A large chunk of questions people ask me about motorcycles relate to tyres. I neither claim to be an expert on motorcycles nor tyres. But being a mechanical engineer, I’m curious to know how things work and why they fail. I tend to dig deeper into subjects that peak my interest and one of these subjects happens to be motorcycle tyres. More specifically, motorcycle tyre tread patterns.
There are basically four types of tyre tread patters – street, 60/40, 40/60 and dirt. There are more. But if you understand the difference between these four, you should be wise enough to pick the right tyre for your motorcycle.
The tread patterns of street tyres have no knobs. They have grooves which usually run diagonally across the face of the tread. A good example is the Pirelli MT 75.
The purpose of the grooves is to let water escape. Under normal conditions water is an incompressible liquid. So if the grooves didn’t exist water would stay sandwiched between the rubber and tarmac and act like a sheet of glass, with disastrous consequences for the motorcycle and rider.
60/40 means 60% street and 40% dirt. These tyres have knobs with a relatively larger surface area. As a result the contact patch on tarmac is significant. An example is the Pirelli MT90.
An easy way to figure out whether you are looking at a tyre with a street or a 60/40 tread pattern is to check if the grooves intersect each other. In the case of the MT 75 they don’t intersect and as a result don’t give rise to knobs. In the case of the MT 90, the grooves intersect yielding knobs of large surface area. The grooves are also wider and this lets the knobs latch onto uneven surfaces when riding off-road yielding in much needed traction.
40/60 is the opposite of 60/40. The knobs of these tyres have a smaller surface area than those of the 60/40 tyres. The distance between knobs is also larger. This allows the knobs to grip stones and rock when riding off road more effectively than 60/40 tyres. An example is the Pirelli MT60, which is what I chose for my KTM Duke 390 while converting the street bike to a trail riding motorcycle. It’s a good compromise for me because I don’t ride too aggressively on tarmac and lean too much into corners. But I want good traction when riding off road.
The tread pattern of dirt tyres is basically made up of small knobs spaced far apart from each other and are meant strictly for riding in dirt. You really can’t ride motorcycles with these tyres on tarmac without feeling all wonky. People trailer bikes with these tyres to the dirt, ride in the dirt and trailer them back. An example is the Pirelli MT 21. The large gap between knobs allows the tyre to grasp larger stones and rocks.
So as you can see, its all about the surface area of the knobs and the distance between them. Of course, you can have 70/30 or 30/70 and so on. But I think you get the point. Figure out what kind of riding is most important to you and buy a tyre with the appropriate tread pattern.
Note that I said most important and not most frequent. You may ride your bike on tarmac most of the time and every now and then take it off road. So you may be tempted to go in for a 60/40 tread. But if you do not ride too aggressively on tarmac then a 40/60 tread will work for you well on tarmac. And when you go off road the 60% dirt tread will more effective than a 40% dirt tread. That’s what I’ve been doing and it has been working out quite well for me so far.
Another frequent question that comes up is whether the tread patterns of the front and read tyre need to match. No they don’t. The tread patterns need to be of the same type though. I mean if you go off road with a 40/60 tread pattern at the rear and a street tread pattern in the front, things may not end well for you.
The rear tyre of a motorcycle has drive and not the front. So you might say why bother with the tread pattern of the front tyre since the rear tyre is going to do all the hard work and needs traction. However, it’s important to note than when braking the weight of the motorcycle as well as rider is transferred to the front wheel and the front brake works more than the rear to slow down the motorcycle. That’s why the front discs are larger than the rear. Some motorcycles even have two discs at the front. Now imagine you are riding a motorcycle downhill on dirt and you apply both brakes, the weight of the motorcycle and rider will move to the front wheel even more due to the downward incline. If you have a street tyre at the front it won’t get the traction it needs to slow down the motorcycle, the wheel will lock up, you will loose control and come crashing down the hill. The rear tyre with the proper dirt tread pattern will simply follow the front tyre as it doesn’t have any weight pressing it down to the dirt to hold onto something.
I would like to end this post with a piece of advice. I often see people ride their tyres till they are completely bald and sometimes till the innards of the tyre start to show. That is very unsafe. I change tyres when there is still some rubber on them and the tread pattern is still clearly visible. The knobs on the tread of a tyre are like small cantilever beams sticking out of the tyre. Longer the beams more is their ability to bend which yields in greater traction. In fact, I use the ABS to determine when its time to change the tyre. As the rubber wears out the tyre loses the ability to hold on to the tarmac and the wheels begin to lock when braking thereby kicking in the ABS much earlier than when the tyres were new. Tyres are not meant to be ridden till they have no tread left on them. You can. But that doesn’t mean you should.
Ride hard. Ride safe.