Wheel Offset and tire sizes

[hd2805]

At last I think I found some wheels I like...American Racing "Magnet" they are available in 18 x 8, can ayone tell me what offset etc that I need?? Also I would like to put a wider tire on at the same time, I think KB uses wider anyone know??? Any help will be appreciated...Thanks

[prchrman]

50 mm is what is being quoted

[russ in VA]

From the wheel colors thread:
5 on 4.5" is the same as 5 x 114.3 mm

I believe the factory wheels have 50mm positive offset (this is based on the markings on the back side of the wheel corroborated by some rough measurements I took).

Some custom wheel companies may prefer you to specify back spacing instead of offset. A brief explanation:

Backspacing and Offset are two different ways of describing the same thing. Backspacing is the old school way to describe it while offset is the more modern terminology. Backspacing is easier to measure while offset can be more useful.

Backspacing is the distance from the back edge of the wheel to the bolt face (the part of the wheel that touches the car) Some folks measure from the actual back edge of the wheel while others measure from the inside bead seat of the wheel (just to make things confusing). There will be about a 1/2 inch difference in these two measurements so be sure to find out which one they want.

Offset is the distance from the geometric center of the wheel to the bolt face. In our case the bolt face is 50mm closer to the outside of the wheel measured from center.

To calculate the backspacing of our 50mm offset wheels:
Our wheels are 8 inches wide .... this means that the bead seat is 8" wide, the total width of most wheels is 1" wider than the bead seat so that gives us 9". Therefore the center of the wheel is 4.5" in and then you have to add the 50mm offset to get backspacing. 50mm / 25.4 = 1.97"
1.97+ 4.5 = 6.47" backspacing measuring from the edge of the rim or
1.97 + 4 = 5.97" if measuring from the bead seat. (If you are actually going to order wheels, please measure yours first to verify my calculations!)

Of course, this is for a rim of the same width as stock. If you go with a wider rim you will need different backspacing to keep the tires centered in the factory location. This is where offset becomes a more useful number because you can use the same offset regardless of wheel width and still have the tire end up in the same position under the car.

[LincMercLover]

:confused: :sleepy:

[Billatpro]

Originally posted by LincMercLover
:confused: :sleepy:

What's this about? are you board with this topic?

[LincMercLover]

LOL, no... I was refering to russ' backspacing lesson...
:confused: (like wow, that's a lot of info to take it) :sleepy: (like I fall asleep during all my classes)

[Billatpro]

OOOOHHHHHH, OK. I still don't know what the real numbers are! seems like no one really knows "for a fact"

[LincMercLover]

50mm

[Billatpro]

Now there's a damn good kid!

[looking97233]

here are some cobra wheels 18x8 for front and 18x9 in back. Go to the very bottom of the page. The also sell engines and have new 2003 cobra engines in the crate. Only $12,500. with supercharger/intercooler.

http://www.karkraft.com/wheels.htm

[Thomas C Potter]

Fiske Custom Wheels makes a 17 x 8.5 with 7.25 backspace, with MM having 6.5" bs as someone stated, $720 each! BFG KDWS 255/50/17 is 27.0" diameter. Big question is how much can tire diameter vary from stock before computer says 'nope'. If anyone knows the answer, we'd love to hear it! Also, Sean Hyland Motorsports offers wheels.

Thomas Potter
Blue MM

[looking97233]

Actual tire size dosen't matter, just to the speedo. What is important is to maintain the ratio front to back. This is for the ABS module, and it gets very unhappy if you messs with it. I believe the the correct ratio frt/rear is: 1:1.05.

[CRUZTAKER]

:sleepy:

Most snow birds run 16's all winter without ANY issues. Except the small issue of the rim backspace issue.

LML: I fall asleep EVERYTIME someone brings up aftermarket wheels!!!

We need a FAQ that states that this (MM) wheel application is unique, and there WILL NOT BE EXACT MATCHES OUT THERE!!!!!!!!.
No one seems to get it. The exact fit ISN'T GOING TO HAPPEN.
Wheel manufactures are not going to re-die and cast their vast selection of wheels to specifically fit ONE CAR!

Believe me, I'll be the first in line for new wheels...black anodized for me.

OK, back to :sleepy:

[gonzo50]

Originally posted by CRUZTAKER
Believe me, I'll be the first in line for new wheels...black anodized for me.
I'm with you man. :up: