Clutching - Clutch - "Stalling the shift" Spring force & Ramp angle

[Dynamo^Joe]

I modified the gentleman's email to reduce the content just getting to the facts of his sled details and calibration.

Hello Joe, I've been researching clutching/ gearing tips for my Summit 800

I am normally a mountain rider, into boondocking and hillclimb.
My 800 has a few minor enhancements: Reeds, can, high-flow intake, hot-air elimination kit.

Calibration
19:47 gearing
1mm oversized rollers
14g~20.5g pins
I don't know how much weight is installed.
160/320 primary spring.
48/40 helix

Since the sled was new, and even after the work I did last year, I am forced to run my primary clickers at position 6 and still do not believe I am getting the proper RPM's out of it. I think I may be close to having a setup that rocks and I hope that with your help I can kick some a$$ this season. Thanks very much for your time.

Copy this spring picture to your computer and print it off for yourself.
To illustrate your own primary spring - take a ruler and pen/pencil and draw a line from the 160 point and go up to the 320 point.
You will be able to see the differences in spring forces that will help out out with your calibration.

At the moment you have a 160/320 installed however have to run clicker 6 to get correct rpms.
Let's pretend you cannot change the flyweight; imagine the flyweight is fixed like a solid pin or a hollow non-thread able pin.

What you have left to calibrate with is the primary spring and the tra ramps.
Spring analysis:
PRINCIPLE - Raising a spring "force"(not rate) "stalls the upshift" and promotes higher rpms.
What you can do is take the final force of the primary spring and raise it.
(in the case presented on the spring chart @ 45mph)
From my own testing experiences; 1 clicker increase at a midrange shift ratio is equal to 10~15 lbs spring force (possible 150~200 rpm change).

You could go from the 160/320 to a 160/350 or 160/380
Each spring with higher final force will stall the upshift.
160/320 @ midshift offers a force of 240 lbs.
160/350 @ midshift offers a force of 255 lbs
160/380 @ midshift offers a force of 270 lbs

Clicker analysis:
PRINCIPLE - Raising a clicker "stalls the upshift" and promotes higher rpms.
What you can do is take the Clicker and raise it however you being at position #6 there is no more room.
Having no more room with the 415, the only thing you can do is change the ramp angle by changing the ramp itself you mentioned "If you were to lower the clicker then as you have observed the rpms will drift lower forcing you to turn out"

Your stock ramps should be 415. I have looked through all the ramps that would have the ability to raise rpms by increased ramp angle.
You can change the ramps to stall the upshift with the 412 or 417.

In the final analysis;
*You will be able to lower the clicker number by increasing the primary spring final force.(the word is FORCE...spring FORCE...F.O.R.C.E., not rate) I weigh 220 lbs of force not 220 rate. The spring has 160 lbs force, not 160 lbs rate. A 160/320 spring has 123lbs/in rate.
*You will be able to lower the clicker number by changing the ramp angle itself.

Tuners don't particularly need to calculate rate. Rate is just a fun calculation to exactly measure another element of any spring.
BRP clutch springs have an installed height of 2.6 inches. At full shift overdrive the spring is compressed to 1.3 inches. So just think how much the clutch strokes in and out from engagement rpms to full shift overdrive highest mph = 1.3 inches. How much clutch sheave stroke for a normal operation of riding?...about 1.04 inches which is around 1:1 clutch ratio.
PRINCIPLE - Raising spring "rate"(not force) reduces the time for the engine to accelerate from one rpm, to-a-higher-rpm.
(320lbs-160lbs)/1.3inch = 123lbs/in Rate
(350lbs-160lbs)/1.3inch = 146lbs/in Rate
(380lbs-160lbs)/1.3inch = 169lbs/in Rate
The higher the "rate" value, the quicker the engine will accelerate rpms from one rpm, to-a-higher-rpm

 

[Dynamo^Joe]

A fun ramp page

 

[ReTodd]

Hi Joe,


You have a lot of great information. I notice that you write a lot about the angle of the ramp but I haven't seen the thickness of the ramp really discussed. I ask this only because when I ground my stock ramps, I took out almost 1/8" inch in the middle and also the base. This gave me a much flatter initial angle and a steeper finish angle which gives me great upshift and the steeper finish angle keeps my clickers on 3 or 4 at WOT in the deep stuff.

So, the question is, have you calculated the amount of force the roller arm will exert at different ramp thicknesses based on how far out it can swing........?

As seen above, the pivot point for the arm is located "outside" and the roller is "inside" and rotates outward with centrifugal force. Wouldn't the arm produce the maximum force the closer it gets to vertical with the pivot. If that is the case, increasing the upper ramp thickness would not allow the arm to pivot quite as far and would create less force and thus, higher rpm's but you would not be getting the maximum force available.

As an example, you could gain rpm's by going from two identical angled ramps just by increasing the thickness, or you could gain rpm's by keeping the thickness the same but going to a steeper angle. However, it would seem that the ultimate goal would be to get the maximum centrifugal force which can only be accomplished at the vertical position and thus a thinner ramp with a steeper angle would be preferred.

Using the photo above as an example, the 412 is slightly steeper but I would suspect the larger factor is that the 412 is twice as thick which keeps the arm from reaching its maximum force. If the 415 was ground in the middle slightly to match the finish angle of the 412, shouldn't it theoretically have more force applied to the ramp?

It seems like the clutches would be most efficient if Doo had made the pivot point a mm or two fruther in. Just thinking out loud here and not trying to say anyone is wrong. Thanks again for all your great info.

Rt