Just went to the tuning shop with the Kart.
Can't purchase / install anything, not even tires.
It's a little misleading in your garage / tuning screen, as Weight/Ballast, Power Limiter, Transmission, and tires appear to be adjustable/ tunable, but most are not.
The only adjustments I was able to make were to:
1. Weight / ballast
2. Transmission (1st gear, final gear, and top speed - max 140km/hr)
PP rating is 512, 33hp. (as a comparison, F40 =503 PP, GT-R Black Mask = 512 PP, and a race tuned Lotus 111R = 513 PP, that's some serious competition for a Go Kart).
Oil change, Paint car, and car wash are the only things available in the maintenance shop. (maybe frame damage?? mine is ok.)
Really wanted to throw on race tires, and a turbo/engine upgrade
Oh well, still love Karting!
Please fill in if I've missed something.