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Manual transmission is fantastic for many reasons, and one of the top reasons (in my book) is the ability to slow down ahead of red lights without touching the brakes. (And, incidentally, it is to my chagrin that most North American drivers never know the joy of driving MT, which means that the 1% of us who do must also forego it at some point.)

And so I'm a bit puzzled when I hear that lugging the engine is harmful.

I've routinely used engine braking with no harm, and so, empirically at least, I know it's perfectly alright. To be clear, I would never slow down by down-shifting and slamming the clutch. I would simply remove my foot off the gas pedal, slow a little, then shift by one, and never more than one, gear down, and gently ease into it, and so on. Often enough, lights would turn green and I would not even need to touch the brakes—plus I would have saved momentum. If this is flawed thinking because I am extending the life of the brakes and saving a bit of gas by putting extra stress on the engine, I've never felt that it does (reduce engine life).

When does slowing down by down-shifting become lugging an engine?

(Or, put more simply, suppose I make certain I never drop below, say 1200 rpm while engine-braking, could I still be lugging the engine? Already at 1500 I can hear and feel that the engine is heading towards stalling, and so I get plenty of warning to keep the rpm up.)

Aside: Nightmare scenario

It's worth adding that there is one exception to the never-more-than-one-gear-down rule. I've never done it, but I keep thinking that one of the many benefits of having manual transmission is that even if the hydraulic lines of the brakes suddenly fail and I lose all pressure, I would still have a chance of surviving a nightmare ordeal by slowing down using, say, second gear while driving at highway speeds. The transmission would almost surely become metal shards, but I would at least have a better chance of surviving.

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  • Brakes are cheaper to replace than clutch plates or thrust bearing. When driving an automatic I adjust my driving style: look further ahead and make a speed plan for the next obstruction or clear road. Slack off sooner. It will also be different for a car with regenerative braking. You are free to drive on the gears if you choose to. Others will brake and shift gear ready for the next power demand. Anyway a modern automatic's power delivery and engine braking are little different to a manual. Are you driving a 20th century design? Has the DSG box made its way across the pond?
    – Weather Vane
    Commented Nov 14, 2023 at 19:21
  • @WeatherVane There is zero stress or wear on the clutch when you engine-brake. Well, ok, it's entirely trivial, because no one can get the engine to spin at exactly the rpm that'll match the wheels for a given speed, but one can get close. But yes, regenerative braking is superior, of course. As for automatic transmission, no, I'm still eager to stay with manual for as long as possible. It's a losing proposition. They're pulling every single model with MT, year-by-year.
    – Sam7919
    Commented Nov 14, 2023 at 20:13
  • Every time you declutch there is stress on the clutch thrust bearing. You can minimise clutch plate wear by careful matching of engines speed, but there will still be some.
    – Weather Vane
    Commented Nov 14, 2023 at 20:22
  • @WeatherVane - That's really a trade off. You can either minimize wear to clutch and thrust bearing by doing what you are saying, but it will be at the cost of your synchros. I'd much rather be replacing a clutch and throwout bearing rather than doing the much bigger job of changing out synchros. I prefer to use the clutch and throwout bearing for what they were designed to do rather than forcing synchro wear under power due to the fact you can never be careful enough while changing gears. Yes, some transmissions are made to do this, but not your average standard transmission.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 14, 2023 at 20:49
  • @Pᴀᴜʟsᴛᴇʀ2 my point really was that replacing the brakes is cheaper than clutch parts, but that good anticipation and use of the throttle is even cheaper.
    – Weather Vane
    Commented Nov 14, 2023 at 21:38

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When does slowing down by down-shifting become lugging an engine?

The upfront answer is: It never will. Lugging occurs upon the attempt to accelerate using too high a gear for the speed of the vehicle. If you're trying to slow down using engine braking, you'll not lug it during that practice.

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  • @Sam7919 - Your "question" is a borderline driving technique question. By your comment, it is my opinion that's all you're really asking. I'll see what others contend.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 14, 2023 at 14:22
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    I answered your question. The question doesn't quite cross the border into driving technique. Your comment does (in my opinion). The second thing which is at issue is, you are using comments to create a secondary or follow-up question, which is bad form. That's not what comments are for.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 14, 2023 at 14:37

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