| ▲ | frollogaston 2 days ago |
| And manual transmission cars kinda, though the energy is still wasted of course |
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| ▲ | OptionOfT 2 days ago | parent | next [-] |
| Depends on how you drive. I never engine braked on my manual. Brakes are easy to replace. Clutches are not. |
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| ▲ | MindSpunk 2 days ago | parent | next [-] | | 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 2 days ago | parent | next [-] | | 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. | | |
| ▲ | beau_g 2 days ago | parent | next [-] | | 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. | | |
| ▲ | dotancohen a day ago | parent | next [-] | | Everything on the QPs was always breaking. I've never driven an automatic Ferrari or paddle shifted Ferrari to compare, but the QP that I drove (Ferrari V-8, I think that it even said Ferrari on the valve covers maybe) didn't have anything outstanding about the transmission that I remember. I thought it was a regular hydraulic automatic with a torque converter, so they really did tune it nicely. The robotic Toyotas I could feel. Maybe had they not tuned it so nicely it might have lasted longer? | | |
| ▲ | frollogaston a day ago | parent [-] | | Only the 2004-2006 and maybe some 2007 QPs came in automated manual. Anything after was regular automatic w/ torque converter. |
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| ▲ | jve 2 days ago | parent | prev | next [-] | | 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. | | |
| ▲ | masklinn 2 days ago | parent [-] | | I think their point is that you eat clutch when you slip it e.g. when you’re getting in and out if parking on hills, or in city stop and go traffic. When the clutch is fully engaged there’s little wear even hard-driving, and doing a straight in-and-out does not bother clutches much. Hence Quattroportes eating clutches like nobody’s business while the harder-ridden higher-power Ferraris don’t. As such downshifting would not wear clutches much. And anecdotally I’ve never suffered from or heard of engine braking causing clutch issues. |
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| ▲ | frollogaston 2 days ago | parent | prev [-] | | I semi-daily drive a DuoSelect Quattroporte, but usually in light traffic. The clutch-eating problem is sorta inherent to the car. First off, it uses extra clutch to smooth out shifts in non-sport mode, and you don't always want sport mode because it stiffens the suspension a lot. But even in sport, you can't always get it to behave predictably. So given an experienced driver with both cars in city traffic, the DuoSelect will eat clutch faster than a stick. Some install an aftermarket box (Formula Dynamics) to improve this, but still. Idk how the Ferraris are different. They're lighter at least. Think they also have a different version of the "Superfast" software. Anyway... I do engine-brake it. The real brakes appreciate not having to stop that limo by themselves. | | |
| ▲ | frollogaston 2 days ago | parent [-] | | Forgot to clarify, there is a clutch-eating problem when driving the car properly, but it's not THE clutch-eating problem people talk about where it dies in 10-15K miles from treating the car as a regular automatic. |
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| ▲ | mort96 2 days ago | parent | prev | next [-] | | I didn't quite get if you think changing gears for the purpose of engine braking wears the clutch more than normal or not. Are you using the force from the clutch to force the engine to go from a low RPM to a high RPM? In cases like that where the difference in RPM is significant, I would press the clutch pedal, then speed up the engine by pressing the gas pedal, downshift, then release the clutch. Rev matching, basically. It does wear the clutch a teeny tiny bit, but not more than any other gear change. If your comment wasn't meant to imply that engine braking wears the clutch more than normal gearing, if you just want to avoid gear changes as much as possible, disregard this comment. (Although... I'm not sure that that's a valid worry, modern clutches last a LONG time when used properly) | | |
| ▲ | frollogaston 2 days ago | parent [-] | | You might not execute the rev-match perfectly every time, esp if you're doing a heel-toe. I think it's also harder on the synchro. | | |
| ▲ | mort96 2 days ago | parent [-] | | Sure, and I definitely don't rev-match close to perfect every time. I'm just saying you don't have to use the clutch to accelerate your motor all the way from minimum RPM, which it sounded like my parent comment might be suggesting | | |
| ▲ | frollogaston 2 days ago | parent [-] | | I think that suggestion was that you're holding the clutch pedal in longer while you bring up the RPMs, compared to upshifting which is faster. The clutch does wear a bit even when "fully" disengaged. But I don't think it matters enough here, just don't leave it like that during a red light. |
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| ▲ | throwawaysoxjje 2 days ago | parent | prev | next [-] | | Are you really shifting so much that your clutch slip in the middle of the shift effects clutch lifetime? | |
| ▲ | supportengineer 2 days ago | parent | prev | next [-] | | Clutch wear occurs when the clutch is slipping so you always want to minimize the slipping time. | |
| ▲ | wazoox 2 days ago | parent | prev | next [-] | | My 300k km Volvo S60 still runs on its original clutch, and I changed the brake pads only once. Engine braking is the way. | |
| ▲ | prmoustache 2 days ago | parent | prev | next [-] | | Most of clutch wear comes from making it slip, while accelerating from a standstill. You don't make it slip when shifting gear. | |
| ▲ | pbmonster 2 days ago | parent | prev | next [-] | | The clutch wear on a standard downshift must absolutely negligible when compared to accelerating from a full stop and especially when compared to slower-that-idle operation, i.e. parking. Also, I have never ever had to replace a clutch, and I drive my cars way past 100k miles. | |
| ▲ | potato3732842 2 days ago | parent | prev | next [-] | | Yes but actually no. It wears the clutch but clutch wear is massively dominated by starts from a stop or other cases where you actively slip it any noteworthy amount so just rowing the gears up and down doesn't do much. | |
| ▲ | NwtnsMthd 2 days ago | parent | prev [-] | | It's a negligible amount, especially if you (or your car) does rev matching. My last car (BMW 328) made it to 300k miles on the original clutch. |
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| ▲ | raverbashing 2 days ago | parent | prev [-] | | Actually you'll get some engine braking by just letting off the gas and stepping on the break. Fuel will get cut off in these cases in most cars (unless you're running a very old carburetor car) |
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| ▲ | eptcyka 2 days ago | parent | prev | next [-] | | You need not burn your clutch to engine break. | |
| ▲ | 01100011 2 days ago | parent | prev | next [-] | | 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 2 days ago | parent | prev | next [-] | | 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 | |
| ▲ | hassaanr 2 days ago | parent | prev [-] | | 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 2 days ago | parent [-] | | 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 2 days ago | parent [-] | | 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. |
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| ▲ | cloverich 2 days ago | parent | prev [-] |
| 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. |
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| ▲ | masklinn 2 days ago | parent | next [-] | | No reason for it not to work, even more so if you think to downshift. It’s more common with manual as downshifting is a lot more natural but not fundamentally different. It’s just trivially easy with electric thanks to regen braking. Though with modern cars getting heavier if you have a small ICE these days you have almost no engine brake which makes some cases more difficult (unless it’s a mild hybrid with an electric kers like some of the small engined fords). SUVs tend to have giant engines and pretty high rolling resistance, which I’d think would somewhat compensated for their higher inertia. It’s all about learning your car’s behaviour and planning for it. | | |
| ▲ | dotancohen 2 days ago | parent [-] | | I don't know about today's engines, but some early fuel injected engines would actually use more fuel when engine braking. In those early designs spark could not be cut off, so if this extra fuel were not added then the mixture would run very hot and risk pre-ignition and damage. I don't know about carbureted vehicles. | | |
| ▲ | wazoox 2 days ago | parent [-] | | It only applies to mechanical injection and carburettor engines. With electronic injection, which is the norm since the 80s, this is not a problem. |
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| ▲ | MindSpunk 2 days ago | parent | prev [-] | | 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. | | |
| ▲ | agurk 2 days ago | parent | next [-] | | 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_bra... | | |
| ▲ | potato3732842 2 days ago | parent | next [-] | | What everyone is missing is that a petrol engine is sucking against a vacuum behind the throttle blade. It's basically like an air compressor that just keeps running despite hitting max pressure and every pump just goes out the blow off valve. | |
| ▲ | MindSpunk 2 days ago | parent | prev [-] | | You're right. Petrol engines are air pumps so I should've realised the explanation wasn't correct. Though the ECU would be doing the AFR management on modern EFI engines as the injectors aren't vacuum operated like Carburetors were. You should be able to cut fuel injection when coasting in a modern engine, can't run lean if there's no fuel at all. Not sure if carbs could do the same. | | |
| ▲ | agurk 2 days ago | parent [-] | | On all the fuel injected engines I have owned there is a physical cable that controls the position of the throttle plate. There is an airflow mass sensor the other side of the plate to measure the amount of air and therefore how much fuel needs to be injected. So interestingly in these sort of engines you're really just controlling airflow to the engine rather than fuel/air mix like on one with a carburettor. More modern engines have electronically controlled throttle plates, and this is definitely somewhere you could do something clever like you suggest - cutting fuel flow but also maximising airflow when there is zero throttle input. I assume engine braking is generally considered a beneficial thing by manufacturers, but it could be fun to be able to customise the amount. Or do something like have the braking come on gently at first then harder. Maybe even try and have a linear or flat response curve vs. engine rpm. | | |
| ▲ | sokoloff 2 days ago | parent | next [-] | | > cutting fuel flow but also maximising airflow when there is zero throttle input You don't want to do this. Much of the engine braking effect is from pulling the intake air charge past the mostly closed throttle plate. On a car with a wide open throttle plate [even with no fuel], the engine is acting more like a spring than a damper. On the intake stroke, it will pull an intake air charge past the small restriction of the open intake valve(s), then compress it on the compression stroke, then release that compressed energy on the "power" stroke, then exhaust it past the small restriction of the open exhaust valves. Pushing air past the valves will cost energy, but it's not much. This is why diesel trucks' engine braking works differently. (Diesels don't have a throttle plate.) They can open the exhaust valves to prevent the energy recovery in the "power" stroke to create a higher net braking force. Jake Brake: https://en.wikipedia.org/wiki/Compression_release_engine_bra... | |
| ▲ | yetihehe 2 days ago | parent | prev | next [-] | | > Or do something like have the braking come on gently at first then harder. You can do this by letting go of gas pedal slowly. I have "current amount of fuel used" info in my car (liters/100km), it shows pretty clearly, that when going fast and slowly letting go of gas, amount of fuels slowly goes to 0. If I let go of gas fast, the engine is intelligent enough to not close throttle as fast as possible, still probably takes 1 second. > More modern engines have electronically controlled throttle plates, and this is definitely somewhere you could do something clever like you suggest - cutting fuel flow but also maximising airflow when there is zero throttle input. They cut fuel flow and close throttle plate almost completely but still allow some small amount of air, in order to actually do engine braking. If you need to coast, you can apply clutch in manual. Don't know that much about automatic, but from what I've driven, they use "lift gas" as a "engine braking" signal, so probably they can't really coast that good. | |
| ▲ | MindSpunk 2 days ago | parent | prev | next [-] | | I've got both at the moment on my two Hondas. Both manual, one with a throttle cable and one with throttle-by-wire. There's quite a bit of difference in how they handle off throttle. The cable will just slam the throttle shut if you just jump off the pedal (obviously) and it jerks pretty hard. The throttle-by-wire car hangs the throttle a little when letting off and doesn't just immediately start decelerating. Then it's much smoother once it does start slowing down. The ECU definitely doing something to smooth it out. Funny because the cars build dates are only 2 years apart, 2005 and 2007, and they're both K20 engines but the engines handle so different. | | |
| ▲ | potato3732842 2 days ago | parent [-] | | The ECU is doing that because rapid changes in state are bad for emissions. Letting you just slam the throttle closed could result in a tiny, but measurable at OEM scale, amount of extra fuel going half burnt out the tailpipe. Slamming it open can cause too lean combustion and oxide byproducts which. The OEMs try real hard to prevent this because the amounts of emissions byproducts that aren't water or C02 they're allowed to produce are on the order of single digit grams per multiple miles (you can mentally file it as "about the baseline air quality in urban areas" though the rules are hugely more complex than that) so these edge cases matter. | | |
| ▲ | tkj922 2 days ago | parent [-] | | An idling I4 has about 10 injection cycles per second. And the ECU clocks injection time corrections at least at that rate, more likely at double that rate or more. So I think that the smoothing is mostly there for the owner's wellbeing, not emissions. |
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| ▲ | vladvasiliu 2 days ago | parent | prev [-] | | > it could be fun to be able to customise the amount Some recentish motorbikes have an option to customise the amount of engine brake, I suppose cars could have something similar, too. |
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| ▲ | frollogaston 2 days ago | parent | prev | next [-] | | Auto trans downshift is designed for long hills, not downshifting frequently to stop signs etc like you'd do with a stick. Even with paddles, there's a delay, or it briefly goes neutral, or it doesn't rev-match well. Or you can't double/triple-downshift, which is worse when you have 8-12 gears. Allegedly wears them down faster too, which idk but would not be surprised if it were true given how unhappy it feels. | |
| ▲ | yakkers 2 days ago | parent | prev | next [-] | | An aside on your last point: In the D gear, a lot of auto transmissions will be set up to allow for the wheels to spin somewhat independently of the engine (in any gear) when you aren't accelerating, which accounts a lot for how well an automatic will coast when you release the throttle, even if you're not going fast enough for top gear (especially apparent with older four speed boxes). Using the numbered gear options will enable clutches/bands that provide more engine braking. | | |
| ▲ | MindSpunk 2 days ago | parent [-] | | Huh, interesting. I had thought it was just from the higher gears being used. Vast majority of my driving is with manual, I've only really driven modern autos with 5+ gears (and a Toyota hybrid, which don't really have gears at all). |
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| ▲ | vladvasiliu 2 days ago | parent | prev | next [-] | | It depends on the implementation. I ride an automatic motorbike which will downshift if I grab the brakes a bit harder, even if I'm only slowing to a speed to which it wouldn't otherwise shift. For example, if I brake somewhat hard from 130 km/h to 90, it will downshift from 6th to 5th. When riding normally, it would stay in 6th down to around 50. | |
| ▲ | bigfatkitten 2 days ago | parent | prev | next [-] | | Many modern automatics are smart enough to do this for you if you tap the brakes while rolling downhill. | |
| ▲ | peterbecich 2 days ago | parent | prev | next [-] | | Related to this: https://en.wikipedia.org/wiki/Compression_release_engine_bra... | |
| ▲ | jve 2 days ago | parent | prev [-] | | I'v bee downshifting manually with automatic especially when riding downhill. The effect with Chrysler T&C 2009 was very noticable and effective. Toyota Sienna 2015 - the braking effect is unfortunately minor. |
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