Dr Pulley 20x12 14GR

[TANWare]

Ah, ok, yes at speeds like that it will raise. Also with use it goes up as well.................

[Cortez]

Short WOT top speed showed also 92 MPH but now 7,800 RPM not 8,200. I have not had a long enough run to see if it would go higher. Now this too was sitting streight up, not tucked in for the run.

That's interesting.
I'm not sure I understand why lighter weights then stock would take the revs down at higher
speeds, I figured the revs would rise evenly from 0 to top speed.

[TANWare]

No, the lighter "you" are.

Edit;  the bike and rider at 560 vs, 660 LBS has lower resistance against the torque, especially at breaking static inertia. This will with a lower resitence not pull the variator as tight so RPM's will be slightly lower as without the really tight variator the gear ratio does not raise as high to increase the RPM's.

Now the difference may only be 100-200 RPM but as can be seen this makes a difference. Now 200 more RPM may be there but also to get that you have that extra 100 LBS so side by side performance the bike will be slower with the heavier load.

Edit 2; without going into the complex math and physics involved in variator design they are made so the RPM's do not evenly go up between 0 to top speed. The design of slider compared to round rollers make the RPM variance at the same weight greater. In the end you have a wider range of ratios.

The stock rollers are actually 23x12 with a service limit of 22mm by the service manual. The reason for 20x12 is to further raise the initial gear ratio and rpm. This is why even with the stock 15.5 gram weight you still would have a higher low gear but because of the ramp/slider design you change over to a taller top gear earlier (essentially (guessing at the sizes here) with the contact points the slider is acting like a 27x12mm roller as it sets into high gear).

[TANWare]

Well first full tank on the new rollers. To my suprise no loss in MPG. It returned 72 MPG and this is with a few WOT's in acceleration and top end. Now this is only the first tank so consider this a preliminary report so far.

As far as 75 MPH the revs at cruise were 6,700. So this felt a bit rushed. I would recomend if your primary driving is at that speed to get at least the 20x12 15 gram sliders. At 75-80 then the 16 gram sliders. Of corsse the heavier the slider the less improvement to low speed as it will drop the revs there as well.

For 70 MPH the 6,200 RPM is very comfortable, 65 MPH at 5,700 even more so. Riding at 50 MPH or under the RPM's are slightly higher and hitting the throttle will raise them higher than before too. With the fact the CVT is a torque multiplier the 10% or so higher revs gives the 10% back as added torque to the rear wheels and the fact the engine produces more torque per rev at higher RPMs adds to this as well. You defin ately feel the difference.

Now I should add though my engine note about 3/4 through the tank changed slightly. I think the engine has found another step in breaking free. The rev responce seems to be slightly quicker and from a stop the exauhst note almost has a small rap to it at first. The carb with 50% throttle also seems to have a slightly throatier sound to it from when the tank started. This could just be a placebo effect too or maybe my ears just cleared out as I was not expeting/looking for this and was not paying close enough attention.   

[Cortez]

Well first full tank on the new rollers. To my suprise no loss in MPG. It returned 72 MPG and this is with a few WOT's in acceleration and top end. Now this is only the first tank so consider this a preliminary report so far.

As far as 75 MPH the revs at cruise were 6,700. So this felt a bit rushed. I would recomend if your primary driving is at that speed to get at least the 20x12 15 gram sliders. At 75-80 then the 16 gram sliders. Of corsse the heavier the slider the less improvement to low speed as it will drop the revs there as well.

For 70 MPH the 6,200 RPM is very comfortable, 65 MPH at 5,700 even more so. Riding at 50 MPH or under the RPM's are slightly higher and hitting the throttle will raise them higher than before too.

Thanks, great info!
Sounds like the 14g pulleys are a great choice for everyone except guys who spend a lot of time
on the freeway at 75mph+, but this scooter is probably not a good choice for that kind of riding
anyways.

I'd like to have 80mph at no more then 6600-6700 for ME to feel comfortable doing that speed for
2-2,5 hours that I'd have to be doing to get me beyond the boring roads here. Sounds like that might
be possible with 15g pulleys, eh?

Of course, the 0-60 acceleration should be under 10 seconds too..
Gaah, we need to transplant burgman 650's CVT..  

EDIT: Amazing MPG figures, too! If that's US gallons.

[axy]

I still do not understand that "fear or revs". It is unhealthy. 
I bet my 250 cc scoot could spend its life at 75 mph without any issues.
Much more likely than the same scoot driven at 25 mph with frequent stops/go's in city traffic.

[TANWare]

Yes, US gallons. I was expecting a hit to MPG of at lesy 2 but more likely 4 MPG or more. It is a pleasant supprise not to see one at all. Most of the ime I tried to ride normally, for me at least, so this I am sure helped. It is hard not to give it that extra juice as it really wants to GO!

Personally I am not comfortable at 80 or even 75 on this bike. 75 now though feels a bit rushed with the RPM's althogh the bike was rock steady. I would say for daily/extended use at 75 MPH go with the 15 gram and for 80 MPH the 16 gram. With the 15's I'd say 10 second 0-60 is definately possible. Unless you are only 160 LBS or lighter, the 16 gram I don't think will get you there but it should still leave you with an 11 second or slightly better 0-60 MPH time or better than with the stock rollers.

Ia gree for casual use the 14's are an awsome choice but if you like the lugging style of ride I would suggest the 15's. The 14's up to 50 MPH provide a slightly winding feel to the bike, like an auto trans always in high performance mode. The 15's should provide a more relaxed feel to the engine but of course less acceleration performance.

It isn't a "FEAR" of revs, just some prefer the feel of lower rev's. When riding at higher rev's when you hit the gas or let off the acceleration/deceleration is stronger. When you are riding a bumpy road with a twist grip it is hard to be 100% constant and locked on the throttle position and this then can actually make a bumpy road feel worse than it is as just one example. So with the lower gearing while acceleration is lessend it is smoothed out a bit and feels less twitchy.

And yes, this bike could easily sit at 6,700 RPM all day long. Rev's do not kill a motor any faster so long as it is taken care of. Rev's though, if not watched out for, can easily eat up more fuel..........................

Edit; another less thought of situation is in the rain or other slippery surfaces like stones. The lowered torque to the rear wheel of a lugging engine will keep you better planted.........

[Cortez]

I still do not understand that "fear or revs". It is unhealthy. 
I bet my 250 cc scoot could spend its life at 75 mph without any issues.
Much more likely than the same scoot driven at 25 mph with frequent stops/go's in city traffic.

Yeah, it probably could, but it would probably fall apart sooner at constant 8000 then
7000, and then there's the fuel economy thing, and noise/vibrations.

The Downtown (stock) is very smooth at virtually all speeds, but the vibes get to you
after around 7500, so it would be nice if it would be as fast as possible at 7500 or under,
but without loosing too much of 0-60mph acceleration (which is not impressive at all for
a 30hp scooter, but that can be changed easily as you can see).

I just don't want to end up selling the thing after two years because I've put 40.000km
on it at almost 8000 revs and can't stop thinking about how long it will last beyond that
point. Maybe it's not a realistic fear, but if it's bugging you, you won't take the trip, right?

[Cortez]

Edit 2; without going into the complex math and physics involved in variator design they are made so the RPM's do not evenly go up between 0 to top speed. The design of slider compared to round rollers make the RPM variance at the same weight greater. In the end you have a wider range of ratios.

The stock rollers are actually 23x12 with a service limit of 22mm by the service manual. The reason for 20x12 is to further raise the initial gear ratio and rpm. This is why even with the stock 15.5 gram weight you still would have a higher low gear but because of the ramp/slider design you change over to a taller top gear earlier (essentially (guessing at the sizes here) with the contact points the slider is acting like a 27x12mm roller as it sets into high gear).

Never thought of that, thanks, makes perfect sense.

BTW; you shouldn't edit posts that much, especially after a reply to it has been made, I
stumbled upon the edit2 by accident, the forum won't notify people you edited your post
and will end up reading under it and never see you edited the original post!

Just write a new post, and edit only when you write something wrong or miss a word or
something.

[axy]

Yeah, it probably could, but it would probably fall apart sooner at constant 8000 then
7000, and then there's the fuel economy thing, and noise/vibrations.

Yes, whole 100 kms before.

The Downtown (stock) is very smooth at virtually all speeds, but the vibes get to you
after around 7500, so it would be nice if it would be as fast as possible at 7500 or under,
but without loosing too much of 0-60mph acceleration (which is not impressive at all for
a 30hp scooter, but that can be changed easily as you can see).

I just don't want to end up selling the thing after two years because I've put 40.000km
on it at almost 8000 revs and can't stop thinking about how long it will last beyond that
point. Maybe it's not a realistic fear, but if it's bugging you, you won't take the trip, right?

Well, it certainly is not easy being you. 

How about letting go the fears of things falling apart, imminent expenses and trouble, excessive consumption and just drive the scoot?
Like, you know, relaxed style?
Did that idea ever cross your mind?

[TANWare]

to do 8,000 RPM even stock you would have to be at like 85+ MPH, almost WOT. At 80 MPH stock you should be about 7,200 to 7,500 or so RPM for cruising........

I edit alot as I don't want to artificially raise my post count. Apparently I had edited while you were posting and reading the non edited version, sorry about that.

[racewalker]

I don't know what you guys are worrying about. My S125 has 31000K on it almost all WOT and I changed to sliders to get more top end. It runs as good as the day I purchased it. My 300I is doing the same run at about 110Kmh 6 days a week. I am planning a 6000+ K trip next summer with it, 3200 in 4 days. I don't even think about how long the bike will last, it is built well.

[TANWare]

Personally I'm not too woried about longevity just MPG and ride. These small displacement motors are made to be wound out in general.

Now performance of a 30HP engine is actually a bit misleading. All gas engines have a torque curve. Some are flatter than others and this can greatly effect performance in acceleration. While the 400cc Suzuki is compareable to our 300cc performance the rev points and also the torque curve is different. More than likely through added efficiencies the new engines have better efficiency than the older 400cc so peak HP is better per cc but low end torque the 400cc may easily trounce our bikes.

Now the 400cc bike has almost a 100 LBS totat weight disadvantage yet acceleration stock to 60 MPH is not far off. This is a good indicator of the 400cc's higher low end torque. The old addage is there is no repalcement for torque generation than displacement. So far even today this is still a good generalization but not as true in efficiency or total HP anymore.

For the best ballanced performance of acceleration and MPG you want to operate within the RPM range of the max torque curve of an engine. This is the range the engine is most efficient in converting fuel to power. Opertaing above that is where the torque curve is going down but has not ramped below that of the RPM ramp until it goes to RPM' above the max HP. Above the max HP your torque ramp has fallen below that of the RPM ramp to red line.

Now for reference we get 26.5nm torque at 6,500 RPM. That is 24.2 HP from the crank at that speed. If the torque drops to 25.5 at 5,800 RPM that is 20.8 HP available. This gives us 16% more HP and 12% greater power multiplication from the gear ratio so percieved power for acceleration at WOT is almost a 30% increase (1.12x1.16 is 129% increase). This is simplistic math and there are other factors but just to show you a generalization.

For further comparison at the crank the Burgman 400cc is 34nm at 6,000 RPM so at max torque curve that is 28.66 HP available. To get to max HP on the Burgman you raise the RPM to 7,500. With us max torque is 6,500 but max HP is @ 8,500 RPM. So this is further food for thought especially where the burgman 400 is at speed against wind resistance....................

Edited for some typo's

[Goodrich]

I found a set of 20x12 13GR.....would this be ok if the majority of my riding is below 65mph?

[TANWare]

I wouldn't, it would place your low speed cruising RPM's too high. If you don't mind winding it out that is fine, but I would suggest against it. Try emailing the guy below. It is expired now but maybe he still has some stock etc.

http://cgi.ebay.com/ebaymotors/Dr-Pulley-slide-rollers-20x12-Kymco-Downtown-300i-YP250-_W0QQcmdZViewItemQQhashZitem2312671f59QQitemZ150632603481QQptZMotorsQ5fATVQ5fPartsQ5fAccessories