[Kevin M]

I think the momentary lateral forces in autocross match or exceed those on a track. It's not long, sustained forces that break parts (and this applies mostly to the drivetrain of course) but sharp instantaneous forces. Powershifting fro 2nd to 3rd with 200 whp is harder on it than rolling into it on a dyno with 350 whp. Going to the track is much harder on brakes, but not necessarily on tires. I'm not talking about wear and tear that causes you to replace consumables like brake pads, tires, clutches. I mean stuff getting broken. Stripped gears, busted halfshafts, that sort of thing. What breaks a WRX gear faster- a handful of 7000 RPM clutch dumps, or running around RFR at full throttle? On a Solo 2 course, you shift almost as many times as you would during a lap or two on a track. More importantly, you're doing it between 1st and 2nd gear, which means way more torque is going through the drivetrain than at higher speeds. And the average beginner or intermediate autocrosser is less than silky smooth with shifting when they're chasing time.

In terms of engine wear, I don't think either autocross or tracking is particular hard on a motor since you can't hardly shock load the engine without putting yourself bass-ackwards into cones or weeds. As long as you aren't making more power than the engine can physically handle or doing bad things to the engine management at least. In the absence of detonation, and with sufficient cooling, no motorsport is particularly hard on a fresh, well-maintained modern engine.