At the worse, it is inferior
picking worse and paying extra for it..... I mean do I have to spell it out?
Sometimes there is no other option. Is it still stupid?
you misunderstood.. when (chronologically) there was no known alternative,
that backplate thing was a -maybe- acceptable drawback for very tight ocasions (mini bikes!)
NOW (chronologically) since there is a known to work alternative that has less drawbacks
requiring exactly as little space ... it's still stupid.
And I know that people tend to stick with things and setups they know and are familiar with (I'm no exception to that)
but that is at best lazy.. at worst it's again stupid.
I only answered his question with a viable option
asking him to spend more money for a yellow spring he doesn't need to end up with an inferior setup.
ah well.. we turn in circles.
indeed there was a research paper published a couple of years ago,
it described in great (mostly boring) detail how a non-positive-traction CVT
cannot be more efficient than (i think it was) 79.8%,
it described how a taller belt contacting surface requires higher bending forces and the resulting kneading forces
as well as a bigger slip due to circumference difference of the inner vs the outer edge of the
moving belt eating up the benefit of a bigger contacting surface from a certain point on.
(less contacting surface equaling less potential to transmit power of course)
and it also brushed over the topic of how less than perfect alignment quickly raise the powerlosses
to additional kneading forces required to move and laterally shift the belt to align with the second pulley.
Then the details escape me tbh but it also explained that those effects are actually growing with engine power
to remain a percentage of instead of a fixed wattage.
IIRC it's the torque related clamping force to keep the belt rotationally stable while accelerating
pinching the belt requiring more force to break free from the pulley... I think there was something else.. but I don't quite remember.
Powerloss was scientifically correctly measured by induced heat btw.
generally speaking thermal mass of involved parts, heat delta and out comes power loss.
forced air cooling of rotating pulleys and moving belt was taken into account by running those fully enclosed
and measuruing the temperature change of the known air volume as well.
So no false dyno reading could compromise the data.
Now.. I think we do agree that the belt WANTS to run true, don't we?
let's do a simple test..
The belt get's offset by one belt width on a series 40 with your setup.
(you can measure that yourself if you like.. but it's 7/8" according to comet)
so get a 7/8" thick board and place it on your bench, lay your belt in a 5" OD semi circle onto the board (~4" off the edge)
and a 5" semi circle onto your table your center to center distance apart
now put weights on the two half circles so that the belt is perfecly flush with the bench and board.
combined weight in kilograms times 9.81m/s² is Newtons of force, distance of the two semi circles in inches times 0.254 to get torque (in Newtonmeters) which is equal to wattseconds of energy
engine rpm times Pi divided by 12 times the belt OC to derive your belt rotations per second at you favourite speed
and you can then simply multiply the wattseconds with the belt rps to get the
static powerloss in watts for the offset belt
clamping and kneading forces not fully included but I'd bet you'd be surprised already
and I'd also bet you'd be considering getting the red spring back in to flip the driver instead just to make use of the few hundred watts you are already loosing there.
with a 33.8" belt at 8 3/16" ctc
and just 1kg *(2.2lbs) combined weight we talk a powerloss of roughly 711Watts static for 4.5k rpms (570 Watts @3600 rpms)
(6.44% loss on a 15horse compared to my 5% WAG [ 5.16% @3600 rpms... just so you know where the 5 came from] )
So yeah.. test it, be surprised, change to red spring and flipped driver.. PROFIT!
'sid
* I don't own a series 40.. so I tried to get an estimate with my series 30 belt...
I need MORE than just 1kg combined weight to get them flat on the bench and 3/4" thick board so yeah...