For what its worth at home in the US, i always downshifted in my little car. So much more fun, but it makes my wife nervous cause she never drove a stick… so in an automatic im coasting much more, compared all the braking. When i have my bike, ill be downshifting all the time on that too… its just a much more viceral feeling.
[quote=“canucktyuktuk”]I ride an FZR so I am constantly shifting, up, down, sideways (just kidding). Yep gotta rev the motor up before you let the clutch out nicely. I don’t remember not downshifting. I’ve had a few jobs driving trucks in BC so you learn to use the engine to slow you down. [/quote]Right. Those bikes have closely spaced gears but you need that to keep the revs above 6000 or so.
[quote=“canucktyuktuk”]I hate how regular scooters coast to a stop with little or no engine friction. When I’m driving in the mountains (scooter) I am always wondering if I’m using the brakes too much going down hills and they will get hot and fail.[/quote]It is a bit annoying. What’s even more irritating is when a scooter gives you some engine braking down to a certain point then the clutch suddenly disengages and you really are coasting. I wonder if the maxi scooters do this too.
Not sure if that’s a reply to my post, but I’ll respond as if it was. Apologies if you weren’t talking to me.
The above thread started with an “in praise of downshifting/engine braking” post, and then widened to include (critical) mention of coasting. I continued with that, taking the opposite, minority view. I maybe didn’t specifically state the obvious, that these are two separate (but related) things. You can deprecate and avoid engine braking without being in favor of, or doing, coasting.
My driving instructor was criticising the practice of “slowing down through the gears”, using engine braking, as taught to/by my girlfriend. He obviously wouldn’t have recommended coasting, which is generally disapproved of, I think specifically deprecated in the UK Highway Code, and would have earned me a fail in the test. I intended to start doing it after passing, and did, kind of as a reward to myself.
The most valid arguments I’ve heard against coasting are that it’ll take you longer to respond to a total brake system failure since you’ll need to get in gear, and that, in the event of heart attack, stroke, or bullet from an unseen assassin, your uncontrolled vehicle won’t slow down until it hits something. These are way down at the bottom of the list of accident causes and I class them as acceptable risks. To quote Butch Cassidy “Hell, the fall’ll probably kill ya anyway”.
Of course, in doing so, I’m also accepting a small risk to innocent bystanders, which gets bigger with the size of the vehicle. I hardly ever coasted when I drove an HGV.
I’ll admit that the desire to conserve momentum can sometimes tempt the coaster to take a bend too fast, but it’s inappropriate speed that’s the problem here, not coasting per se. (Example:Anyone who knows the Rest and be Thankfull pass in Scotland will realise that a fast coast is possible all the way down to Arrochar IF you have enough nerve not to brake where the road kinks left across the bridge.)
In Palestine coasting was common practice and quite competitive. Could you conserve enough momentum on the downgrade (engine off) to take your VW Beetle over the next upgrade without restarting the engine? It was fun. Motor racing without fuel. Vacuum-servo braking systems spoilt it a bit, though.
I like coasting, and I don’t see the point in engine braking apart from where sustained heavy use of the brakes is causing them to overheat and fade. In the contemporary Western World these are eccentric views. Can so many petrol heads be wrong? Nah, must be me, so what are the arguments?
Ed, you make some good points. I liked the last paragraph of your post. What I find though is when coasting to a red light, it’s physically more demanding having to squeeze the brake lever and use your foot to slow down. Quite insignificant for short drives but if you hit the road for 8 hours in one day, it makes a big difference. As for racing and technical riding…Nevermind, you were talking about casual riding. 
bobepine
Another good thing about downshifting is that you are automatically in the right gear when you want to accelerate. If that light you were engine braking down for changes to green, you are in the right gear. You can accelerate quickly and confidently.
I don’t understand why you would ride your motorbike without power. Engine braking doesn’t wear out your clutch or tranny as long as you do it properly.
I seem to remember long ago when I took my drivers test in Canucktyuktukland there was a point n the booklet they gave us to study. I believe it is illegal to drive without engine power there. IE: coasting to a stop, coasting down out of the mountain range, etc. I understand why.
I like coasting to, but I shouldn’t do it. I coasted down some mountains in San Xia just for fun. However, when I am riding properly and not messing about on a little used country lane that I’m very familiar with, then I always use the engine.
The use of down-shifting, rev matching and engine braking not only allow you to have full control of the brake forces you have, but they also allow you, with practice, to balance the dynamic forces across all two or four wheels (depending on your mode of transport).
Force distribution and balance is a key part in safe driving which allows you to take corners at the optimum speeds without skidding or braking unecessarily.
Infact, there are so many reasons why working through the engine is more desireable than coasting - you just don’t have the level of control without the engine.
I like coasting to, but I shouldn’t do it. I coasted down some mountains in San Xia just for fun. However, when I am riding properly and not messing about on a little used country lane that I’m very familiar with, then I always use the engine.
The use of down-shifting, rev matching and engine braking not only allow you to have full control of the brake forces you have, but they also allow you, with practice, to balance the dynamic forces across all two or four wheels (depending on your mode of transport).
Force distribution and balance is a key part in safe driving which allows you to take corners at the optimum speeds without skidding or braking unecessarily.
Infact, there are so many reasons why working through the engine is more desireable than coasting - you just don’t have the level of control without the engine.[/quote]
These (and most of the other counter-posts) are assertions rather than arguments. At the risk of becoming repetitive, my technical (but certainly not VERY technical, and perhaps simplistic) argument is that for nearly all vehicles (the obvious exceptions being all WD and tracked vehicles), engine braking is effective on 2/4 or 1/2 wheels only (cars and m/c’s respectively). How then, does it “balance the dynamic forces across all two or four wheels”? Isn’t that what brakes are designed to do?
Let’s leave my “sinfull” addiction to coasting as a separate issue. The basic argument isn’t really a straight choice between engine braking and coasting, but whether you work down through the gears using the engine as your primary means of slowing, or slow with the brakes and then drop into the appropriate gear. I still havn’t seen anything that (to me) justifies the extra transmission loads and uneven distribution of braking forces involved in the former.
The argument that “you are always in the right gear” has some validity, but it doesn’t take very long to put it in (or change) gear. If you are forever downshifting through the gears are’nt you going to be passing though neutral (and therefore “coasting”) more often than someone who stays in top until they’ve braked down?
Driving is very much a matter of habit and practice (someone mentioned “wiring the neural net”). I’d speculate that the drivers who’ve become highly skilled, and therefore comfortable, with engine braking, might become just as skilled and comfortable with an alternative style, if they’d spent an equivalent amount of time practising it.
Anyway, as I admitted before, it seems likely that there are valid arguments for the majority view. I just havn’t heard them.
I wan’t arguing, edithgow, I was just trying to explain the advantages.
Let me explain something from an aviation point of view.
Pilots use reverse thrust and brakes to help slow down an aircraft on landing. Now, reverse thrust doesn’t slow the aircraft down by itself; the brakes do it. Reverse thrust doesn’t necessarily help the aircraft to slow down in a shorter distance either. What reverse thrust is doing is taking the pressure off the brakes and therefore the wheels by taking up some of that braking force.The pilots have alot more control over what the wheels are doing and how much traction they have on the runway surface because the forces of the braking action are spread through the whole frame of the aircraft.
Reverse thrust on a dry runway represents about 20% of the total braking force, and up to 50% on a wet or icy runway and the chances of skidding or aqua-planing are much reduced.
The same principle can be found in engine braking on road vehicles. The forces of the braking action can be more evenly spread through the frame of the bike rather than the wheels, giving the rider much more control over what the wheels are doing and giving the bike more traction as a whole.
Using the engine to slow down and then the brakes when needed (it is obvioulsy better to use both) is desireable because if you are coasting and need to brake even more suddenly then you intended, then the chances of you skidding and not having total control over your bike are higher.
[quote=“Dangermouse”]I wan’t arguing, edithgow, I was just trying to explain the advantages.
Let me explain something from an aviation point of view.
Pilots use reverse thrust and brakes to help slow down an aircraft on landing. Now, reverse thrust doesn’t slow the aircraft down by itself; the brakes do it. Reverse thrust doesn’t necessarily help the aircraft to slow down in a shorter distance either. What reverse thrust is doing is taking the pressure off the brakes and therefore the wheels by taking up some of that braking force.The pilots have alot more control over what the wheels are doing and how much traction they have on the runway surface because the forces of the braking action are spread through the whole frame of the aircraft.
Reverse thrust on a dry runway represents about 20% of the total braking force, and up to 50% on a wet or icy runway and the chances of skidding or aqua-planing are much reduced.
The same principle can be found in engine braking on road vehicles. The forces of the braking action can be more evenly spread through the frame of the bike rather than the wheels, giving the rider much more control over what the wheels are doing and giving the bike more traction as a whole.
Using the engine to slow down and then the brakes when needed (it is obvioulsy better to use both) is desireable because if you are coasting and need to brake even more suddenly then you intended, then the chances of you skidding and not having total control over your bike are higher.[/quote]
I don’t use “arguing” in any perjorative sense, I like a good argument.
However, I think your aviation analogy isn’t valid, because it isn’t comparable to the road vehicle situation. Less importantly, you also appear to contradict yourself a bit.
Aircraft may use several separate and independent means of slowing on landing, including “passive” aerodynamic braking from flaps/airbrakes/parachutes, and arrestor hooks on carrier based aircraft. Reverse thrust (the reaction force generated by directing the jet or prop thrust forward) certainly DOES “slow the aircraft down by itself” and would operate if the wheel brakes were not available. How could it not? “For every action there is a reaction”, “Ye canna change the Laws O’Physics, Captain”, etc, etc
None of this applies in a road vehicle, where ALL controlled braking forces, whether generated by the engine or the brakes, MUST act through the road wheels. Unless you open your car doors, put up an umberrella on your bike, or throw out a boat anchor from the back of your pickup there is NO controlled wheel-independent braking.
Strictly speaking, ANY braking (or any other) forces MUST be “spread evenly through the whole frame of the aircraft” while the airframe is in one piece. Where reverse thrust scores is in acting in line with the centre of mass (and therefore directly opposing the momentum) of the airframe. The wheel brakes are off-centre, on the end of the undercarriage, which thus has to be strong enough to transmit the braking forces to the airframe without breaking.
The same applies to a bike (or car, etc). While its in one piece, the braking forces from the wheels MUST be “evenly spread through the frame of the bike”. That is what being in one piece means. The only difference in “eveness” between engine braking and brake-braking is that the former only acts through the driven wheel(s), so its arguably less “even”.
Skidding occurs when the braking forces exceed the grip of the tyres. It can’t make any difference whether these forces are generated by braking or engine braking.
Sorry. Unconvinced.
OK, I took it too seriously. 
Here’s more argument:
[quote]certainly DOES “slow the aircraft down by itself” and would operate if the wheel brakes were not available. How could it not? “For every action there is a reaction”, “Ye canna change the Laws O’Physics, Captain[/quote]”,
What I mean is that the in normal aircraft operation, reverse thrust is not used to slow the aircraft down by itself.
Due to design limitations, only a small percentage of the total engine power is directed forward of the engine, and then only at a maximum of 45 degrees in most civillian aircraft.
Not only that, reverse thrust must be used in conjunction with conventional aircraft braking systems as per ICAO guidlines. The aircraft must be able to stop on the runway it is landing on using normal brakes before it is allowed to operate from or to that runway. Because of the drag co-efficient on most aircraft, reverse thrust alone would not be enough to slow an aircraft down enough on a regular 2,500ft runway before going through the hedge.
As well as this, reverse thrust relies on compressed air produced when the air from the engines meets the air meeting it as the aircraft moves forward. Thrust reversers are completely innefficient below 70KTS on most civilian airliners. The compressed air here relates in some way to the air inside a cylinder of a normal combustion engine which I will write about later, hence my analogy isn’t that distant in principle.
Yes, they do act through the wheels, but the forces are different.
Engine braking forces are acting against air which is being compressed in a cylinder.
This is where some of the braking force is taken up by the engine and effectively moved from the wheel brakes. The cylinder is acting against compressed air (hence my reverse thrust analogy) and the forces are distributed along the drive shaft and other areas of the car. Using the engine to dissipate energy leads to an immediate removal of energy.
The rest of the forces are taken up through the brakes.
[quote]Where reverse thrust scores is in acting in line with the centre of mass (and therefore directly opposing the momentum) of the airframe.
[/quote]
Which is exactly what the compressed how the compressed air inside the cylinder heads is doing - acting against the forces and opposing the forward momentum of the vehicle. The pistons become ‘dead weight’ and physically anti-torque the converted power to the axle reversing the energy generated into the flywheel into negative energy.
There are therefore two forces acting on the wheels: the force of the road through the brakes to the wheels and the (negative torque) force from the engine to the wheels.
This effectively dissipates the force through two mediums instead of one. This is better, because all your energy is not being channelled through one point, allowing you greater control from the spread of energy.
“What I mean is that the in normal aircraft operation, reverse thrust is not used to slow the aircraft down by itself.
Due to design limitations, only a small percentage of the total engine power is directed forward of the engine, and then only at a maximum of 45 degrees in most civillian aircraft”
You apparently have detailed knowledge, and presumably experience, of aircraft operation. I have only flown gliders, so can’t match that. However, I still think that, for the present purposes, the details of aircraft reverse thrust procedures don’t matter, since the analogy is invalid.
Reverse thrust operates independently of the wheels, road vehicle engine braking does not.
“Yes, they do act through the wheels, but the forces are different”
No they aren’t. The limit (before skidding) is the adhesion limit of the tyres. This is unaffected by the means used to generate the braking forces (i.e. resist the free rotation of the wheels).
“Using the engine to dissipate energy leads to an immediate removal of energy…
The rest of the forces are taken up through the brakes…This effectively dissipates the force through two mediums instead of one.”
This is true, and it is useful if your brakes are overheating, or likely to. Otherwise it doesn’t matter
“…this is better, because all your energy is not being channelled through one point, allowing you greater control from the spread of energy”
This is ambiguous. If the “one point” being considered is the brakes (which in fact are obviously more than one point but thats a semantic quibble. “one component” might be better) then the first part is true. Its not clear (to me) however, why (if not overheating) you have less control over braking using this “one point”.
But in fact all your braking forces, in either case, are still “channelled through one point”, the tyre contact patch.
In normal operation, functional brakes are capable of delivering more braking force than you can use, so load sharing with the engine seems (to me) simply unnecessary.
Sorry, still unconvinced. You may be right, but your air support is vulnerable to ground fire.
I can assure you that stopping certain aircraft within 2,500ft of runway with reverse thrust is very possible (no brakes)…and i’m talking about high performance aircraft over 12,500lbs MTW and of cruising speeds in excess of 250kts…
…wanna take a guess?
[quote=“skylarkpuma”]I can assure you that stopping certain aircraft within 2,500ft of runway with reverse thrust is very possible (no brakes)…and I’m talking about high performance aircraft over 12,500lbs MTW and of cruising speeds in excess of 250kts…
…wanna take a guess?[/quote]
I’m not sure who this is directed at. I said that reverse thrust alone would clearly in principle stop an aircraft, and the poster who introduced the reverse thrust topic excluded military aircraft (which those numbers sound like) when he stated his limitations on reverse thrust performance, so you don’t seem to be disagreeing with anyone.
In principle reverse thrust is just a special case of vectored thrust, so you could argue that a Harrier would be an example of an aircraft using reverse thrust to stop in 0 feet.
In any case reverse thrust is simply irrelevant to the original topic of downshifting/engine braking. Its just not a valid analogy.
[quote=“Ducked”][quote=“skylarkpuma”]I can assure you that stopping certain aircraft within 2,500ft of runway with reverse thrust is very possible (no brakes)…and I’m talking about high performance aircraft over 12,500lbs MTW and of cruising speeds in excess of 250kts…
…wanna take a guess?[/quote]
I’m not sure who this is directed at. I said that reverse thrust alone would clearly in principle stop an aircraft, and the poster who introduced the reverse thrust topic excluded military aircraft (which those numbers sound like) when he stated his limitations on reverse thrust performance, so you don’t seem to be disagreeing with anyone.
In principle reverse thrust is just a special case of vectored thrust, so you could argue that a Harrier would be an example of an aircraft using reverse thrust to stop in 0 feet.
In any case reverse thrust is simply irrelevant to the original topic of downshifting/engine braking. Its just not a valid analogy.[/quote]
No worries, I’m not disagreeing with anyone, just getting into some plane talk! 
Cheers
If you fail to diligently change your oil and allow your piston sleeve to become scratched, you get very effective engine-braking indeed. 
[quote=“sandman”]If you fail to diligently change your oil and allow your piston sleeve to become scratched, you get very effective engine-braking indeed. [/quote]Actually…If your piston is scratched, you lose compression=you lose engine-breaking. Unless you mean the bike stops dead. Then yes, that’s pretty effective.
I notice that you do not read your notes from the mod’s brunch and now this! No oil change?! You’re slippin mate…slippin… 
bobepine
[quote]I notice that you do not read your notes from the mod’s brunch and now this! No oil change?! You’re slippin mate…slippin… Sticking my tongue out…
bobepine[/quote]
Huh! Laugh all you like bobepine. Another few years and it’ll start happening to you too. Little things at first – where did I put my spectacles? that kind of thing – and before you know it you’ll be walking around in public with no trousers on and brushing your teeth with peanut butter.
Military or civilian?
I think most STOL aircraft have the potential to stop using reverse thrust without brakes and would be able to do it easily on a 2,500ft runway. but these aircraft are generally small. I couldn’t see a 737 doing it. 
[quote]This is ambiguous. If the “one point” being considered is the brakes (which in fact are obviously more than one point but thats a semantic quibble. “one component” might be better) then the first part is true. Its not clear (to me) however, why (if not overheating) you have less control over braking using this “one point”.
[/quote]
OK, I’ve been thinking about this. There is alot of stuff on the internet about engine braking and how to do it, but not about how it works
Now I’m no physicist, but although the energy ultimately meets the road through the tyres of a vehicle, when using engine braking, it makes sense that alot of the momentum of the car is expended through the engine as heat, as friction and from the moving parts. Energy is also lost through the drive shafts and soaked up through the compressed air in the cylinder and vibration through the axles.
If you are only using brakes, then the energy caused by momentum is only channelled through the wheels.
Because of negative torque, I would imagine (but I’m not sure) that instead of the road giving leverage to the engine, the engine is giving the energy back to the road. With brake use only, the road is giving leverage to the brakes only and the momentum is dissipated just through the brakes and wheels… I’m confusing myself with this concept as my mastery of physics is, to be blunt, shite.
As for control, I think because of the above, traction is improved because the kinetic energy being passed through the axle to the wheel is different to the simple braking action of conventional brakes.
Secondly, my argument for greater control with engine breaking is with road surfaces.
If you are using only brakes and you are coasting, it is possible to lock up if you hit ice, sand or grit, or even a pot hole or damaged surface.
If you are using a combination of engine braking and brakes, the likely hood that you lock up when hitting an undesireable road surface is minimal, and if you did lock up the engine would either stall or traction would be lost resulting in a skid. Nevertheless, it is far more difficult to enter a skid using engine braking.
I think it is far safer to enter a skid when you have the control and braking/accelerating power should you need to release the brakes or drive out of the skid.
Sorry DM, but I have to argue this one. Deceleration torque is deceleration torque regardless of where it comes from. The torque is still applied at the center of rotation. But, the drivetrain on a motorcycle with suspension does create other forces besides merely rotating the wheel, or being rotated by it. What I think is missing in the discussion is the shift in center of gravity back and forth while either accelerating or decelerating. Using the wheel’s momentum to turn the engine loads the rear suspension and probably helps reduce the amount of forward weight transfer during braking. Our resident shaft-drive contingent will feel this most acutely but it also occurs in most chain-driven designs due to the relative position of the swinging arm pivot and the pitch line of the drive sprocket. Obviously the load on the rear tire is a major factor in how much friction it can apply to the road and contribute to decelerating the bike.
[quote=“sandman”][quote]I notice that you do not read your notes from the mod’s brunch and now this! No oil change?! You’re slippin mate…slippin… Sticking my tongue out…
bobepine[/quote]
Huh! Laugh all you like bobepine. Another few years and it’ll start happening to you too. Little things at first – where did I put my spectacles? that kind of thing – and before you know it you’ll be walking around in public with no trousers on and brushing your teeth with peanut butter.[/quote]Yeah, it’ll come my way…I think I need to downshift, it’s coming too fast.