03-07-2015, 01:44 PM | #133 |
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Its safer to engine brake on slippery or downhill slippery surfaces than using footbrake alone. Lesser chance of wheels locking and losing traction. I will drive in lower gears in these conditions so as soon as i take foot off of the accelerator, the car will start slowing down, I will then go through the lower gears and slow down further, then use footbrake for the final stop once I am at a very low speed. Much safer.
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03-07-2015, 02:10 PM | #134 | |
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The bottom line is that if you're in an emergency stop situation, guess what... you're using your foot brakes, not engine braking. If you can't safely foot brake without losing control of your car, then you should not be driving in those conditions. |
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03-07-2015, 03:16 PM | #135 |
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03-09-2015, 10:03 AM | #136 | |
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03-09-2015, 06:57 PM | #137 | |
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When braking, it is optimal (meaning, "provides the minimum stopping distance") for the applied braking force at each wheel to be proportional to the tractive force at each wheel. The tractive force is a linear function of the amount of weight supported. Therefore, in any vehicle which has non-driven wheels (e.g., any two-wheel-drive vehicle), engine braking will necessarily be less effective than using the service brake. This is because in order to achieve the same net braking force (sum over all wheels), the driven wheels of the car using engine braking will be closer to their maximum tractive force than the car using only the service brake. This is bad because once the braking force exceeds the maximum tractive force, the wheels lock up and you lose control. Therefore, under the same net braking force, the car using engine braking is closer to going into a skid and losing control. In other words, the car using only the service brake can be braked even harder without going into a skid. Aside from some special circumstances on a track, the only time that engine braking is *necessary and effective* is if you are driving a truck with an exhaust brake in a hilly/mountainous area under dry conditions. In such a situation, attempting to maintain highway speeds without the use of the exhaust brake will result in the heat capacity of the brake system being exceeded. This is known as "brake fade." If you add decreased traction to the above scenario, the answer is to decrease speed dramatically on descents (primarily through use of the service brake). If you rely on engine/exhaust braking you will enter a drive-wheel skid and may well get yourself -- and others -- killed. That isn't to say that using engine braking isn't a comfortable and convenient way to control speed on long descents in a passenger car. It is. But it is not necessary to stop the vehicle, and it should never, ever be used under conditions of decreased traction. Edit: In the case of an AWD vehicle, engine braking is less dangerous under conditions of decreased traction (than doing so with a 2WD vehicle). However, it is very typical for people to pull off the gas suddenly, which results in "jerk" and may induce a loss of traction that could have just as easily been avoided if the clutch had been depressed and the service brake used. There really just isn't any good reason to engine brake under conditions of decreased traction. On a side note, I'm interested to know whether or not the torque splitting that many center differentials utilize applies in the opposite direction as well. I suspect that it does. In that case, even with AWD, the force applied during engine braking is still greater on certain wheels than others (most likely the rear), and therefore lends support to my argument against the use of engine braking. Last edited by educated_layman; 03-09-2015 at 07:12 PM.. Reason: addition; clarity |
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03-10-2015, 10:48 AM | #138 |
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I am referring to stopping on a downhill in slippery conditions. The chance of locking up the brakes and slipping when you engine brake, is zero. The chance of locking up the brakes and sliding when you try to use just the brakes on a downhill in these same conditions, while slim if you are very careful, is not zero.
The nervous feeling you get when driving on a steep downslope in the snow towards a stop sign with cars traversing the road in front of you is almost eliminated for me when I engine brake to a crawl before touching the brakes. I also find that when driving on the highways at speeds 30-50 while in slush/snowstorm conditions, using engine braking instead of needing to touch the brakes everytime I see car brake lights ahead makes me feel better as well. Ive used this method in dozens of storms over 25 years of driving in the Northeast. No issues. Ive never owned snow tires, and until 8 years ago never owned an AWD car(only FWD). Just my personal experience
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03-10-2015, 11:20 AM | #140 | |
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03-10-2015, 12:00 PM | #141 | |
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Everyone is free to get snow tires if they like. Just giving my experiences for those who have AWD and don't have snows, and how to easily manage it.
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03-10-2015, 01:15 PM | #143 | |
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There is no comparison. With the exception of climbing very steep grades in deep snow, my RWD with studless winter snow tires outperforms my Subaru AWD with DWS tires. For a manual car or an automatic car that cannot rev-match downshift, you risk locking up your wheels momentarily when downshifting. If you are a decent driver and can modulate your brake, your risk of lockup is equal to your skill level. Foot brake offers the driver substantially more control than engine braking. I didn't need to engine brake when I drove the Subaru Legacy GT in the snow either. If you can't use the brake without going into a lockup, you either need to get rid of your summer tires or you need to attend a few car control clinics. With studless winter tires, your braking threshold before locking up is so much higher that engine braking becomes unnecessary. And even if you do lock up, you can recovery so much more easily and quickly that it's not a concern. What you're forgetting about using your foot brake vs. strictly engine braking is that on a highway, you need to assume other drivers are idiots. If you are solely engine braking, your brake light is not lit. People who are not paying attention behind you may not realize that you are actually slowing down until too late and rear-end you. This is a video of RWD + studless snow tires at highway speeds on a hard snow packed surface. No where did I need to engine brake. This would not be possible in my Subaru Legacy GT AWD with Continental DWS tires. Last edited by Polo08816; 03-10-2015 at 01:25 PM.. |
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03-10-2015, 11:41 PM | #144 | |
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On a separate note, today was a surprisingly warm day here. Starting to look and feel like our record-breaking cold winter is almost behind us. I can't wait to remove the winter tires and put on a brand new set of Michelin PSS tires. Good times ahead.
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