350xcloud

Do you break or downshift when you stop? Which is better for the car? I was told that for city driving to use the brakes, and for highway driving downshift.

Silver Bullit II

I do both (well, don't downshit, hate to do that), depending how fast I need to slow down and what the situation is : going to stop, onramp, offramp etc.
JMS in TX

Inova

i always clutch, gear out, de-clutch, and brake. why else are the brakes there for? it's just much easier that way...

slaponte

iTrader: (2)

I would have to agree. We are taking friction, either clutch or brake pads.

To my logic, it does not seem that the clutch needs the extra pounding of torque in the OPOSITE direction. In racing I think this is done to decelerate faster (clutch+brakes) and to save the brakes.

What else do you want the brakes for??

StackZfan

Brake pads are a lot cheaper then replacing a tranny or drivetrain part.

professor

Down shifting is not meant to slow the vehicle with the clutch, but with the engine. Down shifting and letting the clutch out to SLOW the car is a BAD thing!

Down shifting is designed to use the engine, by harnessing its’ “pumping losses” as a way to slow a vehicle down. Using the engine to slow your car down should NOT be used to slow down when strong braking is required, as it can cause the rear wheels to break traction and spin the car out.

How to do it properly? Rev matching. Rev matching (RPM matching) is when down shifting you bring engine RPM up to the RPM of the input shaft of the transmission for the gear you’re in.

If you would like to learn how…………..

Do this.
Drive at 45 MPH in 2nd gear, and note RPM (maybe 4000 RPM?). Shift into 3rd and the RPM will drop. Continue at 45 MPH in 3rd, but now push in the clutch, and push the gas down enough (it should not take much) to bring the RPM to the level it was in 2nd.(maybe 4000 RPM?)

Now shift into 2nd and let the clutch out, the car should not jerk forward or backward if the RPM was truly matched, and you have NOT done any measurable wear to the clutch. Now let up on the gas (gently) and the engine will be slowing the car down.

After a little practice, you will not have to look at the tachometer anymore to do this and driving a stick will have a whole new meaning.

Scott

slaponte

iTrader: (2)

Gee professor, while I agree with most of your post, this first bit seems silly. If you use the "engine" to slow down, don't you pass the power (or -power when slowing) through the clutch? Seems in the equation the fragile piece is the clutch. The engine revs up and revs down all the time anyway, it is the clutch you are asking to reverse "direction" : instead of applying friction to go faster, now I am applying friction to slow you down, in the "oposite" direction.

It is my humble opinion that by "braking" using the engine (via the clutch), you are reducing clutch lifetime. Like somebody said, brake pads are a lot cheaper (and easier to install)...

ranger5oh

I religiously downshift in all of my stickshift cars. I typically get a very very long lifetime out of my clutch also. The best part of downshifting is the radical reduction in brake wear. I got 80,000 miles out of a set of brakes on my last 240sx, and mind you this was the last 100,000-180,000 miles on the car. I also never replaced the clutch during that time. The clutch wear from acceleration is much harsher than the wear from downshifting. This is just my 2cents, but I definetly downshift 6th, 5th, 4th, 3rd, 2nd, 1st.....

professor

Sorry you do not understand how exactly how a clutch works.

With the clutch pedal all the way out (foot off the pedal) the clutch is not slipping, grinding, or wearing and tearing in any way. All the wear is when you ask the clutch to “SLIP”

For example, when you start out from a dead stop, you have to slip the clutch a little to get the car speed caught-up with the engine speed. If you could start the engine in first gear, (foot off the clutch) you would not even need the clutch to get going..

Bottom line is…..
When your foot is off the clutch, it is not getting worn out! (friction surfaces)

Holding a car on a up hill at a stop light by riding the clutch? Wears the hell out of the clutch.

Revving up to 4000 RPM and “dropping” the clutch to do a burn out? Big wear.

Slipping the clutch in any way is what causes wear, not power going through the clutch assembly.

Hope this makes things clear.

Scott

slaponte

iTrader: (2)

Just because the conversation is interesting, lets go on.

Sir, I have meet a clutch, and you are no clutch!!

Ok, to me a clutch is basically an Oreo cookie. There is the engine with a flywheel firmly attached to it, lets consider it a unit. There is a transmission with a pressure plate. The thin wafer of clutch sits in between.

Lets just leave the clutch pedal up, in gear. If you acelerate, the engine presses hard (clockswise or counter, whichever). The material that is the clutch middle is getting stressed in the direction of rotation. The rest of the car is the weight to be moved.

Now, take your foot of the acelerator. The engine revs down, inmediatly stressing the clutch in the oposite direction. The rest of the car does not want to stop.

Even without considering slipage, etc, you can see where this constant "stress you one way and now the other" would fatigue the clutch waffer over time.

Hope that made sense.

Cool topic.

I shift down when I need to slow down in a big hurry (+brakes)

hfm

iTrader: (1)

I agree with your 2 cents. That's my 2 cents. Three more people and we will make a dime.

professor

slaponte wrote

Yes, the flywheel is firmly attached to the engine. one happy face for you.

The pressure plate is also attached to the flywheel, and turns at engine speed.

The disc is between the two.

The design of the clutch assembly is that it is not "stressed" and if the clutch was never released ( pedal pushed down) the clutch would never wear out!

Exceptions? Sure. Add a lot more power than the stock clutch was designed to handle, and yes, that power could "overwhelm" the clamping force of the pressure plate.

Scott

slaponte

iTrader: (2)

Well Prof, here is where we disagree. You state that if the clutch was never released the clutch would never fail. I think it would. You are only considering slip/friction, which I agree is the main "wear" reason in a clutch. But I believe the constat torque been aplied in both direction does reduce the lifetime of a clutch, besides the constant friction/slip.

We can agree to disagree.

digerydingo

I slow the car primarily with the brakes (habit from racing where most cranks will snap due to extreme heat and/or big slicks if too much load is applied), however, I continue to heal and toe (downshift) in case of any emergency you need to avoid. A truck backs out or looses some of it's load, it is always way easier to avoid then trying to stop. You can avoid ten times better by releasing the brakes, but if your driveline is not engaged, the car will become unstable after the avoidance maneuver making recovery very difficult.

No amount of money saved on the breaks or clutch will ever equal one smashed up car, and that's a fact.

PSekula

If I'm going, say, 60mph on the highway and approaching the offramp. i ride the clutch to the stoplight. Is this a bad thing?

danotto

I was a "downshifter" until the clutch in my GSR went south after only 50K miles. I came to the realization that brake pads are much cheaper than clutch parts. Downshifting may be the best technical approach, but not for everyday driving.

danotto

Definitely not a bad thing.

Buub

iTrader: (1)

OK, so what about gridlock stop-and-go traffic? I think using the engine to moderate speed is pretty much required here, because otherwise you're going to be clutching every five to ten seconds, and that wears out your foot before it wears out the clutch.

Only those who actually participate in traffic bad enough to be called "gridlock" need respond. :-)

350xcloud

I spoke to the nissan dealer and they told me that no matter how rough you drive, you gotta replace the clutch at 50 K anyways.

So I like to downshift because it's more fun, and I don't like to wear out the breaks, although the breaks are cheaper.
What is the cost of the clutch, i know the break pads are like what 20 bucks?

professor

Yeah, you wish! Look here for a "hint" for how much they will cost.

http://www.stillen.com/sportscars_de...d=30399&page=1

Scott