Ken Shaw
There’s a recurring discussion about which kite or buggy is better/faster involving all manner of intricate factors that are virtually impossible to quantify with any degree of accuracy without employing a small army of techie types armed to the teeth with accelerometers, strain gauges and data logging software. In the Motorsports community, we call these discussions “Bench Racing” and we find it righteously entertaining because it’s always a good excuse to imbibe heavily of Spirituous Golden Nectar. Typically these sessions result in little more than a bad head the next morning but occasionally they serve as impetus for a leap forward in technology and/or chassis tuning or design. Bench racing in the Kite Buggy community often has similar effects on both technology and the liver.
Invariably some ambiguous, over-exploited term comes into play and then the game is afoot. For the Kite Buggy folks, that term is “holding a line”. What does that even mean? For the greater portion of us who find this sport a recreational fancy, it really doesn’t mean much at all. However, it seems some folks like to use this term as a measurement of superior buggy or kite design. For the Neophyte to opine this kite or that buggy “holds a better line” in the presence of the Hardcore, the Racer, the Builder, the Kite Maker, this will most certainly garner one much derision and a swift lesson in humility if not a lengthy physics lecture.
In reality what is being measured is a complex combination of inter-related vector forces and inertial moments; center of mass, center of lateral force, axle height, roll center, roll axis, the torsional relationship between the roll axis and center of lateral force, tire contact patch, side wall stiffness, overall chassis rigidity, roll stiffness, coefficient of friction and so on, add nausium, that allow us to redirect the force a kite produces into forward momentum. Mind you, all these factors are being measured by the seat of one’s pants because no one but the quintessential geek truly enjoys long division. There’s no accounting for personal taste either so the whole premise of “holding a line” as a valid measurement of performance is a bit suspect. However, it’s certainly no great mystery either… or it doesn’t have to be in order to get one’s head wrapped around what’s really happening and what gross factors have the most bearing on getting a grip.
By this point you may be asking what qualifies me, a self-proclaimed novice, to blather and babble on such a weighty topic, especially since my dyslexia renders me virtually useless at doing even simple sums in my head. In reality, I have over a quarter century of practical experience in setting up race cars to go around dirt circle tracks, asphalt road courses and across open desert traces faster than the other guys. Ya don’t hang around that long without getting a grip and many of the same principles apply to Kite Buggy. Like most any engine on the planet, the piston goes up and down, the crankshaft goes round and round, it ain’t rocket science… unless you’re talking Wankel… but that’s an altogether eccentric discussion and I digress.
More to the point is that “holding a line” is really about “getting a grip” or transferring the lateral force a kite produces into forward momentum and that requires making a buggy tire grip the surface most effectively. So let’s start with tire characteristics.
Pick up one side of your buggy’s rear axle about chest high, lean on it and watch closely what the tire on the ground does. The side wall of the tire will begin to flex a bit. Now, drop it down to about waist high and do the same. More than likely, that same tire will slide sideways and the sidewall will not flex as much. There you go, that’s the concept behind “side bite” in action. The trick to making any buggy as efficient and as fast as possible is to get the maximum amount of side bite out of the downwind tire as is humanly possible without being yarded out of the buggy sideways. One of the easiest ways to tune side bite is by adjusting air pressure. All too often I hear people say they run just enough air pressure to keep the tire beaded up on the rim but they seldom consider the fact that tire pressure affects sidewall flex, the size of the tire’s contact patch on the ground and may invite some degree of bounce that decreases the overall grip of the tire on rough ground. There is a happy place for every buggy and every rider in that buggy and it takes a bit of experimentation to find it.
Weight and balance are just as critical in a Kite Buggy as they are in an aircraft and for much the same reason. If an airplane is nose heavy or tail heavy, it will tend to rotate in flight, upsetting the angle of attack on the wing which will require some steering input to correct its flight path through the sky. The same is true of a Kite Buggy with the tow point of a harness when using a strop line or chicken loop or hand position when flying untethered, acting as the center of lift of an airplane wing. If your center of gravity is too far behind the center of pull, the front axle will wash out first, which is frequently the case. Your body weight is typically much greater than the buggy’s weight, so a simple shift in seat position or changing the length on the down tube/swan neck a slight bit can have a profound effect on handling. Sure, it’s a bit cramped but, if you’re suddenly cutting upwind better than you ever have… it might be worth the effort. What’s important here is to understand the concept that weight distribution across all three (or four) tires is important and the distance between center of gravity and center of pull (or lateral force) is really a lever that causes the buggy to rotate, slide out and lose overall side bite. In other words, this is something more to tinker with before claiming a “hold a line” value.
Then there’s the question of cambered axle bolts. Those simply set the tires at an angle so the tire contact patch is square to the surface when the tire sidewall flexes under massive side loading. In other words, those are reserved for the guys who have done their homework, done all the math, played with tire pressures, weight and balance, are faster than GAWD already and need just a little bit of an edge on the competition. Is there value in cambered axles and axle bolts? Most certainly there is. Should this be the determining factor when shopping for your next buggy? That depends on whether your skills, the rest of your gear and perhaps more importantly, your gall is capable of putting them to good use. I would rather you spend some time looking at how you’re using jam nuts on your current axle bolts and making sure your bearing pre-loads are set properly.
One final thought and the manufacturers are going to hate me for saying this but, it’s for the good of the order. There is so much to explore in my current quiver and that poor little Flexi bug, Scout Buggly, that I doubt very highly I’ll be done testing and experimenting with these anytime in the near future. As sexy and avant garde as the new product lines are, I’m nowhere near mastering the possibilities I already have. Please take time to experiment, explore and come to fully appreciate the qualities of your current cache of gear. The skill and experience acquired in doing so will serve you well for decades to come and help you make informed decisions about where you want to go next. If nothing else, it will help you in Getting a Grip.