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· Registered
52 Posts
Discussion Starter · #1 ·
I have read what seems to be every post and reply on this subject, but could not find the answer. I have 33,000 miles on a 2005 Burgman 400. The variator was off at 21,000 miles and the rollers were in good shape, but I want to lower the rpm's @ hiway speeds. I am debateing on whether to stick to rollers and put 21gr rollers in, or to put 21gr DRP sliders in. I was wandering which would give the lowest rpm's at 60-80mph. The better acceleration around town with the SLR doesn't mean much to me, but I do want the lowest rpm's at cruising speed. Has any one ever tried both 21gr rollers and 21gr sliders.

BTW- while reading through the posts I noticed that quite a few people say they are going to try a certain set up and post the results and then don't post the results. Post them, this is an information board.:)


· Registered
3,599 Posts
Evidently you have missed some posts on the subject as many have posted their results through the years. You might have to go back 2 or 3 years but they are here. My thought has always been to keep it stock as any change to the dynamic of the weights will effect the clutch performance and belt wear proportionately. "Tuning" the tranny is an art that amateurs have been playing with for years on scooters. But most Pro's agree that the weights and springs must be "tuned" in unison to compliment the performance. I also feel that if you want to run highway speeds more than 65mph for long periods of time you need the newer post '07 400 or the 650. The pre '07 400 were designed more for a commuter bike rather than a highway (high speed) touring bike. Good Luck with your Research!

· Registered
422 Posts

Hi qaz,

I have had three scooters and have tuned them all to my needs each time. I respectfully disagree with scooterno, but it is possible to get it wrong.

These CVT transmissions are very simple and self adjusting. If you have ever ridden a 10 speed bicycle just remember how the gearing works on that. You change gear ratios on the front and back de-railers to suite your need for speed or torque.

First the scooter clutch. It is going to engage at a specific CLUTCH rpm every time, BUT this RPM is determined by linear belt speed not front variator RPM. Clutch engagement is all based on centripetal force generated by the clutch pads spinning, and spring tension, and these are fixed constants. Also a constant, is the sheave half's compressed by the clutch main spring. This serves act as your rear gear shift like the rear de-railer of a bicycle, but it is torque selectable, not rider selectable like a bicycle.

Ohh I can't believe I am thinking so hard on a Sunday night.

Now lets move to the variator. The variator is held to its lowest gear by the belt and the main spring tension on the clutch sheave's. At rest you will see the belt on the smallest diameter of the variator, and the largest diameter of the clutch. Once the engine is running the force of the variator weights begins to move the variator sheave halfs together, causing the belt to ride on a larger diameter pulley, and this causes an increase in belt speed, and a corresponding increase in clutch rpm.

Once clutch engagement rpm is achieved the clutch bell begins to lock up and the wheel spins. (You start moving, don't forget the side stand.:smile:)

So lets say you want to put in heavy rollers, if you do this it will be like staring out on the big sprocket of your bicycle, and lets say your clutch engages at 4000 rpm engine speed. You will wind up with a lower cruise rpm, if you have the torque (legs) to get going. Getting going is hard work on the engine, but once you get going, you can cruise easily.

But lets also say you found a special weight, it is not round, and operates on a principle of leverage. It also is lighter than the stock weight. The special weight lets the engine spin up at a higher RPM, it is lighter. The engine easily makes it to its peak torque RPM, lets say 6000, and the clutch engages, and she moves out briskly and smoothly. Your engine is happy, this is easy work.

In both of these cases the bike will not move until linear belt speed is great enough to engage the rear clutch at its set engagement RPM. (There is some slippage before full engagement, but for the sake of discussion lets not mention it again). The only difference is the engine didn't have to work as hard to get the bike moving with the special weights. More RPM doesn't equate to more work, just more power available to do work.

Now lets cruise. As the engine rpm rises, everything will reach a point where you are in top gear on the variator, and top gear on the rear main pulley. (no longer calling it a clutch, because it is fully locked and all that is at play now is the pulley and main spring back there).

Any increase in speed will come about as a result of increasing engine RPM.

However: Ahh you never thought we would get here. The special non round weights have an advantage, their shape allows the front variator to move just a little bit further inward making a slightly higher gearing, giving a higher belt speed for the same engine RPM over the stock weights. This is where you have your cake and eat it too. More bottom end power, and lower cruise RPM, plus a brisk down shift to bring the engine back to peak torque if needed for acceleration.

Sliders can increase effective starting torque by raising engine rpm initially, but leverage their unique shape to give a final higher top gear on the variator, and downshift faster than rollers.

Hope this helps someone, I didn't come up with this on my own, Many posters on the board helped me understand CVTs. My cruise RPM dropped by 800, over stock at the same indicated speed.

Time to turn some wrenches ehh.

· I'm Retired
8,751 Posts
gaz, at the risk of not being believed ;) , take a look at the animated picture they show on the Union Materials website. It shows the DPS weights on one side with a stock roller on the other side.

One other image might help in understanding how a variator works.

Whoever designed the DPS weights (Paul Wu?), really came up with something. It is the best bang for the buck "performance" improvement for a scooter. "Performance" doesn't have to mean racing from one stop light to another. I just like how the bike will respond more effortlessly to what I ask it to do. And then I love how when I'm cruising along on the freeway, the rpms fall...about 1000 over the equivalent stock or OEM weight. It makes for a very relaxed feeling when you're riding.

I've tried everything from 18 to 23 gram DPS weights. Eighteen and 19 gram weights are great for everyday use with the 19 gram weights lowering your rpms another 500. 21 gram weights would be okay for someone in Florida where the highest mountain is the nearest freeway overpass...or that's what someone from there wrote once. The 23 gram weights made my drivetrain vibrate and shudder a lot like being in too tall of a gear. I had them back out within a couple miles.

As TwoWheelTim wrote, the DPS weights add a "gear" effect, whereas the stock OEM weights are more linear in their performance.


· Registered
360 Posts
Thanks for the awesome explanation, Chris!!!! You have an amazing grasp of the workings of our CVTs!!!! You rock!!
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