Tires and Snow

I received an interesting email from Lynn in Canada with a great question about snow tires. It seems that although the Mudzillas he runs on his Wolverine work great in the mud and muck, they don’t work well at all at pushing his snowplow down his driveway .

So what’s up with that?

Well, tires are far more complex than most folks realize. Think about how much controversy goes on surrounding tire wear, choices, air pressure and compound in NASCAR, F1, or any other racing you may follow.

While we may not be quite as ‘leading edge’ as racing, the same technology applies.

So to answer the question why certain tires work better than others, let’s first take a look at the tire’s compound. Hard rubber will wear slow, but it also doesn’t ‘grip’ the ground, especially when that ground is sand or snow. So a tire with better performance is a softer tire. Too soft though and it will wear out as you look at it. But too hard and it won’t grip at all.

The next part of the equation is the tread. Sure, big tread can move mud just like a paddle moves sand or water for that matter. But in snow (and performance on dirt) the tire’s tread needs to flex. The flexing allows the rubber of the tire to stay in contact with the ground longer, but also gives it a slight slingshot effect in moving the machine forward. Part of this ‘flex’ is helped by the small little slits in the tread called siping. These sipes also help the tread to flex, or squirm, thus allowing it to grab to the surface more. The tread also needs to trap enough of the surface to allow it to grab, but also be able to release that material so it doesn’t ‘clog’ the tread and not allow the tread to work as designed.

Now let’s look at air pressure. Air pressure has a similar but different effect on bias ply and radial tires. But basically you need to have a low enough pressure to allow the tire to flex (there’s that word again) to allow it to grip better, but not so low as to allow the tire to wallow around and roll over in cornering. Basically tire pressure is a very subjective item and the correct air pressure can only be found with a bit of experimenting on your part.

So to sum it up, snow requires a soft tire with a flexible tread with siping to make it even more flexible. That gives it the most traction. You also need to run the tire’s air pressure as low as possible without doing harm to the tire and wheel.

That sounds all well and good until you try to add that information to a specific ATV. In case you haven’t discovered this, ATVs are not all created equal. This inequality for our purpose here, can be focused mainly on the operation of the front differential.

And here’s the problem with front differentials – while lockers are pretty straight forward in their ability to apply equal traction to each front tire, the so-called ‘limited slip’ differentials are exactly that – limited!

Here’s what happens when a limited slip differential detects slip - a difference in the speed of both front tires. When one tire tends to move faster than the other, or slip, the differential tries to bind and attempt to limit the excessive speed of the faster spinning tire. To cut to the quick here, what happens when you have bigger tires with more traction is that they can overwhelm the design parameters of the limited slip differential and it can’t bind the differential enough. So, your limited slip differential doesn’t work as planned!

That means that on many machines with limited slip differentials (and those can come in many fancy names, but are basically every 4wd system that doesn’t have a lockable front differential) a tire with too much traction can actually cause you to have less traction.

Confused? You’re not alone. And if you’re not confused I could go on until you are.

But I won’t.

What did we learn? The best tire is one that has a soft compound with flexible tread and siping. You need to adjust you tire pressure to as low as you can for the conditions, and on ATVs without locking front differentials you also need to remember not to overwhelm your drive system with too much traction.

And just in case you were observant enough to notice the many pictures of the ACT and wondered – yes they are my favorite all around tire…….