Geometry:

Before making any observations on handling it is imperative that your geometry is set-up correctly, the factory settings have been proved to provide good all round performance even in the UK and should be considered the base point. Altering your geometry can have the most dire effect on your cars handling, do so at your peril.

Wheels & Offsets:

The Soarer is specified with +50mm (positive) Offset front & rear with standard sized rims (15" / 16" x 8"). It is difficult to obtain these offsets from the European after market wheel manufacturers and many will say that using +40mm 0r +35mm will fit and make no difference to the steering - they are lying.

The front track is affected by fitting wheels with less offset, for example if you fit wheels with +35mm offset you are adding 30mm to the front track width (15mm per side), this has a big effect on the front steering geometry as it alters the Scrub Radius. This effects the steering "feedback" making the steering wheel more lively as any forces applied to the road wheel are exaggerated by the increased offset, this can make the steering feel less stable and more prone to "tramlining" (the tendency for the front wheels to follow any undulations in road surface, straight line braking can also be affected causing the car to "pull", the greater the difference from standard the more this will effect the handling. 

Some may prefer the more positive feedback and quicker "turn-in" that the wider track will provide when using less wheel offset, generally you should keep as near as possible to the +50mm Offset on the front wheels to retain the inherent good handling characteristics of the Soarer.

Azev are one of the few cast alloy manufacturers who machine the PCD and offset to order, I guess they cast the rims "thick" to allow for various offsets.

Diag1, Front Scrub Radius & Offset:

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"

Rob Hayden from the ALSC uses 10.5"x18" on the rear of his air-sprung V8 with a +46mm Offset and has no clearance problems, this has to be the MAX rear wheel width and the offset here is critical to prevent the tyres rubbing on the suspension or catching the rear wheel arches.

Tyre Section & Rolling Radius
If you take the 225/55/16 as being the standard size & rolling radius, any variance in radius will affect the speedo reading and visual appearance, the tyres look undersized for the car if you reduce the overall diameter.

Tyre Size / Diameter
225/55/16 654mm Standard
235/45/17 645mm Front *
245/45/17 654mm Front **
255/45/17 662mm Rear **
255/40/17 636mm Rear
265/40/17 644mm Rear *

* Normal 17" option.
** My options for 17" rims assuming they dont "rub", the taller sidewalls have more compliance (better ride quality/less prone to tramlining) and are nearer to the correct rolling radius.

18" Rims:

Neil Glynn's TT with TSW 18" rims and Yokohama Tyres looks stunning but could certainly afford to loose an inch all round for that killer appearance. Using the modified (slightly harder) lower front arm bushes (made from Blue Nolothane) allows fitment of 18/20" rims without issues of the larger rims placing too much strain on the arm bushes.

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.