Metzeler Roadtec Z8 Interact Motorcycle Tire Test
Motorcycle tires have peculiar needs simply because they need to lean over – and the more they lean, the more the grip goes away.
Unfortunately, soft, grippy rubber compounds wear out quickly. In 1988, Bridgestone created the first dual-compound streetbike tire which ran a soft (grippy) compound around the edges of the tire, and a relatively hard (longer-wearing) stripe around the middle.
Since then, most manufacturers have done the same and that certainly helps solve the problem. However, there is a transition zone where the two compounds join that, in theory at least, affects the tires’ feel and level of grip. To eliminate that issue, Metzeler came up with a different idea, and promptly patented it.
Metzeler’s thinking is based around the fact that heat affects rubber stickiness. In other words, the hotter a tire gets, the grippier it becomes. If you have watched MotoGP recently, you will be well aware of the problems caused by the race tires’ inability to warm quickly enough.
Heat is principally generated inside a tire as the carcass flexes under acceleration, braking, and cornering. By precisely managing the amount of flex, Metzeler is able to manage the heat generated, and make a single rubber compound act like multiple compounds, and do it without a transition zone.
Naming the technology Interact, Metzeler winds approximately 120 steel wires around the tire and tunes them like a guitar string. In the tire’s center there is very little flex and the rubber stays cool and long-lasting; as the wires’ tension relaxes towards the tire’s shoulders, more heat is generated, and the tire has more grip where it is needed.
The new Roadtec Z8 is claimed to have an improved rubber compound for much more grip and a more effective footprint over its Z6 predecessor. Also produced in a “C” construction for motorcycles over 530 pounds, we replaced the 4000-mile worn Roadtec Z6 tires on our Triumph Sprint GT with the new Z8s for a direct comparison.
Metzeler’s recommended tire pressures at 40 psi rear and 38 front sounded high, but we are glad we listened. The new Z8 definitely has more grip than its predecessor; hard throttle corner exits produced zero squirming at the rear.
The improvement in handling was very welcome. Despite an eightpercent wider footprint area, the new profile reduces steering effort by five-percent, and it was noticeable. Transitions are a little easier due to the quicker steering, yet the Z8s are neutral feeling, predictable on turn-in, and exhibit excellent mid-corner stability.
Feedback from the front is exceptional, especially trail-braking into corners where you really need a lot of confidence. We had a couple of hard, straight-line stops from speed and, although they weren’t panictype situations, we were likewise impressed by how poised the
machine felt on the brakes.
We liked the Metzeler Roadtec Z6 tires and they returned decent mileage; however the successor seems to be a good evolution with improvements in handling and grip. We’ll see how they last; in the meantime, the new Metzeler Roadtec Z8s are a big step forward.