a hard limit.. no, certainly not..
a soft limit .. sure does!
We've had that conversation a while ago because of MrMonks TavKit last year,
that had me think about it ...
anyways
here's how I think it goes:
first some facts
A belt transmission
always slips;
and that slip is what's causing belt wear and also powerloss
(power turned to heat and belt dust instead of movement)
it's the same principle that wear down your tyres eventually.
that slip happens at the transition from semi circular path round the driver
to the straight path (free air) to the driven and back.
those four transition points cause about 20-25% powerloss on an
ideal CVT.
The driver and driven forcefully try to change reduction ratios,
by clamping onto the belt;
that clamping force in case of our torque regulating CVTs
(series 20,30,40 style comets)
is what's regulating the CVT gear ratio,
ideally forcing the belt into a
larger radius path;
the driven by torquing against the spring loaded cam on one side (moveable sheave)
and the wheel and eventually the road on the other (fixed sheave),
the driver by torquing against the flyweights and their centripetal force
(yes.. petal, not fugal... nevermind) on one (moveable sheave)
and eventually the engine's crank on the other (fixed sheave).
the more torque applied to the rear wheel, the bigger the active diameter of the driven,
the more torque applied to the crank, the bigger the active diameter of the driver.
And ideally those two level out since the total belt length is a given
The main difference between the two:
the driven can never apply more clamping force than that of the cam spring.
so that is a hard limit on clamping force until fully compressed;
the driver however can increase it's clamping force by increasing the engines rpm,
since the flyweights are rotationally locked to the crank of course.
I think so far we all are on the same page, right?
Long text already.. no limit explanation so far... bear with me
Now, in our "extreme" situation what I think is happenening is this:
first the driven is fully expanded, the belt is running at the lowest active diameter;
but there's still rpms left in the engine to be released.
you increase the throttle and the engine tries to rev up,
the belt can no longer move up the driver and down the driven;
and what you are hoping for is increased road speed;
since that's the only way those additional revolutions could go, right?
Yeah but what if the load on the rear wheel prevents that?
you cannot move faster, since you simply do not have the power at the rear wheel to do so?
you hit a speed wall for whatever wheel-torque you now have!
that power is then fed back into the CVT.. the belt tries to wedge down into the core hub of the driven, but can't go anywhere..
the force then travels back to the driver and
does as it's supposed to, trying collapse the flyweights back
and reduce the active diameter of the driver.
but the flyweights are spinning fast enough to prevent that..
so the belt wedges itself into the driver pulley even harder
increasing the clamping force
making it harder and harder to feed the belt into and pull it out of the driver at both transition points.
(if you ever tried to wedge a 3/4" belt into a 5/8" gap you know how much force is required to do so
)
So you loose more and more power ...
and the fewer power is reaching the driven pulley, the more it tries to force the driver into lower gear.
Now two things can happen:
a) the belt looses getting too hot, glaze over, and slips, the driver then just revs freely
or what is more likely, because of the clamping force
b) the belt just transmits all the forces back into the crank overcoming the raw engine torque at that rpm and thus slowing it down.
and voilá, we've hit the soft rpm limit!
Why soft limit?
Well that rpm I doubt is a fixed number for all engines..
it's highly dependend on the specific engine itself and the gear ratio used.
I'd say you can have a unmodded engine but gov removed with a series 30 hit 5k
and the same series 30 hit a wall with a stage 3 or 4 at just 4k rpms
mainly because of the idiotic rpms over torque modifications made.
rpms are mostly worthless if not backed up by torque.
So, why does the juggernaut work then you may ask.
I think the juggernaut driver prevents exceeding clamping forces,
and since no additional power is lost to those raising clamping forces,
it can then use that 'additional' power to actualy make the wheel turn a smidge quicker.
but tbh... that is cosmetic and totally pointless in all cases I've heard so far.
unless you are competetive racing (prices to be won, not friends to be beaten)
there is
absolutely no point in a juggernaut..
I'll explain my thinking behind why and how later
'sid
