Controlling the number of RPM's

 I believe i've been instructed in this
NG to go rather high on the number of
RPM's. I think the recommended range
was 7k+/-1k.

Yesterday, i talked to a instructor and
he strongly suggested to to higher in
gears, consequently lowering the RMP's
number.

I have no opinion one way or the other
but one of the above mentioned sources
is likely to be wrong.

Is it the case? Who's more right? Is
the truth of those claims depending on
outer circumstances and if so, which?

--
Regards
Konrad Viltersten
--------------------------------
sleep    - a substitute for coffee for the poor
ambition - lack of sense to be lazy

 
7k sounds very reasonable to me.

Try to find a torque vs. RPM curve for your particular engine. The
average short-stroke Japanese motorcycle isn't going to have much
usable torque below 4000 RPM, and won't accept very much throttle.

My FZR1000 needs to be cruised at about 4500 to 5000 RPM, because of
the short stroke and large valve area. Big bore V-twins tend to have
less valve area compared to piston area and can probably be cruised at
3500 RPM and still have good throttle response.

 On Thu, 17 Apr 2008 20:54:17 +0200, "K Viltersten"


It depends on what you want to do. For smooth cruising on flat roads,
a low RPM will be just fine. If you need more power, you also need
more RPM.

The one thing you must *not* do, is to use a lot of throttle at very
low RPM. That causes high stress on the engine. If the engine is old
or out of tune, it may even cause detonation, which is very damaging.

Many rookie riders have been driving cars for years. In this case,
many have a "feel" that 8000 RPM is going to make the engine explode.
For most car engines, that's perfectly true, but many bike engines can
run all day at 8K without any adverse effects at all. There are
differences, of course. A 1500 V-twin will not like high revs, while a
600 four cylinder sport may barely work below 4000 RPM.

Ask your instructor *why* he recommends what he does. Ask him to be as
technical as at all possible. My guess is that he likes low RPMs
because his students are better off with less power.
--
RoRo

 
I've been told that low RPM number can/will
damage the pistons. Comments?


--
Regards
Konrad Viltersten
--------------------------------
sleep    - a substitute for coffee for the poor
ambition - lack of sense to be lazy

 On Fri, 18 Apr 2008 05:25:03 +0200, "K Viltersten"


The problem is not the low RPM alone. The engine can idle all day
without any problem. The problem occurs when you give a lot of
throttle at very low RPM. In this case, you get a very high combustion
pressure that lasts for a long time. This puts large loads on pistons,
con rods, crankshaft and all the corresponding bearings. Which parts
break first, depends on engine design, age and wear. Normally, the
engine will not take immediate damage, but over time, the wear will be
increased, leading to a shorter engine life.

Also, lots of throttle at low RPM increases the risk of detonation
(ignition knock or "pinking"). If that happens, the engine may take
damage real fast. The crankshaft bearings are probably the most likely
failure point, but I have even seen pistons with a hole right through
them, as if they were hit with a hammer.

Rule of thumb: When cruising at constant speed, a low RPM is fine.
When you open the throttle, the bike should accelerate very
noticeably. If it doesn't, you are in a too high gear.
--
RoRo