Use 16g wire like this...
http://www.zen-racing.co.uk/catalog/...re-black-p-721
...throughout the car for battery and motor connections. Yes, it will prevent the rear pod movement being restricted, and it will also save a ton of weight high up in the car.
66T spur is best, and the pinion sounds about right too. The timing advice is not so clever.
GT12 cars weigh a lot for 1S power, so you need the torque to get the car to accelerate out of the corners. Don't crank the motor up, it will bog down and get too hot which hurts the rotor. Timing around 30 to 40 deg depending on the track and the motor would be more usual.
For the first few meetings I would recommend a setting of 30 degrees and a ratio that depends on the motor you are using. GT12 cars - in fact all pan cars - calculate gear ratios using the number of mm the car moves for one revolution of the motor. This is because the wear of the rear tyres changes the gear ratio.
The amount of work the motor has to do is measured as the number of millimetres the car moves for one revolution of the motor. This neatly relates the amount of work the motor has to do to move the car to the wear on the rear tyres.
Millimetres per rev is calculated as (Tyre diameter x Pi (3.142)) / (Spur / pinion). For a 66T spur and a 31T pinion on a car using 46mm diameter rear tyres the 'ratio' is 67.8mm/rev... which is about for most motors on 30 deg timing. There are apps out there that do the work for you, my favourite is GearIt for iPhone...
http://www.heizersoftware.com
...or search "rc gear ratio calculators apps" for Android ones. Internal ratio for a pan car is 1:1. Before you gear the car let us know which motor you are using and I can tie some more specific advice. With the low tyre wear on GT12 cars, one pinion will go a long way!
GT12 racing is cheap and close, so your son will love it. Don't pick up the Tx and have a go or you'll have to buy another one!!
Not sure where you are based but if you are near SWIFTS Raceway on 8th March, or Chesterfield on 26th April then pop along to the GT Nationals and take a look around. If you bring your son's car along I'd be happy to look it over and give you a set-up to run on it.
If there's anything else come back and just ask - it's what we're here for! HTH
