T4 for a 7 year old, what approx pinion for a silver can 540 stock motor please !

[Colinevan]

I'd like to introduce the youngest to a nice spare t4 that iv got . He's had a go on my brushless t4 and it's way too much as he hasn't grasped the basics such as steering or brakes or why the car turns in the opposite direction when it's coming towards you ha ha.

I basically need a nice slow intro for the time being and have found a spare Tamiya 540 std that should be ample . All I need is a rough idea on pinion size if anyone has done anything similar.

Thanks in advance.

Col.