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

[Ryu James]

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.