SC400TT

iTrader: (4)

Guys, I searched the forum and found much info re: the correct wheel sizing for the TT brake upgrade. There seems to be no clear answer...I ran across conflicting opinions on this matter.

Example:

1)The recommended correct offset for 16" wheels is +50 mm front and rear
2)It appears to be different for 18" wheels. According to London Bill's site:

Wheel Size v Offset:

Iain Wiltshire posted the following on the LSOC about Soarer wheel offsets,
"Up to and inc 8" on the front +50mm O/S
8½"=+38/+46mm, 9"=+32/+38mm.
Up to and including 9" on the rear +50mm O/S
9½"=+43/+50mm, 10"=+32/+44mm"

So, the bigger wheel seems to mean a different offset.

Now, London Bill, please feel free to chime in anytime and share with us your knowledge on this subject.

My point is this: I have recently gotten hooked up on a good deal for a set of Supra TT front brake calipers/matching drilled and slotted rotors, ss brake lines and pads in excellent condition. Those dam.... calipers are huge!!

My wheels are the following:
Altstadt Type 1
18x8.5, +38 mm offset in front
18x9.5, +41 mm offset in rear

Also from London Bill's site:

Caliper Clearance v Offset:

If you want to upgrade the brakes to the Supra TT fitment then wheel choice is important, many after market wheels will not fit over the existing calipers let alone the bigger Supra items. It's not the wheel size that creates the brake clearance fitment issue (specifically 17" rims and above are needed to go over the Supra TT brakes), it is more to do with the shape or architecture of the wheel back space.

As we need to get near the optimum +50mm Offset (specifically for the front wheels) this is forcing the suspension hub and brakes nearer to the spokes on the front of the rim, if the wheel design has the spokes leaning rearwards from the wheel centre they will foul the brake caliper, needless to say the Supra 17" rims do not suffer from this problem. AP Racing say a 4mm clearance between wheel and caliper is also needed for adequate cooling and supply "to scale" drawings of their calipers to check for wheel back clearance.



Iain Wiltshire has been adamant that "offset" is not the factor governing caliper clearance and in that respect is correct, however this issue arises with after market manufacturers attempting a "one size fits all" situation, there is a constant in a cast rim (rear wheel space) which moves in and out in relation to the caliper with differing offsets (but only on the same wheel pattern). Probably why the TSW rims only come in +35mm/+40mm Offset, if they tried to take any more meat from the rear mounting face their wheels would clout the calipers on some cars (specifically Soarers/Supras). Proper 3 piece split rims can be built up to fit around any combination of brakes and offsets.



The easiest way to ensure your new wheels will fit is to specify Supra TT fitment but beware they are not trying to fob you off with shallow offsets just to get them on your car, some people have resorted to using wheel spacers or machining the rear mounting hub on the wheel to alter offsets or create caliper clearance, this practice is frowned upon and should only be used judiciously.


Look forward to your input

legendary

You will need high-disk wheels to clear (front) TT calipers. So it is not offset alone when it comes to that equation.

How do you know if you have high disk? Well, they are pretty much specified as such. I will move this to the Tire Rack forum for more exposure