Michelin Radial Tires
MICHELIN RADIAL TIRES
PREVIEW
World-beating race technology for the rest of us
THEY SOUND LIKE A SNAKE-OIL SALESMAN’S MOST OUTrageous claims: A high-performance motorcycle tire that improves handling and stability and comfort and ease of steering; a tire that achieves superior grip through the use of soft tread compounds but that doesn’t wear as quickly as other tires will with comparable rubber; a tire that performs consistently throughout its entire life, even when effectively worn-out.
You have to admit, those allegations don’t sound very realistic. Most modern tires will do some of those things, but none so far has been able to do all of them. Regardless, every one of those claims is being made by Michelin about its new and long-awaited high-performance motorcycle radiais. And if our two days of riding on the tires during their U.S. press introduction in South Carolina is any indication, these radial wonders truly do live up to their maker’s ambitious allegations.
There’s no question that Michelin has been at the cutting edge of radial tire development. The first radial ever to win a world championship roadrace was the Michelin rear slick on Freddie Spencer’s Honda in the 1984 Italian Grand Prix. And in 1985, ’86 and ’87, the 500cc world championship was won on Michelin radiais; even more impressive, the winner of every 500cc GP event during 1985 and 1986 was riding on Michelin radiais.
Obviously, Michelin knows a thing or two about highperformance radiais. And the company has used that knowledge to produce these new DOT-approved high-performance radiais. The tires come in two styles: the TX-1 1 (front) and TX-12 (rear) Hi-Sport Radiais, designed primarily for production roadracing; and the A59X (front) and M59X (rear), which are all-around high-performance tires intended for street use.
Differences between the two styles are minimal. The Hi-Sports have less grooving, as well as thinner and softer tread rubber, and they generally require quite wide wheels for optimum performance, whereas the street versions are sized to work on the narrower rims found on most streetbikes. But both types use the very same carcass designs, which are based on the company’s racing technology. Indeed, the front tires are identical in carcass construction to the Michelin radial front slicks currently used in GP roadracing.
It’s worth pointing out that these tires use true radial construction, as opposed to the numerous “semi-radial” tires that appeared on the market earlier in the evolution of motorcycle radiais. A true radial has its casing cords running exactly 90 degress to the circumference of the tire, whereas a semi-radial’s casing cords are close to 90 degrees rather than the 20to 40-degree angles that are typical of bias-ply tires. And these Michelins indeed qualify as true radiais, since they have a single ply of casing material running directly across the tire from bead to bead.
There are, however, differences in construction between the front and rear Michelins. The front carcasses are reinforced by two Kevlar belts around the outside, with the cords of those belts angled at about 45 degrees to the tire’s circumference. They are, therefore, bias-ply belts, but should not be confused with bias-ply carcasses; the two serve entirely different purposes. The rear tires also use a single radial ply of casing material, but it is reinforced with a band of Kevlar that Michelin calls a “zero degree” belt. This is a single belt that has its cords running around the circumference of the tire, perpendicular to the cords of the carcass material.
Fundamentally, the zero-degree belt and the bias belts do the same thing: resist tread distortion and minimize tire growth at high speeds, while allowing sufficient flexibility for stability and comfort. The reason for the difference in front and rear belt designs is simple: A front tire has a distinctly different task than a rear tire, and the belts are designed to help each tire do its particular job more effectively.
Anyway, it’s the rear tire that Michelin feels makes its radiais unique, for the combination of radial carcass and zero-degree belt gives the tire a natural tendency to drift outward during hard cornering. This designed-in drift is extremely small and entirely controllable rather than being a hair-raising slide, and it occurs only when considerable engine power is applied while the bike is heeled way over. This “oversteer,” if you will, is so slight that the rider usually doesn’t feel it but instead just senses that the bike is turning more sharply, as though it had a shorter-thannormal wheelbase.
That’s how it seemed to us, at least, during our experiences with the tires in South Carolina. We spent a half-day riding on Michelin’s own roadrace-style test circuit near its U.S. headquarters in Greenville, and a full day chasing through the scenic Blue Ridge Mountains on some of the East’s finest twisties. We rode six pairs of sport-oriented bikes, with one of each pair wearing top-rated bias-ply production-racing tires, the other shod with the Michelin radiais. And so far as we could tell, the Michelins did just about everything claimed of them.
In all honesty, we couldn’t notice any significant differ-
ence in cornering traction between bias-ply and radial; those differences might exist, but it will take a more rigidly structured test session to find them. But the Michelins clearly gave a smoother ride, made for easier steering, were more stable at top speed and during hard braking, and were less-disturbed by pavement chops and ripples when cornering flat-out. And although we never managed to wear out any of the tires, they seemed to work just as well when about two-thirds worn as when brand-new.
In the end, of course, our final judgment on these tires will have to wait until they are available in quantity for a more scientific evaluation. The Hi-Sports radiais have been in extremely limited supply since last fall, and the A59X/M59X versions should start being available about a month after you read this. But we’re confident that these Michelins will soon begin to erase any question marks riders may have about radial tires for motorcycles. They’re what performance-bike riders have been waiting for ever since Fast Freddie won that very first race on a radial. 0
