You’ve no doubt seen racing drivers on a warm-up or yellow-flag lap weaving from side to side to keep their tires warm. The reason is that the rubber compound in race tires is formulated to be at its stickiest at race speeds and elevated temperatures. At cooler temperatures it quickly hardens and loses grip.
You could fairly state that designing a racing tire is simple compared to designing a tire for a street car or SUV. The racing tire only has to last long enough to finish the race, and often not even that long. Fuel economy is well down the list of priorities; ride comfort and noise aren’t even on it.
Not so with a street or SUV tire. Consumers want it all: long tread life and superior cornering traction, high fuel economy and safe braking performance, good off-pavement traction and low noise on pavement. A bunch of mutually exclusive characteristics. As you can imagine, a tread compound hard enough to last 40,000 or 50,000 miles and exhibit low rolling resistance to save fuel has a difficult time also providing above-average cornering and braking traction. Thus since the dawn of pneumatic tires manufacturers have juggled rubber and petroleum compounds to arrive at the best compromise for the application.
A few years ago Yokohama threw a new ingredient into the mix: orange oil, which, just as its name suggests, is derived from the oil in orange (and other citrus) peel—the specific compound desired is called limonene. Why citrus oil? One reason is to save on petroleum, of course, making the tire more “green.” But Yokohama claims a far more immediate benefit. According to the company, the tread compound in a tire constructed with limonene has the ability to instantly change viscosity in response to temperature. During normal driving the viscosity is high, resulting in low rolling resistance and long tread life. But during braking or cornering the viscosity shifts to a more sticky state, enhancing grip.
Proving or disproving this through independent testing might be difficult, since Yokohama does not offer otherwise identical tires with or without the orange oil technology. Most likely only a long period of consumer feedback and real-world tread-wear results will show if the concept is sound or just a marketing gimmick. The company gave me a set of the new Geolandar AT GO15 tires for our Ford F350 pickup, and so far they are performing excellently, with decent off-pavement traction and fine on-road characteristics. I just towed a 9,000-pound trailer full of Overland Expo equipment across the country, and had zero issues with handling or braking—including a couple of abrupt maneuvers to avoid insane suicidal drivers on the freeway through Dallas at rush hour (not fun at the wheel of 15,000 pounds worth of kinetic energy). The tread still appears within new specs, so I won’t be surprised if they last the full 50,000 miles promised by the guarantee. (The lighter-duty P/E Metric versions of the tire have a 60,000-mile warranty.)
I can’t find any other manufacturers using orange oil technology yet. I’m not sure if this is because Yokohama has managed to protect their use of it, if the others are sitting back to see how it goes, or if they are frantically testing their own citrus concoctions. Time will tell.