Low rolling resistance tires are often marketed as fuel savers.

But what actually makes a tire “low rolling resistance”?

James Menzies spoke with Jim Garrett, product manager at Michelin, during the company’s Innovation in Motion road show to break it down.

Garrett: “For low rolling resistance, there’s a couple of major contributors to it. The first one is the rubber compound, or the rubber composition, of the rubber in the tread itself, [which has] the biggest impact on the rolling. So in the past, you could achieve that by having lower tread depth. As a tread wears, it becomes more rigid, right, and less flex.”

As a tire rolls, it flexes. That flexing uses energy — energy that ultimately comes from fuel. Reducing that energy loss improves fuel economy.

Garrett:“Flex is waste, wasted energy. So that’s the way we did it earlier, lower tread depth, [it] was one tool. Another tool was to make the compound less hysteriatic, which means, you make the composition of the rubber in such a way that it bounces back and bounces back at the right time. You know — he had a demonstration with the balls and both balls returned round, right? One of them doesn’t stay flat where it bounced, but it’s just a matter of when it bounces, it’s got to bounce back at the right timing to recover the energy.”

But improving rolling resistance historically meant trade-offs. Especially when it came to traction.

Garrett: “So, normally, to get a rubber that’s less hysteretic — which means it bounces back quickly — you usually end up compromising in traction. A rubber ball that bounces is very slippery. You slide it against the surface. Take a bouncy ball, slide it, or take a ball that doesn’t bounce so much and slide it. And the one that doesn’t bounce much will have better traction. It’ll be hard to slide. So we had to think of new ways to make a rubber compound that breaks the trade-off. So one of the big things that everyone’s using today — that Michelin innovated about 25 years ago — was high silica rubber. Just put high silica in the rubber mix, it breaks the trade-off so you can get the lower rolling resistance, good hysteretic material, but it also maintains traction. So you know, that’s why, over the years, low rolling resistance tires have become more acceptable in the industry, because they don’t have this big a trade off on wear. Fleets only care about wear and traction. They don’t care so much about rolling resistance, because for them, it’s hard to measure. But in reality, if they could measure it — and some fleets do —  they would recognize that low rolling resistance more than pay for themselves . They spend 15 times more in fuel than they do in tires. But yet they’re kind of myopic. The guy who has the budget for the tires is not the same guy who has a budget for the fuel. So the fuel budget guy is pushing low rolling resistance, pushing aerodynamics in the vehicle and all that. But the guy in maintenance who has the tire budget is all about miles.”

You can’t identify a low rolling resistance tire by sight, Garrett said. Fleets have to check the manufacturer’s specifications — or look for branding that signals a low rolling resistance line.

Garrett: “All the tire manufacturers will have some kind of trade name for their low rolling resistance tire, whether it’s Ecopia or something ecological, right? And Michelin, it’s Energy. So if we have the name energy in the name of the tire, it’s a low rolling resistance tire. This is the Line Energy Z+. This tire over here is Multi Z2, it doesn’t have ‘energy’, so it’s not a low rolling resistance tire, per se. So, others will have something in their name about ‘Eco’. One of our competitors is EcoPlus. That means it’s their low rolling resistance line.”