Without a pattern of grooves in a tire tread, tires would get poor traction in varying road conditions, and become almost unusable on the street. We know that tread patterns need to be on motorcycle tires – but have you ever wondered why they look and work the way they do? Here are some answers.
When it comes to tires, the pattern of grooves in the tread is one of the most important parts of enabling a tire to get the traction that it needs. But have you ever wondered what goes into designing a tire tread, and why it looks the way it does? We did, so asked experts at two of our largest motorcycle tire manufacturers, Pirelli and Michelin, for insights on how tire tread works, and what goes into creating the multitude of designs there are out there.
A close-up look at the tread pattern of Michelin’s new top-tier super sport tire, the Power RS, and it’s distinctive dimpled tread pattern. So what makes the difference between the short, dashed grooves on this tire and the long grooves in competitors tires? it turns out it’s equal parts engineering and art.
What’s The Purpose of Tire Tread Patterns?
In any street tire, you will see a pattern of grooves in the surface of a tire. Most people call this the tread – however, technically speaking, the “tread” is the portion of the tire that actually makes contact with the road, and the “pattern” refers to the grooves in between the blocks of tread.
So why is that pattern molded into the surface of a tire in the first place? There are five main reasons:
1) Traction. The primary reason all street tires have a tread pattern is so that a tire can maintain traction with the road surface in varying conditions. To maximize traction, you want as much of the rubber surface of the tire touching as much of the road as possible – so in an ideal world, you would have a tire with no tread pattern (like racing slicks.)
However, in the real world, since road conditions vary, moisture – which can easily break traction – has to be taken into account. So the tread pattern is molded into a tire to give water a place to go as it is squeezed away from the road surface by the tread. The more varying weather conditions a tire will likely encounter, the more grooves the pattern will have – which is why tires for cross country touring, for example, have so many more grooves than those designed only for completely dry track day riding.
One of the best wet-weather tires on the market is the Michelin Pilot Road 4, which gets its excellent wet grip from extensive grooves and thin slits (called sipes) lined horizontally across its surface to give water plenty of places to go as the tire rolls along the ground.
2) To allow the carcass of a tire to flex to conform to the surface of the road. In the real world, road surfaces and conditions vary greatly, and in order to maintain as much traction as possible at all times, a tire needs to be able to flex to adapt to those constant changes. Without a tread pattern to “break up” the tread and give it some flex, the only way a tire could do that is if it were a very pliable compound. The result would be a tire that was so soft, that it would burn up way too quickly – so grooves in a tread pattern allow for the flex a tire tread needs, while still being made out of strong, hard wearing compounds that get reasonably good mileage.
3) To make a tire DOT legal. Slick tires with no tread pattern are not street legal, so even extremely sport oriented performance tires – like the Pirelli Supercorsa SP2, for example – have some tread pattern (even just the bare minimum single line tread pattern you see in the Supercorsa tire.)
4) To facilitate a way for owners to determine when to replace their tires. Measuring remaining tread depth or using “wear bars” are both ways that riders can determine how much life they have remaining in a tire, but grooves must be present in the tread in order to facilitate that. Tires with no pattern at all, like racing slicks, don’t have these features – but it is assumed that motorcycle racers and their crews are knowledgeable enough to know when they need to switch tires without these aids.
5) An artistic element that adds to their visual appeal. At a glance, all motorcycle tires would look identical with no tread pattern molded into them. But tread patterns give each tire its own unique look and that appeals to customers based on their own individual taste and style.
Part Engineering, Part Art
Although there is a lot of science that goes into engineering a tread pattern for a motorcycle tire, the artistic element drives a lot of the design as well. There may be many tread patterns that accomplish the objectives of a certain tire, but since tires are so visible and exposed on a motorcycle, manufacturers also put effort into making sure that their tread patterns look good too – after all, so much about motorcycling is form as much as it is function, and even tires have to look cool!
The Pirelli Supercorsa SP V2 is a dry weather super sport tire that gets incredible grip in dry conditions, and is about as close as you can get to a racing slick for the street. Not much tread on this tire, but the dual “lightning bolt” grooves make the tire street legal, give a place to measure tread depth, and most importantly, give the tire an unmistakable look that just screams “fast!”
The Engineering Inside a Tread Pattern
As we discussed, a certain amount of tread pattern is essential for street motorcycle tires, and the amount of grooves, their depth, distribution, length, etc. all go into achieving the objective set for each tire.
An executive at Pirelli explained it this way: the grooves in a tread pattern create “blocks” of tread, or contact patch, that are constantly making repeated contact with the ground as the tire revolves. Each block of tread has to be considered with respect to how its leading edge will contact the road, how its trailing edge will leave it, and how traction will be affected as it goes around and around, thousands of times, at all possible lean angles.
But it gets even more complex than that, as tread patterns really aren’t designed to work the way you look at them sitting on the rack – instead, they must be designed to work when they are deformed by both the weight of the motorcycle and the torque it produces under load. The way and extent to which a tire will deform under load is determined most by the characteristics of the underlying construction of a tire – its carcass and compound – and the tread pattern design ultimately complements, but does not determine, the tire’s behavior.
“You even have to tune to ride angles based on the intended bike application, estimated loads and lean angle, etc. – much the same way you work with a cam for various engine designs” said the same Pirelli executive, when discussing the various tread patterns in Pirelli’s tires. “This used to be done manually by engineers with a lot of experience, but it also involved a lot of guess work – these days, computers solve all the difficult problems for us, so we can really optimize our tires to perform well in every possible situation.”
As you can see, there is a lot of thought that goes into those grooves!
The “Art” of Motorcycle Tires
Though a lot of thought goes into engineering tire tread for optimal performance, ultimately it has to look good too. Tires are a fundamental component of the overall aesthetics of a motorcycle, and no matter how well they work, if they don’t look good doing it, customers simply won’t vote on them with their wallets.
Thus, the final tread pattern is actually determined as much by designers as it is by engineers. In fact, in most cases, the initial design of a tire is actually done in the design studio, and sketches are then sent to engineers who work backwards to come up with engineering solutions to achieve the tire’s desired performance characteristics.
In fact, the visual appeal of a tire is so important that, when designing the Commander II, Michelin actually produced four versions of what was an identical-performing tire, with the only difference being the tread patterns. They then took those four tires around to dozens of major motorcycle shows across the country to solicit feedback from real riders about which look they liked most, refined it a little based on the feedback, and came up with what is now their most popular cruiser tire in North America.
The Michelin Commander II was designed and developed with more direct customer feedback than any motorcycle tire Michelin has ever created. In development, they actually designed four different tires with different tread designs, and went with the one people loved most – and the result is this great looking tire.
Pirelli described the “art” aspect of a motorcycle tire this way: “because at Pirelli it is important to us that our products look as good as they work, we also have what we’ll call the “artistic element” of a tire in mind at all phases. Once we know we can achieve the performance objectives of given a tire, we can also incorporate a lot of creativity into the tread pattern, like the signature aggressive look of the Supercorsa, or the unique “angel” impression that our Angel ST tire will create in the ground as it rolls over it.”
Probably one of the most unique tread patterns in the motorcycle industry, the Pirelli Angel ST has a sporty tread pattern that looks fast and aggressive at a glance – but if you look carefully, you can also see the “angel” in the pattern, a unique feature that becomes even more apparent when rolling over dust or dirt.
As you can see, a ton of thought goes into the tread pattern of a motorcycle tire – but ultimately, the pattern is just one aspect of what gives a tire its unique characteristics. So once you’ve narrowed your search down to the tires that suit your demands and riding style best – just go with the one you think will look coolest on your bike. Your tires were made to look as good as they work!