Clutch Principles (Law) - A body of law and concepts which have been established by Olav Aaen which is the framework of modern CVT systems.  1)A legal structure based on Newton's laws. 2) generic term is "clutch tuning"

Witness - The tuner him/herself.  Their testimony is more than likely to be true based on his/her experience, knowledge, training and appearance of honesty and forthrightness, as well as common tuning experience.

Evidence - Real, tangible or clear evidence of a fact, happening or thing that requires no thinking or consideration to prove its existence, as compared to circumstantial evidence.
*What was the observed rpms?
*Was there drifting rpms?

Testimony - Oral or written evidence(tuning notes) given by a witness(The Tuner) in answer to questions posed by curious tuners.

Click on, or scroll through the contents.

The Clutch System
Installed a clutch kit - Engine not revving enough...(on trackstand)
Belt Deflection and Height
Lack of Full Shift
Tuning for a straight shift
Clutch temperatures so hot?

Clutch spring forces (higher) equate to higher performance?
Controlling track spin at the start line

How do the primary springs effect mid and top end
Engine braking

The Clutch System
*Primary spring
*TRA Ramp
*TRA Clicker

*Drive belt

*Secondary spring

Consider the function of the parts.
Primary spring pushes the clutch open.
Flyweight pushes the clutch closed.
TRA Ramp provides a shift curve, a shift personality
TRA Clicker, changes the shift curve, changes a shift personality

Drive belt connection between primary[Engine load] and secondary[Converter] and ground load[Purpose to overcome]

Secondary spring pushes the clutch closed
Helix provides a upshift rate and a backshift rate

Each clutch part has magnitude
A property that can be described by a real number assigned to a part so that it may be compared with other parts.
Primary spring example - 160/320 compare to 240/430
Flyweight example - 17.5 grams compare to 25 grams
TRA Ramp example - 415 compare to 419
TRA Clicker example - clicker 1 compare to clicker 6.

Drive belt example - new belt 1-3/8 compare to worn belt 1-3/16

Secondary spring example - 245/350 compare to 135/300
Helix example - straight 44 compare to 50/40 compare to 44/36

Clutching Principle (Springs)
*More spring force will reveal more rpms at full throttle.  If you need more rpms, then add more spring force.
*More spring force will reveal quicker rpms.  If you need rpms to be quicker, then add more spring force.

*Less spring force will reveal less rpms at full throttle.  if you need less rpms, then reduce the spring force.
*Less spring force will reveal slower (opposite of quick) rpms.  If you need the rpms to accelerate slower, then reduce the spring force.

Spring "start force" the value of the spring in lbs. when it is installed.(engagement / at rest)

Spring "final force" The amount of force when the clutch is at full shift (highest mph)


Clutching Principle
"Flyweight determines rpms"
*If; Then- Result[s]
*Need less rpms; Increase flyweight mass - The TRA lever pushes harder.
*Need more rpms; Reduce flyweight mass - The TRA lever pushes less hard.


Clutching Principle
Ramp profile controls the size/magnitude of the shift force.
*Lower angle will provide more shift force
*Thinner ramp allows the tra lever center of gravity to be farther away from the clutch shaft centerline - Provide more shift force

*Higher angle will provide less shift force.
*Thicker ramp allows the tra lever center of gravity to be closer to the clutch shaft centerline - Provide less shift force


Clutching Principle
Clickers changes TRA ramp angle. Determines how quickly the engine will rev/accelerate.
Clicker 6 raises ramp angle to highest point - Quickest engine response
clicker 1 lowers ramp angle to lowerst point - Slowest engine response

*Need engine to respond quicker = raise clicker
Need the tra lever to push less hard/less aggressive = raise clicker

*Need engine to respond slower = Lower clicker
Need the tra lever to push harder/more aggressive = lower clicker


Helix angles - A helix constitutes groundwork for a few details to establish.
"shift rate (personality)"...
"engine rpms under wide open throttle"..."engine rpms under part throttle"...
"ability for engine to accelerate"..."ability for sled to accelerate"

Clutching Principle using 45 degrees as an example.
Angles regarding "Shift"
Angles less than 45 upshift slower "stall the upshift" "prolong the upshift"
Angles more than 45 upshift quicker "speeds up the shift

Angles regarding "Rpms"
Angles "less than" 45 provide more engine rpms" under w.o.t. application?
Angles "greater than" 45 provide less engine rpms" under w.o.t. application?

There are more details.  (angles regarding rpm acceleration) but that is to be saved for my clutch tuning book.
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Change the shape of the parts to change the calibration.
Primary spring example - 160/320 Need to change engagment rpms can change the spring shape to a 200/320 or a 130/320

Primary - Flyweight example - 17.5 grams; need different rpms under wide open throttle [W.O.T.]can change the flyweight mass to less 17 grams or more 18 grams.

Primary - TRA Ramp example - Using 415; need different rpms at wide open throttle then can change the shape to a 412 or 600 ramp.

Primary - TRA Clicker example - clicker 2; need different rpms at wide open throttle then can change the shape to a lower clicker 1 or any higher clicker.

Secondary - spring example - Using a 205/350 need different acceleration can change spring shape to a 225/350 or a 245/350.

Secondary - helix example - Using a straight 44, need different rpms as the shift increase can change the helix shape to a 44/42 or a 46/38

How to read a clutch spring
When reading a BRP primary spring you place it so the colors are pointing down, then read the colours from left to right.
The illustration shows some spring examples.
*insert picture*


Installed a clutch kit - Engine not revving enough...(on trackstand)
I. N. Quisitivetuner; Yesterday I way playing around installing the flyweights. I run the sled on the stand and I couldnt figure out why it wouldnt pull more rpm's.
Joe's 600 setup sheet said to run 24.5g and I can't get more than 7300. So I'm now down to 18g and it still won't rev past 7500 and clickers are on 4.
I think if it won't turn 8200 on a warm up stand, the engine won't turn 8200 ever. I mean, that's how I used to check my other sleds & it seem to work good.

Joe writes:
The kit is not designed to provide correct rpms only having to rotate a 40 lb track.
...and if you were to try the kit on a track dyno it will still reveal a few less hp at the track than stock clutching. On a track dyno you are accelerating your track weight, plus the weight of the 150~250 lb inertia wheel.

The clutch kit is calibrated to provide correct rpms when:
1] The track is engaged with the ground
2] The sled is on snow
3] In winter months
4] Engine provides best power's...cold...outside. [best relative air density for engine power]

I. N. Quisitivetuner; Well wouldnt it still pull 8200 rpm's in summer & it isn't that much especially when it has nothing to resist it.

Joe writes:
Resistance will increase rpms.
Resistance will increase rpms.
Resistance will increase rpms.
Add up the 4 points I mention above 1] + 2] + 3] = "Resistance" Add 4] in there with "engine has more power" and the rpms will further increase.

When you have resistance, the engine has no choice but to increase rpms, the resistance "Stalls the shift of the primary clutch"
One side of the secondary sees the ground and all of it's possible loads - The other side of the secondary sees the push from the engine "primary clutch".

The secondary "Converts" power from the engine and applies it to the dynamic loads the calibration is "supposed to see". [everything you can think of including track weight]

The load from the ground will increase resistance in the secondary vs. the push from the primary = Will increase rpms.
IF You are running 18g right now on the stand and cannot get over 7500,
THEN take it off the stand and go for a ride across the grass right now
RESULTS and you'll reveal high rpms "overrev" and lack of acceleration after like 50 feet.

Remember; Your kit was calibrated for bumps, snow loads-heavy/fluff, dips, hardpack, suspension part wear.
When you have your sled, suspended in the air, the bumps, snow loads...etc etc, don't exist - You are only accelerating a 40 lb track.

Here is another twister....Not enough flyweight will reveal pipe surge "the zoomies" where with engines that have higher compressions of around over 145 lbs, you'll never see correct rpms, only see low rpms from - pipe surge!

Some people will know the sound of "rah rah" or some people call it the "Rah rahs" You press the throttle to the bar and the engine loses 3~400 rpms.
The throttle is pulled back to 3/4 and observe the rpms are back at 8000.  Push the throttle to the bar again, observe 7700, let off the throttle, 8000. WTH???
- That is the zoomies "pipe surge" from lack of flyweight.

My advice is to install the clutch kit as per the vendor setup sheet and then go test in the environment you will actually run in so that when you pin the throttle, you'll see 2 lengths bang, leaping right off the line and keep accelerating away to top end by about 5~6 lengths while you give the "Goodbye my people" hand wave.
The engine rpms follows your thumbtip when cycling the throttle; backshift is incredible. Tach needle pegs 8100 and stays there.
...because Resistance will increase rpms.
Back in the watercross days, my race partner Rocketman Rod, a friendly competitor Scooter McLean and I were walking through the pits.  A fellow racer was revving his sled up on the stand and we stopped to watch.  Scooter said to me "How come Roddy's and your sled dont sound like that Joe?"  Roddy pipes up to me and says "YAH come our sleds don't sound like that, HUH?
I stood silent looking at them till I had both of their undivided attention then said "BECAUSE WE BEAT THOSE GUYS, including YOU Scooter, and furthermore Mark Maki's mom says to us "You are the guys that my son Mark worries about all the time"...
..She don't mention nuthin bout' you Scooter.
Scooter and Roddy shrugged their shoulders, Scooter saying "well you got me there" , Roddy saying "Good comeback Joe" 

The moral of the story is - Running your sled on the track stand and considering the use of it to check clutching....don't mean shit ! 
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Belt Deflection and Height
When I work on Stock or Modified sleds, I take care of details in this order...
1] Secondary Belt Height:
I like to have the chord of the belt showing on the outer dia of the secondary. If you look at the actual belt travel...The distance the belt travels towards the center from the clutch being closed to fully open, the belt travels only 1.25 inches approximately. So to think of it, if you have the capacity to go from 0mph to 100mph...The belt only travels that range of 1.25" in 100mph at 1:1 ratio. Would you not think that you would rather have approx 2mm of belt showing on secondary? 2mm=.080" Now you have ~1.30" to 1.33" of travel instead of ~1.25"
Benefits are:
i] 10% more belt movement from the engagement to top end.
ii] Extra time the belt can spend in the lowest ratio possible in the first 100 feet when you gas on it.

2] Best Belt Deflection = Track Movement:
Lift the sled onto track stand, start the sled, warm the engine up, burp the engine to turn the track, get the track nice and limber, getting the "cold" out of the track and loosen it up. When the sled is on a track stand and the engine started and idling, the track should:
i] Creep slowly or ii] Turn with jerking movements or iii] Track is still, but you are able to move it with by pinching a paddle with index finger and thumb then pull the track around fairly easy. You should now already have proper belt height on secondary. You must get the right belt deflection. If you cannot get this kind of deflection, change drive belt to one that fits with proper length. Be satisfied with that belt then. When buying a belt, take a "Seamstress" measure tape with you and measure the belt circumference. If a parts person gives you a hard time over it, Tell him "Go to hell, It's your money!" The results are very important. You will be quite happy in the end. Your sled will never bog with these conditions. You have found that your track moves on the stand at idle? Great. As long as your track moves or needs just a bit of coaxing with two fingers, you have great belt deflection.

Effects of Improper Belt deflection:
Too TIGHT of deflection: i]Burns the belt cogs when sitting near engagement. ii]Increases Torque at holeshot, but Hi-end mph is down.
Too LOOSE of deflection: i]Bad holeshot, possibly bog. ii]Slow In midrange iii]Possible higher mph in midrange only if engine does not pull off peak[Old speed run trick] iv]Engine pulls down out near big end.

Note: High engagement will eliminate bog, but acceleration deteriorates quickly by 2/3 track distance then 90% of time, engine falls low of peak rpm way out there.

Belt clearance: Prefer to have .025" to .030" on the primary. Tight belt clearance lets the tuner have better control of engine flashing thru the clutches. Tight is good for belts and will let them last a long "consistant" life.

Click for video -

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Lack of Full Shift - Slight Overrev at Start of Shift - (Tuning primary)
I. N. Quisitivetuner; 440 sled. Engage:5500 My rated rpms is 8400. Run the sled and it reaches 8700, drops to 8600~8550 as the mph increases.
Primary mark: 1/4" from top of sheave. No full shift out. Belt residue on sheaves at engagement.
Secondary/helix mark: Looked "ok", but upon disassembly mark is interupted nearing full shift.

Answer; Add slight more flyweight to make engine pull harder. 440 engine @ 8400 rpm peak.
Simple Principle to remember..."Flyweight determines rpm".
* Need less rpms; Increase flyweight mass - The TRA lever pushes harder.
Example, IF you reveal 8600 rpms with 16grams flyweight, THEN increase flyweight to 18 grams.

* Need more rpms; Reduce flyweight mass - The TRA lever pushes less hard.
Example, IF you reveal 8200 rpms with 19grams flyweight, THEN reduce flyweight to 17 grams.


Lack of Full Shift - Slight Overrev at Start of Shift - (Tuning primary)
I. N. Quisitivetuner; Pulls hard on engagement. 2 to 3 second delay at over-revving under W.O.T. before you feel it shift hard.  You can feel the sled shift out slowly at first, then pushes hard during or after the RPM drop. Feels crazy fast after the engine pulls back down. Feels faster then stock setting.

Answer; You just proved what I said. Know what the shift delay is? My explanation for this event would be from knowing the secondary is torque sensing. You accelerate the engine and the engine runs over it's rated rpm. The upshift is stalled, engine torque is diminished and so does the upshift. The engine pulls back on rated rpm and the secondary reacts accordingly by upshifting with your clutching on the engine's hp peak (rated rpms). I would take the primary spring and reduce the start force by 20 lbs so say if you had a 280/390, then can go to a 260/390.
Another avenue is to add slight more flyweight and reduce this "delay" to maximize acceleration off the bottom of the shift.
There could be an opportunity to try a helix with a larger start angle than you are presently using to capture more of the "meat" of the engine by making it push with lower improved rpms. IF you are using a (42 / XX), then can try a (44 / XX)


I. N. Quisitivetuner; Still pulls hard on engagement. Not feeling the slow~hard shift-out @ W.O.T.
What is going on!? I open side panels/belts wet. Wiped clutches and panels. Pipe and motor not very hot. Should have warmed it up for another 10 minutes. Primary still needs to climb another 1/4" for full shift.
Answer; Lack of belt at top of primary then flyweight is too light and will not let tra arm push hard enough. Need more flyweight to push the primary closed an additional amount when nearing full shift.
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Tuning For a Straight Shift. Blended calibration details
Some tuners change a helix to one with a lower finish angle and they get climbing rpms.
Some tuners change a clicker # to a higher number and they get climbing rpms.

Does the engine run with a straight shift on clicker #2?
My definition of 'Straight shift' is the rpms maintaining a certain rpm from bottom end to top end.

On the initial setup, some tuners with a clutch setup have not had a straight shift which resulted in climbing rpms in clicker #2 or #3.
My definition of 'climbing rpms' is "The engine rpms climbing with a range of rpms that indicate the extent or perception of the capacity of their engine fitness or clutch setup."

I have had tuners get drifting rpms (higher) in clicker #3 and asked them to run in clicker #2, however compensate for low rpms by pulling slight flyweight out to achieve the straight shift.

I have had tuners get climbing rpms in clicker #2 and asked them to run in clicker #3, however add slight flyweight to get a straight shift.

Here at this point a tuner can or should adjust with about 4~5 tenths of a gram at a time.
You can adjust the flyweight by shaving the end of a setscrew. 3 threads shaved off on a 1/4 x 28 UNF screw is about 0.4 grams.
Taking the time to adjust the flyweight for top end with small increments as such, it's fun to do and there will be benefits to performing the exercise with this detail for hitting the flyweight mass spot-on for your engines requirements.

Another method to achieve straight shift with RER compression style secondary spring.
For lack of better numbers, if you have the black secondary spring [160-300] and want increased rpms in the bottom end of the shift range, you can leave your clutching on the primary the way it is and simply change to a green secondary spring [180-300].

Previously you had climbing rpms from 78 to 8000 with a black secondary spring.
Now with the new spring calibration the rpms hit the number 8 and maintain 8K right to top end.
The green spring is stalling the shift from the primary making the engine produce more rpms before the primary starts to push again
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Clutch temperatures so hot?
The #1 way to reduce temperatures is to calibrate allowing the engine to run the closest it can at “rated rpms” under full throttle.
Regardless of temperature you measure, whether its hot or cold or warm or burning or freezing - The lowest temperature you'll measure is when having calibration allow the engine to run at "rated rpms" on a sustained wide open throttle pull.
If you run the engine higher than rated rpms [example 8400] the system temperature will increase.
If you run the engine lower than rated rpms [example 8000] the system temperature will increase.

You will find and efficient clutch setup will reveal temperatures;
Hottest temperature is on primary stationary sheave [engine sheave]
Next coolest is the primary sliding sheave
Next coolest are the secondary sheaves.

Some will even find that primary sliding and secondary are cool vs. the engine stationary sheave.
The combustion heat is transmit through the crankshaft into the crank stub and onto the stationary sheave.
The sliding sheave is disconnected from the engine, the disconnection is at the inner sheave bushing....little if no heat will transmit through a bushing - the heat transfer goes through the belt.
Heat in the primary is caused by the belt moving along the sheave faces at a slower rate than full capacity and usually when the engine cannot run at its rated rpms.
If you are calibrating the system to run the engine at "rated rpms" - The belt will travel along the sheave face the quickest when the clutches are calibrated to run at rated rpms. Lower or higher than rated, the belt will not travel at the optimum rate.

Definition - Rated rpms: The rpms the engine makes its maximum horsepower at. Example 800R = 8150 rpms.
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Clutch spring forces (higher) equate to higher performance?

Question) Joe, how does that 200/320 work in the 800, I know the stock doo spring is 160/290, does that work better than the 200/290 like doo has for the 800?  Do those numbers correspond to performance? The more pounds the faster?

Answer)Hello...the spring force values with respect to performance is not an inherent nature. What I mean there is (higher spring forces do not equate with higher performance)

I can work with these springs.
200/320 - my spring.

One of the first details I look at when I start to play with calibrating is the spring selections that are available to me. I try to chose a spring to give me a buffer to work with.
My kit spring is a 200/320.
If I have a certain problem like drifting rpms with a kit, (drifting low) then I can go with a xxx/350 finish - The higher final force will allow correct rpms.
If I have a certain problem like drifting rpms with a kit, (drifting high) then I can go with a xxx/290 finish - The lower final force will allow correct rpms.

200/xxx gives about 4000 engagement.

I want higher engagement, (4200) then I can go

Now the clutch kit is a very versatile one and will put a smile on the face of even a very critical tuner.
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Controlling track spin at the start line

Controlling track spin in poor starting line conditions.

This usually means either taking the primary spring and lowering the start force or taking the secondary spring and lowering the start force or using a primary clutch ramp that will allow the engine to labour more. 

The start force of the secondary spring controls the size/magnitude of the shift force by raising the shift point rpm. (more rpm more hp)
In other words the lower the start force you lower the upshift force and at a lower engine rpm you will apply less hp to the track, but the question arises "how much power can you apply to the start line at this particular day in this particular condition?"
Next question;  what happens to the traction when you apply too much power to the track?

The lower spring force engages the shift point sooner however may accelerate too hard (observe too low of hp) and make the engine labor too much that you get a slow start.
Example springs;  135/300, 160/300, 180/300, 200/300, 225/300, 231/300

When you increase the start force of the spring you increase the upshift rpms to the track.  (how much hp is at that shift rpm?)
Each time you increase the spring force what in effect is you are “stalling the upshift” thus allowing the engine to rev quicker.

So you are trying to get maximum upshift force without letting the engine bog or be slow to accelerate when you hit the throttle….one of those springs will get you out front the quickest…..which one?.....i don’t know.
Add more traction in the track, harder grip on the snow and then you want to on-purpose increase the secondary spring start force, you want the engine to overcome the enhanced traction and allow a higher upshift rpm blowing the track out and have quickest rpms.

Spring forces control
1)the steady rpms under full throttle
2)the upshift point rpm
3)the rpm acceleration from one rpm to-a-higher-rpm.

Spring force to control #3 there, you have to control the time it takes the engine to get from engagement rpms to its peak rpm or whatever rpm you are going to run the engine at.  Torque rpm or hp rpm?

So then can take the start force and lower it and forces the engine to accelerate slower in 10th’s of a second – learned this through using racepack udx software hooked up to everything that turns. powerful of a tool to help you learn what to do to your own personal sled to launch.

The amsnow snowdeo shootout last year i made a 1200 turbo come off the line 1000 rpms lower rpms than rated.  Rated rpms 8300 @ 230hp.  7100 rpms was around 100hp or so...the sled bogged off the line so hard (and sounded absolutely terrible)  however the track did not spin one bit in 60 feet, and pulled off the quickest 60 foot time of the shootout, a snodeo low 60' record.  We walked up to the track and you can look in the dirt at the individual pic marks from the studs.  Justin the driver said it took all of his strength to hang on to the sled. 
Some guys just looked at me when that sled launched and they laffed until the announcer said “HOLY COW a new record”  pretty proud moment.

---less force = less rpms.
More force = more rpms
More spring force “increases the upshift point” and allows the engine to build more horsepower before the clutch starts to upshift.

From the secondary clutch looking at the primary clutch; More secondary spring force resists the push of the primary clutch lever and allows for more rpms.

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How do the primary springs effect mid and top end
The spring force affects rpms, not top end mph.
1)The spring force changes rpms
2)Rpms affect top end.
3)Top end is changed from different rpms.

Effects; Rpms at rated “rated rpms” will get the best top end.  Low rpms or high rpms the top end mph will be lower.

So then you adjust the spring final force xxx/320 or xxx/350 or xxx/380 to get the rpms to be steady and at rated “ rated rpms
Example using 200/350
04/800 rated rpms = 8000
At highest mph the rpms turn down to 7800
The spring force changes rpms
Rpms affect top end.
Higher spring force will raise rpms
If 7800 with xxx/350 then can go to a xxx/380
Raising the final force by 30 lbs.
Retest and now should observe 8000

Example using 200/350
04/800 rated rpms = 8000
At highest mph the rpms turn up to 8200
The spring force changes rpms
Rpms affect top end.
lower spring force will lower rpms
If 8200 with xxx/350 then can go to a xxx/320
Lowering the final force by 30 lbs
Retest and now should observe 8000

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Engine braking

Question; 04 Renegade 800ho. Seems that when I let off the throttle coming into a corner the sled decelerates quicker than it did before the clutch kit in stall (0-3000 ft.)
Seemed to "roll freeer" with the stock clutching. Now my question is what causes that to happen and what is the part making it do that?

Answer; You should have a 225/300 purple doo secondary spring, the strength can be reduced by taking the start force and reducing it to 200/300 as shown in the picture here .

Each time you reduce the force of the spring you will lower the magnitude of engine braking.

One other way is to remove your 415 ramps and install 413 or from any short track 414 ramps.  The steeper the ramp the stronger the engine braking.
Picture compare - 413, 414, 415 ramps
Look at the 6th picture down and the difference between your 415 and the other two ramps.

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