Service

SERVICE

Paul Dean

A horse is a horse, of course, of course

I have always been curious about the relationship between horsepower and the power of a horse itself How did they come up with this relationship?

Alcebiades Athayde

Sao Paulo, Brazil

You can thank James Watt, the 18th centuly inventor who transformed steam engines from inefficient contraptions into practical devices that helped usher in the industrial revolution. At some point, Watt determined that he needed a way to measure the amount of work any given steam engine could perform. Most industrial and agricultural pulling, pushing and lifting in that era was done by large animals, so Watt decided to rate steam engines using a measure of work that most people would understand: horses. To come up with this standard, he conducted some simple tests that involved dray horses pulling loads of coal. He eventually concluded-somewhat arbitrarily, as it turned out-that the average horse could move 550 pounds one foot in one second or 33,000 pounds (550 x 60) onefoot in one minute. He called this measure of work one horsepower, and the term has been the accepted standard ever since.

We should be thanlful that Watt didn ’/ use some other farm animal to calculate his measure of work. Otherwise, we might be discussing the cowpower or asspower of today ’s motorcycles.

Bun Warmers

What's the big deal with the way more manufacturers are putting the exhaust up under the seat versus the standard meth od of mounting it on the side of the bike? Is there a real handling gain like I have been hearing or is it all just hype because it looks cool? Mario Lyn Kingston, Jamaica

A little of both, actually. There i no doubt that underseat exhausts have become quite trendy over the last few years, but they also are-in most cases, at least-very functional. Ducati popularized the con cept in 1994 as a means of increasing cor nering clearance on the first 916. Many racebikes of that era were fitted with swingarms that had one dramatically curved leg that allowed the side-mounted

exhaust system to exit from beneath the engine without compromising cornering clearance. Ducati, however, solved the problem by running the exhaust up alongside the frame ’s right-rear upright to terminate with dual mufflers under the seat. Not only did this design yield exceptional cornering clearance, it added to the appeal of a bike that already was one of the sexiest ever built. Before too long, other sportbikes started to appear with similar exhaust arrangements, and several aftermarket companies even began offering under-seat conversion systems.

While improved cornering clearance usually results from an underseat exhaust, the handling does not necessarily benefit. During Suzuki ’s initial development of the 2005 GSX-R1000, for example, the engineers routed the exhaust up under the seat, after which the test riders reported a distinct degradation of the handling. They felt that side-to-side transitions were noticeably slower due to the muffler having raised the bike s center of gravity, and that overall, the bike did not seem as well-balanced. After a few attempts to come up with an acceptable underseat configuration, the engineers moved the exhaust back to the right side and the testers were pleased with the results.

Also, on some bikes with under seat exhausts, passengers have complained about

heat from the muffler toasting their but tocks, especially in hot weather The manu facturers tiy to prevent such occurrences by using various types of heat-shielding materials between muffler and inner fend ei~ but that a daunting challenge when a passenger is perched just an inch or two above a blistering-hot muffler

Heavyweight belt holder

In refer~ce to Fie "Tracker Tidbit" that appeared in the May issue regarding the belt final drive on the Lawwill Street Tracker: Kevin Cameron stated that "belt width would likely be prohibitively wide if applied to a 160-horsepower racer-rep lica." Just thought I'd let you know that the 350-cubic-inch, 355-horsepower Boss Hoss and its 502-inch, 502-horse power big brother have belt final drives of what would appear to be conventional width. Would Cameron care to explain why a 1200-pound bike with 502 horse power can use a conventional belt drive while a 160-horsepower racer-replica cannot? Bruce Meinsen Hamden, Connecticut

Kevin Cameron certainly is capable of explaining his comments, but since I said virtually the same thing about belt drives in last month Service ("Gimme a belt, willya?"), Ifeel obligated to respond.

First, there is the matter of application. Whatever Boss Hoss motorcycles might be, they are not “racer-replicas ” by any stretch of the imagination. They are cruisers, and even though they are incredibly large and powerful ones, their drivelines are not subjected to the kinds of constant, expected abuse (full-throttle upshifts, hard launches, rear-wheel-chattering downshifts, etc.) that racer-replicas and their actual racing brethren are designed to endure.

What s more, because the Hoss has an automatic transmission with an automotive-style torque converter instead of a clutch, there is no mechanical connection between engine and rear wheel; the power is transmitted through oil, which is why a torque converter is referred to as a “fluid coupling. ’’ The converter softens the delivery of that 355 or 502 horsepower enough to prevent the belt from being subjected to the kinds of large, momentary driveline spike loads that occur on manual-transmission bikes when the rider dumps the clutch on a hard take-off or does a full-throttle powershift or fails to match engine rpm and road speed when shifting up or down. Even so, the Boss Hoss factory strongly warns that first-tosecond upshifts of the two-speed automat-

ic should not be done at or near full throttle, presumably to reduce those momentary driveline loads.

Drivebelts also cannot tolerate much variation in tension, lest they skip, break or shear teeth. And the longer the rearsuspension travel, the more difficult is the task of maintaining relatively constant belt tension. This is why Erik Buell spent

so much time working out the geometry of the rear suspension and drivebelt tensioner on his namesake XB9 and XB12. But whereas most sportbikes and racer-replicas have somewhere between 4 and 6 inches of rear-wheel travel, the Boss Hoss has only an inch or so; and while that does little for the bike’s ride, it helps keep the drivebelt alive.

Honestly, I don `t know how long the drivebelt lasts on a Boss Hoss, but I can tell you this. If the bike had a manual transmission and a rear suspension com parable to what other bikes have, their drivebelts would either be significantly wider replaced with chains or littering up the roads wherever they traveled.

Healing the squealing

Here's a possible fix for the reader whose Suzuki Marauder has squealing brakes ("Locust invasion") as described in May's Service. I found a product made by SBS called Brake Pad Shims that fit between the caliper pistons and pads. They took the squeal out of my brakes and have not affected the braking power or feel, even on my bike's ABS system. They're only about $8, which is a lot cheaper than buy ing two or three sets of pads and getting them to seat properly, then sometimes finding that the squeal is still there. Danny Stennett Pocahontas, Illinois

I'm pleased to learn that the shims gave you good results. Based on what I have seen and heard, they don `t work almost as often as they do, which is why I didn `t in clude them in my response to Mr. Monk,

the owner of the Marauder in question. Same goes for some of the silicone-based products that you apply to the back of the brake pads. Still, I probably should have mentioned these possible solutions be cause, as you point out, they `re much cheaper than a set of brake pads. Thanks for the reminder~

Won't really wheelie

Two years ago, I replaced my ’78 Yamaha DT400 with a 2000 Suzuki DR650 that had just 1500 miles on it. The Suzuki is much better on the street but is not as responsive in the dirt. I replaced the stock air filter with a K&N, but the only performance change has been in gas mileage-for the worse. I want to be able to throttle-lift the front wheel like I could on the DT without dumping the clutch. I was considering a jet kit and a rear-sprocket change, but now I’m wondering if that would do the trick. What will happen to my cruising speed if I make this change? The bike is supposed to have 10 more horsepower than the Yamaha, but I don’t see or feel it.

Rob Kelly Ivor, Virginia

In a way, you `re comparing oranges and tangerines. Even though both are dual-

purpose bikes, the DR650 is a very different animal when judged against a DT400. And unless you were to re-engineer your Suzuki from the ground up, it will never snap its front wheel in the air as easily as would a properly tuned DT400. It’s much heavier, especially at the front, and its fourstroke, comparatively heavy-flywheeled engine does not deliver the kind of off-idle throttle response that a light-flywheeled two-stroke offers. Lower gearing might help just a little, but the DR would then be buzzier at cruising speeds. If you lowered the gearing by, say, 10 percent, the engine rpm at any given road speed would increase by 10 percent. So, too, would a jet kit improve the bike’s wheelieability (Ijust made that word up), but not enough to deliver the results you ’re after.

You also seem to have a misunderstanding about horsepower. I don’t doubt that the DR makes 10 more horses than the DT, but those are peak numbers attained at high rpm, which means they have nothing to do with either bike ’s ability to pick up the front wheel at lower rpm. Throttle response, low-rpm torque and flywheel inertia are the prime engine ingredients at work when attempting throttle-induced wheelies, and the DT holds a distinct edge in those categories.

A less-than-tolerant view

For quite some time, I’ve been reading in all the magazines about how BMW’s servo-assisted brakes have “somewhat reduced” braking power when the ignition is off. I first experienced this with my RI 150RS, and it was quite a shock. Some reviews merely say that there is less braking available, and others just state that it takes a bit of getting used to. Even BMW, in its haughty arrogance, has said that this is a normal “reduced braking mode.” To all of this, I say: bull! When the key is off, these bikes have no friggin ’ brakes! The power assist is marvelous when the key is on; but to have less braking than you get with old wet drums when the key is off is a grossly unacceptable condition and a huge mistake by the manufacturer. I doubt that a magazine would print this letter, in view of the risk to their advertising dollars and customer base; but let’s get the truth out anyway and quit this fiddly-farting around. Paul Snyder

Lawndale, California

Don’t beat around the bush, Paul; what do you really think?!

Truthfully, we too have been less than enthralled with the key-off behavior of BMW’s servo-assisted braking system. I once almost allowed a K1200GT to drift back into a parked car while unloading it from a trailer because I didn’t anticipate how feeble the brakes would be with the ignition switched off.

On the other hand. I’m not trying to defend BMW, but have you ever tried to stop a car when the engine is off? And in that case, you don’t just need to have the ignition turned on; the engine has to be running to produce the vacuum that provides the braking assist. I know, it ’s not > the same situation as with a bike, but there is a strong precedent here, even if we don't like it.

Recall Roster

NHTSA Recall No. 05V149000 Big Dog Chopper, Chopper DT, Mastiff, Pitbull, Ridgeback Model year: 2005 Number of units involved: 1418 Problem: On certain motorcycles, the primary-drive sprocket nut may back off the engine mainshaft. This could cause the primary drive to lock up without warning, possibly resulting in a crash.

Remedy: Dealers will inspect and replace the drive-sprocket nut.

Owners who do not receive this free remedy within a reasonable time should contact Big Dog at 316/267-9121.

On the coast highway

I ride with a couple of guys who occasionally coast their late-model Japanese sportbikes down hills to refine their skills by not having the benefits of power. They usually do it with the motors off, coasting at up to 50 mph for three or more miles. I was under the impression that motorcycle transmissions are lubricated by engine oil. If so, isn’t this practice bad for the bike? Jason Wang

Canoga Park, California

The transmissions are indeed lubricated by engine oil through a combination of a direct pressure feed to critical components and splash that occurs as the gears whir around in a maelstrom of oil mist and droplets. Obviously, then, the transmission gets very little or no lubrication when the engine is not running, which can be problematic if the bike is coasted-or towed on its rear wheel behind a car-for long periods. But a brief coast down a hill should not cause any mechanical grief; it only lasts for a few miles and there is virtually no load on the transmission components. In a warm engine with a wet-sump oiling system (which all Japanese sportbikes have), a coasting bike usually undergoes enough jostling and bouncing to allow oil in the sump to slosh around and provide some degree of lubrication.

So, your friends should not be concerned about the mechanical effects of their unpowered downhill races. And if they are, tell them to simply let the engine idle while they ’re coasting, which will keep some oil flowing to the transmission. □

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 949/631-0651; 3) e-mail it to CW1Dean@aol.com; or 4) log onto www.cycleworld.com, click on the “Letters to the Editor” button and enter your question. Don’t write a 10-page 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.