being that i am using the losi kit, it will only let u use the smaller 45t spur. The pics below are from another post where i was having an issue because of the larger 48t spur gear, it was rubbing the bottom of the chassis. After listening to some folks we came to the conslusion that you can only use the 45t unless u want to dremel out the chassis to allow the gear to clear. So i am using the 45t plastic gear just because i want to run my car today and not have to wait another day or 2 for the tekno kit.