ROUND TIRES AND WHY THEY ARE RISKY OFF ROAD
Our answer is simple: It is for your safety.
We refer to a so-called 50/50 or dual-purpose tire as a “round tire” referring to the uninterrupted smooth or “round” profile. It differs from what is termed a DOT Knobby or a real off-road knobby tire by lacking aggressive blocks on the tread, especially on the sidewall of the tire. The simple way to feel how these blocks grip off-road is to slide your hand across the surface of the tire and compare between the different types.
For sure the biggest disadvantage with the knobby tire is the life-span or outright durability. On most knobbies, especially on twin-cylinder bikes the rear tire is pretty worn at 3000 miles. But the question you have to ask is, “How important is my safety when I go in the dirt?” And yes, it is as crazy to expect a knobby tire to perform at high levels on the street as it is for a smooth tire to work out in the dirt.
Problems arise on a round tire when you really need the tire to be working for you. When you start to lose traction, in either the front or the rear, the smoother the tire the quicker and more suddenly that loss of traction happens. Additionally the less likely it is for you to regain traction, especially when on the sides of a smooth tire. You really need traction when the load starts to push on the edges of the tire–to grip rather than slip. Add in poor traction conditions like sand or mud it really becomes dangerous, even a lost cause. There is nothing aiding the tire’s ability to bite the ground.
When all is fine and dandy off-road, just the weight of the bike is enough to move you along. But that weight and lack of grip-finding blocks in the tire will come back and bite you if and when something starts to go wrong. Braking is severely compromised since round tires tend to slide atop the dirt (and slide out from under you). And then they tend to wander more, never grabbing or biting as the bike’s weight resists changing direction no matter the steering effort you put into it. As the bike begins to lose control, this is when the sidewall, or corner knobbies tend to bite in and come to the rescue, but on a smooth tire the traction never comes back. And if you need a burst of power to help regain control a round tire will just spin, no help at all. Stuck? Forget it. There is nothing but a smooth surface to polish the ground or slowly dig a deeper hole. When things are OK, there isn’t much difference. But when you need your tire to work for you it makes all the difference in the world.
Even when a knobby tire is worn down to an almost smooth surface on the center of the tire, it will still get bite and grip in the dirt as the tire tends to sink in and use the edges of the side knobs in soft conditions. Plus in turning you put the tire on the more knobby laden edge where there is still dirt-digging blocks to do work.
How do we know this? Well not only from watching other riders and hearing stories, we actually went out and tested it ourselves in soft sand and in mud. Very carefully, we might add. Even with high-level riders on the bike, it was just plain scary as there is no recourse when things start to go wrong. The bike gets stuck much easier and is nearly impossible to get unstuck without assistance. Knobby tires are the single best thing you can do to improve the performance of your large-displacement bike off-road. And if you thing they are expensive, we say they are cheaper than a cast.