Difference between Base and TT wheel fitment

[TT4ME]

I'm not sure why an old thread was bumped.. but here goes nothing.

I have a 92 es, 92 tt, and 94 tt. I have not tried stock ES wheels but my Moda R6s for the ES DO NOT fit on my 92 TT, or 94 for that matter. My 92 TT stock wheels DO NOT fit on my 94 TT.

1st gen or not, Base & TT calipers are different sizes.

Keep in mind that I only tried on the FRONT of each car. So front brake sizes go as this: ES < 1st gen TT < 2nd gen TT.

[Struggly]

This is the worst thread ever. Wheel fitment is not that complicated.

First of all, the shape and size of the caliper as it protrudes outward from the hub is what makes TT wheel fitment difficult. Diameter is nothing. If you want to confirm that a particular wheel has a large enough inside diameter to clear TT brakes, take a tape measure, measure from the outer edge of the caliper (where the retaining pins go through) to the opposite edge of the rotor, and then ask the wheel vendor if the inside diameter is larger.

Confirming that a given wheel has sufficient space inside the spider to clear the brakes, however, is another matter. Unlike the N/A caliper, the TT caliper is particularly wide, so we need wheels with liberal amount of space in the spider. You'll notice that many of the popular TT wheels have low offsets and small lips. This is to ensure that the caliper will fit inside the wheel. Wheels with significant lips tend to have little space "inside" the wheel--meaning little distance from mounting surface to spoke.

Further, some wheels are designed such that offset is changed by moving the entire spider in and out on the ring. That means that, regardless of offset, the space inside the spider for the caliper is fixed. Decreasing positive offset will not help fitment with wheels of this design. Other wheels, however, change offset by increasing or decreasing the thickness of the wheel hub. For wheels of this type, lower offsets result in more clearance.

Since wheel manufacturers and vendors often do not have spider depth measurements readily available, the best way to ensure that your wheel will fit is to select a model with relatively little lip, or a model with spokes that bow outward significantly (like the FN01RC).

There is a bit more to it, and I could explain, but it's all been posted on 3si before anyway. There are also articles explaining the challenges of wheel fitment in general and 3/S wheel fitment in particular (including one on my website). This is enough for an old-ass thread.

Clint