I have a stock TC4. It has a 72t spur and a 23t pinion with a 17t motor. I want to increse the speed by changing the gearing since its the cheapest way to go. What size spur and pinion should i get and how much will this increase the speed. Any help would be great.

It may not be exact, but if for example you can go 23 mph then a 25 tooth will go < 25 mph (as long as it has the power to pull the extra load)

Im think of a 26t pinion and a 69t spur. Whould this be ok or will my Team Associated Reedy Radon 17 turn motor over heat.

The spur change will give even another 1 mph, it will sure run things a lot hotter. If you are on a nice large, smooth lot here you used to top out real easy and quick then it can probably handle it. Getting some cooling air past the motor will help if possible and if the motor always ran real cool to begin with you'll likely be ok (and faster)

The problems with wires, batts, motors, esc's start to crop up the fastr you go, but I thik you are still well within reason.

Is there a way I can increase the speed by around 5-10MPH buy just changing the gearing.

Yes, go even higher. Maybe it would fit a 30 tooth pinion?

It will approach a certain point , however , where the motor no longer has the power to pull the higher load and the heat will kepp going up and the speed will not.

An easier way may be to simply add one cell to the battery as this in effect will raise the gearing and speed. It will also increase acceleration where the increased gearing will decrease acceleration .

Ok i will try that. What is the max temp my motor should be?

Hmm, 200 F would be too hot. maybe 180 F max. 150-160 would be a lot nicer.