Engine braking question

[2o6]

I was driving a customer home in our shuttle Chevy Cruze, and I was using the manumatic function to control engine braking when going downhills to maintain control. The customer was quite a gearhead, and had a lot of technical knowledge, and he said that using transmission engine braking in a FWD car can actually be harmful and facilitate a spin because since the driveshafts are usually unequal, the engine braking on the front wheels will be uneven.



That sounds like it makes sense, but wouldn't unequal engine braking be better than none at all?

[hotrodalex]

I never had a problem with it in my Saturn.

[VTEC_Inside]

Unless you are on snow/ice the difference would be meaningless IMO. Even then it's not likely to be anything you'd notice.

Consider that you usually have to floor it to notice any torque steer, and that the braking force applied while coasting is a fraction of that acceleration force.

[2o6]

I was on snow and ice.

[FoMoJo]

I was on snow and ice.

Did you notice a problem?

[2o6]

Did you notice a problem?

Not really, but I just asked if it could be, since the customer said what he did with such certainty.

[GoCougs]

He's generally right but for the wrong reason.

Different length half shafts aren't a factor. The different in torsional deflection would be immeasurably slight especially on a slick surface. However, grabbing a lower gear with a large RPM drop (especially without rev matching downshifting) is not too much different than stabbing the brakes on only two sets of wheels, which can cause problems when on slick surfaces.

[2o6]

He's generally right but for the wrong reason.

Different length half shafts aren't a factor. The different in torsional deflection would be immeasurably slight especially on a slick surface. However, grabbing a lower gear with a large RPM drop (especially without rev matching downshifting) is not too much different than stabbing the brakes on only two sets of wheels, which can cause problems when on slick surfaces.

I thought so, but when I downshift I generally rev match. Downshifting in the automatic Cruze seems like it wouldn't do that much difference; the AT computer won't let me do it that fast, and I wasn't going very fast anyways.

[giant_mtb]

If you're on slippery shit and you downshift, there's a good chance the driven wheels will break traction because there isn't enough traction on the snow/slush/whatever to brake the vehicle and, depending on the  ABS's reaction, you could slide one way or another.  It'll happen in any car, FWD or not.

[280Z Turbo]

Too much engine braking in the RX-7 used to get the car fishtailing. It was a lot worse than what you'd get in a FWD car.

[CJ]

I stick it in D and go. 

[280Z Turbo]

If I don't have to change gear, I'm not going to. I don't need my car patronizing me.

[giant_mtb]

I stick it in D and go. 

That's what she said.

[Laconian]

"D" = dumper?

On many manumatic transmissions there is a noticeable lurch during downshifts, which could upset traction, I suppose.

[280Z Turbo]

"D" = dumper?

On many manumatic transmissions there is a noticeable lurch during downshifts, which could upset traction, I suppose.

He's pretty noticeable, I guess

[S204STi]

Engine braking is fine, and in fact my preference. Just don't downshift in a situation where the sudden deceleration could cause loss of control, and realize that as you lift the throttle your car will pitch more due to decel than it would have in a taller gear.

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[Soup DeVille]

I was driving a customer home in our shuttle Chevy Cruze, and I was using the manumatic function to control engine braking when going downhills to maintain control. The customer was quite a gearhead, and had a lot of technical knowledge, and he said that using transmission engine braking in a FWD car can actually be harmful and facilitate a spin because since the driveshafts are usually unequal, the engine braking on the front wheels will be uneven.



That sounds like it makes sense, but wouldn't unequal engine braking be better than none at all?

He's a kook, and is way over thinking things.

[S204STi]

And anyway, a slide is preferred to plowing the nose wide.

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[Rupert]

This sounds like it's from the realm of yeeaaahhh, I gueesssss, kinda, but, eh, meh.

[Rupert]

I stick it in D and go.

Flat dry place = this is OK.

[AutobahnSHO]

At highway speeds wont do anything bad. On extreme snow and ice with auto you might need to throw it into neutral under 10mph so the tranny isn't fighting your braking...

[MX793]

He's generally right but for the wrong reason.

Different length half shafts aren't a factor. The different in torsional deflection would be immeasurably slight especially on a slick surface. However, grabbing a lower gear with a large RPM drop (especially without rev matching downshifting) is not too much different than stabbing the brakes on only two sets of wheels, which can cause problems when on slick surfaces.

Both front wheels starting to slide simultaneously won't cause you to spin.  It will generally cause the front end to pull to one side due to the crown in the road and potentially cause you to slide off the road in certain extreme cases.

Honestly, it's pretty hard to cause a FWD car to spin via unequal braking force between the left and right front wheels.  As long as the rear wheels have decent lateral grip, it's going to take a fair bit of lateral brake imbalance to induce yaw.  You would really need essentially full traction at one front wheel and zero at the other three to induce a spin with the brakes.

[MexicoCityM3]

In most performance driving schools one of the first thing they tell you is to forget about engine braking. It's for 18 wheelers is a recurrent phrase. Basically it's much harder to modulate your "braking" with the engine than with the brakes and thus it's easier to get in a situation where you can break traction without intending to do so.

[Eye of the Tiger]

In most performance driving schools one of the first thing they tell you is to forget about engine braking. It's for 18 wheelers is a recurrent phrase. Basically it's much harder to modulate your "braking" with the engine than with the brakes and thus it's easier to get in a situation where you can break traction without intending to do so.

+1

It's not even great for 18-wheelers on snow and ice, as the inbalance makes it more likely to jackknife.

[S204STi]

In most performance driving schools one of the first thing they tell you is to forget about engine braking. It's for 18 wheelers is a recurrent phrase. Basically it's much harder to modulate your "braking" with the engine than with the brakes and thus it's easier to get in a situation where you can break traction without intending to do so.

My doctrine regarding engine braking on public roads, regardless of weather, is this:  basically, be in the correct gear for a corner such that opening or closing the throttle will produce an impact on the attitude of the car.  I'm not a performance driver, however.  I'm just basing this on years of driving on snow-packed and icy roads (which it might surprise some to find out don't occur only in the U.P....)  I prefer to have the ability to slightly alter the yaw rate of the car with the throttle, as well as having brakes as a backup.  Also, I don't ride my brakes much if at all on any road.  I brake deliberately when traction allows, but otherwise use throttle to control the attitude of my car when I'm on slick surfaces.

On a track I imagine that since the best lap times are generally produced when you are using full application of your controls at all time (i.e. WOT as soon as possible, on the brakes as late and as hard as possible at all times) then yes, engine braking becomes moot.

[280Z Turbo]

In most performance driving schools one of the first thing they tell you is to forget about engine braking. It's for 18 wheelers is a recurrent phrase. Basically it's much harder to modulate your "braking" with the engine than with the brakes and thus it's easier to get in a situation where you can break traction without intending to do so.

I'm not exactly sure what that means. Anybody who comes up to a corner with the clutch in is not going to be fast.

[GoCougs]

Both front wheels starting to slide simultaneously won't cause you to spin.  It will generally cause the front end to pull to one side due to the crown in the road and potentially cause you to slide off the road in certain extreme cases.

Honestly, it's pretty hard to cause a FWD car to spin via unequal braking force between the left and right front wheels.  As long as the rear wheels have decent lateral grip, it's going to take a fair bit of lateral brake imbalance to induce yaw.  You would really need essentially full traction at one front wheel and zero at the other three to induce a spin with the brakes.

Yep, hence my lack of the use of the term "spin" in that reply.  .

[MexicoCityM3]

I'm not exactly sure what that means. Anybody who comes up to a corner with the clutch in is not going to be fast.

You don't use the engine for braking, that doesn't mean that you go into a corner with the clutch in. You downshift as necessary during braking, that's what heel & toe is for.

[Rupert]

In most performance driving schools one of the first thing they tell you is to forget about engine braking. It's for 18 wheelers is a recurrent phrase. Basically it's much harder to modulate your "braking" with the engine than with the brakes and thus it's easier to get in a situation where you can break traction without intending to do so.

Engine braking is very useful in the non-performance driving world. That's what it means to put the car in a lower gear as you head down a steep mountain pass, for example. You shouldn't ever really be shifting down to slow down for a curve or stop light, though I do sometimes, just for shits.

[hotrodalex]

I downshift for stoplights all the time (when I drive a stickshift car). Might as well. A little bit of brake pressure to keep the brake lights on, but downshifting can almost get me to a stop if I spot a red light early enough.