Engine breaking instead of handle/pedal

 

I'm not entirely sure what it's called in english but i
understand that one's supposed to break without the
actuall brakes being hit. It's due to the fact that
energy gets consumed to make the engine spin, i got
to know.

So, i went for a drive today but i don't seem to be
able to get it to work. The only thing i managed to
accomplish was to accelerate (turning the gas more
"on") and then decelerate (by the very opposite
action).

By other words - if i add gas i speed up, if i lower
gas i slow down. Great, but where is the engine
breaking i'm supposed to take advantage of?!

Also, i wonder what can happen if i release the
clutch entirely and let the gas slowly to be turned
off. Will the engine die? Will i stop rapidly?

What happens if the clutch is entirely released and
the gas handle gets released fast instead?

--
Vänligen
Konrad
---------------------------------------------------

Sleep - thing used by ineffective people
            as a substitute for coffee

Ambition - a poor excuse for not having
                 enough sence to be lazy
---------------------------------------------------

 

What you're reaching for is the practice of downshifting, changing to lower
gears as you slow down, but its use is at least debatable, as brakes are
easier/cheaper to repair than clutches and rings.

 

Konrad Viltersten wrote:

It's called "engine braking". Your engine acts as an air pump, expending
about 1/3rd of all the energy available from the fuel in pumping fresh air in
and expended gasses out of the engine.

Engineers call this wasted energy "pumping loss". Engineers also include the
air under the piston that gets compressed on the down stroke as "pumping
loss".
They provide passageways between cylinder pairs so the air has somewhere to
go insterad of being compressed.

When you want to slow down slightly, just closing the throttle will cause the
engine to have to work harder to suck more air into the engine against the
restriction of the closed throttle.

So the motorcycle will slow down a little, but not as much as it would if you
were
engine braking in a lower gear.

If you downshift into a lower gear, the motorcycle will slow down because
energy is expended in overcoming crankshaft inertia. The crankshaft doesn't
"want" to suddenly speed up, its mass resists being speeded up, so the
motorcycle slows down instead.

Motorcycle transmissions are generally designed to have a rather low first
gear so you can get started from a stop and you can climb steep hills.

When you shift UP into 2nd gear at red line, the engine RPM will decrease
about 30%. OTOH, if you are riding at about 6000 or 7000 RPM in 2nd gear, and
you decide to downshift into first gear, the engine RPM will suddenly
increase to 9000 or 10000 RPM and the motorcycle will slow down dramatically.

If you are riding on wet pavement and suddenly downshift into 1st gear, the
rear tire may slide and you may fall down.

That's why experienced riders always keep track of what gear they are riding
in.

Suppose you were riding along in 3rd gear, and you wanted to slow down by
shifting into 2nd gear. There would only be about a 15% increase in engine
RPM, and the motorcycle wouldn't slow down so dramatically


Effects of changing throttle position are less if you are riding at lower RPM
in the higher gears. Effects become more noticeable if you are running along
at higher RPM in lower gears.

You're running the engine too slow in a higher gear to feel the effect.

I'm not sure what you mean by "release the clutch entirely". Do you mean
"release the clutch lever"? The engine won't die if the idle RPM is set
correctly.
Rolling off the throttle is good practice. How fast you stop depends on how
much front brake you use.


If you're talking about releasing the clutch lever, quickly closing the
throttle might
transfer a little mjore weight to the front tire, and, if the pavement is wet,
the rear tire could lose traction and you could slide the rear tire.

You need to get to know what happens when you roll the throttle off quickly
on wet pavement.

Single cylinder motorcycles generally slide the rear tire easily on wet or
slushy pavement, V-twins aren't quite so bad about that, and inline-4's and 2-
strokes
don't slide the rear wheel when you roll the throttle off suddenly.

Then, too, you must consider the tread pattern on your rear tire. If you have
a dual sport tire that is intended for 90% pavement riding and 10% off road
use, it won't slide on wet pavement as badly as a tire that has a knobbier
pattern or a trials universal block pattern.

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/bike/200708/1

 



I don't believe that. 33% energy loss to pumping strikes me as
unreasonably high. Can you find me a reference for that number?


There's also the PCV valve which directs crankcase gases into the intake
manifold.

(How does a single-cylinder engine, or an inline twin with 0° piston
offset manage the air?)

<snip>

--
Timberwoof <me at timberwoof dot com>
faq:  http://www.timberwoof.com/motorcycle/faq.shtml
It's easy to say a war is so important your neighbor should go fight it for you.

 



I suppose that superstitions about not using a motorcycle's brakes still
survive from when they were made of leather and could eventually slow
you down if you were going uphill. Modern motorcycle brakes are made of
advanced materials and designs that can stand up to hard braking.

You *should* use your brakes to slow down. At least 2/3 of your braking
power is in the front wheel, and you won't tip the bike up and over
unless you're riding a sport bike and you brake really, really hard. You
should practice hard braking. That way, when you need to do it in
traffic, you'll already know how.


When you close the throttle and the bike slows down, that's engine
braking. Others explained it in greater detail.


The engine should not die. It should drop to its idle speed. With the
clutch squeezed, there's no connection between the engine and the rear
wheel; the bike should continue to roll freely.


Engine braking.

--
Timberwoof <me at timberwoof dot com>
faq:  http://www.timberwoof.com/motorcycle/faq.shtml
It's easy to say a war is so important your neighbor should go fight it for you.