nige Posted January 27, 2009 Share Posted January 27, 2009 (edited) Yes I know that engine braking slows the vehicle on it's own and i can also understand the necessity for engine braking on slippery surfaces like snow. What i can't understand is how engine braking can make your vehicle stop faster. Threshold braking is the absolute fastest method of a controlled stop which isn't always easy to do on slippery surfaces. You do not have to have the vehicle in gear to perform threshold braking so how would it decrease your stopping distance via increased braking power accredited to the engine? I am interested to see a road test result nonetheless. It would be really great to see the difference between dry pavement and snow if possible! It might give better stopping distance on snow, but it shouldn't be significantly different on dry pavement even if you have rear abs on your truck. As for avoiding accidents, it's always better to have the vehicle in neutral if you know you don't have room to stop the car in time. That way you can lock up the front tires, steer them in the direction you want to go and slowly release the pedal to make the vehicle track in the direction the wheels are pointing. Of course you could to this with the vehicle in D, but the effect slightly diminishes if you are in 4wd. You definitely don't want to be stuck in 4wd and 2 or 1 gear to perform this maneuver as the wheels will not be turning at the same speed the vehicle is moving after you release the brake. If you try doing that in 2wd and 2 or 1 gear on dry pavement, you are liable to spin the vehicle out and fail entirely. You're young and a new driver so I don't expect you to know about that yet, but the best advice I can give you is the same as Precise1: Keep sane stopping distances, slap it in neutral (or step on the clutch) and use your good brakes appropriately. Edited January 27, 2009 by nige Link to comment Share on other sites More sharing options...
alexrex20 Posted January 27, 2009 Share Posted January 27, 2009 (edited) that's nice fueler, would you care to explain to everyone why? he doesn't know what he's talking about, so that's the best response he can muster. the quicker we all just accept that, the easier it will be for the big boys to talk. Because I don't notice a difference in braking performance with my own truck when the auto tranny is in D or 2 it all comes down to how much grip your tires can provide. if you can already lock them up and/or engage ABS, then you've reached maximum braking potential. you're right: the absolute quickest way to stop is threshold braking. in theory, you would be slowing the vehicle and the engine, but really, the engine can probably slow down much quicker than the vehicle, so i doubt it would hinder overall braking performance. upgrading to aftermarket pads and rotors, or calipers, or whatever, will not shorten braking distances, if your brakes are already capable of locking the tires. what they do afford, however, are resistance to fade, consistency, and improved modulation. the only things touching the ground are your tires. Edited January 27, 2009 by alexrex20 Link to comment Share on other sites More sharing options...
alexrex20 Posted January 27, 2009 Share Posted January 27, 2009 Maybe if I have the time, I'll head down to lower river road and paint up some lines, and do a stopping test with and without engine braking to see what the difference really is. that's not necessary. we already know the answer. i outlined it above, but i will reiterate: if your brakes are already capable of locking up the tires, then you do not need more powerful brakes - nor do you need assistance from engine braking. [that concept makes me lol.] you can have the most powerful brakes in the world, but if you're running on donuts, you will have longer braking distances than an identical vehicle with less powerful brakes, but grippier tires. Link to comment Share on other sites More sharing options...
nige Posted January 27, 2009 Share Posted January 27, 2009 (edited) it all comes down to how much grip your tires can provide. if you can already lock them up and/or engage ABS, then you've reached maximum braking potential. you're right: the absolute quickest way to stop is threshold braking. in theory, you would be slowing the vehicle and the engine, but really, the engine can probably slow down much quicker than the vehicle, so i doubt it would hinder overall braking performance. upgrading to aftermarket pads and rotors, or calipers, or whatever, will not shorten braking distances, if your brakes are already capable of locking the tires. what they do afford, however, are resistance to fade, consistency, and improved modulation. the only things touching the ground are your tires. Yes i agree, it depends on the tire compound, contact patch, road surface and temp. And will add if you have a larger tire contact patch than stock (i.e. bigger tires), a larger contact patch between the pad and rotor surface (eveything else about the brakes unchanged) will help stop that tire more efficiently over stock equipment. Edited January 27, 2009 by nige Link to comment Share on other sites More sharing options...
shift220 Posted January 28, 2009 Share Posted January 28, 2009 The fact that your vehicle is stopping faster after you manually slam your automatic transmission into first gear simply shows us that your back brakes are in either need of a tune up or just plain underpowered. No it doesn't hurt the engine and yes its hard as hell on the tranny. You should never downshift your automatic when your under a load like that. Why people are arguing about engine braking in general I don't understand? He's talking about slamming it into 1st gear to panic stop, not coasting down a mountain Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 Brakes work just fine. I'm not saying I HAVE to use the engine to stop my truck, it stops damn well on its own. BUT what I am saying is, if brakes alone just simply aren't enough to stop in time (not whether or not they are powerful enough to lock the wheels, which they can, but a 100% not-enough-stopping-distance issue), whats wrong with the little extra that engine braking provides? Am I expected to hit the guy when I can do something else as a last-ditch effort? I just don't see how using ONLY the brakes can stop a vehicle as fast as using the brakes AND engine compression to slow it. Link to comment Share on other sites More sharing options...
alexrex20 Posted January 28, 2009 Share Posted January 28, 2009 the brakes ALONE are powerful enough to reach MAXIMUM AVAILABLE stopping performance. what part of that do you not understand? if you're already at that maximum, what the hell is throwing it into 1st going to do? i doubt the transmission will even shift into 1st quick enough to make a difference. if anything, it will lockup the rear tires and make it even worse. engine braking is great for preventing brake overheat in the mountains, or when pulling trailers. but it's not worth a damn if you're in a panic braking situation and you still can't stop. at that point, either brace for impact or swerve. Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 the brakes ALONE are powerful enough to reach MAXIMUM AVAILABLE stopping performance. what part of that do you not understand? if you're already at that maximum, what the hell is throwing it into 1st going to do? i doubt the transmission will even shift into 1st quick enough to make a difference. if anything, it will lockup the rear tires and make it even worse. engine braking is great for preventing brake overheat in the mountains, or when pulling trailers. but it's not worth a damn if you're in a panic braking situation and you still can't stop. at that point, either brace for impact or swerve. Bold: That's why I'm taking it to lower river road and testing that. How do you KNOW its at that maximum? I was talking to my grandpa about it, and he said in all of his driving experience, panic stopping with the gearing saved his ass a few times, manual or automatic. Though he did say manuals were more effective at slowing. Link to comment Share on other sites More sharing options...
silverlion Posted January 28, 2009 Share Posted January 28, 2009 Maximum stopping= quickest stop without skidding the tires If your brakes skid the tires, you have crossed the max. threshold. There is no need to use the engine to assist in making the tires skid any further. Tire skid = loss of traction. Loss of traction = decreased, not increased stopping power. To give the horse one last whack, If your brakes can skid the tires, there is more than enough stopping power available. There is no need to go through the trouble of downshifting in a panic to stop faster. The stopping power is already there if your brakes are able to skid the tires. Avoid skidding the tires for maximum braking efficiency. Link to comment Share on other sites More sharing options...
alexrex20 Posted January 28, 2009 Share Posted January 28, 2009 Bold: That's why I'm taking it to lower river road and testing that. How do you KNOW its at that maximum? I was talking to my grandpa about it, and he said in all of his driving experience, panic stopping with the gearing saved his ass a few times, manual or automatic. Though he did say manuals were more effective at slowing. well, my uncle's coworker told me that your grandpa is wrong. unless you can replicate a scenario without fault or deviation, many times for a control, then neither you nor your grandpa can determine whether or not the engine braking was the reason his ass was saved on that single specific incident. as for knowing if the truck is at its maximum... if it is a panic situation and you are trying to get all you can from your brakes (which you claim are in good working condition), then you are also at the limit of adhesion from your tires. but, it's obvious you don't believe me or anyone else. so in your stubbornness, go ahead and test your truck. hell, throw it in reverse to see if that works. just don't kill yourself. Link to comment Share on other sites More sharing options...
alexrex20 Posted January 28, 2009 Share Posted January 28, 2009 Maximum stopping= quickest stop without skidding the tiresIf your brakes skid the tires, you have crossed the max. threshold. There is no need to use the engine to assist in making the tires skid any further. Tire skid = loss of traction. Loss of traction = decreased, not increased stopping power. To give the horse one last whack, If your brakes can skid the tires, there is more than enough stopping power available. There is no need to go through the trouble of downshifting in a panic to stop faster. The stopping power is already there if your brakes are able to skid the tires. Avoid skidding the tires for maximum braking efficiency. apparently i like your apples also! Link to comment Share on other sites More sharing options...
silverlion Posted January 28, 2009 Share Posted January 28, 2009 LMAO!!! Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 well, my uncle's coworker told me that your grandpa is wrong. unless you can replicate a scenario without fault or deviation, many times for a control, then neither you nor your grandpa can determine whether or not the engine braking was the reason his ass was saved on that single specific incident. as for knowing if the truck is at its maximum... if it is a panic situation and you are trying to get all you can from your brakes (which you claim are in good working condition), then you are also at the limit of adhesion from your tires. but, it's obvious you don't believe me or anyone else. so in your stubbornness, go ahead and test your truck. hell, throw it in reverse to see if that works. just don't kill yourself. Man, you're an ass. It's not that I don't believe you, it's just that I'm still confused about certain aspects of it the whole situation with braking and engine braking. I'm still trying to get my head around the concept that the engine forcing the drivetrain to slow down, does not, in fact, help the vehicle its self to slow down. It's one of those things that I'll probably never fully understand. Though I do have a funny story about moms and leaning down to get something from their purse and knocking the gear lever into reverse doing 50... Link to comment Share on other sites More sharing options...
silverlion Posted January 28, 2009 Share Posted January 28, 2009 I was arguing with a date ( now an ex) when she threw my '69 Chevelle in reverse doing 70. She looked at me, threw it in R for race and the tranny went all to pisses. I coulda slapped her, but it's just not in my nature. Her daddy bought me a new TCI tranny. Link to comment Share on other sites More sharing options...
BowTied Posted January 28, 2009 Share Posted January 28, 2009 I was arguing with a date ( now an ex) when she threw my '69 Chevelle in reverse doing 70. She looked at me, threw it in R for race and the tranny went all to pisses. I coulda slapped her, but it's just not in my nature. Her daddy bought me a new TCI tranny. Any pics of the Chevelle? Still have it? Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 You have/had a Chevelle?! I envy you! Link to comment Share on other sites More sharing options...
BowTied Posted January 28, 2009 Share Posted January 28, 2009 This is my 69 Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 That thing is orgasmically beautiful. SS396? Link to comment Share on other sites More sharing options...
BowTied Posted January 28, 2009 Share Posted January 28, 2009 Some interesting discussions here. Warping rotors- I think it is important to understand that turning a warped rotor does not remove the warping throughout the rotor, only the surface the pad rides on – the machining process removes the high spots caused by the warp, but any changes to the grain structure of the remaining metal are still there. Fatigue comes about by repeated movement, like when you bend a thin piece of metal by hand back and forth until it breaks. I think the potential for warped rotor to further wrap, assuming it was machined properly, is more about the fact that it goes back into service in the same conditions that caused the warp in the first place (dragging caliper, poor driving habits etc) and now combined with slightly less metal to dissipate the heat. There is one additional item which was already touched on, the quality of metallurgy. This could further impact the potential to warp of course compounding the issue. If a quality rotor that is lightly warped is turned and put into service on a truck with good brakes and used with good driving habits, it should have a useful service life. The whole engine braking thing - the way I was reading what Fueler said… maybe I misunderstand? There is everyday driving with mild braking and then there is panic stopping. I thought fueler was taking about the everyday stuff? Anyway, I would suggest the idea of emergency stop downshifting is not a great idea. But first maybe I can help explain others say it is not beneficial. Assuming the regular brakes are all brand new, the suspension is all brand new, and talking a dry paved surface: When you apply the brakes as hard as you can the wheels lock up. If the wheels are locked up, the transmission in any gear is not going make the wheels any more locked up. Now thinking of threshold braking, the tires are still rotating, but on the edge of locking up. Downshifting won’t get the tires to rotate any less as they are already decelerating as fast as possible (rotating as slow as they can) without locking up. In fact, the additional braking energy provided by the downshift could push the threshold braking to the point of locking up the drive wheels. Locked wheels = low traction and less control. If that is not happening when downshifting, then I think your brakes are not being applied to the threshold. If you are finding that downshifting appears to be helpful, and it may be helpful in your case, I would guess that your rear brakes are not locking up. This means that the front brakes get to that threshold before the rear brakes do. The downshifting then adds some additional braking to the rear wheels only which is actually helpful, assuming they do not lock up. This condition could arise from rear brakes that are not ideally adjusted. But wait, there is more - It is my experience that vehicle loading, especially on a truck that is designed to be towing, is always a balancing game when it comes to braking. Since weight transfer is always an issue and the designers know this, the front brakes often have a larger contact area and/or mechanical advantage from the hydraulic system. To help control rear wheel lock up, a proportioning valve is include in the system. My point is there are a lot of reasons (vehicle condition, vehicle loading etc.), beyond the basic theories, why someone might be experiencing some reduced braking distance using a panic stop downshift. It is CERTAINLY hard on the vehicle. I think that one will find comparable results by shifting to neutral instead with less wear and tear. For regular driving downshifting for hills, especially when towing, is encouraged. I hope that helps. Link to comment Share on other sites More sharing options...
BowTied Posted January 28, 2009 Share Posted January 28, 2009 That thing is orgasmically beautiful. SS396? Thanks! Yes, true SS396 (+.030", 4 speed, 4.10 gears). Link to comment Share on other sites More sharing options...
adamzan Posted January 28, 2009 Share Posted January 28, 2009 Some traffic came to a sudden stop in front of me today. I had kept good distance, but it scared me nonetheless. I slammed the brakes on and this is the first time in my life I've ever heard my pathy's front tires squeal to a stop. I didn't even think about downshifting. I stopped within about 5 feet of the guy in front of me. This was at about 70kmh or 40 miles per hour. He then got out to see if I was ok I then thought, wow, what If I hadn't just replaced these brakes and tires a few months ago. I would've been posting carnage pics instead of this. Link to comment Share on other sites More sharing options...
GrimGreg Posted January 28, 2009 Share Posted January 28, 2009 Back to rotors and to turn or not to turn: With how cheap they are, it is usually chaeper to buy new than to pay a tech an hour labor to turn your warped rotor. Link to comment Share on other sites More sharing options...
nige Posted January 28, 2009 Share Posted January 28, 2009 (edited) yeah, i haven't come across many autoparts chains that charge more than $40 per corner for new ones nice chevelle btw Edited January 28, 2009 by nige Link to comment Share on other sites More sharing options...
Kingman Posted January 28, 2009 Author Share Posted January 28, 2009 (edited) Thanks! Yes, true SS396 (+.030", 4 speed, 4.10 gears). How long have you owned it? Did you restore it yourself? Ever since I was 11, my dream car has always been a 1970 Chevelle SS454 LS6, blue with white stripes. I even get the shakes when I'm around one. And yes, your post did help. Edited January 28, 2009 by kingman92010 Link to comment Share on other sites More sharing options...
Precise1 Posted January 28, 2009 Share Posted January 28, 2009 Back to rotors and to turn or not to turn: With how cheap they are, it is usually chaeper to buy new than to pay a tech an hour labor to turn your warped rotor Ok and the bearings and seals? Who swaps them out, or do you buy them new too and installed in the rotors?? And yes, your post did help. All he did was say the same thing as 6 other people... B Link to comment Share on other sites More sharing options...
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