I’m pretty clear on the AWD engagement process, it’s the disengagement process I’d like to know more about. With AWD turned “on”, once the rears slip enough to engage, what dictates disengagement? I’ve heard theories, everything from it stays engaged until you turn the switch off, to the hubs engaging and disengaging at will when the rear tires slip and stop slipping. Does anyone know the answer?

I’ve tried a bunch of different tires on my machines over the years and I’ve wrestled with this tire size issue to the point of exhaustion. Mechanics and dealers have told me everything from “size doesn’t matter much” to aftermarket tires will “void your warranty.” Obviously, the front and rear tires are mechanically connected when the AWD is engaged. Therefore, a gross difference in the front and rear tire sizes would logically cause stress to this mechanical “connection.” The stock tires, even though their sizes would indicate they are the same circumference front and rear (25s, 24s, whatever), if you measure them with the recommended air pressure they are NOT the same size. The fronts are a little smaller, at least on all the Polarises I’ve owned. So does Polaris compensate for this difference with different gearing front & rear? There’s another question no one seems to be able to answer.

After much trial and error and many miles, here are the conclusions I’ve come to, be they right or wrong. First, the stock tires are pretty close in circumference so I doubt there’s a difference in front to rear gearing. If you look at the extreme possibilities of mismatched tires, discounting the mechanical stress factor, what would happen? Assuming your AWD is engaged, which is the only time it would make a difference, small tires on the rear and bigger tires on the front would have the effect of engaging the AWD immediately at the press of the button because the rears spinning faster would simulate a condition of them “slipping.” The opposite condition, very large rears and small fronts, would require some major slippage of the rears to get the front hubs to engage.

So where does that leave us? Try to keep your tires fairly well matched in size, preferably with the fronts slightly smaller than the rears, like the stock tire ratios. But most importantly, DO NOT inflict unnecessary stress on the mechanism by running with the AWD switch “on” if you’re not on terrain that allows slippage. As long as you have “slippage” you shouldn’t have “breakage.” That’s my philosophy anyway. If anyone can offer supported opinions to the contrary I’m all ears.

------------------
FloodRunner, on the Wisconsin River

 

I don't understand how it tells the difference between forward & reverse!

 

Polaris had an article once in their "Polaris PRO" magazine explaining the whole On Demand 4x4 system and how it works and what it does. I should find it and read it again to refresh my memory, no one should know it better than Polaris!

[This message has been edited by rooster (edited 12-21-1999).]

 

Excellent logic floodrunner. I never thought about tire size's affect on the 4wd system. Supporting your thought, a small tire in the rear and large in the front would keep the 4wd system engaged even downhill. Nobody try this though. You'll burn your belt really fast if you have EBS.

------------------
99' SP500

 

question for you guys..... i own a scrambler 400. the rear tires are 22's and the front tires are 23's. hmmm, there's your bigger tires in the front! so it would have to do something with gearing because the rear tires are already spinning faster then the fronts even without slipage. so that measn that they must have to spin a considerable amount faster than the fronts to allow the awd to kick in. i kind of understand the concept, but still foggy on it. but i tell you what, so far i am very impressed with it. climbs hills like a mountain goat! i just wonder if i am going to have problems finding stock tire sizes. 23's are an odd size. maybe i'll have to post a topic and see what everyone uses, even though i won't need tires for quite some time.

 

To Floorunner, Rooster and Aniel concerning how Polaris 4WD works. I believe that putting large front tires might cause a lockup when you engage the 4WD switch. I think it would cause the front wheels to immediately start pulling the vehicle faster than the rear ones will let it go on hard ground. Would likely damage the drive train unless there is some other design feature to keep that from happening. The Polaris designers surely know the answer to this quandry; it would be interesting to learn it. You and other posters to this question have shown some good thinking as to how mechanism work..... even if we haven't yet figured out the subject at hand.
Al Elston

 

With the Polaris All Wheel Drive System activated (AWD selected), the machine operates as a 2 wheel drive vehicle until the rear wheels lose traction. If the rear wheels lose traction the front wheel rotational speed will decrease,causing the front drive axle to exceed front wheel speed. Restricting the rotation of the drive clutch roller cage will cause the rollers to climb the ramps of the cam and become squeezed between the ramps and the ring hub.
When the hub clutch assembly,wheel hub, and drive axle are engaged, the front wheels will drive and stay engaged until the rear wheel traction is regained. When traction is regained, the front wheels will overdrive the hub clutch, pushing the clutch rollers toward the lower part of the cam, disengaging the clutch. The rollers are held in place by a spring. The tension of this spring is critical to AWD hub operation.

When AWD is selected in a forward gear or in( reverse when the override button is pushed) , current flows through a wire located in the strut housing, creating a magnetic field. An armature plate coupled to the roller cage is attracted to the magnetic field, and resists rotation, creating drag on the drive roller cage assembly. This causes the roller to climb the ramps of the cam engaging the hub.

IT IS IMPORTANT THAT THE FRONT AND REAR AXLE DRIVE RATIO AND TIRE SIZE ARE NOT CHANGED. CHANGING THIS RATIO WILL CAUSE ERRATIC ENGAGEMENT.

Hope this helps..........


------------------
Harold Cowley



[This message has been edited by hc (edited 12-22-1999).]

 

Well if that's the case, how can a Sportsman 500 have 25's all the way 'round? And how can the Sportsman RSE in the shootout have 27" Tri and Bi Claws at all four corners?

 

When the rear tires lose traction and the front axles kick in, can you "feel" this through the handlebars or hear it?

 

It shouldn't matter what size the tires are(25's , 26's ,27's.....) as long as the tires are the same or very close to the same on all corners. It's the difference between the front tires and the rear tires.

------------------
Harold Cowley