<br> Does the SAI cause outer tread wear? I lost about 40% tread driving 100 miles after installing my coilovers.

 

I think you're overreacting. 40% of tread in 100 miles? Realistically, the WORST toe setting wears tires out in about 4-5k, and neither your current or before settings were that out of wack.

To answer your question, no SAI won't increase or cause outer wear. It's the Steering Angle Inclination - how much the spindle support arm leans in at the top. It has nothing to do with tire wear, just assists in keeping the vehicle straight.

Your numbers are fine - granted I wouldn't have gone to Firestone. Only complaint would be the difference in front toe, but it's not drastic. I think the wear is all in your head, or you didn't look at it properly the 1st time around. With your camber, just flip the tires every 5k miles, or now since you're saying you lost X amount of wear so quickly - which is impossible. I doubt you're running that aggressive of wheels to have to run -3 camber all around - you should invest in front and rear camber kits asap if you haven't already.

 

I checked the outer tread and inner tread and they were really low, my center tread was 90%. the wear is kind of weird. I read somewhere that a bad SAI can result in significant outer and inner wear, but wasn't sure if it was true.