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Yamaha Continuously Variable Transmission Basics (CVT)

I wanted to revisit the basics of how the Yamaha CVT system operates because I am seeing so many questions from operators who are new to the system. For many of you, this will just be a repeat of your already known knowledge of the system. I hope this clears up how the CVT operates and minimizes the myths and/or incorrect information that I am seeing in the threads.

Starting with engine idling, the wet clutch is retracted or in a neutral position. As engine rpm is increased, the clutch pucks swing outward and begin to engage the wetclutch bell. At this point, the primary and secondary clutches begin to turn in their lowest ratio.

The CVT will continue to operate at this low gear position until the rpm and vehicle speed has reached the shift out phase. This is when the outward centrifugal force of the weights becomes stronger than the spring pressure on the secondary clutch. On the Rmax, I believe this is about 15mph in stock form. This means that all crawling and low speed driving is in the low ratio position, which has nothing to do with the size of weights installed or any shims or sheave modifications.

Now just to clarify, an added shim or lower cut sheave will produce a lower starting gear ratio. This means you will have more torque to the wheels in the 0 to 15mph range of the clutch operation, however due to the lower gearing, you may now be in a 0 to 12mph range before the weights make contact and begin the shifting cycle. There is no difference in noise, it is just lower gearing for taking off with big tires, crawling, climbing, etc. There is also no difference in rpm for your first shift, it will just come sooner in vehicle speed due to the lower gearing.

When the weights are spinning fast enough to overcome the secondary spring pressure, the weights will be forced against the camplate and slide the primary sheave inward. This forces the belt to ride in a higher position, increasing the gear ration to the secondary clutch. Because the belt remains the same length, the belt is lowered in the secondary as the belt raises in the primary. This gives you higher gearing automatically. It is during this process that the weight sizes effect the operation of the CVT. Heavier weights will apply more force at lower engine rpm. Lighter weights will require more engine rpm in order to obtain the same force required to push the primary sheave inward, over coming the rear spring.

After the CVT is shifted to its highest position, in order to accelerate the vehicle forward at a faster speed will require higher engine rpm. This is where most of the engine and transmission noise becomes a problem. The engine rpm can be lowered by increasing the weight size and/or machining the sheave to operate at a higher gear ratio.

Letting off the throttle reverses the process until the primary sheave slides back into a lower gear positions and the weights slide back to their starting point. There is a one-way bearing which engages to keep pressure on the clutch and limit its free spooling.

A shim will give you a lower starting gear, but it will subtract a small amount from your highest gear ratio. However, a machined sheave will give you both a lower starting gear and a higher top gear.




 

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Thank you for this. Coming from a 4 seat Talon as our first SXS, I am new to the CVT world.

I have the 22gram kit in my basket which includes the 1mm shim. What reduction in top speed should be expected in the RMX? Top speed is not very important to me, I see more need for the combination of a deeper starting ratio and lower operating RPM, but am curious.

The "funny" part is I don't have the machine yet, just the VIN this week. I've always been a tinkerer and will probably dive into the CVT not long after getting the machine.
 

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Thank you for this. Coming from a 4 seat Talon as our first SXS, I am new to the CVT world.

I have the 22gram kit in my basket which includes the 1mm shim. What reduction in top speed should be expected in the RMX? Top speed is not very important to me, I see more need for the combination of a deeper starting ratio and lower operating RPM, but am curious.

The "funny" part is I don't have the machine yet, just the VIN this week. I've always been a tinkerer and will probably dive into the CVT not long after getting the machine.
My Rmax 2 with a 1mm shim tops out at 66 MPH on the GPS speedo. I think it ran 71 when new, so, roughly 5MPH off the top end.

It’s a rare event if I ever get it up to 50 MPH anywhere I drive.
 

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Stock sheave ratio is 2.9:1
A 1mm shim produces 3.25:1 ratio.
It’s about a 15.5 percent increase.
Ive lost 8% of my gearing in tire size but I’ve gained back more than I lost.
It takes less throttle input to get the tires rolling when crawling in rocks than it did stock and less manipulation of the throttle to keep them moving from one big boulder to the next.
 

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"Heavier weights will apply more force at lower engine rpm." Does that mean more torque to the wheels at a lower rpm?
 

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Discussion Starter · #7 ·
I calculated a 4mph loss, actual will vary depending on tire size and terrain. It's not a significant loss in speed, but it is a pretty nice gain in torque.

I had stainless steel 0.5mm shims machined that are exactly the correct size. I have not put them up for sale yet though.

I have the 22gram kit in my basket which includes the 1mm shim. What reduction in top speed should be expected in the RMX?
 

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Discussion Starter · #8 ·
The shim will give you a boost to the wheels during the pre-shift of the clutch. The heavier weights will engage sooner at a lower engine rpm, so engine torque will be less due to the engine's powerband. The weights do not change anything until first shift out, which is about 15 mph.

To clarify. 0-15mph, 1mm shim gives 15% lower gearing so more power to the wheels. 15-40mph or full shift out, less torque due to less engine rpm while shifting, but quieter running. Full shift to top speed, same power as stock.

"Heavier weights will apply more force at lower engine rpm." Does that mean more torque to the wheels at a lower rpm?
 

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The shim will give you a boost to the wheels during the pre-shift of the clutch. The heavier weights will engage sooner at a lower engine rpm, so engine torque will be less due to the engine's powerband. The weights do not change anything until first shift out, which is about 15 mph.

To clarify. 0-15mph, 1mm shim gives 15% lower gearing so more power to the wheels. 15-40mph or full shift out, less torque due to less engine rpm while shifting, but quieter running. Full shift to top speed, same power as stock.
OK. Gotcha. Thanks.
 

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I had stainless steel 0.5mm shims machined that are exactly the correct size. I have not put them up for sale yet though.
Sounds good, I will keep an eye out for that. I will either stick with stock 29's (my gut says this is where I'll be) or possibly go to 30's. 1mm could be more than needed, but we do mostly slower riding and run Moab, Sand Hollow a couple times a year where the deeper starting ratio would be most useful. TBD once I see how the machine behaves stock.
 

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The shim will give you a boost to the wheels during the pre-shift of the clutch. The heavier weights will engage sooner at a lower engine rpm, so engine torque will be less due to the engine's powerband. The weights do not change anything until first shift out, which is about 15 mph.

To clarify. 0-15mph, 1mm shim gives 15% lower gearing so more power to the wheels. 15-40mph or full shift out, less torque due to less engine rpm while shifting, but quieter running. Full shift to top speed, same power as stock.
Ready to buy a 1mm shim if you have them available. Is your eBay store UTV engineering?
 

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Ready to buy a 1mm shim if you have them available. Is your eBay store UTV engineering?
In case he isn’t back on the forum for a bit, yes that’s correct, UTV Engineering
 

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I updated the listing
Thank you! Just ordered. Now I can take everything back apart and get ready for 32s! Is it better to put the shims behind the sleeve (I may not be calling the steel tube the correct name) at the engine side or just under the nut?
 
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