Correct Offset for 18x12? - ZR-1 Net Registry Forums

Black Red '90 · 02-10-2021

I'm thinking of having a set of 18" wheels made. 17" looks fine on the car, but if I've spending the money I want to go a tad little bigger while still maintaining some sidewall. I know tire selection isn't the best for 18's and will need to run a 335/30 in the rear. This requires a 12" wide wheel. I do not want any "poke" with the extra width. I want it all on the inside. If my math is right this means I need a +48 or +49 offset. Is anyone running this setup? Any clearance issues I need to consider?

Thanks

secondchance · 02-10-2021

OEM 11" rear wheels are positive 36 mm offset. If you keep the same offset, additional 1" will grow out board. Increase by 1/2 of 1" (about 1.3 mm) will grow the wheel 1/2" inboard and outboard. At least, that's my understanding.

For reference, I have 11", 57 mm offset Fikses on the rear and 18 mm spacer.

Black Red '90 · 02-10-2021

You description seems to match my understanding. Here's the math I used:

11" = 279.4 mm
center line = 139.7 mm
center line +36 = 175.7 mm (inside) 103.7 mm (outside)

12" = 304.8 mm
center line = 152.4 mm
center line +48 = 200.4 mm (inside) 104.4 mm (outside)

The +48 would "poke" out just 0.7 mm, or 0.03 inches.

Z51JEFF · 02-10-2021

Take the stock offset and as an inch, No need to make it difficult with all the different numbers. I've been having custom wheels made for years,made to my specs and I always take a stock wheel,find out how much room I have on the inside of the wheel well and go from there. I've never had a wheel made that added anything to the outside of the wheel. I know the language here is as basic as it gets but it doesn't need to be complicated. One small area on the inside of the rear we'll wheel liner will need to be trimmed.

AndrewL · 02-11-2021

This may help you check your math: https://www.willtheyfit.com/

dredgeguy · 02-12-2021

Quote:

Originally Posted by AndrewL

This may help you check your math: https://www.willtheyfit.com/

That is an awesome website, many thanks for posting it!

-=Jeff=- · 02-12-2021

Quote:

Originally Posted by secondchance

OEM 11" rear wheels are positive 36 mm offset. If you keep the same offset, additional 1" will grow out board. Increase by 1/2 of 1" (about 1.3 mm) will grow the wheel 1/2" inboard and outboard. At least, that's my understanding.

For reference, I have 11", 57 mm offset Fikses on the rear and 18 mm spacer.

decimal is in the wrong place

13mm ~= 1/2" not 1.3mm

secondchance · 02-12-2021

Quote:

Originally Posted by -=Jeff=-

decimal is in the wrong place

13mm ~= 1/2" not 1.3mm

You are correct. I was thinking cm.

AndrewL · 02-13-2021

Quote:

Originally Posted by dredgeguy

That is an awesome website, many thanks for posting it!

Glad you find it useful!

Z51JEFF · 02-13-2021

Another part of putting together a wheel setup is matching the tires. TIRE RACK has the specs on all of the tires they sale. When I put the wheels on my Z I originally had a 275-35-18 on the front but felt the side wall was too short. I did some digging and found a 265-40 was a hair taller and only a 1/10 narrower than the 275-35 so that's what I went with.

02-10-2021	#1
Black Red '90 Join Date: May 2018 Location: Virginia Posts: 79	Correct Offset for 18x12? I'm thinking of having a set of 18" wheels made. 17" looks fine on the car, but if I've spending the money I want to go a tad little bigger while still maintaining some sidewall. I know tire selection isn't the best for 18's and will need to run a 335/30 in the rear. This requires a 12" wide wheel. I do not want any "poke" with the extra width. I want it all on the inside. If my math is right this means I need a +48 or +49 offset. Is anyone running this setup? Any clearance issues I need to consider? Thanks

02-10-2021	#2
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,710	Re: Correct Offset for 18x12? OEM 11" rear wheels are positive 36 mm offset. If you keep the same offset, additional 1" will grow out board. Increase by 1/2 of 1" (about 1.3 mm) will grow the wheel 1/2" inboard and outboard. At least, that's my understanding. For reference, I have 11", 57 mm offset Fikses on the rear and 18 mm spacer.

02-10-2021	#3
Black Red '90 Join Date: May 2018 Location: Virginia Posts: 79	Re: Correct Offset for 18x12? You description seems to match my understanding. Here's the math I used: 11" = 279.4 mm center line = 139.7 mm center line +36 = 175.7 mm (inside) 103.7 mm (outside) 12" = 304.8 mm center line = 152.4 mm center line +48 = 200.4 mm (inside) 104.4 mm (outside) The +48 would "poke" out just 0.7 mm, or 0.03 inches.

02-10-2021	#4
Z51JEFF Join Date: Dec 2007 Location: Fremont,Ca Posts: 3,057	Re: Correct Offset for 18x12? Take the stock offset and as an inch, No need to make it difficult with all the different numbers. I've been having custom wheels made for years,made to my specs and I always take a stock wheel,find out how much room I have on the inside of the wheel well and go from there. I've never had a wheel made that added anything to the outside of the wheel. I know the language here is as basic as it gets but it doesn't need to be complicated. One small area on the inside of the rear we'll wheel liner will need to be trimmed.

02-11-2021	#5
AndrewL Join Date: Dec 2020 Location: Sydney, Australia Posts: 85	Re: Correct Offset for 18x12? This may help you check your math: https://www.willtheyfit.com/

02-13-2021	#10
Z51JEFF Join Date: Dec 2007 Location: Fremont,Ca Posts: 3,057	Re: Correct Offset for 18x12? Another part of putting together a wheel setup is matching the tires. TIRE RACK has the specs on all of the tires they sale. When I put the wheels on my Z I originally had a 275-35-18 on the front but felt the side wall was too short. I did some digging and found a 265-40 was a hair taller and only a 1/10 narrower than the 275-35 so that's what I went with.