Hi If you need to stop your car really quick downshifting is a good method. I know it works but just dont know the mechanical reasoning as to why it works. Can someone explains this to me? Thanks.

 

when you downshift youre using a lower gear to either go faster slower. the engine at a specific rpm is spinning the driveshaft at that particular speed. the transmission translates the speed from the driveshaft into rpms at the wheels. therefore you can think of it like shifting up through the gears in a 21 speed bike. however the same comparison cannot be made when downshifting. the engines rpm is controlled by the amount of gas the driver is giving the engine. thus someone can lower the gear ratio without using the gas pedal and decelerate the car by letting the engine brake itself because the rpms at the wheel are greater than the rpms at the driveshaft. basically the pressure is taken off of the brakes and onto the transmission.

i hope this helps and i think its accurate...someone correct me if im wrong.

chet

 

downshifting is NOT a good method to stop!@!!!!!!! All it will do is wear down the gears.

 

actually it just uses the engines compression to slow down.

 

what specie is saying is correct to a certain extent. however i would argue that stopping quickly in any manner wears on your brake pads or transmission depending on how you are slowing the car down. fortunately for all of us honda transmissions are very reliable and hold up really well. ive had 3 different crxs with over 150k miles and their transmissions were all fine. im not saying you should downshift from 5th to 3rd everytime you are coming up on a stop light but saying within moderation downshifting isnt going to damage the tranny.

 

When I said really quick I meant to say in emergency situations...not something I do all the time to stop. Sorry for the confusion. Thanks chethewitt and 88EFSir1J1. Is it the engine compression or driveshaft speed? Thanks.

 

compression and driveshaft speed are directly relative to each other.