New Ideas In Tires

New Ideas in Tires

YOKOHAMA ROAD FLASH TIRES

ANYONE WHO HAS ridden a motorcycle long enough to run through the original set of tires knows the names Goodyear, Avon. Pirelli, Michelin and Continental. Recently, however, Yokohama has introduced a new line of tires for large-displacement roadsters. These are designated “Road Flash,” and are claimed by the manufacturer to perform at “sustained speeds of 150 mph.” Road Flash tires feature four-ply nylon low-angle bias ply construction. Both front and rear units are rated in Load Range B. Maximum loads, specified by Yokohama at 40 psi cold inflation pressure, are 470 lb. for the front, 615 for the rear.

The front tread pattern is a semi-ribbed, longitudinally cleated design, with halfdiamond side lugs for bite in corners. For the rear, there is an interlocking chain design with a center groove and smaller, angled side grooves, also for cornering adhesion. Yokohama reports that the Road Flash tread compound is specially formulated to deliver traction in wet running.

For CYCLE WORLD’S evaluation, the Yokohamas were fitted to a 1973 BMW R60/5, replacing a set of German-made Continentals, thoroughly worn at just over 6000 miles. The front Continental showed some cupping of longitudinal ribs, and severe ozone checking of sidewalls after a year’s use. Dry weight of the R60 (with a cafe fairing and saddlebags), is approximately 450 pounds. The Yokohama test spanned three months and covered 3507 miles. Approximately 2000 of those miles were clicked over with a passenger aboard. Rider weight was 210 lb., passenger weight 130 1b.

To provide for the fairest possible test, the R60 underwent a fork overhaul. New front springs were fitted, and 10W hydraulic oil was used to control damping. Front and rear brake linings were inspected, and glazed areas were buffed with emery cloth to ensure even braking. Both front and rear wheels were statically balanced after the Road Flash casings were fitted. In addition, 8 oz. of Liquid Tire Balancer and Puncture Sealer from Advance Cycle Products, Inc. was squeezed into each tire.

Road surfaces traversed during the test included freeways with either seamed concrete or asphalt paving. Top-quality, twolane paved secondaries and rough, potholed, badly maintained one-and-a-halflaners also were traveled. Since all of the Road Flash testing was carried out in California, in summer months, surfaces were uniformly dry and, for the most part, clean. Only one brief rainstorm was en-

countered, thus the wet-adhesion character of the tires could not be fully assessed.

Initially, the Road Flash tread compound seemed tacky enough for a '/s-in. thumbnail depression. As tread wore down during the test, the seemingly resilient surface of the tread wore away, and the tires became more resistant to the thumbnail.

At first, test riding was done carefully. Corners were attacked gingerly to feel out tire potential. As the tires scrubbed in, confidence grew, and soon the R60 was hurled into bends with abandon. Corners posted at 30 mph could be tackled at 50 or 60 mph. and 50-mph corner markers could be passed at well over 70 mph without fear of breakaway loss of traction. The only losses of adhesion during the test occurred at low speeds, on loose crystaline granite sand and dry leaves.

Front and rear Road Flashes were inflated to 27 psi and 30 psi, respectively, mainly for two-up travel. The BMW’s rear coils were tweaked to their full compression notch for stiff springing and passenger load capability.

The stiff suspension setting, with the new front springs and heavier oil in the forks, produced a firm, positive ride that induced feelings of security in hard cornering, even with a passenger behind.

The combination of firm suspension, the Yokohamas’ tread patterns and perfectly balanced wheels improved the R60’s ride and handling characteristics significantly over those with the worn Continentals running in less than true balance.

The Flash also works well in special situations. It tracks straight in concrete freeway rain grooves, unlike some tires on the market.

In terms of wear, the front Flash suffered least, in spite of heavy front brake use during the course of the test. At the beginning of the grind, the front Flash showed 5/32 in. of tread depth. By the end of the test period 4/32 in. of tread remained. If the tire is considered to be w orn out when only 2/32 in. of tread remains, the front tire gave up only 25 percent of its tread in 3507 miles. Thus, the projected wear for the front Flash is 14.028 miles. At a suggested retail price of $30.97. the cost per 1000 miles of operation is about $2.22.

The rear Flash obviously paid the penalty for protracted two-up riding at high speeds. At the centerline groove, when new, the rear tire showed a tread depth of 8/32 in. At the end of the test ride, only 4/32 in. of tread remained along the centerline of the tire. Again determining the tire to be worn out with 2/32 in. of tread remaining, the rear tire displayed a 66-percent wear factor. Thus, projected tread life for the rear Flash is 5260 miles. At a suggested retail price of $41.11, the cost per 1000 miles is $7.80.

Careful balancing and new springs helped the front flash to survive the test period without cupping of the sort that afflicted the Continental rib tread it replaced. The front Yokohama's ribs remained blocky and square, with little lug edge scuffing wear apparent at the end of the test.

The rear tire, equally well-balanced, and installed per manufacturer’s instructions for the rear w heel’s direction of rotation (a small, cast-in-rubber arrow shows the way), presented evidence of directional wear on the center pair of interlocking chain lug edges. This was the result of drive wheel acceleration/deceleration patterns. Outside edges of the chain lugs showed greater scuff w'ear than did inside edges, probably the result of cornering under heavy loads.

Neither tire was treated with a protective compound to prevent deterioration, so they showed a minor degree of ozone checking (small cracks at junctures in tread and sidewall patterns). This was thought to be a result of Southern California’s smog-laden air, in which ozone is found in heavy concentration.

Yokohama tires, then, are worth considering. They offer good traction on a wide variety of road surfaces, they track straight in rain grooves, and they offer average wear. For further information, or to purchase a set, contact your local motorcycle dealer. He’ll probably have Road Flashes in stock.