I have a Subaru WRX which is about to have Brembo calipers and disks. The OEM wheels at 17x7J and 55 Offset do not clear the Brembo calipers.
After spending days measuring clearance from wheel hub, brake disk, center of hub, etc, I consulted with a few wheel manufacturers and was told that my best (and safest) bet is to go for a 17x7.5J at 35 or 37 Offset.
Checking on online offset calculators, I can see that:
- the outer rim will poke 24.4mm more than before
- the inside rim will move 11.7mm further away from the suspension strut
Aesthetics aside (I'm doing this to clear the brakes and for performance on road and track) the new wheels are actually lighter (forged) and the tires will be the same.
So what I'd like to understand is how much of an effect to the car geometry will a 11.7mm move away from the suspension will have, as in will it be positive, neutral or a negative effect.
- will it affect handling (e.g., loss of grip with less warning)
- will it affect performance (e.g., better grip due to being slightly wider)
- will it affect component wear (e.g., wheel bearings or ball bearings)
I know that the same year Subaru STi, has a 17x7.5J at 53 Offset, and a slightly different design to clear Brembo brakes. Which in effect would mean:
- 4.4mm closer to the suspension strut
- wheel will poke out 8.4mm more than before
So there is a clearly shift in geometry, although I'm not sure if it is significant to worry about?
I guess KPI/SIA and scrub radius will be affected. I don't know if the current scrub is negative, but I presume that by changing wheels it will be moved towards positive.
I'm not sure how it will affect SIA, or if it will at all. The fact that Subaru has made wide-track versions, and that the WRX has the narrowest track of all the performance versions, makes me think that the effect might be more not so grave?
The car is currently on OEM caster, camber and toe at:
- Camber -0.45 front left, -0.47 front right
- Caster 3.28 front left, 3.06 front right
- Toe -0.03 front left, 0.01 front right
EDIT - UPDATE
I went ahead and ordered 2Forge 17x8J with ET37 Offset. As suspected, the Wagon fenders are too small, even with severe pulling they simply won't fit the wheels. So the STi archer liners and fenders are needed. However, the wheels easily clear the Brembos (with about 15mm left to spare) and the handling has increased quite drammatically: - The car feels considerably steadier around corners, it has a very evident more planted feeling - The wheels sometimes tramlime (this was expected and doesn't bother me) - There is no rubbing (with fender folding and pulling) the rear wheels cleared the fenders with folding and some light pulling. - The car should now have a similar track width to an STi which has a slightly width (I believe 10mm each side) and whereas the new wheels offset inside (towards the suspension) only +5mm the outside offsets by 23mm Overall a very positive experience, even if it means changing fenders and arch liners. Steering wheel has become slightly heavier.