4 ms·

Only works on stick shifts.

by roel_v 14y ago

mpyne 14y ago
It also works on automatics that can be command-shifted, which are becoming somewhat more common.
TorKlingberg 14y ago
Some automatic transmissions allow the driver to force a lower gear to engine break. It is not used as often, but can be useful in long slopes to avoid overheating the breaks and reduce wear.
- roel_v 14y ago
  AFAIK mine does it automatically (i.e., when driving down a slope, it engine brakes to avoid acceleration). Then again we don't have that many slopes so maybe I misinterpreted what was happening the few times I drove down a parking garage :)
  - luser001 14y ago
    What car? Without cruise control? My car doesn't downshift unless I've set it on cruise control at an intermediate speed like 55 mph and it is a long downhill slope. I understand why: it's most efficient to drive in the highest gear even at speeds as low as 45 mph in a manual. I would imagine it's similar for automatics too.
    - roel_v 14y ago
      2006 BMW X3, yes without cruise control on. I'm not sure if it downshifts - what I meant was that the transmission adjusts itself to brake on the engine when coasting downhill, so that you don't have to brake in order to not accelerate downhill.
      - OldSchool 14y ago
        Interesting, I first saw this automatic trans behavior as early as about Y2K in a midrange Mercedes but only with the cruise control on, and it did actually downshift to set up the engine braking effect. I've never encountered it with cruise control off though. Ford trucks with a Tow/Haul button enabled will do exactly what you describe though, especially if you tap the brake for an instant while going downhill.
      - bradleyland 14y ago
        I can vouch for this; I think this is a BMW thing. Our 2012 X3 does the same thing. If you let off the gas while going down hill, you can see the RPMs on the tach rise as the transmission downshifts. I was really pleased with the feature on a trip to Asheville last fall.
  - deleted 14y ago
    [deleted]
monochromatic 14y ago
Every automatic I've ever seen allows you to shift to a lower gear.
- roel_v 14y ago
  Not unconditionally - yes you can switch to a 'manual' mode, but it won't let you e.g. shift to 1st gear when you're driving 100. The manual shifting is useful when driving on steep slopes, mostly. Furthermore, the gear selector certainly won't let you slip the clutch a little bit, like what you need for engine braking.
  - X-Istence 14y ago
    You shouldn't be slipping the clutch while engine braking. At that point you are simply moving the braking from the brake pads/rotors which are designed for it to the clutch disk/friction material... which is definitely not designed for it. Engine braking works well when you rev-match as you downshift, then when in the lower gear simply let off the gas completely. You will slow down, and at that point your drive/axle is pretty much directly connected to the engine which is simply turning without gas being injected into it, thus using the compression cycle to slow you down. In a manual car you don't want to shift to 1st gear when you are driving 100. That's bloody insane (Whether that is 100 km/h or 100 mph).
    - roel_v 14y ago
      You're driving 100, in 5th. You want to decelerate, so you press down the clutch, put the stick into 4th gear, then slowly release the clutch until you feel it gripping, and you do this until the rpms are low enough to switch to the 3rd in the same way. I don't know much about cars, but that process seems to be what you mean by 'rev matching'. While doing that, the clutch is slipping (even if just a bit), that's what I meant. I think you think I was saying that you switch to 1st and let the clutch come up until you stand still, but that's not what I meant.
      - X-Istence 14y ago
AUmrysh 14y ago
My auto Mazda 3 has 'manumatic' shifting, and you can downshift to slow down in it. I guess it's not really the same though as the computer does a lot of shifting and timing for you even in manumatic mode.
- woogley 14y ago
  I have this same car and exclusively use this technique in tunnel traffic. The computer has saved me a few times from accidentally shifting into 1st gear at 40mph ..
sageikosa 14y ago
Ford Freestyle with continuously variable transmission. Revs the engine way up on downhills.
X-Istence 14y ago
And every single last automatic. Besides D there is always a couple others, like 1, 2, 3 that are used for getting out of sticky situation or when you need a lot of torque... those also apply for engine braking. Do I suggest engine braking in an automatic in the general case? No, generally because the torque converter isn't too happy unless it was specifically designed for it. However if you are going down a steep mountain you better downshift even in an automatic and use the engine, or when you get to the bottom your rotors will be glowing red, your brake pads will be disintegrated, your brake fluid will be boiling and your car will be smelled from miles away. Yes, I have seen people brake all the way down the I-70 coming over the vail pass in Colorado, and it isn't pretty... if it doesn't break everything your rotors are going to be warped completely...
- luser001 14y ago
  Kids, listen to this man. :) When I was newbie, I didn't downshift and was instead keeping the brakes lightly pressed. After a few mins of this, when I pressed them a little harder to slow down more (at a turn), the pedals sickeningly went way more than they were supposed to. Remembered in a flash what had happend. Thankfully, I was able to pull over and let the brakes cool a bit. The brake fluid had overheated and turned into a compressible liquid (if you remember your Pascal's Law (iirc), hydraulics can only work if the fluid is nearly incompressible).
  - X-Istence 14y ago
    Eh, I'm 24 years old ... in the crowd here on HN I would be considered part of that "kids" :P

Only works on stick shifts.

by roel_v 14y ago

Only works on stick shifts.

mpyne 14y ago

It also works on automatics that can be command-shifted, which are becoming somewhat more common.

TorKlingberg 14y ago

Some automatic transmissions allow the driver to force a lower gear to engine break. It is not used as often, but can be useful in long slopes to avoid overheating the breaks and reduce wear.

roel_v 14y ago
AFAIK mine does it automatically (i.e., when driving down a slope, it engine brakes to avoid acceleration). Then again we don't have that many slopes so maybe I misinterpreted what was happening the few times I drove down a parking garage :)
- luser001 14y ago
  What car? Without cruise control? My car doesn't downshift unless I've set it on cruise control at an intermediate speed like 55 mph and it is a long downhill slope. I understand why: it's most efficient to drive in the highest gear even at speeds as low as 45 mph in a manual. I would imagine it's similar for automatics too.
  - roel_v 14y ago
    2006 BMW X3, yes without cruise control on. I'm not sure if it downshifts - what I meant was that the transmission adjusts itself to brake on the engine when coasting downhill, so that you don't have to brake in order to not accelerate downhill.
    - OldSchool 14y ago
      Interesting, I first saw this automatic trans behavior as early as about Y2K in a midrange Mercedes but only with the cruise control on, and it did actually downshift to set up the engine braking effect. I've never encountered it with cruise control off though. Ford trucks with a Tow/Haul button enabled will do exactly what you describe though, especially if you tap the brake for an instant while going downhill.
    - bradleyland 14y ago
      I can vouch for this; I think this is a BMW thing. Our 2012 X3 does the same thing. If you let off the gas while going down hill, you can see the RPMs on the tach rise as the transmission downshifts. I was really pleased with the feature on a trip to Asheville last fall.
- deleted 14y ago
  [deleted]

monochromatic 14y ago

Every automatic I've ever seen allows you to shift to a lower gear.

roel_v 14y ago
Not unconditionally - yes you can switch to a 'manual' mode, but it won't let you e.g. shift to 1st gear when you're driving 100. The manual shifting is useful when driving on steep slopes, mostly. Furthermore, the gear selector certainly won't let you slip the clutch a little bit, like what you need for engine braking.
- X-Istence 14y ago
  You shouldn't be slipping the clutch while engine braking. At that point you are simply moving the braking from the brake pads/rotors which are designed for it to the clutch disk/friction material... which is definitely not designed for it. Engine braking works well when you rev-match as you downshift, then when in the lower gear simply let off the gas completely. You will slow down, and at that point your drive/axle is pretty much directly connected to the engine which is simply turning without gas being injected into it, thus using the compression cycle to slow you down. In a manual car you don't want to shift to 1st gear when you are driving 100. That's bloody insane (Whether that is 100 km/h or 100 mph).
  - roel_v 14y ago
    You're driving 100, in 5th. You want to decelerate, so you press down the clutch, put the stick into 4th gear, then slowly release the clutch until you feel it gripping, and you do this until the rpms are low enough to switch to the 3rd in the same way. I don't know much about cars, but that process seems to be what you mean by 'rev matching'. While doing that, the clutch is slipping (even if just a bit), that's what I meant. I think you think I was saying that you switch to 1st and let the clutch come up until you stand still, but that's not what I meant.
    - X-Istence 14y ago

AUmrysh 14y ago

My auto Mazda 3 has 'manumatic' shifting, and you can downshift to slow down in it. I guess it's not really the same though as the computer does a lot of shifting and timing for you even in manumatic mode.

woogley 14y ago
I have this same car and exclusively use this technique in tunnel traffic. The computer has saved me a few times from accidentally shifting into 1st gear at 40mph ..

sageikosa 14y ago

Ford Freestyle with continuously variable transmission. Revs the engine way up on downhills.

X-Istence 14y ago

And every single last automatic. Besides D there is always a couple others, like 1, 2, 3 that are used for getting out of sticky situation or when you need a lot of torque... those also apply for engine braking. Do I suggest engine braking in an automatic in the general case? No, generally because the torque converter isn't too happy unless it was specifically designed for it. However if you are going down a steep mountain you better downshift even in an automatic and use the engine, or when you get to the bottom your rotors will be glowing red, your brake pads will be disintegrated, your brake fluid will be boiling and your car will be smelled from miles away. Yes, I have seen people brake all the way down the I-70 coming over the vail pass in Colorado, and it isn't pretty... if it doesn't break everything your rotors are going to be warped completely...

luser001 14y ago
Kids, listen to this man. :) When I was newbie, I didn't downshift and was instead keeping the brakes lightly pressed. After a few mins of this, when I pressed them a little harder to slow down more (at a turn), the pedals sickeningly went way more than they were supposed to. Remembered in a flash what had happend. Thankfully, I was able to pull over and let the brakes cool a bit. The brake fluid had overheated and turned into a compressible liquid (if you remember your Pascal's Law (iirc), hydraulics can only work if the fluid is nearly incompressible).
- X-Istence 14y ago
  Eh, I'm 24 years old ... in the crowd here on HN I would be considered part of that "kids" :P