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?
I never had a problem with it in my Saturn.
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.
I was on snow and ice.
Quote from: FoMoJo on December 26, 2012, 05:15:24 PM
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.
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.
Quote from: GoCougs on December 26, 2012, 05:27:23 PM
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.
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. :huh:
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.
I stick it in D and go.
If I don't have to change gear, I'm not going to. I don't need my car patronizing me.
"D" = dumper? :lol:
On many manumatic transmissions there is a noticeable lurch during downshifts, which could upset traction, I suppose.
Quote from: Laconian on December 26, 2012, 07:02:25 PM
"D" = dumper? :lol:
On many manumatic transmissions there is a noticeable lurch during downshifts, which could upset traction, I suppose.
(http://3.bp.blogspot.com/--uEO7iIfh9A/UMFoNWfip1I/AAAAAAAAAUQ/S5jcPtx8GRA/s1600/lurch.jpg)
He's pretty noticeable, I guess
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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Quote from: 2o6 on December 26, 2012, 04:49:18 PM
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.
And anyway, a slide is preferred to plowing the nose wide.
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This sounds like it's from the realm of yeeaaahhh, I gueesssss, kinda, but, eh, meh.
Quote from: CJ on December 26, 2012, 06:20:08 PM
I stick it in D and go.
Flat dry place = this is OK.
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...
Quote from: GoCougs on December 26, 2012, 05:27:23 PM
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.
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.
Quote from: MexicoCityM3 on December 27, 2012, 07:31:03 AM
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.
Quote from: MexicoCityM3 on December 27, 2012, 07:31:03 AM
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.
Quote from: MexicoCityM3 on December 27, 2012, 07:31:03 AM
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.
Quote from: MX793 on December 27, 2012, 07:25:52 AM
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. ;).
Quote from: 280Z Turbo on December 27, 2012, 01:56:36 PM
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.
Quote from: MexicoCityM3 on December 27, 2012, 07:31:03 AM
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.
I downshift for stoplights all the time (when I drive a stickshift car). Might as well. :huh: 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.
No point, other than 'cause it's kind of fun and good rev matching practice.
Quote from: Rupert on December 27, 2012, 05:12:35 PM
No point, other than 'cause it's kind of fun and good rev matching practice.
Yeah, I only do it to practice rev-matching. Otherwise I use the brakes - that's what they're there for.
I'm a downshift kinda guy if I'm slowing down from a highway speed to a stop and I know I'll have plenty of room to stop. Putsing around town, though, at 28mph/1200rpm in 4th gear, I'm just gonna put it in neutral and coast/brake to a stop. And of course, sometimes downshift needlessly just for the hell of it. Always a good feeling to be driving home late at night doing 60; you know no cars are coming, so you rev-match down to third and take a nice ride to 90-95. Also while slowing down, too, though. :lol:
Quote from: Rupert on December 27, 2012, 04:45:47 PM
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.
I agree on the steep mountain pass. But that's the extent of the usefulness of engine braking.
Quote from: MexicoCityM3 on December 27, 2012, 07:21:21 PM
I agree on the steep mountain pass. But that's the extent of the usefulness of engine braking.
Snow and ice?
Quote from: 2o6 on December 27, 2012, 07:45:52 PM
Snow and ice?
I generally try to minimize downshifting for the express purpose of engine braking in slick conditions. It can lead to either the front end side-stepping in a FWD car or fishtailing in a RWD. I don't push in the clutch every time I let off the throttle to remove all engine braking, but I also don't downshift to slow down as I would in dryer, higher traction conditions. I pretty much only downshift to prevent the engine from stalling.
Quote from: Rupert on December 27, 2012, 05:12:35 PM
No point, other than 'cause it's kind of fun and good rev matching practice.
My brakes will last for years. :lol:
Quote from: MX793 on December 27, 2012, 08:45:50 PM
I generally try to minimize downshifting for the express purpose of engine braking in slick conditions. It can lead to either the front end side-stepping in a FWD car or fishtailing in a RWD. I don't push in the clutch every time I let off the throttle to remove all engine braking, but I also don't downshift to slow down as I would in dryer, higher traction conditions. I pretty much only downshift to prevent the engine from stalling.
Right - you want to be in the correct gear, but avoid lurchy movements unless you are doing it intentionally to try to change the attitude of the car.
Quote from: MexicoCityM3 on December 27, 2012, 03:57:14 PM
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.
Oh well, then we're on the same page.
Yeah, I heel-toe nearly every shift all the time. I got nothing better to do than pretend my Accent is a race car.
Quote from: MexicoCityM3 on December 27, 2012, 07:21:21 PM
I agree on the steep mountain pass. But that's the extent of the usefulness of engine braking.
Any downgrade steep enough to gain a bunch of speed, really. I use it a lot on steep logging roads.
Brake job is cheaper than clutch replacement....
(Although I do downshift-messaround in Miata)
Downhill on steep hills at 45mph+, I throw the van from D down two clicks to 3 and usually don't have to brake at all. It'll hold whatever speed, 45-65mph..
Quote from: 2o6 on December 27, 2012, 07:45:52 PM
Snow and ice?
Not a good idea generally- but just for the reason that the engine is not connected to all the wheels, and the brakes are. 4 wheel braking > 2 wheel braking. That's all there is to it. The rest of this talk about enequal length halfshafts is just piss in a rainstorm.
Quote from: Soup DeVille on December 28, 2012, 09:43:26 AM
Not a good idea generally- but just for the reason that the engine is not connected to all the wheels, and the brakes are. 4 wheel braking > 2 wheel braking. That's all there is to it. The rest of this talk about enequal length halfshafts is just piss in a rainstorm.
Whats wrong with using both?
Quote from: 2o6 on December 28, 2012, 10:01:45 AM
Whats wrong with using both?
Nothing, if you know what you're doing. But you obviously don't, or you wouldn't be asking.
Quote from: Eye of the Tiger on December 28, 2012, 10:02:51 AM
Nothing, if you know what you're doing.
+1
Just gotta go play around with it and learn how what does what.
Quote from: Soup DeVille on December 28, 2012, 09:43:26 AM
Not a good idea generally- but just for the reason that the engine is not connected to all the wheels, and the brakes are. 4 wheel braking > 2 wheel braking. That's all there is to it. The rest of this talk about enequal length halfshafts is just piss in a rainstorm.
On the other hand, I'll downshift on a slick hill to control speed when I would leave it in a higher gear normally, but that's not really any different from what I was saying above.
Yeah, on a side note, dude needs to just go out and toss his car around an empty lot sometime. You need to know what happens and why, from first-hand experience.
Quote from: S204STi on December 28, 2012, 11:53:27 PM
Yeah, on a side note, dude needs to just go out and toss his car around an empty lot sometime. You need to know what happens and why, from first-hand experience.
Quote from: AutobahnSHO on December 28, 2012, 10:14:40 AM
Just gotta go play around with it and learn how what does what.
Absolutely. I'm going to take my kids messing around as they are learning to drive. Gravel roads, weird uphills, have them take an exit ramp too fast then hard brake, etc... As controlled as possible to push the limits some. Without that, you never know what to do in an emergency.
When I was a squad leader in Germany it snowed so hard we had to cancel a lot of training out in the field. I posted a 'guard' at the motorpool entrance (big fenced area where they keep vehicles and generators, etc...) then we got in the 2.5ton truck and when and did power slides around the corners. (we were only supposed to drive 5mph there but we got it sliding really good at 20mph because it had rained then frozen then snowed...) Many of the Soldiers had never driven on snow and didn't know what it was like to have the back spin around.
(http://www.readyfordoomsday.com/wp-content/uploads/2011/07/364386281.jpg)
Looking back on it now, I could have gotten in SOOOOOOOO much trouble if we had broken anything!!!
Meh. I think you made the right call... if I were your LT I'd take the blame for it.
Quote from: S204STi on December 28, 2012, 11:53:27 PM
Yeah, on a side note, dude needs to just go out and toss his car around an empty lot sometime. You need to know what happens and why, from first-hand experience.
I was just asking if a persons theory was plausable. Where do you get the impression that ive never driven in snow before? This is my third car with my third winter.....
The driveshaft issus sounded plausable, but it didnt really mesh up with my personal exeprience.
Quote from: AutobahnSHO on December 29, 2012, 07:00:09 AM
Absolutely. I'm going to take my kids messing around as they are learning to drive. Gravel roads, weird uphills, have them take an exit ramp too fast then hard brake, etc... As controlled as possible to push the limits some. Without that, you never know what to do in an emergency.
wat
So you're going to let an inexperienced teenager (already a terrible driving statistic) "mess around" on public roads by taking turns too fast? Not only is it extremely unsafe to do that on public roads, the fact that their father is telling them to mess around and drive too fast is just going to make them terrible drivers.
Plus as teenage drivers, they'll do all the messing around on their own.
Nah, that's fine. Public roads aren't always crowded. Though I'd start on an empty lot somewhere.
Quote from: 2o6 on December 29, 2012, 09:40:01 AM
I was just asking if a persons theory was plausable. Where do you get the impression that ive never driven in snow before? This is my third car with my third winter.....
The driveshaft issus sounded plausable, but it didnt really mesh up with my personal exeprience.
Woah there, billy-jean. I'm not trying to insult you, just pointing out that with experience that claim in and of itself would instantly be implausible.
Quote from: S204STi on December 29, 2012, 10:56:33 AM
Nah, that's fine. Public roads aren't always crowded. Though I'd start on an empty lot somewhere.
I really don't think encouraging your kids to do stupid stuff while learning to drive is very smart... I've done a ton of stupid things thanks to inexperience. Having my dad tell me to drive even faster probably wouldn't have helped. Parking lot or track would be fine but public roads? No thanks.
Quote from: thecarnut on December 29, 2012, 11:23:12 AM
I really don't think encouraging your kids to do stupid stuff while learning to drive is very smart... I've done a ton of stupid things thanks to inexperience. Having my dad tell me to drive even faster probably wouldn't have helped. Parking lot or track would be fine but public roads? No thanks.
I disagree. Education under controlled conditions is better than figuring it out the hard/deadly way.
Quote from: thecarnut on December 29, 2012, 11:23:12 AM
I really don't think encouraging your kids to do stupid stuff while learning to drive is very smart... I've done a ton of stupid things thanks to inexperience. Having my dad tell me to drive even faster probably wouldn't have helped. Parking lot or track would be fine but public roads? No thanks.
You did dumb stuff in a car. I did dumb stuff in a car.
(in fact very first time with no adult in the car I was going "the long way" and ended up on a gravel road, coming around a hilly corner too fast and there were a bunch of kids in the road. I panicked, lifted, and spun out. Luckily didn't hit any of them or go off the road. And sheepishly looked to see if they'd heard me.)
*I* have the judgement to know when it's safe to do some 'extra training'. Maybe it WILL be in an empty lot. Obviously it won't be their first time behind the wheel. Obviously not when traffic is coming. Obviously not when I think there's possibility of hurting the car. And it will NEVER be STUPID, it WILL be more than usual lame driving. I will scare them. I will make them respect the responsibility that comes with driving.
All so they DON'T go doing it when it's unsafe.
Quote from: AutobahnSHO on December 29, 2012, 11:51:32 AM
You did dumb stuff in a car. I did dumb stuff in a car.
(in fact very first time with no adult in the car I was going "the long way" and ended up on a gravel road, coming around a hilly corner too fast and there were a bunch of kids in the road. I panicked, lifted, and spun out. Luckily didn't hit any of them or go off the road. And sheepishly looked to see if they'd heard me.)
*I* have the judgement to know when it's safe to do some 'extra training'. Maybe it WILL be in an empty lot. Obviously it won't be their first time behind the wheel. Obviously not when traffic is coming. Obviously not when I think there's possibility of hurting the car. And it will NEVER be STUPID, it WILL be more than usual lame driving. I will scare them. I will make them respect the responsibility that comes with driving.
All so they DON'T go doing it when it's unsafe.
You're the parent, I'm not, so don't take it as me telling you what to do. All I know is, my parents yelling at me to slow down and not be an idiot while driving helped me slow down and not be an idiot. :lol:
And wrt your last comment - being teenagers, they
will do it when it's unsafe. It's bound to happen.
I did a sweet dorifto around a roundabout type thing in a local park yesterday. :rockon:
When I was 14 and we had our '93 Explorer, I convinced my mom to take me to an empty parking lot during the winter so I could "practice winter driving." Which really just meant...spin donuts for 15 minutes. She didn't ride in the car with me, either, because she didn't want to get motion sickness. :lol:
My dad took me out to a parking lot and pulled the handbrake anytime I turned the wheel, forcing me to correct the slide. And then he took over and did 180s and stuff.
Quote from: thecarnut on December 29, 2012, 11:54:08 AM
You're the parent, I'm not, so don't take it as me telling you what to do. All I know is, my parents yelling at me to slow down and not be an idiot while driving helped me slow down and not be an idiot. :lol:
There's a time and a place for everything. My goal is to teach them some of the limits of the car so they can respond to an emergency.
Quote
And wrt your last comment - being teenagers, they will do it when it's unsafe. It's bound to happen.
Yup. But if they learn how quickly it can get out of control in a more controlled environment, then mebbe they won't kill themselves.
I'm with SHO on this.
If it snows an inch tonight, I might get some PorchRitos in.
I had hoped for snow, but it never stuck and now it's totally stopped. :(
Quote from: AutobahnSHO on December 29, 2012, 06:12:18 PM
There's a time and a place for everything. My goal is to teach them some of the limits of the car so they can respond to an emergency.
Yup. But if they learn how quickly it can get out of control in a more controlled environment, then mebbe they won't kill themselves.
I think the "go too fast into a turn and brake hard" thing just didn't seem right to me. Seems like a good way to crash.
That's just me.
Quote from: thecarnut on December 29, 2012, 08:17:27 PM
I think the "go too fast into a turn and brake hard" thing just didn't seem right to me. Seems like a good way to crash.
That's just me.
Obviously you find somewhere with no stuff to crash into. Why would I want to wreck MY car or get injured???????????
Use some common sense here... ;)
Luckily I grew up driving in an area with little to no winter traffic, so I had plenty of opportunities to explore emergency handling at lower speeds (25-ish) on snow and ice.
When I was a teenager, my buddie's dad had just bought a new 1970 Impala hardtop, small block 400, nice car.
There was a paved over berm in town. Dude took it at 100mph. Impalas can fly. For a while. :nutty:
Quote from: shp4man on December 31, 2012, 02:12:57 PM
When I was a teenager, my buddie's dad had just bought a new 1970 Impala hardtop, small block 400, nice car.
There was a paved over berm in town. Dude took it at 100mph. Impalas can fly. For a while. :nutty:
car was made deaded??
Quote from: AutobahnSHO on December 31, 2012, 03:09:34 PM
car was made deaded??
It made it through- the dad never found out.
Quote from: shp4man on December 31, 2012, 03:40:38 PM
It made it through- the dad never found out.
wowsers!!
I took off a muffler or two on the really old Datsun the Subaru I was "lent"..
A friend once put his parents' MPV in a ditch at 90, and they never found out.
Quote from: MexicoCityM3 on December 27, 2012, 07:21:21 PM
I agree on the steep mountain pass. But that's the extent of the usefulness of engine braking.
In a car, yes. On the bike, if I can't use engine braking, I'm either going too fast or following too closely. Plus those clutches are made to be used more frequently. Driving a car at engine speeds where engine braking can bring the car to a stop is a PITA but on a bike its recommended.
I think its prob most logical to rely on the brakes in the car, but mastering engine braking + rev match downshifting never hurts. For example, if your car's brakes are overheated, shifting down a few gears will help you slow down. Since the brakes are so far below threshold, the risk of locking anything up is much lower.
Quote from: sportyaccordy on January 01, 2013, 02:40:42 PM
In a car, yes. On the bike, if I can't use engine braking, I'm either going too fast or following too closely. Plus those clutches are made to be used more frequently. Driving a car at engine speeds where engine braking can bring the car to a stop is a PITA but on a bike its recommended.
I think its prob most logical to rely on the brakes in the car, but mastering engine braking + rev match downshifting never hurts. For example, if your car's brakes are overheated, shifting down a few gears will help you slow down. Since the brakes are so far below threshold, the risk of locking anything up is much lower.
Most high performance bikes have slipper clutches to limit the force of engine braking, which is far more sophisticated than the sprung clutch discs and driveline lash on most cars.
Quote from: sportyaccordy on January 01, 2013, 02:40:42 PM
In a car, yes. On the bike, if I can't use engine braking, I'm either going too fast or following too closely. Plus those clutches are made to be used more frequently. Driving a car at engine speeds where engine braking can bring the car to a stop is a PITA but on a bike its recommended.
I think its prob most logical to rely on the brakes in the car, but mastering engine braking + rev match downshifting never hurts. For example, if your car's brakes are overheated, shifting down a few gears will help you slow down. Since the brakes are so far below threshold, the risk of locking anything up is much lower.
Agree.