CVT tuning with different dimension belts?

[brianwheelies]

I wanted to try a new belt today because my old one is wearing thin. I went with the only local option opting for a 723-17.7-30. My stock belt is 738-18-30.

This replacement belt is a little shorter but it makes the transmission work well in one way and poorly in another. The typical CVT tradeoff if you will.

I was having problems with the stock belt in that I could never get the transmission to shift smoothly and I could either have the bottom half of the actual speed running smoothly or I could have to top half of my actual speed pulling well. Never both.

This short belt has blended the action into one smooth transmission shift as opposed to the two but I have also lost some top end.

It does bother me that I can't get the variator fully closed or the rear pulley fully open though. Is it just a design flaw or do I need to get a larger than stock belt and tune from there?

What was happening with the stock belt and lighter sliders and 1000rpm contra spring is the rear pulley was staying closed too long and i would get a lot of over rev until 30ish mph where the pulleys would changed and it would rubberband like switch gears and pull nicely up top. Use the next weight heavier rollers and it would accelerate nicely down low and struggle from 25mph and up.

I just switched back to the stock contra spring still using the shorter belt and it is going ok at best. Top speed is somewhere near 42mph maybe 43.

This really is going in different directions. If anyone has any constructive criticisms or knowledge to share, please share.

[agrogod]

I've investigated that same thing myself, the 730-18-30 is the size on the RH50. Your changing to the 723-17.7-30 is extreme, and as you have found out, is affecting your overall performance.
The first number is belt length, the second belt width, third tooth angle.
In my case a 728-17.5-28 will knock a little off the top end but should help the acceleration at take off (but just barely), my only other option is to go longer but then I risk the possibility of the belt leaving the clutch pulley at higher speeds. I have not found a "little" longer belt let's say a 731-18-30, always an extreme length change 738 - 743, way to long unless I consider doing a complete engine swap, but that defeats the purpose of "tuning" what I've got.
From what I have found out you really only want to go 1-2 mm larger or smaller without risking to much of a performance hit.
You either get good acceleration or good top end, pick your poison.

[ericalm]

I was having problems with the stock belt in that I could never get the transmission to shift smoothly and I could either have the bottom half of the actual speed running smoothly or I could have to top half of my actual speed pulling well. Never both.

I'm not sure this was due to the belt, though. Different roller/slider combos may have gotten rid of this issue, but have you looked at other variators?

One problem with CVT behavior/tuning is that it's often not replicable between different riders. Seems the only way to find that perfect setup is trial and error!

[brianwheelies]

I've investigated that same thing myself, the 730-18-30 is the size on the RH50.

We have the same engine and yours has a 730 instead of a 738?

I wonder why they changed sizes? When I look up the Roughhouse on Scooterworks it says 738-18-30 like the one that came in my bike.

[waspmike]

Malossi belts tend to be wider than OEM for some applications. This gives more top speed as they get squeezed further out of the driven pulley.

Usual belt rubbing on casing warning.

One problem with CVT behavior/tuning is that it's often not replicable between different riders. Seems the only way to find that perfect setup is trial and error!

Or for road use get a J Costa as they have already done all the work. At least for stock scoots and yes they are tunable just like any other variator.

[babblefish]

The shorter the belt is, the lower your top speed will be because it won't be able to ride up to the variator's outer circumference. May be a way for manufacturers to limit the overall top speed of a scooter...

[agrogod]

I've investigated that same thing myself, the 730-18-30 is the size on the RH50.

We have the same engine and yours has a 730 instead of a 738?

I wonder why they changed sizes? When I look up the Roughhouse on Scooterworks it says 738-18-30 like the one that came in my bike.

Because of the fantastic writings of the owners manual, and the lack of many useful specs., shortly after buying, it prompted me to crack the CVT open so I could see what belt was in there. Now if indeed our engines are the same setup, an investigation as to whether I can use a "much" longer belt warrants a little further delving into this matter.

As for SW's listing I am baffled, because earlier this year it did show the 730 not the 738 as being the correct size for my scoot.
So now I need to ask anyone that has a 2011 RH50 to check the belt length, not something written in a manual or on the internet, but physically open the CVT and and look at the size stamped on the belt.
I am very curious to find out if this is the new belt size, and if so the new length may just fit mine without being as drastic a change as I initially thought.

[brianwheelies]

I would like to find a 730 belt. The local vendor has a 729 gates belt which should be close enough.

When I first got my scooter it was quick and smooth accelerating and had decent top speed. I had the local Genuine dealer do my first service and it has never been the same. Always slow in the middle of the power band. Now I am wondering if they changed the belt to a longer belt(for what reason I do not know) and this is why it has that soggy performance in the middle rpm range.

[agrogod]

Try here