Losi rear diff - 10t in truggy and 13t in buggy. why?
 

so i was going to try my Fioroni tractive IV diff in the rear of my Losi 8t and it wouldnt sinc up with the gear in the diff case. but i have a tractive IV diff in the rear already in my buggy and it fits fine. so i opened it up and i noticed it was larger than the one in my truggy. my truggy rear diff pinion is 10t and the buggy is 13t. why is this? also, will this have the same effect as the center spur/pinion that if i put the 13t in my truggy instead of the 10t will it be faster? or will this only result in too much heat, etc. to run the Fioroni diff i have to use the 13t but will it be worth it. any help on this is appreciated.

They used different diff ratio because of the different size of the vehicles. Buggy is lighter than the truggy so they can maximize the motor's power by using taller gears compared to the truggy.

Truggy - 43/10 = 4.3:1 ratio
Buggy - 43/13 = 3.3:1 ratio

George got it, also to compensate for larger truggy tires

so is it best to stick with the stock truggy gear even though i am running a very powerful brushless motor? i just tried it with the buggy gear and i dont notice any speed increase. the only benefit is that i can run my fioroni diffs, i guess. but will this cause efficiency issues by using the buggy gear in the truggy?

just change you Pinion/spur gear ratio to compensate

make sense

You could, but if you haven't already bought the buggy ratio, get the truggy. It would be a simpler and cheaper setup.... Save you from having to buy a whole new ring/pinion gears.