Engine Braking in Emergency Situations

[Prodigal Son]

enjoy you stick shift while you still have it.

?

I was replying to paul34. Your post intervened. I should have quoted him.

[screenname]

An emoticon!? Prodigal Son used an emoticon!?

[Prodigal Son]

An emoticon!? Prodigal Son used an emoticon!?

[Shaolin]

Now my friend, you have got me. You would probably still get a couple less feet by downshifting, but barley, so it'd be better not to downshift at all. Nice point. Very nice. i'll probably still downshift in an emergency, but i'll be thinking about how wrong i am the whole time.

so let me reeiterate, in an emergency where wheel lock up would not be a concern, downshifting will give you better distance. (inwhich case it wouldn't be a real big emergency.)

I'm talking about a car with abs, where the wheels won't lock up. if you don't have abs, service brakes will lock you up, plenty of power in those breaks to do that, however, i stand by my theory that in a abs equipped car, you'll stop quicker with compression.

(corrected)

But how though? I thought about this, and now im inclined to disagree with you on this specific point.
When you slam on your breaks with abs, there is more than enough stopping force there to do its job. Actually, the abs will activiley limit the force from the discs, in order to not lock, and keep traction. The threshhold of your tire against the road, slowing you down, is already achieved, not even harnessing 100% of your discs power.

So how will adding more force to the equasion help?

Yes, 100% agreement on this. ABS systems are designed to detect lock up and to release the brakes momentarilly to keep the wheels turning. The threshold for ABS activation will be the same regardless of where the braking force is coming from. The only way that engine braking could add anything is if it overrode the ABS and locked the wheels anyway -- which it obviously can't do -- and even if it could do it, it would obviously be a bad thing.

Adding brake force into a system designed to limit brake force is obviously not going to slow you down any faster since the system that limits brake force still kicks in at the same threshold.

Yay so it wasn't just a drunken ramble

I thought I was going to get something blatently obvious pointed out to me.

[comingbackdown]

The simple fact that a downshift at the wrong rpms can lock the wheels on a non-ABS vehicle has always screamed one thing to me... Before you go manhandling any car (especially "spirited" driving), know what it's got... That way you can react correctly in any situation...

Speaking of which, what happens if you do lock the wheels on a non-ABS car, by downshifting or otherwise? As far as I know, you just do your best to steer out of it, and hope you don't wind up leaving a you-shaped indent in the firewall...

[Prodigal Son]

Speaking of which, what happens if you do lock the wheels on a non-ABS car, by downshifting or otherwise? As far as I know, you just do your best to steer out of it, and hope you don't wind up leaving a you-shaped indent in the firewall...

First, you cannot lock the wheels by downshifting. Not unless you stall the engine. But you can upset the balance of the car, and you can force the wheels to spin slower than they should, causing you to lose traction.

Second, you cannot steer with your wheels locked. With the wheels locked, you are sliding on four bits of stationary rubber and you have no directional control at all. If a wheel is not rolling, it is not steering. You have to get the wheels rolling if you want to steer.

[Johnf514]

PS - I have briefly locked my wheels up when downshifting, but the slide could only be measured in tenths of a second. Simply, the downshift was not rev-matched properly, and the tires slid until they got up to speed with the rest of the vehicle.

That said, the wheels will not lock up for a prolonged slide - but like PS said, they can and will upset the balance of the vehicle and possibly send you off the road.

[Prodigal Son]

PS - I have briefly locked my wheels up when downshifting, but the slide could only be measured in tenths of a second. Simply, the downshift was not rev-matched properly, and the tires slid until they got up to speed with the rest of the vehicle.

How did you manage to do that? Heel/toeing on ice? You would have to be in neutral and hard on the brakes to lock the wheels. Otherwise the engine would keep them turning.

Other than that I have to think that what happened was that the wheels lost traction and were therefore skidding, but still actually turning, just not at the speed that the pavement was passing by underneath them.

[jomotopia]

PS - I have briefly locked my wheels up when downshifting, but the slide could only be measured in tenths of a second. Simply, the downshift was not rev-matched properly, and the tires slid until they got up to speed with the rest of the vehicle.

How did you manage to do that? Heel/toeing on ice? You would have to be in neutral and hard on the brakes to lock the wheels. Otherwise the engine would keep them turning.

Other than that I have to think that what happened was that the wheels lost traction and were therefore skidding, but still actually turning, just not at the speed that the pavement was passing by underneath them.

i agree. if you were in gear and the engine was running then your wheels weren't locked, though they may have been instantly slowed so much they lost traction and you were sliding, but they were still turning. unless the engine died and came back there's no physical way the wheels could have been locked.

[Johnf514]

I was coming into a turn at about 50 MPH and downshifted from 5th-2nd, but did not rev match. The roads were a little wet (no ice in FL), and coupled with the quick gear change produce a very short slide. Careless driving on my part - I learned from that.

[comingbackdown]

I was coming into a turn at about 50 MPH and downshifted from 5th-2nd, but did not rev match. The roads were a little wet (no ice in FL), and coupled with the quick gear change produce a very short slide. Careless driving on my part - I learned from that.

I don't have words for that... Just thinking about what it might've been like to be in that car in that tiny bit of time, all I can do is go ...

[Johnf514]

Yup - the Camaro was RWD as well - so the rear end kicked out a ways. Thankfully, the corner was wide and forgiving - and no traffic was around. Again, a good learning experience.

[Charly_GK7]

whaat? you made Steve leave?
But he was the only user on this board with the same car as me=(

No you are not the only one!

BTW, don't you feel the ABS on this car are way to ... sensitive?

they just kick in at any slight road imperfection, who knows maybe an ant even activates them!

It really screws the braking I have to zig zag to avoid hitting or stop were I want to.

Saludos desde MTY.

[ClutchFork]

I had a bad engine braking experience on the freeway a couple months ago. It was a snowy morning and traffic was heavy, speeds around 35 mph. Road seemed to have good traction. Traffic was slowing, I downshifted, not hard either and the engine braking caused by tail end to come out to the side. I disengaged the clutch, steered into it and recovered. Probably a good thing it was at slower speeds and thankfully there were no cars beside me as I was in the right lane and that is the side the tail end went. In 35 years of driving stick I don't remember ever having that happen before.

[AHTOXA]

Wow. Prodigal Son, JohnF and Jomo all on the same thread page. That brings back memories.