Service
SERVICE
PAUL DEAN
The ratings game
Q Last month, I bought a used ’99 Yamaha V-Max with 9200 miles on the odometer. I wanted to put new tires on it, so I ordered a set of IRCs-a 110/90-18 front and 150/90-15 rear. I then looked in my manual to see how to remove the wheels and discovered a warning that said, “This motorcycle is fitted with super high-speed tires. Never fail to use the specified tires in tire replacement. Other tires may have a danger of bursting at super high speeds.” It then says to use Bridgestone or Dunlop tires for a replacement. How fast is high speed? And are the IRC tires good to use for basic riding around town or on the highway at speeds of around 75-80 mph? Robert Verrigni Glenville, New York
A Among the several ratings that apply to motorcycle tires is the speed rating. It represents the highest sustained speed a tire has been tested to withstand when operating with the maximum recommended inflation pressure and subjected to the maximum recommended load. Bike makers and tire manufacturers never recommend using tires with lower ratings, but the IRC replacements you have selected are one entire level below the V-Max’s original-equipment rubber. The original tires were V-rated, which means the maximum sustained speed they are rated to withstand is 149 mph; the IRCs you have chosen are H-rated, which imposes a 130-mph limit.
Speed ratings and maximum load recommendations are listed on a tire’s sidewall by either of two methods. In some cases, the speed rating is incorporated into the tire’s size designation, such as the “H” in the 150/90H15 labeling on the IRC rear tire you bought for your V-Max. When the speed rating is part of the size designation, the load index is a two-digit number listed after the size. On the OEM Dunlops and Bridgestones, the front load index is 61 (567 lbs.) and the rear is 74 (827 lbs.). Sometimes, the speed and load ratings are listed together after the tire size (as in “74 H”). If you type “motorcycle tire ratings” into your web browser, you’ll be able to select from numerous sites, including those of the tire manufacturers, that display a complete listing of speed and load ratings.
The tire and bike manufacturers are legally obligated to issue stern warnings regarding tire fitment. They have no control over how any given motorcycle will be ridden, so they have to assume the worst-that some riders will overload their bikes on underinflated tires and then ride as fast as the bikes can possibly go. If you in fact never ride faster than 75 or 80 mph or exceed the IRC tires’ load ratings and always maintain the recommended inflation pressures, you should not experience any ratingrelated tire problems. But if you exceed any of those parameters, don’t be shocked if the tires fail.
Hitting the trail again
QI deeply appreciate your description of rake and trail (“The geometry of geometry”) in the May, 2006, issue. Now could you please explain the practical implications of these geometric features? That is, what riding characteristics result from increased/decreased rake and trail? Jim Tunney Indian Wells, California
A I’m glad you used the word “practical”; the behavioral aspects of steering geometry are much too involved to permit a detailed explanation in the limited space available here. But in general, trail affects the self-centering attributes of the front end; more trail generally equals more self-centering. Rake primarily affects the steering’s feel as well as the front suspension’s effectiveness.
Rake and trail have to work in concert with one another for the bike to deliver the right feel and feedback, but technically, you don’t need rake to have trail. A furniture caster is a perfect example. Its swivel pivot (analogous to a motorcycle’s steering head) is perfectly vertical, so it has no rake at all; but the caster’s wheel is offset, so there is distance between the point where the pivot’s axis intersects the ground and where the vertical centerline of the axle intersects the ground. Just as with a motorcycle, that distance is the trail.
A vertical steering angle wouldn’t work very well on a motorcycle; it would provide virtually no feedback and hamper front suspension action. The forces acting on a motorcycle’s front wheel are both horizontal and verticalthe horizontal being the direct backward force caused by the wheel’s resistance to rolling as it moves forward, and the vertical being the direct upward force of the wheel’s attempted reaction to imperfections in the pavement. The result is a force vector, which is a combination of the horizontal and vertical forces. Rather than working directly rearward or directly upward, the force vector works at an angle that is both upward and rearward. And since the impact of bumps is greater than the resistance to rolling, the vector is more vertical than horizontal-something close to the 25to 30-degree steeringhead angles of current motorcycles. If the fork (rake) were vertical, the suspension would have more of a tendency to bind rather than compress. on a car tire is supported evenly across the entire width of the contact patch because the tread is flat; a motorcycle tire is round, so all of the load is supported by the narrow contact patch, with the greatest part of that load concentrated at the very center of the patch. Bike tires usually are made with less tread depth than car tires; tall tread blocks tend to allow a tire to squirm, and that’s an undesirable trait on a streetbike.
Rake also affects the feel of the steering. Sit on any bike and simply turn the handlebars back and forth. As you will see, any time you move the front wheel off center, the front of the bike lowers slightly, and vice versa. That’s because the angled steering axis intersects the ground out ahead of the tire’s contact patch, causing a mild “flop” in the front of the bike. The more rake (without a reduction in trail), the greater that effect. That’s why motorcycles-particularly those with a lot of rake and trail-tend to be harder to stand back up when they’re banked over in a turn than they were to lean into it in the first place; you’re essentially “lifting” the front end when doing so. Conversely, when leaning into the corner, allowing the weight of the front end to drop helps make the turn-in easier by partially offsetting the gyroscopic resistance of the spinning front wheel and the self-centering effect of the trail.
Recall Roster
NHTSA Recall No. 06V184000
Kawasaki ZX-14 Model year: 2006 Number of units involved: 2321 Problem: On certain motorcycles, the bolts holding the vehicle-down sensor may come loose and allow the sensor to fall out of its mounting bracket. If this occurs, the engine may stop running during vehicle operation, creating the potential for a crash that could result in injury or death.
Remedy: Dealers will tighten the vehicle-down sensor mounting bolts to the proper torque setting free of charge.
Owners may contact Kawasaki at 866/802-9381.
NHTSA Recall No. 06V122000
Big Dog Bulldog Model year: 2005
Number of units involved: 364 Problem: On certain motorcycles, the front fender brackets could fail, allowing the fender to detach. If this condition occurs, a crash could take place without any prior warning. Remedy: Big Dog dealers will replace the front fender brackets free of charge. (Big Dog recalled certain Bulldog motorcycles in May, 2005. Big Dog has since revised the repair instructions and is recalling all 2005 Bulldog motorcycles. If your motorcycle was repaired under the previous campaign, it will need to be remedied again.) Owners may contact Big Dog at 316/267-9121.
In many ways, steering geometry is an uncertain technology involving a mix of known principles 9 combined with a bit of finger-inthe-wind guesswork. When developing new models, the engineers usually can get the steering’s feel and function in the ballpark on the first try, but in the end, ongoing feedback from test riders is what fine-tunes the geom? etry that goes into production.
Sex, lies and hp figures
QI have a question regarding the
quoted horsepower of literbikes in various articles I have read lately, most specifically regarding the Yamaha RI. I
recently purchased an ’06 R1 and just had it dynoed. The results have me a little surprised due to the dyno numbers I’ve seen in not just Cycle World but other magazines, too. My bike has about 200 miles on it and is completely stock, and the dyno runs were made back-to-back in fourth gear; obviously, the ram air wasn’t in effect because the bike was sitting still. The temperature was is the mid-60s that day, and the dyno recorded 145.0 and 145.6 hp. I’ve seen many articles with R1 power numbers ranging from 154 to 159. Is there that much variance in these bikes from the factory or are dynos that different? Do you maybe make your dyno runs in different gears? Obviously,
I won't notice the small difference in horsepower on the street; I just want to understand this for my own knowledge.
Robert Sessock Posted on www.cycleworld.com
A Actually, the dyno numbers on your bike aren’t much different than those we got on our ’06 test R1 during the June-issue comparison of one-liter repli-racers. Our bike posted a best run of 149.9 hp at 12,600 rpm and 70.9 ft.-lbs. at 10,100, with all runs conducted in fourth gear. A 4.3-horse difference amounts to just 3 percent, certainly not enough to call out the National Guard.
Since I know nothing about the other dynos you are referring to and even less about the ’06 Rls tested on them, I can’t accurately explain the discrepancies you have noted. But I do know that comparing numbers compiled on different dynos usually results in more questions than answers. Not all dynos are calibrated equally, even when they are of the same make and model. And there’s a saying in the performance world that the numbers generated on a dyno are only as good as the person operating it. If the parameters and techniques used in the test sessions are not the same for all the dynos in question, the numbers are not directly comparable.
What’s more, neither are all motorcycles of the same make and model identical. The stack-up of critical tolerances in an engine can easily result in one being slightly more or less powerful than most of the others. In this modern era of computerized manufacturing, there generally is very little difference in any one of a given model, but such anomalies do happen nonetheless. Some companies have been known to run quick dyno tests of bikes as they roll off the assembly lines, designating some of the better-performing ones for use in magazine tests. Technically, this selection process is not “cheating,” since all those bikes use stock parts and all came off the same assembly line, but it can help identify bikes that produce slightly betterthan-average power.
Hoop dreams
Q Reading about the Metzeler Sportec M3 tire in the May issue, 1 was reminded of a tire characteristic that has always bothered me. Your article said the M3 lasted only 2500 miles before wearing out and that 4000 miles would have been acceptable. I’ve ridden motorcycles for many years, and even if some bike tires last up to 10,000 miles, that still doesn’t match the tire wear of cars50,000 to 75,000 miles, in some cases. The weight of a car is significantly more (even taking into consideration 2 versus 4 tires), yet the car tire lasts so much longer. Why can’t motorcycle tires be made to last longer? The cost savings provided by the fuel economy of a motorcycle are severely compromised by the cost of and frequent need to buy tires.
Ronald D. Glaum Livermore, California
A The short answer to your question is that a motorcycle is not a car. Both are transportation devices and both involve engines, wheels, suspension, brakes, etc., but there are enormous dissimilarities in their performance dynamics that dictate significant differences in the design of their tires.
Now for the long answer. Not only does a car have four tires that are wider than either of a motorcycle’s two, the
Homebrews
I love to ride in the evening, about the same time the bugs all love to fly, so I always bring home a few dozen of them on the faceshield of my helmet. A week later, after they’ve dried out, I can’t see through the shield any more, so I figure it’s time to do something about it. After trying just about everything, I stumbled upon the best solution yet the other night. I sprayed the shield with the Scrubbing Bubbles foam we use on the tubs and sinks, let it sit for a few minutes and presto, wiped away a week’s worth of dried bug guts. A followup wipe with Windex and the shield was like new! Maybe this idea will help others with the same problem. I’m a little reluctant to try it on my teeth, but you never know... Frank King
Gastonia, North Carolina
And it leaves your shield smelling so.. .so fresh, too!
tínmoom
contact patch of each car tire is rectangular and spans the entire width of the tread; a bike tire’s contact patch is oval in shape and never wider than about a quarter or third of the tread’s overall width. All of a car tire’s patch remains in contact with the road at all times; a bike tire’s patch moves side to side as the machine leans, even in very mild turns, which means there usually is some form of “scuffing” going on. The
Those aren’t the only differences. Cars corner through what is called “slip angles,” motorcycles via “camber thrust”; that fact alone requires tires that reside in different areas of the design spectrum. A little bit of tire slippage in a car might go virtually unnoticed, but on a bike it can put you on the ground; so for safety, if for no other reason, the tread compounds in motorcycle tires tend to be grippier (i.e., softer) than those in car tires. Plus, most motorcycles, even the lower-performance ones, have a better power-to-weight ratio than cars, so they can-and usually do-accelerate more quickly, increasing the rate of wear on that narrow little contact patch at the rear.
If you tally the net effect of all these differences, it should become easier to understand why bike tires don’t last nearly as long as car tires. On the other hand, when performance-oriented cars are driven as aggressively as most modem high-performance bikes are ridden, they don’t get very good tire mileage either. At our sister magazine, Road & Track, it’s not uncommon for one of its long-term high-performance test cars to chew up four very expensive tires ($1000 or more per set) in just 10,000 miles.
Nevertheless, comparing car-tire mileage with that of bike tires isn’t akin to comparing oranges and apples; it’s more like comparing oranges and watermelons. U
Got a mechanical or technical problem with your beloved ride? Can’t seem to find workable solutions in your area? Or are you eager to learn about a certain aspect of motorcycle design and technology? Maybe we can help.
If you think we can, either: 1) Mail a written inquiry, along with your full name, address and phone number, to Cycle World Service, 1499 Monrovia Ave., Newport Beach, CA 92663; 2) fax it to Paul Dean at 949/6310651; 3) e-mail it to CW1Dean@aol.com; or 4) log onto www.cycleworld.com, click on the “Contact Us” button, select “CW Service” and enter your question. Don’t write a 10page essay, but if you’re looking for help in solving a problem, do include enough information to permit a reasonable diagnosis. And please understand that due to the enormous volume of inquiries we receive, we cannot guarantee a reply to every question.
