Savage XL TVP length and center diff gearing

[thzero]

1) Er, yes they are 55mm longer. I have them at home, could measure them tonight.
2) 46/15 is probably still a bit high even on 1500kv. Probably want to run like a 11-14t pinion. 13t is ~40mph. 14t is ~45mph. (From BrianG's calc).

Lower kV with 5S or 6S has the benefits of running cooler and being more efficient. Which is a good thing. I'm thinking of swapping my RC8T to a 1800/1900kv motor and my Savage Flux 5B thingamabob to either 1500kv or 1800kv myself.

Downside is that you need the smaller pinions due to the 43/13 gear ratio of the front/rear diffs. If you swap out to 43/10 truggy diffs (which do fit, I checked with my RC8T diffs and they just needed a tiny amount of shimming) you won't need to run as small of pinions. I.e. 16t to 18t on the 46t spur, although the rollout is quite a bit away from 1:1.

Originally Posted by _dV

I have been prepping for a center diff XL length Flux project for a while now. Just starting to protoype the layout with wooden TVPs. I have a couple of questions before i really get underway. I'll probably create a thread here for the project btw.

1) Simple question, a double check really. What length are normal HPI Savage XL TVPs? Can someone measure between the top bulkhead mount points for me please (should be about 356mm). AFAIK the XL wheelbase from axle to axle should be 55mm longer than the Flux. i.e the TVPs are 55mm longer.

2) Gearing. Arithmetic and more arithmetic.
Think i have it right but i have no experience with setting up gearing.
Gearing for Flux gearbox from tooth count is (44/18)*(29/32)*(44/20) = 4.874 (20 pinion for 4s battery)
For 6s a 25 tooth pinion is used = 3.899
I want to run 5s so this should require a gear ratio between 4s\6s = (4.874 + 3.899) = 4.387

For my build i will need to run a 46t center diff so that the center dogbones sit at similar angles to the original setup.
The pinion i would need for 5s = 46/4.387 = 10.486. Which is pretty small (will wear faster?).

So i was thinking i would use a different kV motor, around 1500kV.
To achieve the same speed with the slower motor i would need a porportionally lower gear ratio.
So gear ratio for 1500kV = 4.387*(1500/2200) = 2.991
Pinion for 5s with 1500kV = 46/2.991 = 15.380

To sum it up. For 5s battery with 46t centerdiff and 1500kV motor i need a 15t pinion.

Does the above checkout ok? Does using a lower kV motor seem reasonable?

Cheers