Source: MotorcyclistOnline.com
A lot of science goes into stopping a motorcycle in the wet, but you don’t have to be an absolute unit like Aaron Colton to reap the benefits. (Bridgestone/)I’m here today to make you a promise: If you’ve got a decent set of modern motorcycle tires, you’ve got nothing to worry about when you ride in the rain.Don’t believe me? I don’t blame you.Like buying oysters in Oklahoma or a Rolex on the streets of Bangkok, one person’s guarantee is rarely enough to establish trust, regardless of how charming or handsome they may be. That’s why, for the purposes of this article, the goods are coming straight from the source. After all, adjacent to motorcycle gear, tires are an essential Motorcycle Parts and Accessories component.After a few dozen emails and several hours of interviews with engineers, designers, and experts from Dunlop, Bridgestone, and Michelin, I’ve been able to distill the fine science of wet traction into three simple steps.Editor’s note: We recently test rode a variety of new-for-2024 street bike tires during the Top Five Features of Michelin’s Power GP2 Motorcycle Tires, What You Need To Know about the Michelin Anakee Road Tire, Top 5 Reasons We Like Riding Bridgestone’s Battlax S23 Tires, Bridgestone Battlax S23 Motorcycle Tire Review With Videos, and Top 5 Features of Bridgestone’s Battlax S23 Motorcycle Tires articles.Step 1: Remove Water From the Road SurfaceGrooves and sipes on tires like this Michelin Road 5 are your first line of defense in the wet. (Kurt Spurlock/)“Hydroplaning is what happens when you reach a certain speed and the tire can no longer dissipate enough water. At that point, you’re basically driving on top of the water, and that’s where tread pattern becomes important.” —Neill Rampton, manager of advanced engineering for Dunlop/Sumitomo RubberWe all know that traction is what happens when the rubber meets the road. That’s pretty cut and dry on a clear sunny day, but when there’s water on the pavement, our tires have to “cut through it” to get to the grippy surface underneath.Motorcycle tire engineers like Neill Rampton achieve this feat by two distinct means. There’s the tread pattern you see on the outside of the tire, and then there’s the profile of the tire itself. Let’s dig into the tread pattern bit first.Related: How To Tell If You Need To Replace Your Motorcycle TiresWhen it’s actively raining or there’s standing water on the road, tire grooves are a bedrock necessity. (Michelin/)Your tire’s tread pattern is made up of larger grooves and/or smaller sipes, both of which are engineered to transport water away from your tire’s contact patch. A tire that disperses more water can put more rubber in contact with the pavement below, maximizing available grip while also minimizing the risk of hydroplaning at speed.Now when I say “at speed” it’s important to understand even the most grooved tires out there have their limits. Several factors are at play including the profile of the tire, the weight of the bike, and the layout of the tread pattern, but as you see in the graphic below, even the most rain-friendly tires have their limits.This computer analysis shows how speed reduces a tire’s contact patch in the rain. The tire on the left is in good form, while the faster rolling model on the right has its contact patch reduced to the size of a dime and is moments away from hydroplaning. (Dunlop/Sumitomo/)As your tires roll faster, your tread pattern has less and less time to grab and disperse water, causing the contact patch to shrink as you add speed. Outrun your tire’s ability to shed water, and you’ll find yourself surfing on top of it with no grip at all. Lucky for us, that’s harder to do than it might seem.“Fortunately, motorcycle tires are for the most part ‘pointy’ which gives them higher contact pressures. Even on a slick tire with no pattern at all, a motorcycle tire is still a lot harder to hydroplane.” —Neill RamptonYes, the rounded shape of a motorcycle tire carries an inherent advantage in wet weather. Unlike your typical car or truck tire, a motorcycle tire is tapered both from front to back and shoulder to shoulder, allowing it to slice through standing water much like the hull of a boat.Ever wonder why racers often get away with slicks on a wet track? A motorcycle tire’s profile is actually sharp enough to disperse some water on its own, even without grooves. (Michelin/)This explains why you’ll often see roadracers head out onto a wet track with a slick tire rather than a dedicated rain tire: The sharply rounded profile of a racing slick provides enough water dispersion on its own to prevent hydroplaning, leaving it up to the rider’s skills to find grip where they can.Of course that scenario doesn’t apply to us mere mortals, which is why modern marvels like sport-touring tires remain the weapon of choice for most street riders. With that being said, compound clearly still plays a major part in the wet grip equation, which brings us to our next talking point.Step 2: Maximize Available Grip“We design compounds in such a way that they have a consistent level of grip over a very large range of pressures. We want tire warmup to have as little to do with the performance as possible. We’re trying to simply take that stuff out of the equation, so whether it’s 40 degrees and raining or 90 degrees and sunny, you’re going to have a consistent level of grip.” —Keith Willcome, application engineering manager at BridgestoneMotorcycle tires work best when they’re nice and warm because rubber becomes more supple at higher temperatures. Unfortunately wet conditions make it harder for tires to generate the heat they need because there’s less friction on offer from wet pavement.While a wet surface will always have less available grip than a dry one, motorcycle tires are engineered to make the most out of a bad situation. This is where the fine science of rubber compounding comes into play.Related: Motorcycle Tire Construction ExplainedAll-weather tires require less stress to achieve optimal grip, so they work better across a wider range of conditions. (Michelin/)Before the invention of silica-infused compounds, tire engineers had to employ very soft rubber if they wanted a tire to perform well in the rain. Unfortunately soft rubber also has the unwelcome side effect of wearing extremely fast, so we don’t have much use for it outside the racetrack.When the folks at Michelin introduced the first silica-reinforced motorcycle tire to the public in the 1990s, they effectively gave birth to the modern street tires we all use today. The mention of silica has gone hand in hand with wet-weather performance ever since, but to truly appreciate the miracle of these compounds, we need to understand how they work.“Silica increases the hysteresis of the rubber compound at lower frequencies (more grip) while decreasing hysteresis at high frequencies (low rolling resistance). It essentially breaks the wet traction/wear performance link and allows good wet traction while maintaining sufficient wear.” —Caleb Smith, Michelin 2-Wheel OE account managerAt risk of stating the obvious here, “hysteresis” isn’t exactly a household term. As you might expect, there’s a long and complex explanation of hysteresis that the physics junkies in our audience would appreciate, but for the sake of everyone else, we won’t get into it here. The short explanation is that “hysteresis” is the amount of heat energy rubber generates as it rolls across the pavement.It’s complicated: Rubber loads and unloads at different rates, and the difference between the two factors creates energy in the form of heat. (Dunlop/Sumitomo/)When tire engineers optimize a compound for wet grip, their aim is to increase hysteresis at the lower operating stresses associated with wet conditions. This allows the tire to build and maintain more heat at lower speeds, which in turn keeps the rubber as supple and grippy as possible even when you’re riding cautiously in colder, wetter weather.As my friend at Michelin noted above, silica also solves the problem of excessive tire wear because it reduces rubber’s natural tendency to generate excess heat at higher speeds. Because street riders don’t need tires that regularly take knee-down corners at 150 mph, this is a welcome trade-off that most of us will never actually detect.Step 3: Allow for Braking, Acceleration, and Cornering Forces“If you look at your front tire pattern versus your rear tire pattern, you’ll see the patterns point in opposite directions. By aligning the grooves like this, you maintain stability in the blocks so they don’t move around as much.” —Neill Rampton, Dunlop/SumitomoTread patterns differ wildly between manufacturers, especially when we’re talking about something like a sport-touring tire that’s designed to grip well in the worst conditions. Despite this difference in appearance, all tread patterns essentially share the same goal when it comes to wet-weather traction.Here we see the Sumitomo/Dunlop’s original patent for a tread design that maximizes tread block stability to maximize feedback and minimize tire wear. (Dunlop/Sumitomo/)Adding grooves to a tire’s tread helps disperse water, but it also creates a major trade-off. The more we groove a tire, the more prone that tire’s surface becomes to squirming around under the stresses of braking, acceleration, and cornering.Over the years engineers have learned to combat this issue by arranging their tread grooves in very specific ways. There are plenty of great examples of this on the street today, but the best illustration of the concept actually comes from the world of roadracing.These Dunlop rain race tires illustrate why our street tires often look the way they do: Tread grooves are angled in the direction of sliding forces to minimize the “squirming” of the individual tread blocks they create. (Dunlop/Sumitomo/)Looking at the two rain race tires above, we see a major asymmetry in how the front and rear tires make the most of their tread. Out front, the grooves are all straight lines down the middle and 90-degree angles to the shoulder, while out back we see a much more “conventional” layout that slopes toward the shoulder of the tire more gradually.Tread blocks are their most stable and resilient when they’re directly aligned with the direction of the forces they’re resisting. We see straight grooves down the middle of both tires because the hardest braking and acceleration forces happen when a motorcycle is fully upright. Both tires feature their sharpest angled grooves on their furthest edges to resist pure cornering forces, but only the rear tire gets angled grooves in between because the direction of acceleration forces changes as the bike leans.The Big Picture: What To Look for in a Wet-Weather Motorcycle TireA lot of variables are at play, but at the end of the day, ample grooving and the right compound are universal requirements for wet traction on the street. (Michelin/)Understanding how our tires grip in the wet is great, but what does all this mean for your average rider out on the street? Here are my main takeaways after many late nights of research and several hours on the phone with the industry’s best and brightest.First: All motorcycle tires represent some degree of compromise between maximum grip, maximum longevity, and wet-weather performance. Luckily for us, computer modeling and compounding technologies have become so advanced that most riders will never actually find the limits of a modern sport-touring tire on public roads.Second: If you’re struggling to truly “trust your tires” in a wet corner, rest assured: There are NASA-grade geniuses at work engineering these things to be idiotproof in more ways than one. Stick to your manufacturer’s recommended inflation pressures and let the science handle the rest.Third: Motorcycle tires have an inherent advantage in the wet due to their rounded shape, but all tires have their limits. Excessive speed effectively shrinks your tire’s contact patch in the rain, so you’d be wise to keep those freeway speeds in check if hydroplaning isn’t your bag.Last but not least, I asked each of the folks I interviewed for their “insider advice” to anyone shopping for a wet-weather tire. I’ll leave you with their parting words of wisdom.Caleb Smith, Michelin:“Our testing shows it’s not possible to achieve a max lean angle in the wet, so pay attention to the tread pattern in the middle 75 percent of the tire. You want enough tread void to evacuate water but not so much that the tread squirms more than necessary in the dry. For sport-touring purposes, you also want to look for a slick area on the edge of the tire to get additional dry traction at the higher lean angles you access during nice weather.”Keith Willcome, Bridgestone:“Buy the best tire you can afford, and choose a brand with a good reputation. We try to design tires to inspire confidence so you can forget about the forecast and go ride. When you’re looking at all the different choices out there, pay attention to how the manufacturer talks about each specific tire. That’ll give you a pretty good clue as to where they put the most effort into designing their tire.”Neill Rampton, Dunlop/Sumitomo:“Do your research and make sure your tire matches your intended use. Don’t buy a hypersport tire if you’re looking to do a road trip in the rain. Also, don’t be scared to talk directly to the manufacturer. We get a lot of questions from customers and there are a lot of people here willing to give you advice. Just call and ask.”
