XRAY - Model racing cars

hey its me again i'm running on carpet with rubber tires

So am I

I would suggest 18-21 with rubbers, depending on grip and layout. Lower sizes for high grip and/or tight layout. For foams I'd go up one to three teeth depending on diameter.

With 84t spur and 63mm rubbers, ratio & rollout calculations:

pinion / internal ratio / rollout
18t / 7.933 / 24.948
19t / 7.516 / 26.344
20t / 7.140 / 27.720
21t / 6.800 / 29.106

With 84t spur and 60mm foams ratio & rollout calculations:

18t / 7.933 / 23.760
19t / 7.516 / 25.080
20t / 7.140 / 26.400
21t / 6.800 / 27.720
22t / 6.491 / 29.040

With 84t spur and 58mm foams ratio & rollout calculations:

19t / 7.516 / 24.244
20t / 7.140 / 25.520
21t / 6.800 / 26.796
22t / 6.491 / 28.072
23t / 6.209 / 29.348

With 84t spur and 56.5mm foams ratio & rollout calculations:

20t / 7.140 / 24.860
21t / 6.800 / 26.103
22t / 6.491 / 27.346
23t / 6.209 / 28.589