SR Finds the Optimum Number of Cylinders for a Sportbike—From The Archives

This article was originally published in the June 2000 issue of Sport Rider.

Ever since the first multi-cylinder motor­cycle was built, the search has been on for the best engine layout. Sportbikes have had any number of cylinders arranged in any way you can think of—V, square, transverse, upside down, sideways, you name it. But what's the optimum number of cylinders for a sportbike? Is a four-cylinder with its rev-happy smoothness best? A twin with its traction enhancing lumpy power pulses? Some­thing in between? We gathered a twin (Suzuki TL1000R), a triple (Triumph 955i Daytona) and a four (Kawasaki ZX-7R), along with some Drack data acquisition equipment, to find out.

Men and Machines
Our selection of motorcycles may seem a bit odd for this comparison. After all, twins and fours are not supremely defined by the TL-R and ZX-7R. Why not get a Yamaha R1 and call it a day? But the choice is not so obvious; in order to concentrate on engine characteristics, it would be wiser to compare three bikes with similar handling traits, and not bias the test toward one bike that has a superior chassis. Plus, a four-cylinder with 20 horsepower more than a twin would obviously perform better. Our choice of machinery, then, was dictated by power and weight characteristics, rather than having the ultimate bike from a particular category.

Start looking around for a triple, and the number of models is pretty limited. There’s the Triumph 955i and…not much else. Okay, so that became our triple—all 500 pounds and 106 horsepower of it. Keeping within the ballpark of the Daytona in terms of power and weight leaves the Kawasaki (at 527 pounds and 109 horsepower) and the Suzuki (510 pounds and 119 horsepower). Furthermore, each of our trio offer similar features in the chassis and brake departments, as well as fitting the same size tires.

In theory, a triple should put its power to the ground better than a four, and a twin should be better again (see “The Pleasure—and the Pain—of Power,” at the bottom of the page for the nuts and bolts, or ask Colin Edwards II for a demonstration). But each configuration has its pluses and minuses—some of which surface in handling characteristics that are attributable to the engine layout. In order to explore these characteristics, we organized street and track portions of the test with riders of three differing skill levels. And we kept track of everything using a Drack data acquisition system to record gear selection, lap times, speed, rpm and throttle position.

Our least experienced rider, Dean Groover, is a freelance photo­grapher by trade. Although he has been riding for 14 years—with a couple of track days thrown in—Groover doesn't have actual competition experience. Middle level rider Evans Brasfield, SR's feature editor, has been riding for 11 years, and racing a Kawasaki EX500 in club events for three years. The most experienced rider of our trio, associate editor Andrew Trevitt, has more than 20 years of riding experience, and has been racing for more years than he's willing to admit.

Testing, Testing, Testing
The street portion of our comparison took place on a section of local canyon road, which consisted of tight, second gear turns, a long sweeper and some elevation changes. Data was monitored over a one-mile stretch. Each of our testers was instructed to ride at whatever pace he felt comfortable for a street ride, with the same amount of effort—or perceived speed—for each of the three bikes. Outright speed was not as important as being consistent among the three bikes.

For racetrack testing, we chose the Streets of Willow course, which—with its tight, bumpy layout—places an emphasis on agility and traction. Data and lap times were monitored for each rider on all three bikes, and the best laps were chosen for comparison. Our graphs represent speed (top) and throttle position (bottom) comparisons for the ZX-7R, TL-R, and 955i organized by rider, with data for both street (left) and track (right) tests.

But life is not about one-mile ribbons of asphalt and controlled conditions; what are these bikes like to ride? Kawasaki’s ZX-7R—in its current guise—has been virtually unchanged for half a decade, and is what we consider one of the most overlooked bikes of the last few years. The seven is on the heavy side when compared to today’s featherweight open-class machinery, but utilizes a sturdy chassis and virtually bullet­proof motor. You definitely sit in the Kawasaki, and there’s a longish reach to the low-mounted clip-ons—definitely the raciest of our three bikes when combined with the high footpegs. The ZX-7’s mill starts easily and runs smoothly, but suffers the typical Kawasaki trait of a lean bottom end when pulling away from a stop. Aside from this glitch, and a definite lean spot around 5000 rpm, the ZX-7 has rheostatic power right up to redline.

Handling is crisp, if a bit on the slow-steering side, and the green machine hides its weight well. This is one of those rare bikes that after you blast through your favorite section of road, you think, “I could have done that quicker, no problem.” The solid chassis and friendly engine characteristics combine to provide confidence for riders of any skill level. However, there’s no denying that the Kawi is a bit dated—Suzuki’s GSXR-750 has the edge in terms of power and handling, but there’s something to be said for the smoothness and stability of the ZX-7R.

As with any big displacement V-twin, the Suzuki TL1000R oozes soul and character. The Suzook is somewhat the overdog in this comparison power-wise, with a 10 peak horsepower advantage over the Kawasaki—12 on the Triumph—and a brutish midrange. But it’s in the power delivery department that the TL is let down by its fuel injection, as the slightest throttle opening has the big twin firing with a lurch. Combine this with strong compression braking—even with the slipper clutch—and midcorner work is difficult at best, downright scary at worst.

Like the Kawasaki, our Suzuki TL1000R pays the penalty for being constructed for WSB use—even if it never made it there—with its slight porkiness. But also like the green meanie, the extra weight is in a stout chassis that remains planted at speed and provides sure-footed handling.

Triumph’s 955i Daytona, a revision of that company’s T595, offers the middle ground, powerwise, between our twin and four. The well-sorted fuel injection and midrange power combine to make this bike deceptively fast—both on the street and the track—as the user-friendly power delivery lets you make short work of corner exits. But the Trumpet is a slight let down—in this lineup—in the handling department. Suspension is definitely on the soft side, and while fine for street use, when pressed hard on the track the Daytona is the first of our trio to come unraveled. The widely placed clip-ons give plenty of leverage for hard steering inputs, but their low placement and the long reach over the tall tank, make it difficult to use that leverage to full advantage. And in a similar fashion, the extremely high and forward footpegs make using your feet for any steering inputs difficult.

Delect­able Data
Our testing took place during California's rainy season, and both our track and street days were hit with rain showers which left us collecting data on damp/drying pavement. While this may be seen as a curse, it can be taken as a blessing also, as there's nothing like a damp road to put a premium on traction characteristics and throttle response. And while it did hamper lap times at the track, the comparisons among our bikes are still valid, and maybe even be highlighted due to the weather conditions.

First thing to notice on the graphs is lag time between the ZX-7, 955i, and TL throttle position curves. With its small carbs and excellent throttle response, our riders were able to jump on the ZX-7’s throttle the soonest and get it open smoothly. Midrange power on the seven is the least of our trio, and correspondingly taller bumps on the graph show more throttle being used. The Trumpet sits slightly later than the Kawi in initial application, and the smaller humps show the midrange torque of the triple coming off corners. The TL, with its giant fuel injection bodies, requires finesse to wind on the power exiting turns: looking at the traces, most show a slight opening of the butterflies, followed by a period of constant throttle while the bike settles itself. Only then can our testers get on the gas with more authority. But the Suzuki, with its midrange abundance of jam, requires smaller throttle openings to give similar acceleration as the triple and four on a straight section.

In the End
Going straight by the numbers, the decisions are easy: For riders lacking experience, the triple is best with its ample midrange and user-friendly powerband. Somewhere in the novice-intermediate range, the optimum ride becomes the four-cylinder. And experienced riders will get the most out of a twin.

Looking deeper the reasons for this are apparent. Novice riders are not at the limits of a machine’s handling to discern chassis differences that could be due to a triple’s tall engine. And the triple’s grunty powerband is very forgiving in terms of recovering from mistakes and operating over a wider rev range. Theoretically, a twin should provide more bottom end and midrange, but the carburetion difficulties that arise due to the large intakes and touchy injection on our TL were difficult to overcome for a novice (and even an intermediate) rider.

Intermediate riders, able to better discern handling characteristics, will appreciate the vertical compactness of the in-line four compared to the three, but may not be sufficiently experienced to cope with the twin’s abrupt throttle. And here too, the distinction between street and track clouds the issue. Our middle experienced rider felt more comfortable on the four cylinder; and while this was borne out with the street test with hard data, his track results indicate he was just as quick on the triple.

Riders with a lot of experience are better prepared to cope with handling and power delivery characteristics and quirks with any given configuration, and these riders will be able to utilize the twin’s advantage—on both street and track—to good effect.

Groovin' Dean
During the street portion of testing, Groover—our low man on the experience pole—was most confident on the Triumph, noting that its smooth power delivery and slightly-softer chassis was less intimidating than the racier Kawasaki and Suzuki. Groover had trouble coping with the TL's off/on throttle response on the street, and this resulted in a speed curve with more variations than the trace for the ZX-7 and 955i. He also noted that the TL—with the most compression braking effect—pitched forward when the throttle was closed more than the other bikes, and this, combined with the abrupt throttle response, sapped his confidence on the street. From the rpm and gearshift traces (not shown here, but collected for reference), it is evident that the cameraman's style is to leave the bike in a single gear for a given stretch of road. On our particular section, Groover kept each bike in third gear, and this style is partially the reason for his favoring the Triumph. The Daytona has the best engine for this type of riding, with good throttle response, and enough bottom end and midrange to pull out of slower turns; the Kawi lacks grunt (note how much throttle is needed, and how shallow the speed traces are exiting the slower turns); and the TL—while having plenty of steam down low—is hampered too much by its poor throttle response. Groover was actually quicker over the street portion on the Kawasaki (note the speed traces for the portion shown) but nonetheless favored the Triumph.

Heading over to the Streets of Willow, the G-man encountered similar problems with the Suzuki, and it’s obvious from the speed traces that he was much quicker—and more confident—on the Kawasaki and especially the Triumph. As with many novice track riders, Groover’s style is definitely of the point-and-shoot variety. The speed traces have steep slopes, with low spiky corner speeds, and the throttle graph shows judicious use of jam in short bursts. Once again, the lensman favored the Trumpet on the track, saying, “It just does everything right for me.” For point-and-shoot work, the Kawasaki has to be in the meat of the powerband, and the rpm traces show DG to be in the softer part of the ZX-7’s power. And the TL once again proved too unwieldy with its jerky power and throttle response, although a twin with more sorted injection may have worked even better than the Triumph for a novice rider.

Brash Evans
Our intermediate rider, Brasfield has a flowing style that emphasizes corner speed rather than corner entries and exits. Note that his throttle on the street traces show him using less peak throttle than Groover, but the gas is definitely on for longer periods of time. His graph also shows similar lag times among the three bikes as does Groover's throttle traces, but to a lesser extent; obviously, experience counts for a lot while getting back on the gas when leaned over in a turn. The feature editor's speed traces on the street graphs show very different curves among our three bikes, with the Kawasaki on top. Brasfield favored the ZX-7 on the street, saying the green machine's stable chassis allowed him to keep good corner speed, and the clean carburetion didn't cause problems getting back on the gas at high lean angles. EB's experience helped him deal with the TL's abrupt throttle to a certain extent, and he was only slightly slower on the street portion with the Suzuki and its superb chassis. However, the Triumph's slightly inferior handling didn't work well on the street with Brasfield's style, and the speed traces reflect the slower corner speeds he was forced to utilize.

Brasfield got on well with the Kawasaki on the Streets of Willow racetrack also, citing its solid chassis and flexible motor as strong points. The lack of midrange definitely hurt his lap times, and the engine traces show him down in the 5000 rpm flat spot at times. Surprisingly, Brasfield was slightly quicker on the Triumph, and once again the deceptively quick motor had us fooled. “I would have never believed it; I felt faster on the Kawasaki,” he responded when shown the lap times. Brasfield also felt the Triumph’s chassis was noticeably looser than the ZX-7’s or the TL’s, and this serves to underline the strength of the triple’s stellar engine.

Treacherous Andy T
With associate editor Trevitt at the controls, it is evident from the graphs that his street style is somewhere between our other two testers. With less emphasis on corner speed—and, in some instances, less actual corner speed than feature editor Brasfield—and more point-and-shoot Groover style, Trevitt's throttle position traces show the smallest lag among our three bikes, indicating that experience can make up for the Suzuki's touchy throttle, and also for the Kawi's lack of midrange steam. Also, the speed curves appear very similar, with the TL and 955i virtually identical over the span shown, and the ZX-7 having only a small advantage. As with middleman Brasfield, AT-dog felt most comfortable on the Kawi, feeling the Triumph's chassis to be a slight hindrance in switchbacks, and also citing compression braking and the twitchy throttle as holding the TL back. Interestingly enough, Trevitt's times over the street section were all within three-quarters of a second for each bike—an indication that perhaps the constraining factor was his discretion, rather than any limitations in the bikes.

Trevitt’s throttle graph for the racetrack session shows the leading edge of his throttle traces almost identically timed, and in fact, he says, “The TL’s throttle response was no problem on the track. I thought it would be, but it was virtually transparent.” With that and the Suzook’s solid and quick-turning chassis, the associate editor posted his fastest time on the TL, almost a second quicker than on the Kawi or Trumpet. While the Suzuki’s heavy compression braking was a problem on the street, its slipper clutch worked much better on the track, and that also didn’t cause difficulties. In fact, with the Kawasaki having a slipper clutch too, it was the Triumph that gave Trevitt the most difficulty downshifting for turns. With his times for the triple and four within one-quarter of a second of each other, note by the speed graphs that the Kawasaki suffers in fast Turn One—where it should have had an advantage with its stability—but makes up the difference elsewhere on the track. Once again, the Triumph surprised us with its deceptively quick lap times. Although it was definitely the least composed of the three bikes on the track, the potent triple makes time on the two fast technical sections where its midrange and smoothness allowed Trevitt to stay on the throttle longer than the other bikes.

Suspension Settings:
Kawasaki ZX-7R
Front: Preload: 4 lines showing. Compression damping: 4 clicks out. Rebound damping: 9 clicks out.
Rear: Preload: 25mm thread showing. Compression damping: 19 clicks out. Rebound damping: position 3.
Suzuki TL1000R
Front: Preload: 5 lines showing. Compression damping: 10 clicks out. Rebound damping: 7 clicks out.
Rear: Preload: 5mm thread showing. Compression damping: 21 clicks out. Rebound damping: 5 clicks out.
Triumph Daytona 955i
Front: Preload: 3 lines showing. Compression damping: 1.5 turns out. Rebound damping: 7/8 turn out.
Rear: Preload: 10mm thread showing. Compression damping: 1.5 turns out. Rebound damping: 1.5 turns out.

SR Opinions:
What a workout this test was, and it taught me a lot about my own riding and personal preferences to boot. It's tough trying to ride each bike at exactly the same level of effort, a job made tougher knowing the electronic eye was watching the whole time. And the lap timer didn't always agree with my perception of how fast I was going, which really points out the benefits of the Drack system.

I have a newfound appreciation for the TL after finally getting the suspension set up to my liking. I was quickest on the street and track while on the Suzuki, and when the pace gets hot its definitely the bike and engine to have—but the rest of the time it’s tough to live with the compression braking and touchy twist grip. The Triumph surprised me the most during the test; I never thought I was going overly quick on it, but the Drack lap timer said otherwise. It’s the nicest engine as far as usability, but the bike as a whole is a bit tall, and things get out of hand pretty quickly when it’s pushed hard.

The ZX-7R has long been one of my favorites, ever since the editor made me ride to Pahrump in the snow and take the Star School on one. The motor is super smooth, sounds great and has almost enough steam. And the thing is so stable in the corners that I can concentrate more on my riding than on the quirks of the bike. I'm picking it—the bike—as the best all-rounder, but I'm anxious to see what someone could do with a triple in a serious chassis.
—Andrew Trevitt

The triple is well balanced for street or track. It has great low end grunt that makes it fun to hammer out of corners, lots of midrange and plenty up top. The smooth, responsive power delivery all the way through helps it pull out of corners without need­ing to downshift. Stable, smooth, and confidence building, it’s great on the streets, great on the track. I love this bike.

Initially I hated the twin (and I love twins). It has the most jerky on/off throttle I’ve ever ridden. In slow corners needing first or second gear the bike did a lot of lunging; between that and the engine braking, the twin felt top heavy and quirky in tight turns. When I began running at higher rpms (more like the four) I had better luck, but still the slow turns were beating me. On the straights it was all love, I couldn’t wait to slam the throttle. The TL is not my pick for the street, but probably the most kick-ass for the track if you can make it work for you.

The 7R seemed a bit on the sluggish side until I realized I was riding it like a twin, but turn up the revs and enjoy the ride. It seemed on the street that a four is more work than roll on/roll off like the triple was. This bike still has plenty of umph to get you out of corners, even in the wrong gear, which makes for some smooth, easy and fast riding for the Sunday tourist.

The throttle starts pulling down low and doesn't want to give up. The Kawasaki is an all around nice package, but I'd rather take the triple.
—Dean Groover

Riding with Big Brother watching my every move was both nerve wrack­ing and enlightening. When I made a mistake (like bobbling midcorner) I knew Andrew’s eagle eye would pick it out and a bit of ribbing was sure to follow. Still, the Drack system outlined key elements of my riding style.

Of this trio of engines, I’d expected the triple to be my favorite. The Triumph’s sound is infectious, and the meaty midrange has always put a smile on my face. I was surprised to find out that I didn’t ride quickest on this bike in the street portion of our testing. Unfortunately, the soft suspension outweighed the smooth transition from off to on throttle. The other fuel injected bike, the TLR, has a reputation for abrupt transition onto the gas, and I made a conscious effort to get on the throttle sooner with the Suzook in hopes of mitigating the jarring effect of coming on the power midcorner. I couldn’t believe it when I saw that I was consistently later on the throttle on the TL than with the other bikes. I believe my quest for smoothness made me more tentative on the initial throttle application.

Of this assemblage of bikes, the ZX-7 is the one for me. The suspension is rock solid, making quick work of both street and track. (The TL runs a close second in the suspender department.) The engine gave me the maximum flexibility to get the drive I wanted out of every corner. Want more scoot? Run a gear lower to bring the rpms up. Want to continue as Mr. Midrange? No problem either.
—Evans Brasfield

AIM Sport Systems' Drack Data Acquisition:
In our continuing effort to support subjective editorial opinions with empirical data we employed data acquisition in our twin, triple, four test. Aim Sport's Drack Gold System and Windows Drack software was used to measure analytically the input/output of three motorcycles with different engine configurations ridden by three different skill levels of rider.

Our system came to us contained in a convenient plastic carrying case. The data logger box, sensors, and infrared beacon fit into preformed foam spaces inside the case. Using the system is easy and it is a fraction of the competitor’s price at just under $2,000.

We opted for the basic motorcycle system. With this we measured engine rpm, throttle position, rear wheel speed, lap times, and produced a track map. With additional sensors the Drack logger box has the capability of measuring air box pressure, air/fuel ratio, exhaust gas temperature, front wheel speed, suspension travel, and water temperature. In addition the software uses math functions that calculate gear selection, lean angle, linear acceleration, suspension speed, and wheel spin.

Most of the setup is easy. With a little ingenuity and some sheet metal the necessary sensors can be mounted to any bike. We mounted the rear wheel speed sensor on the swing arm of each bike on the sprocket side. A magnet attached to a bolt on the sprocket carrier triggers the sensor as it passes by. We tapped into the Suzuki’s wiring harness for throttle position data. The Kawasaki ZX-7R has doesn’t have a throttle position sensor and the finicky ECU on the Triumph Daytona was sensitive to voltage drop so we made our own throttle position sensors on the ends of the handle bars where the bar weights are attached. We removed each bar weight and glued the shaft of a potentiometer into the bolt head. A soda can was cut into strips and used to connect and turn the sensor with the throttle barrel. These worked well so we didn’t have to worry about tampering with the wiring harness.

The Aim Sport Drack data acquisition system gives club racers volumes of information at an affordable price. For more information visit www.aimsports.com or contact Aim Sport Systems at (800) 718–9090.
—Kurt Risic

**The Pleasure—and the Pain—of Power **
The reasoning behind our twin/triple/four comparison is something that dirt trackers have known for years—and pavement riders have only in the last decade begun to appreciate. The further apart the individual—or grouped—power pulses are in a multi-cylinder engine, the more time the rear tire has to recover from any sliding that's occurring and regain traction. This means a big bang 500GP engine—which has all four cylinders practically firing together and the rest of the crank's rotation as downtime—should offer more traction and longer tire life than a "screamer" engine with equal spacing. And a big displacement V-twin, such as a Ducati, should outperform an in-line four of similar horsepower.

Our Kawasaki ZX-7R features a run-of-the-mill transverse four. This gives nice even power pulses spaced 180 degrees of crankshaft rotation apart for smooth power and good vibration characteristics. The Triumph triple is also of the transverse style, but the three crankshaft throws are evenly spaced at 120 degrees; the result is a cylinder firing every 240 degrees. A secondary imbalance would have the ends of the crank walking in the cases if a balance shaft wasn’t fitted, and the Trumpet incorporates such a shaft in front of its engine.

Manufacturers love in-line engines because they can churn them out relatively quickly and easily; one cylinder block and head, a single set of cams and the required drive gear, fewer planes to machine, and so on. Packaging-wise, an inclined engine usually fits nicely, with width being the major problem—especially with the four. A triple has less concerns with width, but with the longer stroke necessary to achieve a similar displacement, engine height becomes a bother, forcing the steering head to be higher than optimum.

A 90 degree V-twin such as the Suzuki TL engine has two connecting rods sharing a common pin, giving a comparatively enormous 450 degrees of rotation between pulses—more than a big bang 500. Secondary vibration is in a plane along the length of the motorcycle and as such, is easily absorbed. V-twins with the V arranged like the TL trade width constraints for front-to-back space concerns, and manufacturers are constantly battling to attain enough forward weight bias for good handling.

With fewer cylinders, one could assume that a V-twin would be easier to manufacture and have fewer parts, but such is not necessarily the case. Two separate heads (and cylinders if they're not cast into the cases), twice as many cams and drives, two carbs or injector stacks that have to be oddly linked together, and dual exhausts leave the twin almost as expensive—and nearly as heavy—as a triple or four of similar displacement.
—Andrew Trevitt

Nine cylinders, One tire: Bridgestone BT56SS
To ensure tire selection wouldn't bias our testing procedure, we spooned Bridgestone Battlax BT56SS street tires onto each of our twin/triple/four machines. From our giant tire test (February '00) and also from the tires' introduction at Willow Springs (August '99), we knew that they would have exemplary performance on the street as well as hold up to abuse on the racetrack with no problem. The Bridgestones feature a silica-reinforced tread compound for wet weather grip, dual-aligned compound (DAC)—with harder rubber in the center of the tire—for good wear properties, and the rear SS incorporates a monospiral Kevlar belt to aid stability.

The Bridgestones provided excellent traction and handling characteristics on the street portion of the test, with the Kawasaki showing the most improvement over stock traction-wise. Our Triumph’s original front tire (a standard Bridgestone BT56) had such a rounded profile that it was impossible to wear the last half inch of tread on the sides, and front traction was slightly off; the BT56SS, however, wore right to the edge, and showed signs of working much better than the stocker. In wet weather, the silica compound tread provides great traction, although the somewhat pointed front tire tends to follow pavement imperfections—such as rain grooves—which can be a bit unnerving.

On the cold and damp Streets of Willow road course, the tires provided excellent grip, although by no means up to DOT race tire standards, and wore well over the course of a track day. All three bikes took to the Bridgestones well, with good handling and stability over the Streets' bumpy and tight layout. The BT56SSs are available in a wide variety of sizes to fit most popular sportbikes.
—Andrew Trevitt

For more comparisons from the past, visit the SR Archive!