Install is: take off the tire, fit the spacer over the wheel studs with a torque wrench and put the tire back on. Check for tightness regularly.
Safety: If you check the tightness often will help with safety. Personally I think the body roll on the matrix is a little much already and the spacers will just make its handling harder.
Performance: it places strain on your axle & hub. negatively affects your cornering.
As for the length, I'm not sure. and its raining so im not going to check.
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