Downshifting: Why Reduce Speed Before Stop?

Hi!

Since historical regulations have already been brilliantly analyzed and debunked as myths (see the 'Low RPM' discussion) in this forum, I'd like to ask the forum about the reason for a similar habit:

Many people driving a vehicle approaching a clear stopping point do the following: They downshift without applying any load, shifting gears one by one, causing the engine to roar with each gear change (first the synchronizer ring, then the engine), and the vehicle jerks slightly each time.

I've never driven like this before. I'm a hardcore sailor, and besides, my first car, a Trabant, had a freewheel in 4th gear anyway. That was extremely practical because, on mixed driving conditions, you didn't have to take the gear out or use the clutch (4th gear engaged at 50 km/h, so it was also suitable for towns).

My girlfriend used to drive my car like that at first (4.-3.-2.-1.), but I got her out of the habit. She said she learned it that way in driving school.

Okay, here's my question to the forum: What is the technical/historical background of this habit? I mean, brakes are clearly there for braking, and a worn-out transmission/clutch will certainly be more expensive than a 10% increase in brake pad wear. In addition, there's the noise pollution and the jolting when engaging the clutch. Speaking of brake pad wear: My first brake pads lasted 60,000 km. So, sailing plus using the brakes can't possibly be *that* damaging to the brake pads, right?!

By the way, the pinnacle of this driving style is when you briefly accelerate after each gear change.

I completely agree, that's utter nonsense. I also shift directly from 5th to 3rd or 2nd, depending on the vehicle's speed.

At driving schools, instructors are usually happy when a student can master the sequences 1-2-3-4-5 and 5-4-3-2-1. Specifically, if the student doesn't come to a complete stop but only slows down to 30-40 km/h, the driving school method ensures that the correct gear is selected when it's time to accelerate again. Without a tachometer and a quiet engine, a wrong gear selection using the 5-4-3-2-1 method is also less likely.

When Formula 1 cars still had manual gearboxes (which wasn't that long ago), there were two camps: those who believed in 'shifting every gear' and those who advocated for 'choosing the right gear.'
Gerhard Berger, for example, was a 'real clutch saver' because he wanted to protect his clutch.

Okay, this is how I learned it at driving school: Whenever possible, skip gears. I was actually never supposed to shift directly from 1st to 2nd to 3rd to 4th to 5th (although I did it once, just to try it). Nowadays, I do it like this: Sometimes I shift directly from 1st to 2nd to 3rd to 4th to 5th, sometimes I skip two gears, and sometimes I rev the second gear a bit more and then immediately shift into fifth. When downshifting, I always stay in fifth gear until just below 50 (km/h), then I shift to second and let the car coast.

Best regards, WarLord.

Oh my...

This is yet another fundamental issue. It has already been extensively debated in the German-speaking forums.

result: there are no compelling arguments to be made for either option.

The advantage of the 54321 method is that even inexperienced drivers will have the correct gear readily available before the vehicle comes to a complete stop.
It's possible that this method also originated when engines didn't have such a wide operating speed range.

The only real advantage of the 5-4 method is the reduced wear on the clutch and synchronizers. However, based on my experience as a mechanic, I can say that there are no significant differences in wear between vehicles using different shifting methods. Over time, you get to know the different driving styles of your customers, and all styles are represented. But we rarely see synchronizer failures, and when we do, it's usually with drivers who are reckless and aggressive (typically young men, 18-25, who think they're Schumachers).
Clutch failures are rare and cannot be solely attributed to driving style. One person is a construction contractor and has almost 400,000 km (248,550 miles) on their Audi A6 (2.6L engine) with the original clutch and transmission. Others have experienced clutch failure after 120,000 km (74,564 miles) because they consistently start the car at 5000 rpm, which lasts for 300 meters (a housewife).

Extensive research has been conducted to determine whether engine braking (deactivating the engine's power) reduces fuel consumption or not (since it often leads to stopping more frequently than coasting). Similarly, comparisons have been made between the wear and tear on the clutch and synchronizers versus that of the brakes, but all these efforts have yielded inconclusive results.

Sometimes I even manually turn off the automatic system. This is especially true in the city, where traffic, despite all predictions, often comes to a standstill (due to traffic lights, pedestrians, or elderly people). In those situations, it doesn't matter whether you decelerate using the engine or the brakes; in fact, it would even be more fuel-efficient to use the engine.

I've only blown out one clutch and one synchronizer ring so far, and they've earned their money .

otherwise, I would naturally recommend an automatic .

CU Gremlin.

Automatic transmission wouldn't be for me.

Best regards, WarLord.

Extensive and lengthy efforts have been made to determine whether engine braking reduces fuel consumption (by deactivating the engine's power) or not (because one tends to come to a stop more quickly than when coasting). Similarly, the wear and tear on the clutch and synchronizers has been compared to that of the brakes. All of this has yielded no conclusive results.

I personally never use the motor for braking, not even on a flat surface or with a gentle downhill slope. Sailing or gliding is a much more pleasant experience than constantly feeling the vehicle being held back by the roaring and braking motor (the 4-3-2-1 method). Furthermore, I can control the braking force much more precisely with the foot brake than with the motor and gears. Also, the foot brake is silent. Finally, it saves me the unnecessary work of shifting gears.

'Besides, I didn't buy the motor to use as a brake. Every rotation should provide me with energy, not consume it. I'm too precious to waste it as a brake.'

ideeAlist wrote:

Furthermore, I didn't buy the motor for braking. Every rotation it makes should provide me with energy, not consume it. I'm too precious to waste it as a brake.

Diesel waster!!
Your engine saves the most fuel when it's coasting.

By the way, if you ever ride a tandem bike, you'll quickly start using the engine brake. If you've ridden down a long downhill stretch with your foot on the brake, and a child suddenly runs in front of you at the bottom, and you can't stop because your brakes are glowing --- have fun.
Then exactly what happened to the tanker truck in Herborn will happen to you. It was unable to downshift!

Your engine saves the most fuel when it's running in the optimal speed range.

'That's incorrect. Since the engine is using its power to counteract thrust and dissipate kinetic energy, it's essentially burning the fuel it previously used to accelerate. (It's almost like it's wasting the fuel after the fact). So, it's a simplistic calculation to completely forgo braking during glide mode, meaning starting the glide very early before reaching a town. There's a trade-off between the idle fuel consumption during gliding and the longer period of driving under load. However, I don't believe that the longer period of driving under load is offset by the brief period of thrust reduction.'

When driving articulated vehicles or heavy-duty trucks downhill, the situation is different, and it becomes a safety-critical issue. Trucks are equipped with special engine brakes. Therefore, in cases of extreme and prolonged braking, the engine brake must assist the entire braking system to ensure the operational safety of the wheel brakes at all times.

Hello,

It's strange that my MFA (Multi-Function Display) is showing a fuel consumption of 0 liters while I'm driving.
Could it perhaps be that these engines already have something like "thrust cutoff"?

Heavy-duty trucks also have an additional retarder (either electric or hydraulic). For example, tank trucks are required to have a hydraulic retarder. This is much more powerful than the engine brake and can also be adjusted in terms of its strength.

Michael II wrote:

Hello, It's strange that my MFA (Multi-Function Display) is showing a fuel consumption of 0 liters while I'm driving. Could it perhaps be that these engines already have something like "thrust cutoff"?

So, I'm experiencing the same thing .

ideeAlist wrote:

Quote: Your engine saves the most fuel when it's running at a steady speed. Mistake. Since the engine, during the thrust phase, is occupied with dissipating kinetic energy, it essentially burns up exactly the fuel it previously put into acceleration. (it essentially wastes the fuel posthumously).

... which is a shame because the EDC doesn't inject diesel when it's in boost mode. So, what fuel are you wasting? The fuel that isn't being pumped? I'd check my fuel tank for leaks!

Quote:

Therefore, we have idle consumption during gliding versus longer periods of operation under load.

What idle fuel consumption? There isn't any! You wouldn't depress the clutch pedal if you don't need any more forward motion, would you?

Quote:

So, we have idle consumption during gliding versus longer operation under load. But I don't think that the longer operation under load is compensated for by the brief thrust cut-off.

Then get in a car with a fuel consumption display and drive it. You'll quickly realize that while strong acceleration leads to extremely high fuel consumption, the average consumption drops just as drastically when you're coasting afterwards.

The key is consistency, and that includes the acceleration phase.

The "oversimplified calculation," as you call it, is perfectly correct; otherwise, you wouldn't arrive at the stated consumption value.

Case 1: A car is accelerated to 50 km/h and then allowed to coast to a stop.
Case 2: A car is accelerated to 50 km/h and then brought to a stop using full braking.
For both scenarios, we assume that the energy required to accelerate the car to 50 km/h is always the same (assuming we are neglecting air resistance and rolling resistance).
In case 2, the motor energy is completely converted into braking energy, and you come to a stop approximately 15 meters after the end of the acceleration phase.
In scenario 1, you'll travel several hundred meters further, and the energy you would normally use for braking is now being recovered and used to power the motor, just as you described above.
In which case is the amount of heat consumed lower (despite the same total consumption)?
The energy you expend when braking is enormous, and the engine doesn't need that much fuel to compensate.
Calculate how much energy a car weighing 1500kg consumes when braking, and you'll quickly realize that this energy could be used in other ways (even if it's just 10% of it!).

Extensive and lengthy efforts have been made to determine whether engine braking reduces fuel consumption (by deactivating thrust) or not (because one tends to come to a stop more quickly than when coasting). Similarly, the wear and tear on the clutch and synchronizers has been compared to that of the brakes. All of this has yielded no conclusive results.

I personally never use the motor for braking on a flat stretch of road. Not even on a gentle downhill. Sailing or gliding is a much more pleasant feeling than constantly feeling the vehicle being held back by the roaring and braking motor (the 4-3-2-1 method). Furthermore, I can control the braking force much more precisely with the foot brake than with the motor and gears. Also, the foot brake is silent. Finally, it saves me the unnecessary work of shifting gears.

Furthermore, I didn't buy the motor for braking. Every rotation it makes should provide me with energy, not consume it. I'm too precious to waste it as a brake.

Please review my previous quoting again.

Do you notice anything? There is NO CONCLUSIVE RESULT.

Why? Because the driving system knows ALL possible conditions. No matter which method has which advantage, it can only utilize that advantage if the accompanying circumstances are ALWAYS the same.

'And especially in urban traffic, they are never like that. If I see the traffic light ahead turning red, or someone wants to turn left, etc., I even disengage the automatic system and use the engine to brake, because I have to brake anyway. So, method 1 is the norm in regular traffic.'

I almost never have an opportunity to use method 2.

CU Gremlin.