What does downshifting to slow down wear out?

[chickentendah]

There's something that's been bugging me for quite a while now. I normally coast in neutral before approaching my stops, because I once heard that downshifting excessively is "bad".

But........What car components are getting worn out if you excessively downshift for slowing down (instead of coasting + brakes)?

And why does the downshifting help you slow down? (Physics explanation is very welcome)

[KDashy]

Downshifting puts the engine at a higher RPM and thusly slowing the car down because the rpm's are dropping when you dont gas it.

I'd assume (I dont drive a manaul) that when you have to downshift a lot, it just wears the clutch out faster, but probably by not much.

Coasting and braking just makes you use the brakes a lot more, so thusly you'd have to change your pads more.

Some people prefer one, some people prefer the other.

[w1ngzer0]

teh downshift

[NoStickers]

pads are cheaper than a transmission

[w1ngzer0]

i know i just like downshifting :Pbut downshifting doesn't ware your clutch, its a myth. my dads truck is proof of that.

he has over 200,000 miles on his toyota 88' 4runner. he has only changed his clutch slave not his clutch or transmission. He has just done regular oil changes and normal fluid changes. I don't think he has ever flushed the radiator :pface

[420_240sx]

my friend does that too, downshifting to stop. I say screw that, only time I do that is if I have to stop ASAP, in those times downshifting can save you from a wreck combined with braking. But besides that, why put that kind of stress on the clutch/transmission and even the motor. Brakes are cheap and easy

[sohc90adel]

you probably waste gas too.

[Bryan Smith]

What would you rather replace brake pads or clutch assm.? I desided to waste the last bit of useful surface left on my clutch on my se-r, downshifting to slowdown, without rev matching, clutch fried very quickly. If you must downshift cause you like the sound, please, revmatch.

[Silvia2b]

hey, isn't the reason you slow when downshifting due to the compression of the cylinders? So it is possible that this could wear on the rings as well? I'm not sure it causes any excess stress though.

[silkk]

i rather replace my brake pads than my clutch

[Meantime]

^^^what he said.

[KDashy]

I remember watching an episode of Top Gear and Jeremy mentioned something about when you're slowing down in gear, you're not using much gas, as opposed to slowing down in neutral you're using gas to keep the engine from stalling.

[SloMoe]

Excessive down shifting without rev matching will wear out your synchros. When your synchros wear out its harder to shift between gears because the dog teeth on the collar wont synch up to the drive gears before they engage.

[vuse1]

i personally downshift to slow down, thats just how i learned how to drive a 5 speed. im running a stock clutch with 190k miles, so i dont believe it wears out your clutch faster, however i do rev match like a champ so maybe that helps

[gabossie]

^ What he said.

[nab911]

i know i just like downshifting :Pbut downshifting doesn't ware your clutch, its a myth. my dads truck is proof of that.

he has over 200,000 miles on his toyota 88' 4runner. he has only changed his clutch slave not his clutch or transmission. He has just done regular oil changes and normal fluid changes. I don't think he has ever flushed the radiator :pface

Any time the clutch has to engage or dissengage, it slips and wears. The more you engage or dissengage the cluthc, the more it wears.

[marshun]

theres allot of disinfo in this thread. if you revmatch while youre downshifting, you wont ruin your synchro's. but if you **** up. youre wearing them out. it does help braking. but only a little. you do waste more gas rather than coasting.

[stash420sx]

why do you guys think you waste more gas with down shifting? I do it, i rev match or heal toe too. It does cause excessive wear on the transmission and clutch. but jeez, driving my car peroid puts excessive wear on some component or another. I guess it would use a bit more gas when matching the revs. but i wonder if the injectors are on at all when the rpm's are dropping and my foot is off the accelerator.

[sponge bob]

OK, i just have to clear one thing up here.

YOU DO NOT WASTE ANY GAS DECELERATING IN GEAR. Sorry I had to be so loud.

When decelerating in gear in a fuel injected car, the fuel injectors shut down, thus, there is absolutely ZERO fuel consumption!

Thanks, Asgar

[nab911]

Do they really shut down? Im not doubting you at all just didnt know that? Seems like a little fuel would go in just so its not totaly leaned out. But fuel consumption is ENTIRELY based on the throttle openess (word?). Its based on how much air is flowing through the MAF which is controlled by your throttle.

[chickentendah]

^_^

good lord, i started this thread in the first place because I was really confused with all the different theories.....

but when I say downshifiting, I implied WITHOUT rev-matching

will the physicist please stand up. why does downshifting (no rev-match) slow the car down. where is the kinetic energy going? thus which part of the car is taking the beating?

[sponge bob]

the compresion/power stroke of the cylinder slows the car down.

[240Knightrider]

I have given thought to this as well but, I cant understand that it will help you slow down faster when used with the brakes but to avoid an accident the first thing any regular driver thinks of is to "brake" not break and downshift. I have been in enough accidents to know this. Also I cant imagine (could be wrong) that you will stop so much faster in an emergency that you will even notice the difference in the end results. But if you are going over 60, that I see using both will work.

[Projex240]

the syncros arent affected--the only time the syncors are even being used is during shifting itself. The fact you downshift to slow down does nothing but put reverse pressure on the rods. Instead of them being pushed on, they are pulled on. The can strech if theya re aluminum rods, and the crank and rods bearing will take more abuse.In the end, dont do it. Just use the brakes, or if you do ds to slow down, do it only at a reasonable RPM--dont do it at 5 k to hear the car start screaming as most do it for.Like dude said--brakes are cheaper than transmission's, and trannys are cheaper than motors--you decide

[SloMoe]

theres allot of disinfo in this thread. if you revmatch while youre downshifting, you wont ruin your synchro's. but if you **** up. youre wearing them out. it does help braking. but only a little. you do waste more gas rather than coasting.

What I implied was if you downshift withOUT revmatching it will wear them out faster than if you used revmatching.

[SloMoe]

the syncros arent affected--the only time the syncors are even being used is during shifting itself. The fact you downshift to slow down does nothing but put reverse pressure on the rods. Instead of them being pushed on, they are pulled on. The can strech if theya re aluminum rods, and the crank and rods bearing will take more abuse.In the end, dont do it. Just use the brakes, or if you do ds to slow down, do it only at a reasonable RPM--dont do it at 5 k to hear the car start screaming as most do it for.Like dude said--brakes are cheaper than transmission's, and trannys are cheaper than motors--you decide

True, when your in gear and let out the clutch after downshifting the synchros are not affected. But the act of downshifting (ie 3rd to 2nd) places a load on the synchros as your output shaft is spinning faster than your input shaft so the collar has to catch up so the dog teeth can engage smoothly. Rev matching spins the input shaft at the same speed reducing the load on the synchros.

[ca18datsun510]

wow. i cant believe i just read this whole thing.

some people on here, im not gonna mention names, should go buy a book, and learn what they are talking about before they give advice.

and besides, everybody knows the only thing downshifting wheres out is the leather on your shift knob.

[stash420sx]

if you match revs with the transmission in neutral, and the clutch engauged(foot off the pedel). it puts even less stress on the transmission. this way all the transmission internals are spinning about the same speed as the engine and the output shaft. i just got my hands on a nissan consult, so im going to see if the injectors really do shut off when the rpm's are falling.

[stash420sx]

i used to drop it down to second gear and drop the clutch while going down hills. the rear of the car would slide around a bit. I used to think i was cool cause front wheel drivers couldnt do that.

[ca18datsun510]

shift lock. whatch drift bible and you could be a jdm mad tyte drifter maniac too!