Engine Braking

bonnie_rick

the News and Views Conference's Engine Breaking:
Good or Bad? (Topic #206).

Check out the beginning and come right back here
to continue the discussion!

Bonnie Rick
Town Hall Community Manager, edmunds.com

C13

"I agree with those who say that downshifting from each gear from 4th to 1st without using the brakes is a bad idea. But disengaging the clutch, keeping the car in 4th & stopping ONLY using the brakes sacrifices control."

You're right, but those aren't the only 2 choices.

When you're doing 60 and a light up ahead turns yellow then red, you just lift off the gas and apply the brakes. Downshifting (at this point) is wrong and disengaging the clutch or putting the trans in neutral are wrong.

When the vehicle's speed has reduced a lot, there comes a time when you have to disengage the clutch or you'll eventually stall the engine. At that point, if the light has changed, you can double-clutch, select a new gear and re-engage the clutch. If the light hasn't changed, and you're going to have to come to a dead stop, continue using the brakes with the clutch disengaged.

You're also right that you have to downshift on turns, but you do it (as on straights) when you need the lower gear in order to accelerate, not before that. Again - you don't want to engage the lower gear to reduce your speed, but to accelerate. Your brakes (with the clutch engaged and with the trans still in the higher gear) are the tool to use for decelerating.

klug

C13, I've seen you post on a number of different boards & you've always backed up your points well. The problem for me is that I drive stickshifts instinctively & Its hard to rationally pick out EXACTLY what I do when I slow down. And noone has ever picked on me for downshifting to slow down. But I'm slightly confused when you say "Double-clutching" Now, If I'm not mistaken, double clutching is disengaging the clutch, moving the stick to nuetral, reengage the clutch, disengage the clutch again & move the stick to the desired gear, and finally reengaget the clutch. I THINK its was invented before gearboxes had syncro's. I thought Semi's shift like that. Modern gearboxes have synchronized geargboxes & no driving instructer ever told me to double clutch a car. If you mean something else by "double clutching" then enlighten me.

C13

Thanks for your kind words. I'm also known to be a pompous [non-permissible content removed], but I'm always right, so it's OK.

First of all, if you're happy and comfortable with the way you're driving now, there's no reason to change it unless you want to. You could play with new techniques if, like me, you find it kind of interesting.

It's true that double-clutching was necessary once, and that it's optional now. It still puts less strain on the parts though, and makes your synchros last longer, and it's fun, if you're into that sort of thing. It's harder on some cars than others, on account of the arrangement of the pedals.

If you don't double-clutch, you'll definitely want to at least blip the throttle before you re-engage the clutch, to match the engine revs to those of the trans.

I think that postponing downshifting till it's necessary is easier and simpler than any other way. You just pretend it's an automatic - brake to slow the car down without ever thinking about the clutch. Not until you're either: a. going pretty slow, or b. need to accelerate, do you need to downshift. If you didn't slow a lot and you're engine's pretty flexible, you still might not need to downshift. My engine's weak at low revs but my car is light, so I'll usually go ahead and roll on the throttle to re-accelerate, unless I have a need to regain speed quickly.

shiner

Klug, if you're slowing down from, say, 60 mph and you use both the brakes and engine braking in 4th, 3rd, 2nd and 1st are you heel-and-toeing?

Recently I started playing around with the toe-and-heel method. I can tell I need lots of practice modulating the brake with my heel. But I can also see how it could be useful on a sporting occasion.

markbuck

Combine it with double clutching, and your tranny synros and clutch will last forever.......

klug

Heal-Toe? I don't but my brake & gas pedals aren't setup right to do it right with. If I'm just slowing down for a normal stoplight then I just use the brakes & don't downshift except at the end to prevent stalling. But if I'm slowing down in preparation for a turn (Maybe I'm doing my Juan Fangio immitation), I downshift to both slow down & keep my RPM's in a range where I have good usable power. Which on my engine is aroiund 3500 rpm or so. ('95 Saturn SC2)Heal/Toe would come into play when while braking through the corner. You want to keep your RPM's up AND continue your braking. Then when you want to accellerate again you would be at the correct RPM & could launch quicker from the corner. you keep your heal on the brake & angle your toes to the gas to keep the rpm's up. At least I THINK that's how it works. I could be wrong. Like I said its hard to do on my car.

shiner

To the beginner (me) it seems like the heel-toe is too much effort for everyday driving, especially in traffic.

myoung1

Well, I am CERTAINLY no expert. (I tried to heel and toe and almost wound up in the ditch...I did manage to stall the car!) But I DO know that break pads are a lot cheaper than clutch plates.

I agree with those who cite the desirability of being in an appropriate gear but I don't agree that this requires downshifting through each gear. My personal preference is to plan ahead, leave the car in 5th (or whatever depending on speed) and select an appropriate gear a second or two before the transission from breaking to power (Which should be at or before the apex if you want an optimum exit speed.)

Just my opinion, but I'm always right and I never lie.

volfy

I agree that for performance street driving, downshifting really only is necessary to get into the proper gear entering into a corner. To do this in concert with late and trail braking, you have to toe-and-heel.

People with different cars and different foot sizes do it slightly differently. I tend to slide my right foot over closer to the accelerator, keeping the "ball" of my foot on the brake pedal. I apply a steady pressure on the brake pedal for braking and swing my kneel to the right to blip the throttle with the edge of my shoe. I find it a lot easier to modulate braking this way, rather than the traditional toe-and-heel movement.

copelanduk

This is interesting.

When I learned to drive, I was never told to downshift 4-3-2(only to 1 when stopped) in the 60mph stop light example from above.

However after driving my 318i for a couple of months I experimented with it. I drive very aggressively (only towards the road not other drivers) and wanted to experiment. I am convinced this is how to drive.

When I drive my automatic 735i with the steptronic to sport mode, and after the car is used to my driving style, I notice something. The instant I take my foot of the gas the car downshifts as it can tell something is up, either a stop or corner. Now why would the car do this? I think it's because it know's I will not be accelerating anytime soon, and is slowing the car before I apply the brakes. This is always right for me, thank god for BMW's.

Anyway when in a stick, thank god for sticks too, I shift down to slow down with my brakes. Now am I wrong here but how can it hurt the trans if you match revs to downshift? It's the exact reverse of an upshift under power. I think it's fine and my car runs like a beauty and I am sometimes right.

jazzcat

copelandduk:
If you're manually rev matching on your downshift, then there should be no transmission wear. However, for those of us who usually rely on the transmission synchros to rev match, we need to be careful.

guitarzan

Copelanduk, I asked the same q many posts ago. One of the hosts let me know that if the car is heavily braking due to the downshift, there is enormous stress put on various parts of the transmission. Perhaps the BMW has bullet-proofed these parts, as they are known for being good quality cars, that I don't know.

hy3

how long can a bwm 325i usually last in terms of miles?

ggosselin

In certain vehicles; particulatiarly those with timing belts(YUCK!)downshifting will not hurt the trans, rather the engine. Suddenly increasing engine RPM and load by downshifting aggressively will eventually cause the timing belt to get its teeth knocked out by either the crank or cam sprockets, causing major engine damage i.e. pistons hitting valves. In most newer vehicles, this will be the case. Solution: buy vehicle without timing belt, or better yet- get an AUTOMATIC!!

zhuxiaoqing

ggosselin:

Why do you mention automatic? Does is has anything to do with timing belt? I mean, whether timing belt will last longer on automatic cars or what?

spokane

The sudden engine speed changes associated with very aggressive downshifting (or upshifting) would indeed increase the likelihood of timing belt failure if the belt were old, worn excessively, or loose. An automatic transmission is less likely to subject the engine to such abrupt changes in speed. As ggosselin indicates, in some engine designs, a failed timing belt can cause catastrophic damage to the engine. However, if the timing belt is replaced at reasonable intervals (60K miles for most vehicles) and the tension is checked/adjusted at 20K intervals, the likelihood of failure is minimal. An extremely aggressive driver should replace the belt more often; such a driver should not notice the cost of an occasional timing belt because he will already be paying for frequent clutch replacements and other repairs. For normal driving habits, many of us are not worried about having an engine equipped with a timing belt.

sugardog

I agree with GLENROSE, KLUG, JAZZCAT and others who say that downshifting is a normal part of driving if done with reason. I have been driving stick shift cars for 44 years, I have never replaced a clutch, tranny, or engine. I also rode a motorcycle for many years and downshifting is a natural, normal, way to slow down, again, within reason. Especially in snow, I find that the tranny gives me additional control, it's all a matter of control, especially with a 4cyl engine, you can feel when the car slows down that you need to downshift to recieve more power, you can feel the engine straining. People who drive automatics do not care much about performance.
(I'm sure I will get a lot of responses on that)
If I drove a V6 or V8, sure, I would use automatic, but with a 4cyl, I need a stick.
I like the 4cyl for economy, and the stick to get the most performance from the 4cyl.
Sugardog.

frank1956

I feel sorry for you all that have timing belts and not timing chains. Go out and buy a vehicle with a timing chain, so you won't use the excuse of having a wimpy timing belt; pertaining to engine braking that is. Engine braking is taught by some truck driving schools; especially when going down a long downhill. If you use only your brakes down a long hill with a heavy load, you run a chance in loosing your normal braking due to overheating. I have an associate degree from Denver Automotive and Diesel College with a 24 month Associate degree. Out of the 24 months, we had 6 months of training on transmissions on both automatiic and manual transmissions. Engine braking is an acceptable style of driving and some cases it would be advisable when going downhill with a load. Must be careful in this situation though (downhill with a load); would be a good idea to put into a lower gear before the downhill starts. I've had a course in truck driving and the rule of thumb they taught is use the same gear going downhill as you would use going uphill at the same grade.

ejs

Tell me if I'm mistaken in any of this.

THE PROPER WAY TO SLOW DOWN AND STOP
(Manual Transmission)

1. Apply the brake.
2. When you feel the engine about to stall, downshift.
3. Continue applying the brake. Repeat #2 as necessary.
4. Only when you're just about to stop, at which point you should be in second gear, disengage the clutch.

With this technique you are always in gear, but the work of stopping the car is on the brakes.

IMPROPER WAY TO SLOW DOWN OR STOP #1

1. Disengage the clutch.
2. Either keep the clutch disengaged or put the car in Neutral.
3. Use the brakes to slow down or stop.

This technique is dangerous because you are freewheeling, and in case you need to get moving again you are a) not in the correct gear and b) your engine's revs will not match the gear you need to be in.

IMPROPER WAY TO SLOW DOWN #2

1. Without braking, downshift.

This technique is bad because it shocks and stresses parts of your car that shouldn't be shocked and stressed that way.

PROPER WAY TO GO DOWN A LONG GRADE

1. Select a low gear.
2. If necessary, use your brakes to control your speed.

You're sharing the work of slowing the car down between the engine and the brakes.

IMPROPER WAY TO GO DOWN A LONG GRADE

1. Disengage the clutch or put the car in Neutral.
2. Ride your brakes all the way.

The brakes will lose effectiveness and you won't be in the proper gear for your speed.

Feedback?

quickshift

I heard that coasting in neutral is illegal. It must be in gear at all times in case of a emergency accleration.

C13

You're not mistaken in any of it.

I'd make only this small adjustment to the first category:
(Assuming a non-panic stop)
1. Lift throttle. Compression braking will slow you.
2. Skip the downshifting unless you're planning to accelerate again. If you're slowing to a stop, apply brakes gently until *just before* the engine tends to bog.
3. Shift to neutral, continue braking.

If it's a hard-braking stuation, get on the brakes and use as much of them as necessary. That's what you've been saving them for.

ejs

Thanks much. When I learned to drive stick, I learned some bad habits. Time to work on those reflexive responses!

C13

We all learned some bad habits. Fortunately, learning to drive right is great fun.

I hope to do some driving schools before too long.