DX3S Telemetry has me stumped

[fastbaja5b]

Ok picked up a DX3S after flogging my DX3R (downgrade maybe?) but the onboard temp is a bloody godsend in this climate, absolutely hammered my buggy tonight motor peaked at 109f so I am set up fine there. But the rpm sensor, I fiddled with it and mounted it with a sticker on the diff case figuring it'll spin at the same rate as the spur being a centre diff

Telemetry says 28600rpm? From the Diff?

Calculated my drive ratio as per the book, and as per the calculator for rollout (4.5") which gives a top speed (according to the Spektrum) of 177kph?

I don't think so!

It's a MM 36-60-2000kv, 16t pinion and 4s lipo, so I expect top speed to be 55-60kph (given a theoretical top on the calculator as 63kph)

So how do I set this up?

And wtf is this zoom thing?