Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
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A word of thanks Without the cooperation of the pa rticip ating tire com panies, this com pa rison would never ha ve gotten off the ground. A special note of thanks to Gary Bryson from Goodyear, the entire cre w at RICKEY RACER in Pomona , and to Karen Pebley our statistician. • Pirel1i: The 470 MTI8 Pirelli has a combination of medium hardness and a very broad tread face when leaned over. The big Pirelli seemed to be the most easily controlled when the tire was sliding. Lots of warning when the limits are reached . The 470 size rear tire also offers the advantage of a bit more ground clearance because of its larger diameter. Unfortunately the smaller front tire really limits how' effective the set might be on a motorcycle. A 325HI9 isn't enough for a 530 + pound bike. Under hard braking the bike hunts back and forth , ' using up most of the available road . The small front tire also seems pron~ to pre,?ature lockup . Steering and stability when the bike was really pushed hard was excellent, but again the lap times were hindered by th e poor braking capabilities of the front tire . If Pirelli wer e to offer a 400 or 410 size front tire I'm sure these. deficiencies would disappear. Avon: The 470 rear tire is so tall that the motorcycle feels precarious or imbalanced, like it wants to fall off of its perch. Once you get . the knack . it's not bad. The 410 front tire showed only 4 % wear on the edge of th e tread while capturing the second fastest lap times . The front tire felt extremely secure under hard braking. The broad contact patch made th e motorcycle steer a little b it heavier, but not at all unacceptably. The 425 rear tire worked the best of the two as witnessed by the lap times. This combination felt secure whether the suspension was unladen or heavily taxed . No surprises , a very predictable. neutral set of tires Continental: I was really disappointed . I think a major portion of the rear tire's lack of performance was in the rim width. We were forc ed to use a 2.15 rim rather than the 3000 that Continental recommends . On top of that, I don't think either of these tires warmed up enough to start working properly. The tr ead blocks are so well braced, that there is next to no tread squirm . Hence , there is little heat build-up . The pressure never varied during the testing of these tires , another indication that they never got up to temperature. Both the front and rear seemed to reach the limits of adhesion rather quickly compared to the others. Both tires are well mannered and predictable. When pushed pa st the limits of good sense, the motorcycle understeered rather severely. Braking was good . but not exceptional. . ROCKY CYCLE CO.,/NC. 1250 Elko Drive. p.e.B. 1431 Sunnyvale. CA. 94086 Cheng ShIft Ti,., used by the winners Imported by Sport Tracks Co. Bob Balentine - winner of - the first Bounty Series never fai led to fin ish 213-361-5955 Also stock Brldgestone and Dunlop, Kal Gard, Armoratl, SealeN~Alr. see your local dealer Knowles Cycle Co. Ph. 214-2 53-7411 Since 1967 Complete parts & service Yamaha 42 637 E . Irv'ng 81. Irv'ng, Texas 75060 Yokohama: Seat of the pants told me that these tires were working well , but the lap times were disappointing. The wear percentage for the rear center. rear edge and the front edge gave me a clue to what was happening. The smear of rubber across the tread faces of both tires also helped to confirm m y suspicions. Both tires are too small for a motorcycle the size of a Z·I . I submit that these same tires on a 350 or 500 would be a hell of a combination. They are super predictable. Up to the limits of the contact patches there's super traction and an excellent feel for what the tires are doing under extreme condition. I would be interested in comparing a 460V18 and a 350 or 400V19 size set. Michelin: A very strange set of tires . We chose to run the Michelins at a much lower pressure than the others. The .Michelin Distributor (Hamer & Jones) had told me prior to the test that 23-24 pounds would work best on the Z·l. Boy did it work! The Michelins worked so well that we ran into severe problems with the chassis. Straight line braking is absolutely ferocious, as is the hook-up Or bite coming out of a corner full- throttle. On the minus side, the tires get so much traction during the transition that .the chassis is incapable of going where pointed. The best way I could get the test bike around Willow was to run up to a corner and flop it over as quickly as possible, thus avoiding the transitions as much as possible. After just one lap with these tires on the .test bike, our fearless test rider D . Berg returned to the pits wondering if perhaps something like the swingarm hadn't broken. Dunlop K91: Quite a combination. Almost as fast as the K81's, but more precise in highspeed steering, and more . stable during the transitions. The front tire reminds me - of th e Dunlop roadracing front tires. A very distinct rib des ign with tread halfway to the edge of the rim . Very controllable under hard braking. Lots of warning when braking while leaned over. The rear feels a bit stiff in the carcass. This is compounded by a center tread design that do esn 't hav e any breaks in the tread face that might allow the rubber to squirm some under loading. The net result is a tire that not only feels stiff, but really does ride stiff. Downhill braking seems to put the biggest strain on the rear tir e. While the front is working hard, the rear tire is chattering and hopping about. Rear center tire wear seems to bear this out. The K9l had only 5 % tread wear in the cent er, while the same center tread on the K81 wore 25% . Goodyear HP: This combination of tires felt very twitchy or wiggl y on our test bike. The transitional stages were unnerving. Once the bike was on the pipes, the tires felt predictable; anywhere else they felt very strange, as if the front and th e rear were headed in two different d irections. T he front HP had a tendency to hunt back and forth across th e road under hard braking. Braking when th e bike was in the transition stages was virtually uncontrollable . The slow but violent front to rear undulation is pretty strange. On the plus side, I might mention that when your fearless (?) test riders did manage to get all the way over. the traction was excellent. I know , DuHamel doesn't seem to hav e any problems with these tires. GOOdyear GT: My notes read: Very safe , steady feeling at high speed l Excellent braking control. Very predi ctable wh en accelerating hard out of the slower corn ers. The big Z-l was almost neutral when driven past the limits of adhesion with the GT tires mounted . Understeer could be dialed in with less thrott le, oversteer with more throttle. Really easy to play hero racer with these tires. About the only thing not to my liking was the amount of deflection in the 2·ply front tir e. Large chuckholes and bumps caused the tire to mov e back and forth on the rim thus numbing steering precision. Dunlop K81: A very rapid almost hassle -free combination. Very solid when heeled over in a turn. These tires' really made the motorcycle feel secure at or past the limits of traction . The 410 and 425 combination is just about neutral. with the (sane) rider finding trailing throttle oversteer to be the normal reaction to improper entrance speeds. The main weakness in the K81s is th e small contact patch when traveling in a straight line. Straight up and down braking finds the rear tire chattering and hopping a bit , while downhill braking finds it barely manageable. T ra nsist ion wh en the suspension is lightly loaded is another area that the K81s are less than perfect when stacking them up against the competition. Conclusions (OT lack oj) We decided that the big loser thus far was the 6.75 16.5 General Jet-air Jumbo van tire that failed 30 miles (and $50) from the Willow Springs test track. The Avon tires surprised both the test riders and the statisticians that helped with the test. The problems encountered in testing the Michelin and Goodyear HP tires shouldn't be construed as problems with the tires ' themselves. rather as problems in coming up with a suitable test vehicle for this type of comparison. I think that I am going to reserve my conclusions for ' when all of the three segments of the comparison are finished . •