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Ned Nerdy Buys a Bike
Copyright © 1994 by Dr. H. Paul Shuch

OK, I admit it. I'm a nerd. I just can't go riding without my helmet and leathers and glasses and sliderule and pocket protector. What do you expect after nine years of engineering school, five years in the Aerospace industry, and twenty playing Professor? So when I set out to buy a new bike, it's only natural that I required massive infusions of data. Armed with my trusty Cycle Buyer's Guide, I was able to peruse the vital specifications of a dozen likely contenders. It was all there: list price, engine type, bore, stroke, displacement, carbeuration, starting system, transmission and drive, brakes, wheelbase, seat height, fuel capacity and weight, along with a spiffy photo of each machine on the market. What more could an engineer ask for?

Only, how to make sense of this plethora of data? I thought about the stereo magazines of my youth (OK, we called it Hi-Fi then) with their performance benchmarks and objective ratings, one through five speakers. Wouldn't it be nice, I pondered, to have a set of objective rating criteria for motorcycles, perhaps to rate them one through five oil-cans?

Yet how can you objectively rate such diverse characteristics as form, function and finesse? One rider's dream machine is another's demon. Any rating scale devised, I decided, would be highly subjective, tailored to the particular rider's tastes. OK then, thought I, guess I'll have to devise my own method. Rate all these bikes according to my particular proclivities, and let the spokes fall where they may. This, then, is the result of my quest for quantification, my scale of cycle specifications. I hope you find it interesting, and perhaps even useful.


If you see me on the street, you're likely to overlook me. Let's face it, folks, I'm short! Five foot five in my stocking feet. And my twenty-eight inch inseam means I can't flatfoot half the bikes on the market, let alone straddle-walk them. So seat height is an important consideration to me, perhaps more than it is to you. But if he's seeking stability in the slalom, even Paul Bunyan really wants to be sitting low. After all, the pilot's weight adds to that of the bike, so the lower the seat, the lower the loaded center of gravity is going to be. Up to the point where your knees knock your chin, lowriding is a positive attribute. So I tend to put seat height in the denominator of any rating equation (the lower the seat height, the higher the score).

Wheelbase, on the other hand, is a pretty good thing to maximize. Stretch out the bike and you increase stability, improve the ride. Ever notice how the customizers stretch out the front fork? Go too far and you'll never corner, but within reason, the longer the wheelbase the better. So let's build a little equation here, and rate bikes in part by their aspect ratio, the ratio of wheelbase to seat height, a relative measure of stability. In equation form, it looks like this:

Aspect Ratio = (wheelbase) / (seat height)
On my old Honda Nighthawk, for example, the wheelbase is 56.2 inches, and the seat looms 29.3 inches above the asphalt, for an aspect ratio of 1.92. As a rule (for me, at least,) bigger is better. Most of the cruisers measure in at a little over two.

Notice that it doesn't matter whether you measure seat height and wheelbase in inches, centimeters, or hands. As long as the units are the same in the top and the bottom, they'll cancel, and you'll end up with the same unitless ratio. If riding comfort is important to you, you'll want to pay special attention to this number.


Admit it, friend, most of us cycle for a certain sense of power. We like to be quickest off the line, fastest around the curve, the first hound home from the hunt. The power plant and the mass of the machine both contribute to a bike's performance. We engineers like to talk about power to weight ratio, which recognizes that the more stuff you're dragging around, the more engine you'll need to drag it. Well, the claimed dry weight is listed right there in the Buyer's Guide, but the rated horsepower usually is not. So we're going to have to estimate.

Fortunately, the old generalization is true: there's no substitute for cubes. The engine displacement (in cubic inches, cubic centimeters, cubic zirconia, whatever) is a pretty good first order approximation of power. If we're going to build a power-to-weight equation, displacement belongs up in the numerator; the more, the better. I'm going to use cc in my equation, because I'm a metric kind of guy.

As for weight, I really prefer kilograms (see, I'm a metric kind of guy). But the spec sheets usually rate a bike's heft in pounds. So to keep it simple, let's stick to that. It's the ratio (cubes over pounds) that's important, and big is again better. The final ratio looks like this:

"Power" to Weight Ratio = (displacement in cc) / (empty weight in pounds)
OK, I know cubes and power aren't really equal, but they're related, aren't they? So a 500 cc bike weighing 500 pounds (ratio of one) isn't exactly going to be a screamer. My little old Nighthawk is even worse: 234 cc engine, 298 pounds. With its puny 0.78 ratio, it can't even get out of the way of it's own ... well, Shadow. On the other hand, my favorite Harley boasts 1340 cc for 575 pounds, a respectable ratio of 2.3. Like the aspect ratio derived above, you might consider any number over two to be a pretty good bet. If performance is your prime concern, this is the number to heed.


When I head out on the highway, I want to cover ground. Since fuel stops take time, I figure the length of my legs is determined pretty much by the size of my tank. Some of the prettier bikes have minuscule fuel capacities, and correspondingly limited range. Let's build yet another ratio, this one with fuel capacity in the numerator.

This time, however, I'm going to insist on a metric measure. Though most spec sheets list fuel capacity in US Gallons, I'm asking you to go with liters (there's 3.785 of them in a gallon). And now (to make the numbers come out in the right range), let's play a little trick. There's exactly 1000 cubic centimeters in a liter. So move the decimal point three to the right, and you have your fuel capacity in cc's.

CC's, you say? Damn straight! If it's good enough for engine displacement, why not be consistent and rate fuel that way too? It's not that hard -- you don't even really have to think about liters. Simply multiply gallons by 3,785. Back to my Nighthawk example: its 4.1 gallon tank, multiplied by 3,785, equals about 15,520 cc of fuel.

Of course, all that fuel costs real bucks, but so do cycles. Our final analysis here is economic. The more bang for the buck, the better. So to build a ratio which reflects economy, let's put the cost of the cycle (in Dollars) in the denominator. Our final ratio now looks like this:

Range to Cost Ratio = (fuel capacity in cc) / (purchase price in $)
I'm told, for example, that the Nighthawk 250 lists for $2899 these days. Dividing that price into our 15,520 cc of fuel, the Range to Cost Ratio figures at an astounding 5.35! The Nighthawk, of course, is an entry level bike. With bigger machines, cost grows much faster than fuel capacity, so for most performance machines the ratio is closer to 2. But if range and cost are your main constraints, this is the ratio to watch.


My mate has a fondness for ordinal scales. After a dinner out, or a weekend away (or even an evening alone) she's likely to inquire "How did you enjoy that, on a scale of one to ten?" So it's no surprise that she asks the same question about every cycle we discuss.

What I've long needed to respond in kind is a simple, overall value rating for each cycle in question, preferably on a one-to-ten scale. Well, each of the three ratios which we have thus far derived (that is, aspect, power-to-weight, and range-to-cost) is open-ended, with the better bikes clustering around a value of two on each of the three scales. As I've mentioned before, you might want to give more credence to one or another ratio in particular, depending upon your specific cycling needs. But it occurred to me that two cubed happens to equal eight, which my calculator says is a little less than ten. And a scale of one to ten is what we seek. So for a single rating of all-around value, you can score any bike by simply multiplying its three ratios together, thus:

Value Rating = (aspect ratio) x ("power" to weight ratio) x (range to cost ratio)

which in turn breaks down to:

(wheelbase / seat height) x (displacement / empty weight) x (fuel capacity / cost)

where wheelbase and seat height are measured in the same units (say, inches), displacement and fuel capacity are measured in cubic centimeters (cc), empty weight is expressed in pounds, and cost is in Dollars.

For those mathemagicians out there who enjoy dimensional analysis, the units of the resulting product are: { ( cm^6 ) / ( $ # ) } That would be pronounced "centimeters to the sixth power to the dollar pound." Convoluted, to be sure. For the rest of us, suffice it to say that most all bikes will yield a score somewhere between one and ten, * which should serve to keep my lady happy.

Back to my Nighthawk 250 example. You may recall that little bike had a respectable aspect ratio of 1.92, a power-to-weight ratio of merely 0.78, and an astounding range-to-cost figure of 5.35. Multiplying these three numbers together gives us a most impressive overall value score of 8. On anybody's scale of one to ten, you can see that this little bike is a pretty good buy.

Just one word of caution, though. These scores only make sense when comparing bikes in the same class. Stick to analyzing standards, or cruisers, or touring machines separately. If you try comparing apples to kumquats, the convoluted numbers will yield meaningless results.

Please note that I am not advocating any particular bike over any other. That's determined by various subjective factors, which we will discuss next.


So what about all those things which you can't quantify? The subjective factors are sure to play as great a role in cycle selection as performance-to-cost ratios. Though I can't assign numbers to them, here are a few factors to consider in selecting your mount:

  1. Drive train. Do you prefer a belt, chain, or shaft? Drive shafts are smoothest and quietest, chains cheaper and more "traditional", belts probably most maintenance-free. Here personal preference will have to guide your decision.
  2. Brakes. Do they actuate electrically, mechanically or hydraulically? Hydraulics gives you considerable mechanical advantage, but you have to watch your fluid levels. Electric brakes can fail when the battery dies, mechanical when a cable breaks. And do you go with discs, drums, or hybrid? Disk brakes are less prone to fading, but cost more to obtain and maintain. Again, the tradeoffs are hard to quantify.
  3. Wheels. Spokes, solid or cast? Wire spokes have a classic appearance, but can't support tubeless tires. Solid disk wheels look great, but watch out for wind loading, especially in side gusts. Cast wheels are spiffy, sporty and costly. You get what you pay for.
  4. Engine Cooling. Air cooled cycle engines are traditional, but thermal expansion and contraction mean they require lots of built-in slop. Liquid cooled engines are quieter, and run cooler, but you have to maintain a radiator, thermostat and water pump. Only you can determine whether it's worth the extra cost and complexity.
  5. Cylinder layout. A single jug will shake your bones. V twins are classic, traditional, and hugely popular. Germany's leading cycle maker now pushes a three-cylinder engine. The old Indian in-line four was powerful beyond belief. The big touring bikes now sport flat sixes, smoother than most cars. What do you think a motorcycle should feel and sound like? And how many jugs do you want to grind come rebuild time?
  6. Aesthetics. This one gets rather personal. Sleek and sexy is in the eye of the beholder. Just how much is it worth to you to straddle a fuel tank whose compound curves match your lover's thighs? To each his or her own!

Having derived an algorithm for rating cycles for all-around value, it made good sense to crunch some numbers before I crunched a clutch. I was in the market for a sport touring machine. I ended up rating eight different candidates on my one-to-ten scale, and ranked them all top to bottom. Then I went out for some test rides . . . and fell in love!

Did you ever slip onto a saddle and know at once that this was the bike for you? It's happened to me three times in thirty years of riding: the old Honda 305 Super Hawk, my little 250 Nighthawk . . . and Honda's recently re-introduced Pacific Coast. Now I'll admit that I have a certain fondness for Hondas, this being my fifth and all. But it was the machine's gestalt which grabbed me. So what if it scored 6.4 on my scale of one to ten. Never mind that the PC-800 ranked a sad seventh on my list of eight objectively analyzed machines. Yes, it just happens to be the most affordable bike in its class, but dollars be damned, it also just felt right! I know we two are going to be very happy together.

Does this mean I'm advocating ignoring objective considerations? Of course not! I'd love to be able to read reviews in the cycle mags which rate various machines, on m'lady's scale of one to ten, for overall value. I even harbor hopes that all bikes will some day be rated on the Shuch scale, although such honors are generally awarded posthumously. Some of my students would say "Fine, and the sooner the better!"

Objective criteria are great. I hope the engineers keep applying them when they design tomorrow's cycles. But those of us who are engineers are sometimes also lovers. In the final analysis, we buy a bike because it calls to us, looks good, rides great, just sort of feels right. And isn't that what cycling is really all about?

* Actually, using this method, some of the newer high performance bikes have even yielded scores as high as eleven or twelve, which would seem to qualify them as "best buys"!

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this page last updated 14 June 2007
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