Equivalent belts?

[stepthrutuner]

I would like to start an interesting discussion.

Is this belt?:

Description:	CVT Scooter belt
Width:	18.5mm
Height:	8mm
Length:	0.811m

Equivalent to this belt?:

16.8x8x840

They both seem to be listed for my scooter.

Does this seem to make sense? Who can think of advantages or disadvantages for either? Think a bunch before you answer. I wish I had them both in hand to test out.

[90GTVert]

I would definitely say they are not equivalent. Obviously going purely on specs you would be looking at an 18.5x8x811 vs a 16.8x8x840.

I always thought the middle number was the angle of the belt, not the height though, so they could be way off of each other there... or I could be 100% wrong. I've also heard that the middle number is the spacing between teeth of the belt.

On top of that, none fo the belts I've used have been the width they specify. For example, the 788x17x28 belts I get tend to be 16-16.5mm. The 788x18x28 Gates belts are closer to 17mm. So if the 18.5mm belt is truly 18.5mm, its huge compared to the other. The wider belt will be more willing to travel all the way out in the variator and rear pulley. You can add spacers to make it work like the stock belt in the front pulley, but you can't really make it travel down as low in the rear pulley. I have not enjoyed the effects on the wider Gates belts on my engines, and I believe 2strokd shares my opinion there.

The shorter length is going to make it harder to get your max gearing as well. 29mm seems like a pretty good decrease in length. I've never messed with shorter and longer belts though.

[redorchestra]

My experience on this matter is 1mm width equals about 5km/h, but this would only be applicable if your variator halves were unable to close up the full amount. My stock belt is 16mm wide and it gives me a top speed of 55km/h with an 18mm my belt can travel the full pulley face. I had no washer restriction. When I got the scoot the belt was worn down to 13mm and it only reached 35 or 40.
My stock size was 667x16.
Now I have two belts that I am trying: 669x18 and 680x18. The 680 gives a bad shudder and slips before it gets going but top speed is around 75 or 80km/h. the 669 has great take-off and is smooth but top speed is 65km/h.
so on my scooter the belts are definitely not equivalent.

I do have two ideas to make them both work though. 1. grind out a little on the torque converter ditches to allow it to close a little more at idle. To take up all the longer belt slack and stop the slipping and shuddering. 2. grind of a mm of the variator "boss" to allow full travel. like removing the restriction washer for everyone else

[stepthrutuner]

I have mulled this over in my head and have come to these conclusions. :stars: The shorter/wider belt will not 'downgear' as much as the more narrow/longer belt due to the fact that the wider/shorter belt is more limited to the amount it will travel down into the front variator pulley. At the same time, since it is shorter, as well as the fact that more of it's length being encompassed upon the front pulley it necessarily rides lower and thus at a less numerical or multiplicative overall ratio (more like a street bike rather than a dirt bike). However, because more contra pressure is being exerted back there due to the wider belt width as well as it's riding lower in the torque-driver pulleys, more resistance to the variator's centrifugal shifting exists and therefore ratio changing will proceed at a slower pace and acceleration will be enhanced. When full variator weight travel is achieved the wider belt necessarily rides higher in the front vees (higher speed) while at the rear, because of the extra belt being taken up on the front pulley, it is drawn down further into the rear pulleys (higher speed mode as well). This argument assumes that the rear pulleys will not come up against their 'spread' limit.

The behavior of the longer/narrower belt will be that the belt starts out lower in the front pulley and thus higher in the rear pulley (dirt bike gearing). There will be less resistance to the front pulley's shifting and ratio changing will proceed at a quicker pace not allowing engine speed to rise so much. When full variator travel is achieved final gearing will not be as direct or street bike-like. Top speed will be less and the chance of belt slippage will be greater.

So according to my diagnosis the longer/narrower belt will jump out of 'the hole' quicker but will accelerate at a more leisurely pace thereafter to a lower top speed while the wider/shorter belt will not get off the line as quick but will accelerate quicker to a higher top speed. :spin:

[90GTVert]

I dunno how far your Derbi's rear pulley spreads, but I think that "spread limit" may be a big limiting factor with the wide belt.

[90GTVert]

I went out and did a little testing for you since I do have a couple of belts here. They are both the same length, but the widths are different, so I figured I'd try seeing how far down each rides in the rear pulley...

Belt 1


Belt 2


Belt 2 - The mark you see was traced around belt 1.


The difference in these two belts... only 0.8mm. Belt 1 is 16.5mm wide. Belt 2 is 15.7mm wide. If the numbers you have are accurate, you are looking at a margin of 1.7mm.

EDIT : Photobucket seems to be screwing up for me right now, so hopefully those images appear. I can't see them in my album or here. :doh:

[redorchestra]

So you are open to the limit of travel on that rear pulley?
Would it be possible to modify the rear pulley to allow it to open up a bit more?

[stepthrutuner]

I'll see if I can beat Brent to this.

Here's the info, Redorchestra:

49ccscoot.proboards.com/index.cgi?board=transtech&action=display&thread=358

[90GTVert]

Since I have a stock and the modded pulleys sitting around right now I took a comparison pic of the two. The belts are just there to hold them open.



I used the wider belt from above and measured from the edge of the pulley to the top of the belt at it's lowest position. Stock : 22.1mm Modified : 25.7mm

[2strokd]

Makes total sense. In fact over the weekend i played around with belts on my fathers scooter myself. I was kinda surprised when i pulled his stock 780 out and put in the 788 i had brought down with me. At first i left the washer in the vari to feel the real difference. It did launch better but was revving higher to hold speed. Hhhmm, took the washer out and the launch was still tire spinning wonderful and it didnt have to rev higher at speed. Overall conclusion, its bb,d now, leave the long belt in and let her hum. It pulls up the hills and valleys to good not to. Just a better set-up for Pop in the hills. With the stock motor i think the short belt with the washer was best, but top-speed was still limited by the washer. Its a give and take thing w/o an overrange.

[supermel74]

Is there an equivalent kevlar belt in the size of 878*17*28?

[redorchestra]

Thanks guys. That is exactly the info I was looking for.

[90GTVert]

May 19, 2010 15:32:37 GMT -5 supermel74 said:

Is there an equivalent kevlar belt in the size of 878*17*28?

Is that a type meant to be 788 17 28 (common minarelli) or are you really looking for an 878 17 28?

[supermel74]

May 19, 2010 16:44:31 GMT -5 90GTVert said:

May 19, 2010 15:32:37 GMT -5 supermel74 said:

Is there an equivalent kevlar belt in the size of 878*17*28?

Is that a type meant to be 788 17 28 (common minarelli) or are you really looking for an 878 17 28?

I guess a lot of the Adly's use an 878 17 28. I had originally ordered the 788 17 28 and found out it was the wrong size. I have a backup already but I'd like to try out a kevlar. Scrappydogscooters has good prices on the regular belts in that size but no kevlar.

[2strokd]

Allot of Adly's (the ones i have seen) are Minarelli powered. My cuz has one thats a Adly Hammerhead and has a mina shortcase emmision motor on it.