what kind of gearing would be good to start with i have a b4 with a lrp stock spec 13.5 motor the track is pretty good sized dirt off road. also i have a trinity 5.5 in my t4 what would be good for it? any help would be great thanks!

A good brushless motor can take some gear. But I wouldnt go beyond the recommended final gear ratio. For a 13.5 in a B4 you should be somewhere around 7 to 7.5 fdr. This could be done with several different spur/pinion combinations. For example: a 76T spur and a 27 tooth pinion would work out to a final drive ratio of 7.30. I told you these brushless motors can take some gear!! I dont even know if you could fit the gears to get it lower. You can work out the fdr by taking the spur gear size and dividing it by the pinion size and then multiplying the result by 2.6 for both the B4 and the T4 which use the same tranny. 76 divided by 27 = 2.81, 2.81X2.6 = 7.3. The T4 with a 5.5 should be geared much higher, around 12.5 final drive ratio.

What he said^^^^

i have a B4 that i am working on now to race as a latremodel next year. i have replaced the topshaft in the tranny with a B3 topshaft so i can run a B3, custom works slipper clutch. in my sons intimidator with the 2:40 tranny and custom works tires on anywhere from a 240' to a 290' driveline track we ran a 69 to 75 tooth spur and most of the time a 32 tooth pinion. i have run as large as a 35 tooth pinion with a 72 tooth spur and the motor was barely warm.