Why do people sometimes change gear while going to a stop?

hmmm Never had my clutch explode coasting down hills while in gear... Although now I have a feeling I won't be doing it anymore...
 
Renesis said:
All brake tests are done to get the best results and guess how they do? they use the brake and clutch, no gear change
Hmm... statistics like brake distance require a controlled environment. One control is braking without downshifting, because it would be harder for an automatic car to get accurate results, because obviously engine braking is more efficient/better than idling to a stop.

Engine braking is the same reason why your manual car will stall if you leave it in gear without giving it gas. Although engine braking does add wear to the engine, it is vital to get better brake efficiency in a race. If you have ever seen Formula One, there is a very good reason why the cars downshift while braking, not only to get into a comfortable corner exit speed gear, but to aid braking. That's why you see them downshifting while they are braking, not just through the corner.

Try it yourself with Live For Speed. Do a lap and threshold brake at the finish line with the clutch in, remember your spot, then threshold brake while downshifting. It makes a big difference.
 
wow... interesting thread... there is about as much true information as false and a whole bunch of people look to learn.

Myth - Engine braking will stop you faster
The deal here is that once you've gotten to the limits of your tires you're not going to stop any faster regardless of if your brakes or engine or anything are responsible for slowing the wheels down. Almost every modern disk brake car has enough stopping power lock the wheels up. Bigger and better brakes come into play because they won't fade as fast. (fading will kill your ability to stop fast)

so why use engine braking?
The first reason is because you only have so much braking power before they fade so you can take a decent chunk of that work off of the brakes by using engine braking. The next reason is because unless you are coming to a complete stop you're going to want to get back on the gas at some point -and you'll want to start out in the power band.

There are lots of other things like electronic brake distribution and ABS and traction control systems that I'm just going to leave out for now.
 
IMO engine braking makes most sense when you are trying to achieve a balance of speed reduction for the purposes of a corner, but if you want to all out stop, then slam on the brakes as hard as possible if your vehicle has ABS and you will come to a stop far quicker.

I usually heel and toe on my Civic Si hatch whenever I want to enter a corner (like a highway onramp) at the correct speed, and engine brake my way to the right speed while tapping the brakes gently. But if I want to stop, I just push the clutch all the way down, and modulate the brakes at the edge of lockup. (ya.. old 1992 Civic Si hatch.. hee hee.. it's all I can afford for my own car.., the other car is a 2001 Corolla.. for the wife and kid)...

From what I have understood in racing, these cars usually have a super light flywheel, which helps generate additional braking forces, as the mass of the flywheel is more closely matched with engine revs. Thus, as the engine slows down, the whole transmission slows down far quicker due to lower mass in the flywheel, and since the transmission is connected to the engine more "directly" in a way, engine braking is far more effective.

my 2 cents, but as a comment from my mechanic, he mentioned that if I really want to use engine braking to avoid doing so in 1st gear, because that is really hard on the motor, 2nd gear is the lowest to use on my car, and of course, watch those revs!.
 
yeah... on almost all cars it's a really bad idea to even downshift to 1st while moving (even if slow)

my evolution has a flywheels that lighter than most non-performance cars, but nothing crazy. I rev match and heel toe almost all the time when slowing down because I hate cleaning my rims mostly :lol: but it is good practice and saves the brakes.
 
I rev match and double clutch simply to have something to do, ADD and all. And it does lessen the wear on things, probably not that much, but i'll take it. However, I don't really engine brake per say as the flywheel is very heavy and clutch is trickier than most.
 
800hpfury said:
but if you want to all out stop, then slam on the brakes as hard as possible if your vehicle has ABS and you will come to a stop far quicker.
That's true in a sense, but slamming on the brakes is a bad idea, even with ABS. First of all, you will get maximum braking if you threshold brake, and that means without ABS and without locking the wheels. Secondly, I would assume that ABS causes substantial brake wear, and would probably heat the brakes up quite a bit, because the brakes are vibrating and causing friction to increase, I believe. Also ABS would probably be slower than threshold braking because the pads aren't creating nearly as much useful friction. Threshold braking is the way to go for performance.

in my previous post, I meant to tell you to do the test without braking. At 60 mph out of the chicane, in neutral I can go nearly to the second sector line. At 60 mph out of the chicane, downshifting, I can stop a ways before the bridge.

While it is true that braking is limited by the efficiency of the tires and brakes and such, downshifting saves wear by aiding the tires and brakes, and on a corner, provides a smooth and comfortable gear to exit the corner with.
 
theblue said:
wow... interesting thread... there is about as much true information as false and a whole bunch of people look to learn.

Myth - Engine braking will stop you faster
The deal here is that once you've gotten to the limits of your tires you're not going to stop any faster regardless of if your brakes or engine or anything are responsible for slowing the wheels down. Almost every modern disk brake car has enough stopping power lock the wheels up. Bigger and better brakes come into play because they won't fade as fast. (fading will kill your ability to stop fast)

so why use engine braking?
The first reason is because you only have so much braking power before they fade so you can take a decent chunk of that work off of the brakes by using engine braking. The next reason is because unless you are coming to a complete stop you're going to want to get back on the gas at some point -and you'll want to start out in the power band.

There are lots of other things like electronic brake distribution and ABS and traction control systems that I'm just going to leave out for now.

Yes you cannot go past the abilities of your tyres but if you engine brake you will make sure the wheels are always in motion. This will prevent lock ups.

So when engine braking you prevent lock ups and reduce brake fade. I'd say that would stop you faster wouldn't you? :p
 
Threshold is definitely faster than ABS. Unless of course you have a super expensive ABS system that can sense threshold and keep it there (Not in street cars so far as I know).
 
Not sure how you could sense threshold braking with an ABS system... for ABS to work the tyre has to lock at some point...
 
Leppy said:
Yes you cannot go past the abilities of your tyres but if you engine brake you will make sure the wheels are always in motion. This will prevent lock ups.
That's not entirely true. While you may prevent lock up, if you engine brake too hard you can get the tires spinning at a slower speed than the road. Sliding is sliding.

I don't think engine braking will stop you any faster in a car with powerful brakes.

PS - that avatar rules! :lol:
 
Before you tires are spinning slower than the road is passing you, you will come across a nasty condition called compression lock.

And thanks about the avatar.
 
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