Is the steering running fast (Normal) with the tires off the ground and when you place it on the ground is slows?
What radio are you running with? Depending on the type you may be only getting 4.8v to the servo and in need of running a Y connector to bump the volts up to 6.0..
If your radio is allowing 6.0v your battery may be low. Do you have a VoltWatch to check the voltage of the battery is enough?
Yes when I put them on the ground they slow.
I'm running a Futaba 3PK, and I'm using 6.0 volts.
I think that I need a voltwatch. Is there any cheap place to buy one ? In Europe ?