Get a grip

BY Kelly Taylor. May 06 04:00 am

DALLAS — There’s a major shift occurring in how run-flat tires are sold. At least, if the latest evolution from Bridgestone/Firestone is any indication.

Driveguard, the company’s newest product name for run-flats, isn’t being sold as a run-flat. Instead, Bridgestone is pitching its ride quality, noise levels, tread life, traction... and, oh, by the way, it can run for up to 90 kilometres after a puncture. Even the name, run-flat, is being phased out in favour of low-pressure mobility.

“This is a true premium tire. You could install it without regard for its low-pressure mobility, and it would still be a great deal,” said John Arnold, education manager for Bridgestone Americas.

Run-flat tires are not new, but they’ve developed a reputation as hard-riding tires, even when inflated, because of the stiffness of the sidewall that allows for run-flat operation. “The typical fix was to increase the sidewall stiffness so it would stay rigid, but I’ve just described a concrete tire, haven’t I?” Arnold said.

With Driveguard, Bridgestone has developed a new sidewall rubber compound that allows it to stay flexible but sturdy when empty, and cooling fins that reduce sidewall temperatures by 21 C to maintain the rubber’s integrity.

Also new for 2016 is an expanded range of tire sizes for Driveguard that extends the tire’s reach to 80 per cent of today’s minivans and 43 per cent of today’s crossover and sport-utility vehicles, with more sizes on the way, which is only smart, considering the explosion in crossover sales, particularly among the subset of the population perhaps most predisposed against having to change their own flat tires, namely families with small children. Previously, low-pressure mobility tires were largely limited to passenger cars.

We drove two sets of Driveguard tires and one set of Michelin run-flat tires. The first set of Driveguard and the set of Michelin tires were inflated to specification. The point was to demonstrate a difference in ride quality while inflated. While the ride quality wasn’t awful with the Michelins, the Driveguard tires were considerably quieter over bumps and rumble strips and transmitted — slightly — less of the bumpiness to the passenger cabin.

The second set of Driveguard tires had one front tire with its valve stem removed. In other words, completely flat. There was a loud noise evident at lower speeds and a slight pull toward the flat tire’s side, but otherwise, the vehicle was completely drivable. Bridgestone specifies a maximum 90 kilometres when empty at no more than 90 km/h. Unofficially, they’ve had tires go as far as 400 km empty.

Driveguard tires are repairable: like other tires, the ability to fix them depends on the failure mode. A nail puncture along the circumference is no problem. A slashing puncture to the sidewall is fatal, just as it is for other tires.

In Canada, a growing number of drivers are opting, wisely, for winter tires. Unfortunately, there are no current offerings of run-flat tires with winter compounds and treads. Robert Saul, product manager for Bridgestone Americas, said Bridgestone offers such tires in Europe, but none has a suitable range of sizes for North American cars. “We’re in the thinking stage,” he said of plans to create Driveguard winter tires. “We know there’s a demand and we’re trying to decide the right course of action.”

Another interesting comparison here at the 2016 product launch was the new Firestone Firehawk Indy 500 vs. BF Goodrich g-Force Sport Comp-2s. We drove the tires back to back on a short autocross course kept wet by periodic passes by a water truck.

Before getting to the comparison, there’s some interesting technology going into the Firehawk Indy 500s: the first is what they’re calling Pulse Groove technology, which refers to a large, undulating groove in the middle of the tire, designed to evacuate water as quickly as possible. Bridgestone says the idea is to use the undulations on the side of the groove (see photo) to accelerate water movement, much the way the shape of an airplane wing accelerates air flowing over top to create lift. As well, the edges facing the outside of the car have fewer grooves to provide greater contact surface when leaning during a corner, which Bridgestone says improves responsiveness and grip, and improves the transition from control to a loss of control, making the tire more predictable at the limit.

The comparison, at least against the BF Goodrich tires, bore all that out. While the Goodrich tires were easier to break free, and more prone to understeer, the Firehawks resisted the urge better, carved the corners nicely and were progressive in the transition from being in control. The Goodrich tires seemed to catch themselves at times, regaining traction momentarily, which wasn’t a good thing. Instead of being able to trust your own steering or throttle correction, you had to first correct for the loss of grip, correct for the regaining of grip, and then correct again for another loss of grip.

Caveat time: keep in mind the odds Bridgestone chose competitors at random, or necessarily chose the best competitor tires, are slim. It doesn’t necessarily invalidate the comparisons, but it does provide a grain of salt to take them with.

The new tires will be showing up at Bridgestone/Firestone outlets shortly.

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