Smoothness is more key than ever, because every input you give the kart is going to be amplified by the grip. When you saw the wheel and set the inside rear wheel down, it’ll be a bigger penalty because the binding will be worse on all that rubber. On a low-grip track, you can get away with sliding the kart a little. Not on a rubbered up track. Also, I’ve seen a lot of drivers get slower on a grippy track simply because they aren’t comfortable at the limit anymore, since the grip level and how much speed you can carry have risen so much. So make sure the driver is using all that rubber as much as they can and driving a bit harder than they would on a green track.
You have to be able to feel that inside wheel hiking hard and keep it unloaded, resist the urge to countersteer or set it down. The “under the rubber” technique I always preach about is also really important. If you’re slightly too wide on entry, the kart is going to come across the rubber and you’re going to go from little grip to a lot of grip. This is going to unbalance the kart, and usually drivers will complain that the steering wheel feels like it’s going to be ripped out of their hands.
Not really as important at Phoenix, but sometimes particular track surfaces (usually where tar sealer has been laid down to fix cracks in the asphalt) will build insane rubber. Sometimes it’s so bad the rubber actually gets slippery because it’s just rolling up when you drive on it. A bit like driving above the cushion on a dirt track.
Last thing is fitness. Make sure you’re drinking plenty of fluids and eating things that are going to give you real energy. High-grip driving is brutal on your body and muscles and will tire you out.