgestar F14 because they are affordable and have the offsets I can use. They still aren't ideal. The highest offset they offer in 18x10 is a et42. Which is fine for inner clearance, but I'm certain there will be some poke, but everything I've seen and read is it should clear without issue. I've still rolled the rear fenders and have them a gentle tug. Will see in a couple months when they come in and I'll let you know first hand what a 285 width tire on a 10" rim et42 will look like and clearance. Text if you wanna talk more about it.

Ps. Charge pipes and engine cover came in. Thanks a bunch, and I should know more about what I need for smog on that car which will determine what can come off it. Perhaps we can work something out regarding that intercooler. Drop a line if you find an oem turbo, I might have to swap that too.

Glad the package made it! I was going to ask you today (just got off work!) about it. I'll keep my ear to the group on an OE turbo.

On the wheels piece, I used the calculator I found from another user here, and it looks like it'll take up 5mm more on the inside, and poke about 45mm out. Got my tape measure out, and it looks like I'll be happy with it. I decided to drill the hubs. So I got a single adapter to bolt onto the hub and use as a template. Once done, I'll knockout the old studs and install new ones.

It'll be interesting to see how it turns out. If I end up happy, I'll have wheels for sale/trade (will post on the forum). I plan to wrap the wheels I picked up in a 255 or 265 tire. I just need to look into what impact going to a 40 from a 45 profile will have.

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