One less belt, and a lot less chassis
Kyosho as touring-car innovator? I wouldn’t have used those words to describe the conservative Touring Force series of cars that, while competitive and nicely built, did much more to reflect touring-car trends than to shape them. So much for that pigeonhole; Kyosho’s newest sedan definitely changes my take on Big K’s position in the touring-car universe. The KX-One breaks away from the norm with its single-belt drive train and highly unorthodox ladder-style chassis while retaining the well-sorted suspension of the last Touring Force car, the TF-4. Will the mix of proven and prototype gel as a new standard for Kyosho touring cars (if not other brands), or will it flame out as a technological footnote? That Magic 8 ball we call the racetrack will tell the tale.
* Chassis. The KX-One’s chassis is clearly its most striking feature. Though the material of choice (graphite plate) is hardly anything new, the chassis configuration is entirely unique within the touring– car segment. Instead of installing the KX-One’s drive train and suspension components on top of a flat plate with some type of stiffening upper deck, Kyosho built the car around a pair of vertical plates that are joined by thick plastic girders and bulkheads. The left and right sides of the chassis are identical, and the completed assembly has absolutely zero vertical compliance-no flex at all. Despite its slenderness, the KX-One is among the stiffest chassis I’ve built, as judged by the two-handed-twist method. You can force the car to flex torsionally, but it’s tough.
One thing the KX-One’s chassis lacks is space, a problem Kyosho solved by adding plastic “wings” to support the electronic gear as well as a transponder. The wings also capture the battery, which fits into a massive slot in the chassis that can swallow stick or side-by-side packs. To remove the pack, one of the wings must be removed by popping off a pair of body clips.
* Drive train. If the race to build the first single-belt touring car ends at the hobby-shop shelf, then you can consider the KX-One to be the winner (note: I don’t consider the Tamiya T.403 to be a true one-belt car, since its single belt simply connected a pair of gearboxes). The KX-One’s belt loops around both diffs and is then pushed against a layshaft-mounted drive pulley by a wide tension roller. The roller can be raised or lowered in the chassis to adjust belt tension. The drive pulley is larger in diameter (20 teeth versus 15 or 16) than that of a typical two-belt car, and correspondingly large differential pulleys are employed. Each has 39 teeth, for a ratio of 1.95:1. When combined with the included 110-tooth spur gear and 43-tooth pinion, the final drive ratio is very stock-motor– friendly at 5:1. The spur gear is held on the layshaft by a plastic hub that accepts standard spurs.
The rear differential is a 12– ball unit, with aluminum flanges and Delrin outdrives. To prevent slippage, sharp facets machined into the flanges grab the outdrives when the diff is tightened, and thick collars slide over the outdrives to prevent spreading under acceleration. The front diff is a one-way design, and as such, it uses hardened-steel outdrives to survive the pinch of the one-way when it grabs them.
Kyosho specs universal axles at both ends of the car, and their design closely follows the MIP CVD standard. Well, mostly; Kyosho omits the pivot incorporated in the classic MIP design and simply slides a crosspin through a slot in the “ball” end of the axle, and a collar slides over the assembly to capture the crosspin.
* Suspension and steering. Fans of Kyosho’s TF-4 will recognize the KX-One’s suspension parts, which were lifted directly from the last of the Touring Force cars. It’s good stuff; the front arms are capped, the front hub carriers hold the outboard hinge pins very close to the wheels’ centerline, and the parts are stiff. To hold the suspension arms to the chassis and provide front-arm kickup and rear anti-squat, small arm mounts are installed on the chassis plates. Steel turnbuckle camber links are used throughout.
The shock towers are carbon fiber, and the shocks are an all-new design for Kyosho. Floating pistons are the shocks’ most interesting feature. As the pictures show, a floating piston slides up and down on the shaft over a fixed pinion that is permanently attached to the shock shaft. As the shock compresses, the floating piston settles over the fixed piston, which increases damping. As the shock extends, the floating piston rises off the fixed piston, which decreases damping force. This allows the shock to rebound more quickly while maintaining the relatively heavy compression damping preferred by most touring-car drivers. Other shock features include soft bladders, Teflon shaft guides, single O-ring seals and snap-on preload spacers. The included springs are identical front and rear and feel relatively stiff, but Kyosho does not specify their rate. Yoke-type swaybars are the final element of the KX-One suspension; both ends of the car are outfitted with 1.2mm bars.
One casualty of the KX-One’s unique chassis design is a conventional bellcrank steering system. Luckily, touring cars can be steered effectively with direct-link steering, and that is the route Kyosho took. To maintain proper geometry, the original TF-4’s steering arms must be modified slightly by trimming away the original tie-rod pivot location, then relocating it by means of screw-on aluminum plates.
Since there are no bellcranks, there is no way to incorporate a bellcrank-mounted servo-saver. Instead, Kyosho supplies a servo– mounted unit. Kit-supplied servo-savers of this type are usually much too “soft” for high-performance driving, but due to space limitations, the KX-One must use the factory servo-saver. I’m happy to report that the Kyosho unit uses a heavy-duty spring and won’t waste the torque of a competition servo.
* Body, wheels and tires. Not included, not included and not included. I tested my KX-One with Treadz soft-compound V3 slicks and the “pie” (dish) wheels they are factory-glued onto, and I covered everything with a Parma LX200 body.
Before putting a single pack through the KX-One, I swapped out the stock gears for a more mod-motor-friendly setup. The included Kyosho parts work fine for stock racing, but they deliver a ratio that’s too tall for mod motors. After 2 minutes of wrenching, the KX-One rolled out with a 120-tooth spur, a 29-tooth pinion and an 8.06:1 final-drive ratio-a much better match for the Team Orion 12-double motor.
I had a van-load of PVC tubing and comer dots ready to set up a track at a newly paved parking lot that was still empty of painted lines and parking blocks. Before plugging any pipes together, I took the KX-One out for a quick blast to see what sort of generic handling tendencies the car had. With its front and rear swaybars and one-way front diff, I anticipated that a wide-open, no-brakes driving style would best suit the KX-One, and I didn’t want to bother setting up a technical course for a car that preferred to swing through sweepers. It turns out I was right; the KX just did not like to slow down, and it spun very easily no matter how gently I fed in the brakes. So rather than frustrate myself with a lot of switchbacks, I spread out a simple “U-inside-a-U” layout that provided four long straights, two big sweepers and two 180-degree turns to tie it all together.
The KX-One launched impressively, even with all four of its (cold) tires lit up. After a little side step, it hooked up, straightened out and accelerated almost inaudibly to top speed. After I let off, I thought for a moment that I had a runaway car because the KX didn’t seem to slow down. I pinned the brakes, brought it back around and rechecked my radio settings; the KX was coasting so easily that I thought the ESC was pumping voltage at neutral. Nope; everything was set up properly. Thanks to its silky mono-belt drive train and one-way front diff, the KX is as close to frictionless as anything I’ve driven (but I haven’t driven the new Losi car yet).
Pitching the KX-One around the double-U was an exercise in tire-baking slide technique, as I drifted the car full throttle through the big sweepers. The car swung through the turns equally well no matter which way I ran the course, which dynamically proved it was tweak-free, and it was easy to tighten up in the turns by easing off the throttle.
The KX gained traction as the Treadz heated up, but the full swaybar setup still favored a sliding technique to get around the track. The layout’s dual hairpin turns were a problem; because the one-way front diff does not allow the front wheels to brake, the KX liked to lock its rear wheels and spin itself. It was definitely more than I could handle, so I resorted to pitching the car sideways well before the apex, then squaring it off by blasting the throttle when the front bumper was lined up with the next straight. It wasn’t stylish, but it beat slowing to a crawl and tiptoeing around the turn. I also tried deactivating the rear swaybar to get more rear traction, as well as a no-swaybar setup. The KX– One still liked to slide tractably in either configuration, but it did turn in more aggressively without swaybars. When using the front swaybar only, the rear end broke free a little more abruptly instead of reaching and exceeding the traction limits “seamlessly,” as it did with a swaybar. Once in drift mode, the KX handled the same with or without swaybars, and steering by throttle was the best way to adjust the line through the turns.
I’m not signing off completely on the KX-One yet; until I actually run it in high-traction conditions, I have to reserve judgment, and I do want to try driving it with a standard front diff. For now, my only gripe is its cost: at a whopping $380 (give or take), the KX– One is significantly more expensive than other competitive cars. But I can say that the KX-One is ready for fast, open tracks straight from the box. It really is a pleasure to drive, and it feels exceptionally quick. The KX-One is unique among all of the touring cars out there; it’s also very well equipped, with variable-damping-rate shocks, a one-way front diff, lightweight plastic rear diff, universal drive axles and high-quality graphite parts. High performance? Guaranteed. Worth it? That’s your call.
Copyright Air Age Publishing Oct 2001
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