Wheel fitment guide
Introduction
This article is the wheel fitment guide for VWs. It applies to both factory OEM VW and Audi wheels and aftermarket wheels.
Lug patterns and centerbore
When choosing wheels, they must have exactly the 4x100, 5x100, 5x112 lug pattern, depending on year, and at least 57.1 mm centerbore. See 1000q: wheels overview for your model year's lug pattern.
The first number in the lug pattern, for example "5" means that the wheel uses 5 studs/lugs. The second number means how far apart the lugs are, for example 100mm or 112 mm apart. The wheel must match this lug pattern unless you have a custom lug pattern. For example, the touareg lugs are spaced 130mm apart so they will not fit jettas, passats, or golfs, without a lug pattern adapter.
Centerbore is the diameter of the center opening in the middle of the back of the wheel. An exact fit to the wheel hub keeps the wheel properly mounted when torquing down the wheels and minimizes the chances of any vibrations. If the wheel centerbore is larger than the hub centerbore, you must torque the lug nuts with no weight on the wheel and hub or else the wheel may not be centered and will cause vibration.
Hubcentric rings
In reality, this should never occur on modern cars because you should always use hubcentric rings. These are metal or plastic rings that snugly fill the gap between the larger wheel centerbore to match the hub's smaller centerbore. They are generally necessary for aftermarket wheels because this allows the wheel manufacturer to allow fitment with many different cars. Do not attempt to bore out a centerbore that is too small, it may weaken the wheel and may not be properly machined and round, just find another wheel that will properly fit. Rings are generally made out of metal, which can rust, or plastic, which can become damaged. I recommend plastic rings because the damage threshold is still very high and few people have problems with them. Metal rings will rust or corrode over time, losing fitment or getting stuck, so I prefer plastic rings..
Offset
Offset is the difference between the hub face and wheel centerline. A range of 42 to 30 usually works on the MKIII or MKIV, but remember that offset alone means nothing, offset, spoke design, and overall wheel width all play a part in whether or not a wheel will fit under the fenders AND clear the brake and suspension components. A 10" wheel with an offset of 15 will fit under the rear of a MKIV without much fuss, the same can not be said about a 10" wheel with a +42 offset.
If a wheel sticks out beyond the fenders of the car, this is called "poke", wheels that poke are usually either significantly wider than normal with a low offset (10" with an offset of +15) or normal size with a very low offset (7" with an offset of 0 or below).
If a wheel is inside the fender line it is generally called "tucked" (subject to lowering). To tuck wheels you need to run higher offsets and/or skinner wheels (remember it is a combination of Offset and Width). If you run very high offsets you run the risk of the tire/wheel rubbing on the inner fender, or even worse, not being able to fit in the wheel well at all.
Wheels are usually stamped with their offset using the German prefix "ET", meaning "Einpresstiefe" or, literally, "insertion depth". An example would be "ET45" for a 45mm offset.
Spacers
Wheel spacers can be used to change the offset of a wheel. By bolting between the wheel and the wheel hub, they push the wheel further "out" from the car. Spacers SUBTRACT offset from a wheel setup. Therefore if you want to run an et 55 offset wheel (popular OEM Porsche application), you will need either a 15 or 20 mm spacer to end up with an offset in the acceptable range (et40 or et 35).
In general there is a lot of room to play with offset. Stock for MKIII and MKIV cars is about is 35-38, but depending on the width of the wheel, you can go lower or higher than that. Also, there is a significant different between what you can get away with on the front (skinnier) vs. the rear (wider).
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Bolt Pattern
Bolt pattern can be changed through the use of adapters. Adpaters bolt to the wheel hubs using the stock pattern (5x100) and provide studs that are in another pattern (ex. 5x130 of a modern Porsche). Because the heads of the bolts that are used to bolt the adapter to the wheel hub must fully recess in the adapter itself, wheel adpaters are usually pretty thick (~25mm or more). This works well if you want to run a Porsche wheel with an initial offset of 55 (brought down to 30 with the adapters), but not so well with a Non-TT Audi wheel (which have bolt patterns of 5x112 and stock offsets of 35). H&R Makes bolt pattern wheel adapters in several popular combinations.
Hub Bore Hub bore is the diameter of the central hole in your wheels. This hole fits over the central projection on your hub. Since the wheel is centered on the hub it is called hubcentric. Since manufacturers use different hub bores aftermarket wheel manufactures usually do one of two things. Both involve making the hub bore relatively large. In the first case the wheel manufacturer makes the hub bore large, so it fits a variety of cars, then supplies Hubcentric rings, that fit inside the bore and adapt it down to the size of the hub projection on various cars. This way they can make/stock 25 different hubcentric rings instead of 25 different wheels. The "one size fits all" wheel, plus the correct ring, makes the wheels hubcentric for a specific car. The other option is to leave the hub bore large, and not supply rings. In this case the wheel becomes Lugcentric because the wheel is not centered on the hub, but instead the lug nuts/bolts. Lugcentric wheels are much harder to center than hubcentric wheels due to the fact that it is not centered on a central projection. For this reason lugcentric wheels are more prone to vibration and shimmys at speed, if mounted correctly however, lugcentric wheels can be trouble free.
Diameter - From the factory MKIV's have been equipped with 15, 16, 17 and 18 inch wheels. 14 inch wheels will not clear the front brakes on any car, and 19 and 20 inch wheels have been fitted (19's easier than 20's).
The following applies ONLY to cars without brake upgrades.
19's will fit any MKIV
18's will fit any MKIV
17's will fit any MKIV
16's will fit any MKIV EXCEPT R32's
15's will fit any MKIV EXCEPT 337's, 20AE's, or 1.8T (2004.5+) GLI's
*These are subject to certain offset and wheel design restrictions (ie. Wolfsburg wheels are 16" but will not fit on 337's, 20aes, or 1.8t GLI's without a spacer)
Wheel Bolts - Stock wheel bolts are 14x1.5x28 (wire size x thread pitch x length). Longer wheel bolts are needed for adpaters or spacers (ie a 20mm spacer needs 28+20 = 48mm bolts). Stock wheel bolts are Ball Seat Meaning that they are somewhat rounded. Most aftermarket wheels use Conical Seat wheel bolts. You MUST use the correct type for your wheel or they will back out..