How To Read the Cycle World Data Panel
HOW TO READ THE CYCLE WORLD DATA PANEL
That Panel Is The Meat Of A Road Test. It Is Objective And Pulls No Punches. Scan It Carefully, For It May Make The Difference Between A Good And Bad Buy.
Dan Hunt
THE DATA PANEL has been the cornerstone of CYCLE WORLD'S road test procedure since we began in 1962. Respected for its completeness and accuracy, the CYCLE WORLD data panel has been the model for the rapidly growing motorcycle publishing industry.
Data panels are an important source of information for the motorcyclist, because they offer measurements and performance data in impartial standard form.
If you compare the panel for one bike against the panel for another, you are able to see both machines from the same reference point. A collection of data panels, in effect, is a comparison test, which is constantly growing in size and scope.
Much of the information in the CYCLE WORLD panel may seem rather basic—seat height, wheelbase, etc. What makes it useful is that it applies to the actual machine tested. Often we find discrepancies between the advertised dimensions of a machine and its actual measured dimensions. Take wheelbase, for instance. This item is particularly relevant in predicting the handling characteristcs of a dirt machine. A difference of only one inch of wheelbase changes handling considerably. An experienced rider can look at a wheelbase figure and partially predict the handling characteristcs of the machine.
Advertised performance often differs from the performance figures we get in actual testing conditions. Sometimes this is a result of the advertiser's tendency to exaggerate. Sometimes it is a simple difference in testing procedure; manufacturers may use a different way of starting, a hand-assembled and blueprinted prototype machine, or an unusually lightweight test rider.
Nowadays, advertisers tend to be much more factual than they were in the past. But it wasn't so long ago when we discovered, practically every month, wild differences between claimed and actual performance. In our early days, when we were the only American magazine publishing electronically measured performance data, we lost thousands of dollars when a few disgruntled manufacturers cancelled advertising with us in retaliation for publishing truthful performance figures.
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Because of the maturation of the motorcycle industry, and because CYCLE WORLD and other magazines following us into motorcycling have adopted a policy of publishing performance data, coercion by advertisers is no longer a factor in the industry. At least it is not with most of the leading magazines.
The greatest battle a responsible motorcycle magazine staff fights today is with itself. It must strive for consistency in producing measured data in much the same way a scientist or engineer executes his trade.
From consistency comes comparability, the kind which makes a data panel the basic tool to evaluate one motorcycle against another.
It is important that the reader be able to interpret the figures in a data panel. They are there for a reason. So let's go through a CYCLE WORLD data panel point by point and elucidate the meaning of these figures.
List price: CYCLE WORLD quotes the suggested list price as given by the manufacturer or U.S. distributor. If the distributor is unwilling to give us a price we will go to a local dealer and ask for his price. These prices do not include taxes and registration. And they may vary somewhat from dealer to dealer, or region to region.
Suspension, front and rear: This item explains type of suspension. The most common form we see today is telescopic forks at the front and swinging arm (dampened by shock absorber/spring units) at the rear.
Tire, front and rear: These are sizes. A size of 3.50-18 means a 3.5-in. wide tire mounted on an 18-in. diameter rim.
Brake, diameter x width: The diameter and width of a brake offer the basic dimensions from which you may predict the potential braking capability of a machine.
Total brake swept area: This is the total area on which the stopping surfaces, or brake pads, sweep. It is computed from the dimensions of both front and rear brakes.
Brake loading: Taking the weight of machine and rider and dividing it by total swept area, you arrive at a figure which is quite useful for predicting effectiveness of a braking system.
For example, the Honda CB500 with front disc brake has a brake loading of 5.78 lb. per square inch of swept area. This is an excellent, light loading of the system and is reflected in the bike's measured 60-0 mph stopping distance, which was 116.9 feet.
Poorer was the brake loading of the Harley-Davidson Super Glide (8.2 lb./sq. in.) and it behaved as expected, stopping from 60 mph in 153 feet. You'll note that our most recent data panels include the weight of a standard rider (160 lb.) in the loading computation, rather than the weight of the actual test rider; we do this to provide a figure which is comparable outside the actual testing situation, and therefore more useful to most readers.
You'll discover that dirt bikes usually have a higher weight/swept area ratio. This is not a fault, but a designed-in factor to minimize wheel-locking on surfaces offering marginal traction.
Engine type: In a few words, you can convey the basic configuration of an engine. If you read "sohc in-line Four," that describes a four-cylinder engine, with its cylinder placed in a straight line, operated by a single cam located over the cylinder head. The term dohc means double overhead cam. Ohv means overhead valve, and can be used in a general way to describe sohc and dohc engines; however, in the context of the data panel, ohv, when it appears alone, describes a set of overhead valves operated by pushrods from a camshaft in the crankcase. You'll also encounter twostroke Twin, etc., which is usually construed to mean a piston-port aspirated two-stroke. This can be qualified with the terms reed valve, or rotary valve when appropriate.
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Bore x stroke: These figures describe the basic dimensions of the engine. You should watch here for the relationship between the size of the bore vs. that of the stroke. Modern engine design has tended to enlarge the bore in relation to the stroke to increase the available valve or port area and decrease reciprocating weight. An 84mm by 74mm bore/stroke configuration is said to be oversquare. A 69mm by 74mm bore/stroke relationship is said to be undersquare. Undersquare engines are rarely encountered in modern motorcycle designs.
Piston displacement: Taking the volumes swept by each piston and adding them together gives you displacement, which is one of the basic parameters by which you may predict potential performance. Bigger is usually faster. Only usually!
Compression ratio: This is the geometric ratio of volume in the combustion chamber at the bottom of the piston stroke to that at the top of the piston stroke, disregarding either port heights in two-strokes or valve overlap figures in four-strokes.
Claimed bhp and torque: These figures are supplied by the manufacturer and may not necessarily be taken as the gospel truth. They are included only as a rough guide to power output.
Carburetion: Here we give you the number of carburetors in parentheses, the choke or port diameter in millimeters and the brand.
Ignition: The type of ignition system is given along with the brand name, if appropriate. Battery/coil means that battery, breaker points, and coil provide the spark. Also you'll see e.t. magneto, capacitive discharge (CD), and pointless electronic (PEI).
Oil system and capacity: You'll find either wet sump (below-crankcase oil storage), dry sump (oil stored in separate tank), oil mist (non-automatic mixing two-strokes), or oil injection systems for two-strokes. In the case of fourstrokes, the type of oil pump may also be described. Obviously, you do not list oil capacity for two-strokes which must have their oil mixed with the gasoline.
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Fuel capacity: This figure will tend to be large (usually more than 3 gallons) for road machines, and small (2.5 gallons or less) for dirt machines. Combining this figure with the fuel consumption figure, you may estimate how far you may go on a tank of gasoline.
Starting system: It's either electric, or by means of your kick on a folding crank, or both.
Lighting system: Here we are concerned with the power source for the motorcycle's electrical system. If you read "12V alternator," you know that the bike stores power in a 12V battery, generates ac current by means of an alternator, and includes a rectifier and regulator curcuit. "12V generator" describes a 12V dc generator and, of course, precludes rectification.
Air filtration: This describes the filter used to screen particles from the air before they enter the engine. Common types: dry paper, wire mesh, polyfoam.
Primary and final drive: Primary drive is the type of drive used to take power from the engine crankshaft to the gearbox, either by gear or chain. Final drive is the type of drive used from the gearbox output to the rear wheel, usually chain or shaft these days.
Gear ratios, overall: Knowing the overall gear ratios gives you an idea of the jump between each gear, as well as predicting how slow you might be able to go in first gear or how fast the engine will be turning in top gear.
Wheelbase: This is measured from axle center to axle center. Common wheelbases tend to be shorter for a given displacement of road bike than for the dirt bike. For dirt machines common wheelbases are: 500cc, 54 to 56 in.; 250cc, 52.to 53 in.; 100-125cc, 49 to 50 in. Big bore Twin roadsters generally have from 54 to 55 in., while the new generation of 750 Multis run from 57 up to 59 in.
Seat height, seat width: These points are measured where the rider is most likely to sit. They are measured unladen. Seat height becomes particularly relevant on a roadster if you have short legs; anything more than 32 in. will be difficult to handle at rest for a shortlegged rider. Seat height in relationship to peg height is quite relevant to the dirt rider. Anything that deviates far from a seat height of 31 in., or a peg height of 10 to 13 inches, should be looked at carefully. Be suspect of seat widths narrower than 8 inches; they hurt!
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Peg height: This is relevant to both road rider and dirt rider in respect to clearing the ground when banking, and also in respect to knee bend when seated, balancing leverage. Peg height above ground is measured from the center of the peg.
Ground clearance: Getting ground clearance for turning, clearing obstacles off the road must be compromised with the need for low center of gravity. This is measured at the lowest point between the wheels, often a protruding side or center stand.
Curb weight: This is the "wet" weight of the motorcycle, fully equipped and ready to run with half a tank of gasoline. Differentiate this from "dry" weight, or weight without gasoline and gearbox oil (and sometimes, without battery), which is often quoted by advertisers to make the product look less heavy.
Weight bias: The amount of weight sitting on the front wheel in relation to that on the back wheel, expressed in percentage of total weight. This figure gives you an idea of the balance of the machine. Most machines have a slightly rearward weight bias.
If the bias is too far rearward, the bike may wheelie too easily or develop a floating, unsteady wander at high road speeds. If it's too far forward, the bike will tend to plow, and, in the case of dirt bikes, the front wheel will be difficult to lift over obstacles. This measurement is only a rule of thumb, for weight bias and handling are greatly affected by peg height and peg position in relation to c.g. and the longitudinal center of balance. Seat height and the sweep of the handlebars also influence handling.
Test weight: This is the weight of the ready-to-run motorcycle with the fuel tank half full, plus the weight of the CYCLE WORLD test rider who actually executed the performance tests. This figure may be correlated directly with the performance results in acceleration, top speed and braking.
Test conditions: These include air temperature, humidity, barometric pressure, altitude of the performance test site, wind velocity and direction. All these variables affect performance. The most important one to consider is wind velocity and direction, which has a pronounced effect on both acceleration and top speed runs. We list the altitude of our test sites, but the ones we use now—Lions drag strip and Orange County International Raceway—are practically at sea level. Rule of thumb: The higher you go, the slower it goes.
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Humidity and barometric pressure have their most pronounced effect in the testing of two-stroke machines. High humidity and low barometric pressure tend to throw off a two-stroke's standard carburetor jetting and cause a slight peak power drop-off or narrowing of the power band. Yet, some four-strokes like lots of humidity.
Top speed, actual at the equivalent rpm: We measure actual top speed with a digital read-out radar unit which may be calibrated to FCC standards at the test site. It is accurate to within minusone mph. The accompanying rpm figure given is calculated by computing gear ratio, tire circumference and the speed measured.
Computed top speed in gears, at equivalent rpm: These speeds are theoretical top speeds in each gear computed from either red line or peak horsepower rpm and the gear ratios. Note that if a bike's computed top speed in top gear is high, say 1 25 mph, it doesn't necessarily mean that the bike can go that fast; it usually means that the motorcycle is geared extra high to provide low cruising rpm.
Mph/1000 rpm: This means that when the engine is turning 1000 rpm, the bike is geared to run at so many miles per hour. This is a rough indicator of how high a bike is geared and what use it is appropriate for. Big roadsters usually run at 15 mph per 1000 rpm or more. Dual purpose bikes have lower gearing to yield top gear speeds under 10 mph per 1000 rpm, and tiddlers are even slower yet.
Engine revolutions per mile: This is simply another way of looking at the above parameter.
Piston speed at peak rpm: Measured in feet per minute, piston speed is a rough indicator if engine longevity. Directly or indirectly involved with piston speed are cylinder bore wear, piston ring wear, acceleration loads on piston pins, bearings, rods and crankshaft assemblies.
The generally accepted maximum limit is 4000 to 4500 feet per minute. The Harley-Davidson 74 c.i. engine has a peak power rpm piston speed of 2960 fpm—a favorable sign in predicting how long the engine will remain healthy. As the H-D also is geared quite high, it will be turning relatively slowly throughout most of its life, and should prove quite reliable.
Lb./bhp: This figure uses the claimed horsepower given by the the manufacturer, and so may not be completely accurate. By taking the curb weight of the bike along with a 160-lb. standard rider weight, we may divide the result by horsepower to gain a good indication of what performance is to be expected from the machine. We use the 160-lb. standard rider weight rather than the weight of our test rider to provide the reader with a basis of comparison which goes beyond the limits of any one specific testing event.
Fuel consumption: This is the averaged result of the mileage obtained during the test period from two or more tanks of gasoline. The bike is run in-town, on the highway, or in the case of dirt bikes, in the environment for which they were designed. This figure varies greatly from rider to rider.
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Speedometer error: This error is measured electronically by running the bike through the traps at the indicated speed and measuring the actual speed. A reading of 45.12 mph taken at an indicated 50 mph indicates an error of about 10 percent.
Braking distance: After including a correction factor for speedometer error, the motorcycle is stopped from an actual 60 and an actual 30 mph, and the distance from point of first application of the brakes to dead stop (at the front wheel) is measured.
Acceleration, zero to 30-100 mph: These figures are extrapolated from the acceleration curve appearing in the data panel, which is in turn based upon 1/4-mile, 1/8-mile and top speed runs, as well as peak rpm shift points.
Standing start acceleration runs: These runs are measured by means of electronic digital readout timers accurate to 0.01 mph and 0.001 sec. Both 1/4-mile and 1/8-mile runs are repeated several times until the test rider is clocking nearly equal, good results on three or more of the best runs.
A tower observer takes note of starting style, wheelspin, body position through the run, etc., to provide feedback to the rider. The run having the shortest elapsed time is the one published, along with the accompanying trap speed. We do not combine best e.t. along with the best mph from a different run. These performance runs are the most reliable indicator of the power output of a motorcycle.
We stress that acceleration should not be the sole determining factor to influence your purchase of a new machine. The fastest iso't always the best.
You must view the motorcycle as a whole entity, an assemblage of engineering compromises, of conflicting purposes, having strengths and weaknesses. There is no motorcycle component made with a perfect dimension. There is no motorcycle made that is perfect. There is no rider living who is perfect.
Somewhere in the middle ground, the imperfect human viewpoint must meet and assess that imperfect machine, using art and science, intellect and feeling, experience and supposition.
Paradoxically, he has a good chance to make a perfect judgment. Does this seem odd? Not if, as we do, you consider perfection imperfect.
