Ok, I feel like douche for asking, but the comments in the "check your oil" thread make me wonder... I'm no mechanical expert, so educate me on this: do you or do you not downshift while driving to slow the car a little? Not talking about abrupt downshifts that make your RPMs jump like crazy, but the 5t-to-4h, then 4th-t0-3rd downshifts when coming up to a stoplight. Just the normal day-to-day commuting, not on the track or anything? I've only had 2 other vehicles with MT, a Ford pick up and a Lex IS300. I downshifted both to slow down a little every time with 0 ill effects. Fill me in!

(p.s.) Manual seems to have neutral comments on downshifting, just says don't overrev the engine

 

If you downshift, you should try to rev match as well. The engine compression braking is probably not good for your tranny or your engine.

 

yea i always downshift thru rev matching if your not going to rev match it, i wouldnt do it too often....could cause something in the long run IMO

 

I thought it was good to rev match and down shift when coming up to a stop... supposedly it saves gas (as compared to just putting it in neutral, or having the clutch in).

 

if you're engine is not idling, you are not saving gas. when down shifting, your RPM's shoot up and go down slowly as the engine is braking. say you'e at 50 mph in 6th, your tires and tranny are turning at a certain speed. shift into a lower gear (say 3rd) and your momentum is going to force the engine to rev by itself to match the the tire and tranny RPM. instead of the engine turning the tires, you're tires are "turning" the engine. go to a top of a steep hill and drive down hill and keep down shifting to slow the car down. then repeat it with the car in neutral (idling at 700 rpm) and only use the brakes. do you really think the latter is going to use more gas?

 

Yes... for the exact reason you just cited. They explained on top gear that then you idle you are using a tiny bit of gas, but when you are slowing down in gear your wheels are turning the engine and no gas is needed to keep the engine running. This could be completely wrong, but thats how they said it worked on the show. Overall I don't think it makes a huge difference, but they were talking about it on the episode where they were trying to squeeze 40mpg out of a big Audi with a tt diesel v8.

 

I chose "always" since there was not a "most of the time" choice but I always rev match. It's easier with a light flywheel.

 

not saying you're on the same boat as top gear but you're saying there's NO fuel going to the cylinders when down shifting? i'm not saying it's a significant difference but i do believe there's combustion going on (at a higher rate) when down shifting.

 

.

When you drive an MT, you HAVE TO downshift... no matter what the situation is, there's always a time where downshifting is necessary.

I'm assuming you mean downshifting for fun? As in downshifting and flooring the gas?

Yeah I do that too


PS. Sorry I mis-read your post. Downshifting to slow down is a good idea imo as long as there isnt heavy trafic and you Rev-Match your downshifts.


.

 

"when coasting, a modern engine uses no fuel" -Jeremy Clarkson

 

That huge jolt you get when you don't rev-match while downshifting should be enough incentive to do so...

 

I know this sounds dumb but how exactly do you rev match?

 

When you change to a lower gear, you depress the clutch, increase the gas to bring the RPMS up to the level they need to be at in the lower gear.

Once you get used to a car, you have a pretty good idea what the difference is between each gear, and you aim to make the gear change without much stress or sudden jolt to the engine/suspension/clutch/mounts. Then when you get comfortable, you can change between several gears at once. 5-2, 1-3, etc. Downshifting 2 or even 3 gears can be quite fun if you can time and match the revs pretty well.

This makes the driving experience seem much more connected and fluid. It's why we drive a stick when we don't have to.

 

how about driving down hill? i'm not yet used to driving a 6MT. because when i go down hill on a 5MT i down shift to 3rd and letting it rev at 3k rpm going 40 mph. the whole time what i have been doing was going down the hill on 4th gear 3k rpm going 40. is there a safer way? i dont wanna run my brakes either (one of the reasons why i do that. but i always support my transmission going down hill with my brakes. i believe it's cheaper to replace brakes then a transmission anyway, correct?

 

the F are you talking about. when you down shift, you do not need to step on the gas to bring the RPM up.... ????

anyways, the point of downshifting to slow down ur car is not to save gas, its to save ur breaks... downshifting and normral rpm ranges doesnt effect the engine or tranny. lets ur on 6th, ur at 3k rpm.... u see a red light. u down shift to 5th... rpm will be at about 4-5k and slowly goes down... you down shift to 4th... etc .etc...