Guys... are there some threads on here about how the PVT works specifically?
Or are some of you willing to explain the details?

I have a very basic understanding... but it's not good enough. I thought it was set up to react to engine RPM and vehicle load?

But then I started thinking about shorter tires, re-gearing at the chain drive and how this might effect performance. At first I thought all it might do really is limit top speed. But then I started reading and got all confused...

I need schooling....

 

Google how does a cvt work. Check out the high/low gear image on this page. http://auto.howstuffworks.com/cvt2.htm

 

I understand that much of it.


The PVT is designed to engage the belt at a certain engine RPM (which is tuneable) right?

From takeoff it then holds gear ratio to a certain 'shift-out' RPM (also tuneable) right?

Once it reaches the point of shift-out it continues to provide continiously variable gear ratios up to full shift-out of the PVT right?

The drive pulley is on the engine, the driven pulley is on the trans right?

All gearing ratios are created by the PVT belt's effective ratio from the drive to driven, right?

The trans/gearbox provides variable sped drive output based on input RPM from the driven clutch pulley right?

Past this, I am lost... backshifting, how final drive ratios effect things... such as chain sprocket gearing, tire sizes, etc...

 

All gearing ouput depends on the continuously variable ratio of the pulleys. If you put smaller tires on (lower-ratio) you lose speed at the top-end but it should take off quick because of the higher torque it has. Bigger tires (higher-ratio) will be harder to turn but give you a faster top speed. You can tune the engagement speed if you change the pulley springs and weights. If you change sprocket sizes it will change the ratio the same way, and you shouldn't do it unless you have some power mods to overcome a higher ratio, or go with probably a one-tooth difference for smaller tires. Is there one specific thing you're trying to get out of it?

 

Hey Duster the best thing to do to get a basic understanding is to get Aaens Clutch Tuneing Hanbook.Read it over and over.Then get you a tach and a bunch of springs and weights and see what does what.
The basics are simple but the varriables can really get you.The main thing is to know what you are wanting and know the limits.
You dont have to give up top end for low end but.............I can go on and on on this.

 

<div class="FTQUOTE"><begin quote>Originally posted by: jumbofrank

All gearing ouput depends on the continuously variable ratio of the pulleys. If you put smaller tires on (lower-ratio) you lose speed at the top-end but it should take off quick because of the higher torque it has. Bigger tires (higher-ratio) will be harder to turn but give you a faster top speed. You can tune the engagement speed if you change the pulley springs and weights. If you change sprocket sizes it will change the ratio the same way, and you shouldn't do it unless you have some power mods to overcome a higher ratio, or go with probably a one-tooth difference for smaller tires. Is there one specific thing you're trying to get out of it?</end quote></div>

Well, I find it interesting and something new to learn, so I'm trying to get a better understanding out of it... that's first in line.

So the PVT is or isn't torque/load sensing?
It has to be to some degree in order to backshift right?
I know mechanically how it backshifts, I just don't understand what sets it in motion?
Sensing drop in RPM?


Also, I have some engine braking which is nice, but sometimes the belt disengages and it freewheels... OK sometimes, but hard on brakes sometimes and unwanted/unexpected sometimes. Sometimes I can get it to re-engage by blipping the throttle, other times I can't... don't really understand all this all that well either. I'd prefer it never disengaged....



Anyways, the first thing I have been thinking about doing is changing the tires and wheels on the Sport 400. Down at least one size all the way around?

The stock tires are fine for trail riding as far as I can see so far (titan 489). But the quad isn't much for playing around... It's grabby, rolly, tippy....

I hate to loose the clearance, but I figure tires is one aspect, and height is likely another... and I hate to go to a new tread pattern only to find I need to either go lower or make the quad wider... and it's already fairly wide.

I realize shorter tires will cut the top speed, but I don't care. If it slows it down and causes it to need to rev higher to attain speed at the bottom that's great too. More low end feel would be good.

 

Stay with the stock size of tires.For better handling go with a set of WORKS or FOX front struts.
For more info on how the PVT work drop me a pm and I will get you to a web site where most of us are really good at clutching.

 

I keep trying to put it into words then erasing it and starting over. First of all let me assure everyone that I'm not an expert, so I may use the wrong terminology but I know how this works. I don't know how to explain it properly, but I'll try because it's really simple. Here goes in layman's terms because that's all I know.

As the rpms increase, the centrifugal force created by the clutch weights overcomes the spring pressure and closes the pulley, and it shifts from low range all the way through high range. Since it's continuously variable, it can be anywhere in between sitting still at idle and hauling butt at WOT. It's like a thousand speed transmission and all depends on the speed of the drive pulley. When you let off the throttle, the spring pressure starts to overcome the centrifugal force and opens the pulley making it downshift. That's all that that downshifts it. The speed just isn't enough to keep the pressure on from the clutch weights, so the belt slides back toward it's original position. If it's lugging, the engine slows down that slows down the pulley and downshifts it. That's the torque sensing. That may be over-simplified but that's my way of understanding it. I'm a gunsmith, not a mechanic, so if I'm wrong cut me some slack.

The 400 Sport didn't have the Engine Braking System on it, but it could be added on later if you want some engine braking. It costs some $$ to do the conversion but it was worth it to me when I had my ' 97 Sp 500 done. It used to freewheel downhill before that. With EBS it starts slowing down as soon as you ease off the gas. Let off and it slows down for curves, stop signs, whatever. It goes downhill slow instead of freewheeling like it's in neutral.

 

not sure if the sport has a low range. if it does when you go down hill and it starts to freewheel just blip the throttle to bring the rpm's back up and you'll have some engine braking(poor boy engine braking). i put Dougals .190 rims on mine it made a BIG diffrence. if you want to help the performance check with rick ritter at rittercycles.com. the stage 1 kit will wake up your 400 quite abit and the best price going for what you get.

 

<div class="FTQUOTE"><begin quote>Originally posted by: jumbofrank

I keep trying to put it into words then erasing it and starting over. First of all let me assure everyone that I'm not an expert, so I may use the wrong terminology but I know how this works. I don't know how to explain it properly, but I'll try because it's really simple. Here goes in layman's terms because that's all I know.



As the rpms increase, the centrifugal force created by the clutch weights overcomes the spring pressure and closes the pulley, and it shifts from low range all the way through high range. Since it's continuously variable, it can be anywhere in between sitting still at idle and hauling butt at WOT. It's like a thousand speed transmission and all depends on the speed of the drive pulley. When you let off the throttle, the spring pressure starts to overcome the centrifugal force and opens the pulley making it downshift. That's all that that downshifts it. The speed just isn't enough to keep the pressure on from the clutch weights, so the belt slides back toward it's original position. If it's lugging, the engine slows down that slows down the pulley and downshifts it. That's the torque sensing. That may be over-simplified but that's my way of understanding it. I'm a gunsmith, not a mechanic, so if I'm wrong cut me some slack.



The 400 Sport didn't have the Engine Braking System on it, but it could be added on later if you want some engine braking. It costs some $$ to do the conversion but it was worth it to me when I had my ' 97 Sp 500 done. It used to freewheel downhill before that. With EBS it starts slowing down as soon as you ease off the gas. Let off and it slows down for curves, stop signs, whatever. It goes downhill slow instead of freewheeling like it's in neutral.</end quote></div>

Thanks.... that I can visualize and understand... so now I have a good basic base to "think" off of. You have given me my start. Thanks. Now I can understand how the clutch/trans won't just totally compensate for a final gearing or tire size change.

So if I reduce the tire size or lower the sprocket gearing at the chain, it's going to have lower effective final gearing. This means it should be lower geared at takeoff... slower, gruntier... and I should have to give it more throttle to get to say 10 mph.... while still keeping clutch/belt engagement stock/low... at the price of it being slower in top speed.

This I would like... The engine needs a little more throttle after takeoff just to smooth the 2 stroke out... throttle you can't always give it due to it being too much speed sometimes... and throttle my wife sometimes won't give it as she's putting around.

Now on the flip side of this... wouldn't there also be a difference when letting out of the throttle? Or not? Seems like it should be harder for the tires to turn the engine over... but when it does it would try to turn it over faster. Of course what I am talking about is when you let off mine and the belt is still engaged.



Now that brings me on up to the EBS part. Looks like HotSeat has an EBS primary for $420 + $90 for a belt for it... which is supposed to be better, engaging lower and starting you off in a lower gear.... So if it would fit mine, that's $510+. Aaen has a Scrambler setup that will work that takes a different approach for $549+. Polaris has one specifically for 2 strokes for $469+

Ouch!

Honestly, I have to keep things in perspective here. This is only a stock 2 stroke, so engine compression braking is going to have it's limits anyways I would think. If I get it just right as it is right now and it's giving me it's best compression braking, I'm not sure it's $500 worth of help if you know what I mean.

As tuneable as the system is, you would also think that you could tune it in very close to EBS and also get other mod benefits from it. But I'm just starting to get my feet wet here, so I'm not sure about anything.

I do want to save my brakes and I do want to have it be it's best on hill decents, but at the same time, I have to try to guess at what "it's best" really can be and what I am willing to pay for that.