Rim offset and wheel size and track... What does that mean?

Hello everyone, Newbie questions here, sorry if they are basic. I have a 2001 C4 and the manual says the car calls for 18" wheels in sizes: 7.5J x 18 H2 front 50 mm offset 57.7in/1455mm track 10J x 18 H2 rear 55mm offset 58.3in/1480mm track What do the "J" "H2" mean? Also, what is the track tell me? And more importantly, is there a calculation to figure out what offset you will need for different with/height tires? for example, the manual is calling for a 18 x 7.5" wide wheel with a 50mm offset for the front How would I be able to figure out if a 18 x 8" wide wheel with a 52mm offset will fit short of bolting them on? Thanks in advance!

The Tire Rack web site has a good description of offset. http://www.tirerack.com/wheels/tech/...jsp?techid=101 The offset doesn't change with tire height. You could calculate the distance to the back of the wheel to figure out if it still clears suspension parts. You also have to worry about fender clearance when moving to wider wheels/wider tires. You're adding a half inch width to the wheel but I think the question is really whether or not you're using the same width tires or moving to something wider. In your example, the back of the wheel would be closer to the center of the car by about 10.7 mm. And yes, the easiest way is always to put on the size tires you expect to use and bolt them on... This answers the markings question: http://www.tyresizecalculator.com/wheel-markings And notice that the width seems to refer to the width available to mount the tire and not the measured width of the wheel! The track is the distance between the wheels (I think). I know it doesn't answer all of your questions but it's a start!

"J" is the width. "ET" is the offset - of the distance between the centerline of the rim (1/2 of the J) and the hub mounting surface. Smaller ET numbers (less offset) push the outside of the rim further away from the car. The track width is the centerline-to-centerline measurement of the wheels (left to right). Axle-to-axle (front back) is the wheelbase. In your example, a 7.5Jx18 ET50 compared to an 8Jx18 ET52, the distance from the mounting surface to the inside lip is 0.5*7.5*25.4 (to convert inches to mm) plus 50mm = 145.25mm. And, 0.5*8*25.4 + 52 = 153.6mm. Do you have 8.5mm to spare between the inside of the wheel and the strut/spring? That you'll have to measure and find out. I have no idea what "H2" means.

From the second link, for folks that aren't interested in clicking on yet another link in a post... Wheel Markings On the inside of your wheel, you will find markings similar to this: 6 � J x 15 H2 5/112 ET39 Let’s see what each of these symbols mean. 6 � Inner width of wheel in inches (6 � x 25.4mm= 152.4mm). J Indicates the shape of the wheel on the place where the tyre bead sits on the wheel. x Indicates that the construction of the wheel is one-piece. 15 Nominal wheel diameter in inches (15 x 25.4mm= 381mm). H2 Type of wheels flange. Wheels flange is a bulge on the wheel in the place where the tyre bead lies on the wheel. It prevents the tyre from falling inside of the wheel. 5/112 First number is the number of bolts (in our case 5). The number 112 indicates the so-called PCD (Pitch Circle Diameter) which is the diameter of an imaginary circle drawn through the center hole of the screws on which the wheel is mounted. ЕТ39 ET is the offset, that is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. The offset is measured in millimetres and can be positive or negative. In our case it is positive: 39 mm.

That was very helpful, thank you all... very much! lastly, being that it is 20 degrees outside and measuring if I have the required space (although really easy) is something I would like to avoid doing in this weather. Has anyone put 18 x 8" wheels on the front of a Carrera 4? (not to be confused with the wide body C4S, also I am not sure if the narrow body C4's transmission at the front of the car affects wheel/tire fitment). Specifically, I am looking at a set of Sport Design wheels off of an '02 Carrera 2 to put on my '01 Carrera 4

Here's a quick link to the Wheel Enhancement site where they show the 8" wide wheels on a a narrow body Carrera and on a C4S. http://www.wheelenhancement.com/inde...elDetail&id=89 http://www.wheelenhancement.com/inde...elDetail&id=51 So while I have to say I haven't done it myself, clearly there are 8" wheels in use on these cars.

Thanks Jefe, I appreciated the response... Now, I might be splitting hairs here, but I just don't know, so excuse my ignorance please. I do not drive a narrow body Carrera nor a wide body Carrera 4S. I drive a narrow body Carrera 4 and I am not sure if the narrow body C4's all wheels drive transmission at the front of the car affects wheel/tire fitment. I called the dealer and they do not know (some dealership, huh?), in fact they were the ones who brought up the whole transmission at the front issue in the first place...

I understand the conundrum and as I don't know the answer I'd suggest calling the guys at Wheel Enhancement. I am sure they'll know what fits and the right tire sizes that make those wheels work for you. And I did mess up on the math in my original post LOL

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Beat me to it! Very well done!

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I have 18x8 wheels with 50mm offset on the front of my '99 C4 and everything fits perfectly. A 52mm offset should not be a problem.

Thanks Damon! Could you answer his original question about how to figure out whether or not a wheel with different width and offset will fit? Oops! tooloud10 already did!