THROWBACK THURSDAY: 1993 SLINGSHOT BOOM TUBE REVIEW

It would be hard to confuse the Slingshot with any other bike. Harder still would be classifying the Slingshot as a full-suspension bike, front-suspension bike or rigid bike. It's a little of all and none of each. A full-suspension bike has front and rear suspension. The Slingshot has suspension forks, but you can't really call its hinged, Scotchply, fiberglass leaf spring (between the seat tube and top tube) rear suspension. As far as a front-only bike goes, the Slingshot's Manitou forks don't work alone. The front half of the Slingshot (from the seat tube forward) actually splays out with forceful pedal strokes or in bumps. The bike grows and shrinks with the rhythms of the road. It's like an inchworm. Does the splaying of the frame represent rear suspension? No, the rear of the Slingshot is rigid; the rider's relationship to the pedals, rear axle and saddle remain constant.

So, what is it? What is it like to ride a bike that flexes almost an inch in several directions at the same time? That is what the MBA test riders wanted to know when they threw a leg over one of the strangest mountain bikes ever produced. Here are the most common questions and the MBA wrecking crew's answers.

No! Emphatically no. You can't have it both ways in the world of bicycling, and that is what is wrong with the oft-spoken concept that the Slingshot is the "fastest mountain bike, suspended or conventional." You can't worship at the altar of stiffness, insist that crit bikes, sprint bikes, kilo bikes, and road racers be stiffer than General Franco's body, and then turn around and say that a bike that flexes (even on purpose) is able to store energy on the downstroke, and return it to the drivetrain as each pedal reaches the bottom of its stroke. Which one is it? Stiffness or flexiness?

The MBA test riders didn't find the Slingshot to be slow, but it doesn't accelerate better than any other bike, and it is spongy during hard sprints. From a pure power point of view, no test riders felt that they were being aided by the Slingshot's unusual spring-loaded cable downtube during acceleration.

The hinged, spring-loaded, cabled Slingshot is fast once it is up to speed. In motion, the sponginess of the splayed-out cable action is muted. It begins to work, on a harmonic scale, as the speeds increase, and it is here that the "stored energy" concept may begin to actually pay some small dividends. It is possible that the skinny-tired time-trial version of the Slingshot could be incredibly efficient.

Off-road, the inchworm movement smooths out the ride and takes the sharp edge off of fast fire-road riding. It is a very comfy bike to ride (somewhere between rigid and fully suspended).

Skeptical test riders dreaded the first big climb they came to. It was logical. Most suspension bikes have a dead feel on steep faces. They get left for the broom wagon by rigid bikes.

First-timers on the Slingshot expected that a bike that seemed to get longer with each pedal stroke would climb like a Greyhound bus—not so!

The Slingshot climbs as well as a rigid bike. There is some flex, and the bike is definitely not a lively climber, but it does not suffer from the deadness associated with full-suspension bikes, nor does biopace under high torque loads or wag on steep faces.

Slingshot's unique chassis pays major dividends under specific riding conditions. Fast fire roads (bold like soft terrain below): When you arehonking, the Slingshot is almost the perfect bike.It doesn't matter whether the dirt road is smooth or rough, this is a great bike to do bomb runs on. The comfort level of the spongy frame takes the edge off of ripples and braking bumps, while the harmonic resonance (a fancy word for the give of the frame) aids the rider in keeping in contact with the pedals.

Test riders raved about the straight-line resilience of the Slingshot. It went straight, gobbled up rugged road and was accurate at high speeds. The faster you went, the Slingshot wandered less.

Soft terrain: You wouldn't get much argument if you said that mountain bikes and sand don't mix, but don't say that to a Slingshot rider. It shined in the soft stuff. The bike climbed up on top of the sand, and the inchworm nature of the frame is more to blame than the front-geometry setup, but at best they are co-conspirators. The front geometry has a lot of trail, and the combination of compressing forks and stretching chassis results in a bike that not only misses selected lines but ricochets off of obstacles. Most front-suspension bikes get steeper when the front end is collapsed, often as steep as 74 degrees, but they do not get longer. The Slingshot chassis is capable of splaying out longer, dropping down lower, arching its back up higher, and having head angles that can go from semi-steep to very slack.

This is a bike that needs to be ridden out of the saddle in the most technical of situations. Body English, dead-center body weight, and going straight into corners and banging off of a berm were the hot setups.

To tell the truth, the numbers that the Slingshot exhibits on the measuring table aren't what it will show on the trail. Like most full-suspension bikes, which all test riders deny that the Slingshot is, there is a small degree of inherent sag in the system. On a bike with forks and a shock, the rider's weight will drop the front or rear end down to a predetermined number. There is no denying the effect of bike sag on the geometry. With the Slingshot, the effects are quite unique. Assuming there's no sag in the front fork, the Slingshot's 70.5-degree head angle (71-degree claimed) will be slacker when the Scotchply hinge bows under rider weight and, paradoxically, the 73-degree seat tube will get steeper. We said at the outset that the Slingshot was like no other mountain bike ever made.

Slingshots are offered as frames only for $1100, and come in four basic sizes (14-, 16-, 18- and 20-inch) and four standard colors (red, blue, yellow or black). All of the frames, regardless of their size, have a 14-inch measurement from the bottom bracket to the 3M Scotchply spring. Our 16-inch test frame was closer to a 17-inch frame size, although it was long enough (with its 23-inch top tube) to be a 19-incher. The chainstays were a short 16.5 inches, which was achieved by using a wider 75mm bottom bracket. The wider BB allowed for the chainring clearance to have short stays at the cost of mud clearance on the chainstays. The bottom bracket was a tallish 12.5 inches off the ground, but it was clearance that was absolutely necessary. The wheelbase was close to 42 inches without the rider and over 42 inches with the rider.

We expected the Slingshot to be light. After all, it is missing one of the heaviest tubes on a standard frame, and the oversized True Temper tubing gets its strength from diameter, not thickness. Our test bike tipped the scales at just under 27 pounds (without water bottles or the special aluminum water-bottle cage carrier).

The spring that buffers the cable is upped in size from previous Slingshots. The new spring is 1 inch in diameter. Previous springs were three-quarters of an inch. Three spring rates are available to help fine-tune the frame's flex.

The spring collar is made of titanium. Slingshot will be introducing a titanium version of the Boom Tube frame in ’93. The new Ti bike will have a titanium Boom Tube and head tube mated to a chromoly seat tube and rear triangle. The downtube will still be made out of air.

Slingshot uses two different tubes to make its seat tube. A larger, heavy-gauge tube is used to support the upper portion of the seat tube, where the seatpost induces stress, while a smaller tube is used to connect to the bottom bracket. Very clean concept.

Amelia Earhart is missing, and so is the Slingshot's downtube. The looks that the ’Shot attracts make it worth riding.

The frame design shows constant evolution. The MBA test riders last rode the dual top tube Slingshot and found that the quality of both the engineering and frame building had gone up considerably at the Slingshot factory.

We had our doubts about water bottles staying in the forward-tilted "wine rack" water bottle cages, but we didn't lose any. There is a conventional water bottle cage boss on the seat tube for riders who only want to carry one water bottle. There's no room for three, though.

Riding the Slingshot without your hands is a challenge. No-hands riding allows a rider to stretch, drink, remove jackets or goof off, but on the Slingshot the front end wallowed so much that letting go on anything but smooth pavement was a rite of passage.

The cable routing was very clean. Mark Groendal got the idea for his cable bike when he was 11 years old. His Briggs & Stratton-powered minibike broke its downtube while he was out trail riding. Mark noticed that the ride smoothed out without the downtube attached. At the age of 19 he built his first cable-equipped BMX bike using a Hexel snow ski. Slingshot made BMX bikes until ’86, but by then they had moved into mountain bikes. Today, Slingshot makes 700 mountain bike frames a year, along with tri bike and road bike versions.

Preload can be changed on the coil spring by turning an adjuster nut. More preload delays the point at which the spring gives into the initial movement of the frame's hinge.

One of the great things about mountain bikers is that they don't suffer from the snobbery of roadies, or at least they didn't. The Slingshot brings it out in them. It's so different, so unique, so weird and so unfathomable that riders discount it without even riding it. Once they ride it, they are surprised first, that it works at all, and then that it works as well as it does.

How well does it work? Every test rider liked the Slingshot for rolling trails, fire-road riding, high-speed jeep trails and all non-technical trails. For the majority of riding that Americans do, the Slingshot is well-suited to the task. Its best traits are its ability to hammer smooth trails at a constant rpm, descend with comfort and absorb the energy of rough roads. We don't believe that it's the "fastest mountain bike" ever made, but it's not slow, and once in motion the missing downtube and inchworm action do provide a muted, but efficient, spin.

Every test rider wished for more accurate performance than the Slingshot exhibited on tight, twisty singletrack, technical downhills, woods work and at low speed.

There are no other bikes on the planet that offer what the Slingshot does or in the manner that it does it. If you expected it to be unrideable, you are wrong. If you expected it to ride identically to a standard-issue bike, wrong again. It's different by design and in the saddle.