5 ms·

And manual transmission cars kinda, though the energy is still wasted of course

by frollogaston 1y ago

OptionOfT 1y ago
Depends on how you drive. I never engine braked on my manual. Brakes are easy to replace. Clutches are not.
- eptcyka 1y ago
  You need not burn your clutch to engine break.
- hassaanr 1y ago
  engine braking does not have any effect on the clutch, other than while downshifting, which if you're blipping/rev-matching has practically no effect
  - isoprophlex 1y ago
    Exactly, if your clutch suffers abuse when you are shifting gears (unless you're trying to aggressively accelerate of course) you need to rethink what you're doing. Not saying it's smart but when predictably decelerating on the highway I sometimes shift gears by rev matching and changing without even touching the clutch, for the fun of it.
    - stouset 1y ago
      Same on a motorcycle. My current bike has a quickshifter (for both up and down shifting) but even without one you can shift up and down without ever touching the clutch just by pushing on the shift pedal while blipping the throttle off-and-on (for an upshift) or on-and-off (for a downshift). That’s all the quickshifter is really doing anyway, it’s just quicker at it than you are. I’d wager bordering on 100% of my clutch use is when coming to a complete stop.
- MindSpunk 1y ago
  You don't engine brake with the clutch, you engine brake by downshifting and using the higher engine RPM in lower gears to brake the car via wasted compression.
  - dotancohen 1y ago
    And that downshifting involves a clutch operation, moving the engine into a higher RPM. That most certainly wears down the clutch, talking as someone who's replaced quite a few of them.
    - throwawaysoxjje 1y ago
      Are you really shifting so much that your clutch slip in the middle of the shift effects clutch lifetime?
    - beau_g 1y ago
      I've seen an interesting A-B test with this seeing the difference in clutch wear between the Ferrari F1 transmission in the 599 and 612 and the DuoSelect transmission which is essentially the same box in the Quattroporte. The shifting strategy and technique is more of a controlled variable here because the shifting is automatic though it's a somewhat traditional manual gearbox with hydraulic actuation. The QP is a bit heavier but the Ferraris make a lot more power. From what I saw the cars that fared far worse were the Quattroportes, and those that ate the most clutches by far were the ones putting around the city, especially in San Francisco, Marin, Los Altos Hills, etc. where people are slowly creeping into parking spots on hills. On the Ferraris that are weekend warriors that get driven hard the clutches could go 30k+ miles no problem, Quattroportes would come in with smoked clutches in a few thousand miles sometimes.
      - jve 1y ago
        Sorry, ain't native: Which car use downshifting to help braking? Cannot wire in my brains whether this example is pro-downshift braking or not.
- 01100011 1y ago
  Yep, years ago I had a friend with a VW Beetle and he'd never use the brakes unless he had to. I thought it was cool and carried the story with me. One day I mentioned it to a mechanic friend and that was his exact response. I've never changed a clutch, but I've changed plenty of brakes and yeah, not hard or expensive.
- isoprophlex 1y ago
  You don't need to touch your clutch to do engine breaking. If you wear out your clutch by shifting gears you're doing something wrong
- michaelcampbell 1y ago
  You engine brake every time you lift off the throttle and don't depress the clutch. I know what you mean here of course, but I suspect your driving habits are saving you less than you think.
cloverich 1y ago
Surprisingly you can get nearly same effect in automatics. I put around 60k miles on my first automatic (after120k+ on my first two cars, manual transmissions) and when i got my brakes checked at 63k they noted my brakes were still "brand new". I do gamify reading traffic to try and brake as little as possible (to help pass time etc), but was still surprised how far this takes you given i do plenty of stop and go traffic driving. This was a v6 sedan so lighter than an suv / truck. I expected it to not work in automatics but it does to at least some extent. I swapped for an EV before taking it the usual distance and curious if anyones pushed further and how far.
- MindSpunk 1y ago
  It's not "nearly". It's exactly the same effect. Compression braking. Even if you're not on the throttle the engine is still rotating as it's connected to the wheels. If the engine is rotating it is compressing air. If it's compressing air but not igniting fuel (throttle closed) then it will suck energy out of the wheels to compress the air. You can do it in an automatic, you just have to force it to select a lower gear using the gear number options (1, 2, 3, 4) or using the tiptronic mode. The lower gear means the engine will displace more air in the same amount of time, increasing the rate it pulls energy from the wheels. People think you can't do it in automatics because they try very hard to keep engine RPM low where the effect is diminished.
  - peterbecich 1y ago
    Related to this: https://en.wikipedia.org/wiki/Compression_release_engine_brake?wprov=sfla1 https://en.wikipedia.org/wiki/Compression_release_engine_bra...
  - agurk 1y ago
    If it takes energy to compress the air in the cylinder - doesn't it also release most of that energy when that compressed air is expanded on the subsequent stroke? If you release the compressed air without pushing the cylinder down you would lose that energy, but you would need a extra device to do so (by lifting a valve at the right time). This option does exist for large vehicles like trucks as a compression release engine brake [0], but this isn't something you'd have on a family car. In a petrol engine you always want the same ratio of petrol to air in the mix that is taken into a cylinder. As you want to vary the amount of fuel, and therefore power developed, you have to be able to therefore limit the amount of air that is sucked in. Otherwise the engine would always run at full power. There is a mechanical restrictor called a throttle plate that lives inside the throttle body that restricts how much air the cylinder can pull in (and therefore how much fuel is injected to get the same fuel/air mix). This is controlled by the throttle. When you are coasting, this plate is in its most closed position. This creates significant resistance on the intake stroke, and is where the majority of energy is lost during engine braking. This is also known as a pumping loss. Diesels always intake the same amount of air, so they can compress it enough to autoignite the fuel. They vary the amount of fuel injected to the same volume of air. This means no throttle body or plate, so unless an extra exhaust restrictor has been added there is minimal engine braking on a diesel engine. [0] https://en.wikipedia.org/wiki/Compression_release_engine_brake https://en.wikipedia.org/wiki/Compression_release_engine_bra...

And manual transmission cars kinda, though the energy is still wasted of course

OptionOfT 1y ago

Depends on how you drive. I never engine braked on my manual. Brakes are easy to replace. Clutches are not.

eptcyka 1y ago
You need not burn your clutch to engine break.
hassaanr 1y ago
engine braking does not have any effect on the clutch, other than while downshifting, which if you're blipping/rev-matching has practically no effect
- isoprophlex 1y ago
  Exactly, if your clutch suffers abuse when you are shifting gears (unless you're trying to aggressively accelerate of course) you need to rethink what you're doing. Not saying it's smart but when predictably decelerating on the highway I sometimes shift gears by rev matching and changing without even touching the clutch, for the fun of it.
  - stouset 1y ago
    Same on a motorcycle. My current bike has a quickshifter (for both up and down shifting) but even without one you can shift up and down without ever touching the clutch just by pushing on the shift pedal while blipping the throttle off-and-on (for an upshift) or on-and-off (for a downshift). That’s all the quickshifter is really doing anyway, it’s just quicker at it than you are. I’d wager bordering on 100% of my clutch use is when coming to a complete stop.
MindSpunk 1y ago
You don't engine brake with the clutch, you engine brake by downshifting and using the higher engine RPM in lower gears to brake the car via wasted compression.
- dotancohen 1y ago
  And that downshifting involves a clutch operation, moving the engine into a higher RPM. That most certainly wears down the clutch, talking as someone who's replaced quite a few of them.
  - throwawaysoxjje 1y ago
    Are you really shifting so much that your clutch slip in the middle of the shift effects clutch lifetime?
  - beau_g 1y ago
    I've seen an interesting A-B test with this seeing the difference in clutch wear between the Ferrari F1 transmission in the 599 and 612 and the DuoSelect transmission which is essentially the same box in the Quattroporte. The shifting strategy and technique is more of a controlled variable here because the shifting is automatic though it's a somewhat traditional manual gearbox with hydraulic actuation. The QP is a bit heavier but the Ferraris make a lot more power. From what I saw the cars that fared far worse were the Quattroportes, and those that ate the most clutches by far were the ones putting around the city, especially in San Francisco, Marin, Los Altos Hills, etc. where people are slowly creeping into parking spots on hills. On the Ferraris that are weekend warriors that get driven hard the clutches could go 30k+ miles no problem, Quattroportes would come in with smoked clutches in a few thousand miles sometimes.
    - jve 1y ago
      Sorry, ain't native: Which car use downshifting to help braking? Cannot wire in my brains whether this example is pro-downshift braking or not.
01100011 1y ago
Yep, years ago I had a friend with a VW Beetle and he'd never use the brakes unless he had to. I thought it was cool and carried the story with me. One day I mentioned it to a mechanic friend and that was his exact response. I've never changed a clutch, but I've changed plenty of brakes and yeah, not hard or expensive.
isoprophlex 1y ago
You don't need to touch your clutch to do engine breaking. If you wear out your clutch by shifting gears you're doing something wrong
michaelcampbell 1y ago
You engine brake every time you lift off the throttle and don't depress the clutch. I know what you mean here of course, but I suspect your driving habits are saving you less than you think.

cloverich 1y ago

Surprisingly you can get nearly same effect in automatics. I put around 60k miles on my first automatic (after120k+ on my first two cars, manual transmissions) and when i got my brakes checked at 63k they noted my brakes were still "brand new". I do gamify reading traffic to try and brake as little as possible (to help pass time etc), but was still surprised how far this takes you given i do plenty of stop and go traffic driving. This was a v6 sedan so lighter than an suv / truck. I expected it to not work in automatics but it does to at least some extent. I swapped for an EV before taking it the usual distance and curious if anyones pushed further and how far.

MindSpunk 1y ago
It's not "nearly". It's exactly the same effect. Compression braking. Even if you're not on the throttle the engine is still rotating as it's connected to the wheels. If the engine is rotating it is compressing air. If it's compressing air but not igniting fuel (throttle closed) then it will suck energy out of the wheels to compress the air. You can do it in an automatic, you just have to force it to select a lower gear using the gear number options (1, 2, 3, 4) or using the tiptronic mode. The lower gear means the engine will displace more air in the same amount of time, increasing the rate it pulls energy from the wheels. People think you can't do it in automatics because they try very hard to keep engine RPM low where the effect is diminished.
- peterbecich 1y ago
  Related to this: https://en.wikipedia.org/wiki/Compression_release_engine_brake?wprov=sfla1 https://en.wikipedia.org/wiki/Compression_release_engine_bra...
- agurk 1y ago
  If it takes energy to compress the air in the cylinder - doesn't it also release most of that energy when that compressed air is expanded on the subsequent stroke? If you release the compressed air without pushing the cylinder down you would lose that energy, but you would need a extra device to do so (by lifting a valve at the right time). This option does exist for large vehicles like trucks as a compression release engine brake [0], but this isn't something you'd have on a family car. In a petrol engine you always want the same ratio of petrol to air in the mix that is taken into a cylinder. As you want to vary the amount of fuel, and therefore power developed, you have to be able to therefore limit the amount of air that is sucked in. Otherwise the engine would always run at full power. There is a mechanical restrictor called a throttle plate that lives inside the throttle body that restricts how much air the cylinder can pull in (and therefore how much fuel is injected to get the same fuel/air mix). This is controlled by the throttle. When you are coasting, this plate is in its most closed position. This creates significant resistance on the intake stroke, and is where the majority of energy is lost during engine braking. This is also known as a pumping loss. Diesels always intake the same amount of air, so they can compress it enough to autoignite the fuel. They vary the amount of fuel injected to the same volume of air. This means no throttle body or plate, so unless an extra exhaust restrictor has been added there is minimal engine braking on a diesel engine. [0] https://en.wikipedia.org/wiki/Compression_release_engine_brake https://en.wikipedia.org/wiki/Compression_release_engine_bra...