Geared for the same speed they should theoretically have the same runtime. There are a number of other factors which determine runtime, including driving style, battery choice, etc.
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz
hmm for now im geared 18t pinion 84t spur and I get 30mph on the 4370kv motor with the 3500kv for get the same speed ( 30mph ) I should use 84t spur and 22t pinion so the runtime will be almost the same ?