Coasting, brake riding, engine braking

[paulca]

Lots of posts about setting off in a manual and they were so much fun I thought I'd bring up the art of slowing down in a manual.

When going down a long steep hill do you:

a) stay in high gear and ride the brakes the whole way down to maintain speed?
b) clutch or neutral it and free wheel while riding the brakes
c) Down shift to a lower gear and allow the engine braking to restrain the car from gaining speed

Now consider a less steep hill, do you:

a) stay in high gear and apply a little accelerator from time to time to maintain speed
b) clutch or neutral and free wheel to maintain speed

After free wheeling for a while how do you know which gear to select when you need one?

Our highway code suggests you "should not" coast or freewheel. The reasons they give include:

1) Potential lose of steering response
2) Potential lose of brake response
3) Degraded handling of the car
4) Potential of selecting the wrong gear when you put it back into gear

The first I exclude as it relates to old cars with hydraulic power steering pumps run off an aux belt where low revs means low pressure. Two I exclude because i think it applies again to old cars that did not have servo assisted brakes and required engine braking to help you slow, also potentially old diesels that use an aux belt driven vacuum pump for the brake servo. It is however easier to lock up the wheels when coasting, to lock the rear wheels in a GT86 you need to lock up the engine as well.

3 I'm not sure about at all. The car will be in neutral balance, but that will only be a concern if you are near the limit where having the engine braking would give more grip to the front end.

4. I'm a big boy I can select the correct gear based on my road speed.

I would add one they don't. Out of gear you lack the ability to suddenly accelerate to accelerate out of trouble or avoid accident.

Yet I do freewheel a lot as it saves fuel. Our car's ECU will cut the injectors off when engine braking, so zero fuel flows, but it is still more efficient to freewheel as the engine braking will slow you down.

[ZionsWrath]

Engine brake downhill, whatever gear maintains speed.

[HeadBanger]

I live on a giant hill. My town is called Vankleek Hill.


https://goo.gl/maps/4ROXT


The hill that leaves town on the east side is much steeper and longer than the others. for that hill once I'm going about 50km/h I just put it in 6th and coast down.
It's pretty hard to answer this question to be honest. There's a time and place for everything, but now that I'm a more experienced driver I'll hardly ever coast around in neutral.
Like you mentioned, you can't just accelerate if you aren't in gear. The reason I prefer manual transmissions is so that I'm more in control of the car. You're not in control too much if you're in neutral.


Going back to my hill descents, I'll stay in the highest gear that I wont bog in, and if I'm going too fast I'll get on the brakes as needed.


98% of the time I'll heel/toe or rev match when slowing down.

[paulca]

Originally Posted by HeadBanger

The reason I prefer manual transmissions is so that I'm more in control of the car. You're not in control too much if you're in neutral.

The advantage of manual transmission is you have these choices and are the one in control. Can you even put an auto into neutral while travelling?

On the hills thing, my route to work goes up over some hills. Starts from sea level, ends up about 500 foot altitude and then back down to sea level. The way into the city ends with a large hill that drops about 400 feet in half a mile. To maintain 60mph down it I have to select 3rd! 4th and the car still accelerates at idle past 60mph. Coasting down it riding the brakes and they start to fade by the bottom and are probably overheating. Lots of quarry/gravel lorries go down it, they slow to under 30mph and ride the brakes down it, leaves a lovely smell of brake pads and ozone behind them.

Coming the other way, if you get a clean run up the hill in 2nd and 3rd you can accelerate up beyond 60 on full throttle, but it makes your ears pop like taking off in a plane! Great fun though. Even more fun overtaking people up it. Then the downhills are gradual and progressive with at least one mile long section where you can freewheel stably at 60mph for over a mile. Great watching the Avg. MPG rising.

[HeadBanger]

Originally Posted by paulca

The advantage of manual transmission is you have these choices and are the one in control. Can you even put an auto into neutral while travelling?

On the hills thing, my route to work goes up over some hills. Starts from sea level, ends up about 500 foot altitude and then back down to sea level. The way into the city ends with a large hill that drops about 400 feet in half a mile. To maintain 60mph down it I have to select 3rd! 4th and the car still accelerates at idle past 60mph. Coasting down it riding the brakes and they start to fade by the bottom and are probably overheating. Lots of quarry/gravel lorries go down it, they slow to under 30mph and ride the brakes down it, leaves a lovely smell of brake pads and ozone behind them.

Coming the other way, if you get a clean run up the hill in 2nd and 3rd you can accelerate up beyond 60 on full throttle, but it makes your ears pop like taking off in a plane! Great fun though. Even more fun overtaking people up it. Then the downhills are gradual and progressive with at least one mile long section where you can freewheel stably at 60mph for over a mile. Great watching the Avg. MPG rising.

OF course you can put an auto into neutral! Just push the gear selector to N lol


In extreme cases like yours I'd probably go to third or 4th. But how high are you revving in third going down the hill? I wouldn't want to stay at 7000rpm for extended periods of time without proper cooling of the cylinder. I'm not sure how the ECU works, but the fuel cools the cylinders, if there's no more fuel at 7000 than say 3000, I suppose you could potentially run into problems long term

[aznatama]

If you're engine braking at 7k RPM, you're not going to overheat anything, since you're not putting any load on the engine.

ALWAYS engine brake when going down a long downhill unless you like the idea of brake fade. MT or AT, both can engine brake going downhill.

[ZionsWrath]

Originally Posted by aznatama

If you're engine braking at 7k RPM, you're not going to overheat anything, since you're not putting any load on the engine.

ALWAYS engine brake when going down a long downhill unless you like the idea of brake fade. MT or AT, both can engine brake going downhill.

Exactly. There is a reason automatics have gears other than D. Even though most people probably never use them.

[ZionsWrath]

Originally Posted by paulca

The advantage of manual transmission is you have these choices and are the one in control. Can you even put an auto into neutral while travelling?

On the hills thing, my route to work goes up over some hills. Starts from sea level, ends up about 500 foot altitude and then back down to sea level. The way into the city ends with a large hill that drops about 400 feet in half a mile. To maintain 60mph down it I have to select 3rd! 4th and the car still accelerates at idle past 60mph. Coasting down it riding the brakes and they start to fade by the bottom and are probably overheating. Lots of quarry/gravel lorries go down it, they slow to under 30mph and ride the brakes down it, leaves a lovely smell of brake pads and ozone behind them.

Coming the other way, if you get a clean run up the hill in 2nd and 3rd you can accelerate up beyond 60 on full throttle, but it makes your ears pop like taking off in a plane! Great fun though. Even more fun overtaking people up it. Then the downhills are gradual and progressive with at least one mile long section where you can freewheel stably at 60mph for over a mile. Great watching the Avg. MPG rising.

Yes you can put it in neutral while moving. You can put it in neutral and turn the ignition off while moving. In fact once in a while I like to scare friends doing this. Most people don't know you can lol

[s2d4]

Originally Posted by paulca

Can you even put an auto into neutral while travelling?

Yes.

[berkbrzfan]

Originally Posted by aznatama

ALWAYS engine brake when going down a long downhill unless you like the idea of brake fade. MT or AT, both can engine brake going downhill.

Absolutely. Engine braking always while going downhill. Freewheeling down makes me smell brake pads, especially if the incline is pretty steep that you need to brake very often. Being in gear also lets you get on power immediately if needed.

[shiumai]

i never liked to freewheel on hills. i just put it in the gear that didn't require me to step on the gas much or one lower to engine brake.

[teamturbo]

I avoid engine brake unless I need to. All the energy is transferred thru your engine and transmission. Brakes and pads are efficient enough and much cheaper

[serialk11r]

I freewheel down any hill of any grade unless I need to accelerate or slow down. Obviously, a steep SF type hill means stick it in 2nd or 1st, down a mountain with reasonable grade maybe downshift 1 or 2 gears from the top gear.

[paulca]

Originally Posted by teamturbo

I avoid engine brake unless I need to. All the energy is transferred thru your engine and transmission. Brakes and pads are efficient enough and much cheaper

A myth.

Engine braking is just using the engine as an air compressor and the cars momentum as the power source. Compressing air is something the car does anyway whether it's on power or off power. The engine is under orders of magnitude more load when there is fuel in that air which is then ignited to create an explosion.

So as long as lubrication is okay the engine will barely notice the stress of engine braking.

Brake pads on the other hand glaze when heated too high or for prolonged periods. Glazed brakes do not provide anywhere near as much braking force and can take many miles to wear the glazed surface away again.

So I'd say, brake pads are expensive, engine braking is not.

One word of caution as I nearly found this out the hard way. Do not use engine braking to try and slow your descent down slippery snow covered hills it's a bad idea.