Newbie driver here, why do the rpms need to be higher when in low gear? Since its a lower gear shouldnt the rpms be low as well?

Question

My brain cant seem to grasp the concept behind this sorry

In: 0

Answer 1

2 different machines. your engine and the transmission. rpm is engine speed, gear is the transmission ratio preset. first gear is the highest ratio for engine speed vs driveshaft speed. giving completely fake numbers here: at 1500rpm engine speed and first gear being 10:1, the driveshaft will be spinning at 150rpm. if 1mph=10rpm of the driveshaft, then at 1500rpm engine speed in 1st gear, you’ll be traveling 15mph.

at the same 1500rpm engine speed, if second gear is 5:1, the driveshaft will be spinning at 300rpm. thus, you’ll be going 30mph. to reach 30mph in first gear, you’d need an engine speed of 3000rpm.

if 3rd gear is 2.5:1, at 1500rpm engine speed you’d achieve 60mph. many engines are simply not capable of spinning faster than 6000rpm, and wont last long at that speed due to heat. not to mention how fast you’ll burn fuel.

by having many gears, you can keep the engine speed low while moving quickly. this extends the life of the engine and reduces the cost of traveling fast.