By adjustable control arms, there are a couple of factors:
Lowering the car will increase the amount of negative camber front and back. if on a stock car you can go from +.5 degree to -.5 degree in the front (hypothetical ranges) when you lower your new range may be -.3 to -1.3. Same thing in the back, although you are starting from a higher negative amount of camber.
In the back, the toe adjustment has very little range of adjustment. if you lower, you are going to have to run a very high amount of negative camber if you want your toe to be in spec. If you dial out the negative camber to get back to the "stock" setting of around -1.6, your toe will run out of room. That is when you need something like this:
Adjustable Rear Toe Arm-Rennline, Inc.
You can save a few bucks by buying this part:
Inner Adjustable Rear Toe Arm-Rennline, Inc.
And then some TRW front outer tie rod ends.
If you lower the back by 1.2 inches you will probably need the toe arm adjustment.
A different member recently found this set by Megan racing, which looks to currently be an affordable option:
Megan Racing
Cheaper on eBay.
It says Boxster 05-12 but it is the same for 986 Boxsters, with possibly the exception of the very first 1997 Boxsters which had some suspension differences, but I couldn't tell you what.
Hybrid Mode
