UPDATE: I finally got the RR 275/35 mounted on the 9.5" ET35 wheel and tested with the 5mm spacer.
I couldn't get a piece of paper between rubber and shock lower perch. So, I removed the spring and reassembled the shock and tried to find how high I can go before I hit the bump stop.
I measured 9 1/8" between the bottom of the fender arc and the top of one of the studs in the 12' oclock position. I put my older 255/35 wheel on and was surprised that the fender is about half way down the tire sidewall. I though these KWs had more travel before the bump stop...
Next, I put the 275/35 on with 5mm spacer, and I couldn't get the tire to tuck much under the fender. It just sticks out too much and hits the fender right after the tread limit symbol.
So, I had some older BC racing 120mm (4.75") springs in the same rate as my swift 6" springs, so I went and swapped them while moving the lower perch up about 37mm to compensate for same ride height.
I installed the 275/35 without 5mm spacer and it clears the perch with <1mm to spare. The thick purple bottom ring just needs some grinding on the very edge and it will be golden.
I'm able to now tuck the wheel in to about where I would hit the bumpstop and turn the steering ~100deg to the right and it clears the fender liner as well.
Looks like this will work.
My only concern is really two things:
- I guess going from my swift springs to the BC springs is a "downgrade" but I'm not sure I'll notice any real difference...
- going from 6" to 4.75" spring at 12kg, I suspect I'm going to lose suspension travel and compress the spring earlier, potentially causing problems. Swift has a 5" (127mm) spring but that will move my lower perch further down and require I run ~3mm spacer or so. I did the math and my KW has 4" of travel before hitting the bumpstop. The 4.75" spring binds after 2.75" travel, which means I'll most likely bottom out the spring on the track. The 6" spring has 3.88" travel, will also bind before the bump stop but I haven't seen signs of binding on the spring, so I'm probably still safe on that length. I don't think I want to risk the 4.75" spring.
Original Clubsports come with 80-170 (400lb spring at 170mm (6.7") length), with about 2.4" solid height, giving roughly 4.3" travel, which would allow the bump stop to get hit but just barely...
After doing the math, I may just remove the helper spring altogether. If I do this, I have 1" gap between the spring and the perch when the car is lifted in the air. Not sure I will see this situation on the track...