Here's some things we've tried w/ our Tyco TCR cars that sometimes work. It seems it varies from car to car (currently have 27) Some things work for some cars, some don't.
1- Putting a slight arc into the pick-up shoes near the front.
2- Turning one or both rear tires inside out. Some cars pick up speed like crazy w/ one inversion on the left, others on the right. Again, varies from car to car.
3- A very smal shot of Radio Shack tuner cleaner/ lubricant from underneath into the spot where the brushes meet the motor armature. Have to be care ful w/ this, too much and the whole thing gets very messy.
4- A dot of silicone on the chassis front guide where it rubs the track guide. Another on the rear quarter panel where it rubs the track guide.
It takes a bit of experimenting w/ different combos, but we've had some cars go from rolling roadblocks to monsters. Just be careful not to do anything you can't undo.
Good luck! Happy Racin'!