DEATH OF THE RISING RATE

Rising-rate shock linkages are a scam. This so-called innovation has been foisted on American motocross racers for the last 20 years with little or nothing to recommend it. It’s not that rising-rate linkages don’t work; it’s just that they don’t work as advertised, don’t work better than other alternatives and are too complex for what little they do.
The nail is in the coffin of rising-rate linkages, but the funeral will be put off until every motorcycle manufacturer in the world can’t feel the pulse any more. Not surprisingly, that could take years.

WHAT’S GOING TO REPLACE THEM?

If rising-rate linkages are dead, what’s going to replace them? That’s simple! No-link, single-sided shocks. What’s a no-link, single-sided shock? Exactly what it sounds like.
“No-link” means that instead of latching the shock absorber to a complicated series of pulleys, leverage arms and bell cranks, the shock of the future will be attached directly between the swingarm and frame (just like in the good old days).
The lone shock absorber (unlike the good old days) will be mounted on one side of the swingarm.
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WHAT’S RIGHT ABOUT NO-LINK SYSTEMS

In a word-simplicity. A no-link shock can achieve all of the positive things that a rising-rate linkage system can, including having a rising rate, with one-tenth the parts. The benefits of this simple design pay dividends throughout the whole machine.

WEIGHT SAVINGS THAT CAN’T BE BEAT

KTM’s 520SX four-stroke weighs 12 pounds less than the Yamaha YZ426. While some of this weight is saved through careful engine design, a large portion of it came from KTM’s no-link shock eliminating the need for shock linkages, bearings, bushings, dust seals, frame bracketry and beefed-up frame tubes.

MORE FUEL AT A HIGHER VELOCITY

If you want to optimize fuel atomization from the carburetor to the top end, you would design a perfectly straight intake tract. Engine management specialists have spent years developing the perfect shape, diameter and length of the intake to maximize horsepower, only to have the whole formula ruined by a shock absorber blocking access to the intake tract.
A quick look at modern single-shock, rising-rate-linkage motorcycle designs will reveal that the carburetors are mounted askew and the intake tract has a curve in it. Thanks to the fundamentals of flow (based on Bernoulli’s Principle), a curved intake wreaks havoc on the delivery of the fuel air mixture. How much havoc? There is a 25 percent decrease in laminar flow through a curved intake tract versus a straight one. That translates into lost power.
With a single-sided, no-link suspension system, the shock does not block the intake tract. Instead, a single-sided shock absorber is mounted off to the side, allowing the fuel/air mixture a straight shot through the intake tract.

THE END OF RISING-RATE RETRACTIONS

If you are an aficionado of press releases, you already know that rising-rate leverage ratios are changed almost every year. This endless merry-go-round of leverage ratios started in 1980 (when Kawasaki’s Uni-Trak system was introduced to the public, only to turn out to be a falling-rate rear suspension system) and has gone unabated into the current century. Every year, suspension engineers make the linkage less progressive in the first one-third of travel, or more progressive in the last half of travel, or increase the rate change through the middle. Then, the next year, they reverse themselves and go the other direction. After 20 years of yo-yoing, you’d think they would come to the realization that they don’t know what they are doing.

COMPLEX IS AS COMPLEX DOES

Linkages lift the shock at ever-increasing speeds by compressing the shock at progressively greater amounts (for the same amount of rear wheel travel). Since the shock moves faster and farther at the end of the stroke than it does at the beginning of the stroke, its damping increases. Linkages, for all their mysterious allure, can be explained in this simple homespun way-you can’t stuff a large pig through a hole in the fence as fast as you can a small one. Thus, rising-rate linkages change the rate (read speed) at which the shock travels as the rear wheel moves. They speed it up, which slows it down (because the pig gets stuck in the hole).

WHAT HAPPENS TO THE NO-LINK’S PIG?

Guess what? The same thing happens if you mount the shock to the swingarm without the linkage. Don’t obsess on the lack of a rising-rate linkage on a no-link bike. Linkage doesn’t mean much in the real world. It is possible for a no-link suspension system to duplicate the rising-rate of most successful leverage ratios by positioning the shock within the known framework of a scalene triangle (a scalene triangle is one in which all three sides have different lengths and angles). However, from a mathematical standpoint, it is not completely possible to get the same rising rate from a no-link system as on a bellcrank linkage. There are rates that have a severe rising curve in the middle of travel that no-links can’t duplicate (luckily, these are not curves that many manufacturers would use anyway).
Making the rising-rate spoof even more ludicrous is that modern rising-rate bikes use the same approximate leverage ratio as the twin-shock Suzukis that Roger DeCoster used to race. So much for progress!

A LITTLE HISTORY

Rising-rate linkages are not new, but if you’re looking for the father of the idea, you have to go back to the early ?70s and New England inventor Joe Bolger. Long-travel suspension was a new movement in the ?70s, but as racers started moving their shocks forward on their swingarms, they discovered that the spring rates weren’t stiff enough. As they went from four inches of travel to seven inches, the bike bottomed out. Why? The leverage the swingarm applied to the shocks was dramatically changed when the shocks were moved forward. With the shock moved forward, the swingarm became a pry bar that overpowered the 110-pound shock springs that were de rigeur in the ?70s.
The solution was to put stiffer springs on the shocks. Unfortunately, the spindly little oil-damped, non-nitrogen shocks of the day didn’t lend themselves to 275-pound springs. That’s when Joe Bolger got the idea of mounting the shocks on his Ossa all the way forward and mitigating the leverage of the long swingarm with rocker arms.
Joe Bolger invented the modern suspension system that we use today. Unfortunately, he didn’t get rich off of it. Bolger’s idea didn’t catch on. Instead, a Belgian designer named Lucien Tilkens came up with the idea of mounting a single, larger, longer shock under the gas tank. The longer shock could be properly sprung and would have enough shaft travel to handle the demand for increased rear wheel travel. Tilkens put his single-shock on a CZ and tried to talk countryman Roger DeCoster into getting Suzuki to buy the idea. Suzuki dawdled, Yamaha bought Tilkens’ idea and the monoshock was born.
Although the monoshock was a successful marketing idea, it wasn’t the greatest working suspension set-up in the world (nor would it classify as a rising-rate linkage). Yamaha’s Hakan Andersson won the 250 World Championship as soon as he switched to the new single-shock Yamaha, but it turned out that the bike’s long travel made it a success-not its lone shock absorber.

IN SEARCH OF MARKETABILITY

By the early ?80s, all of the manufacturers jumped on the single-shock bandwagon. A single shock had some advantages over the twin-shocks of the day. (1) They had less swept seal area. One big seal was better than two small seals, and the result was less stiction. (2) As carbon and nitrogen-charged shocks became more refined, they required more and more capacity. It was simpler to make one big shock than two medium-sized ones. (3) Suspension travel was increasing every year. By 1981 it looked like the bike of the future might have 14 inches of rear wheel travel. It didn’t come true, but the prediction had designers thinking of ways to handle the ever increasing loads. One massive shock, with a beefy shock shaft and over-sized piston, seemed like the best path to follow.

THE MARRIAGE OF BOLGER AND TILKENS

To make single-shock bikes work, Japanese designers locked on to the previous work of Bolger and Tilkens. They married Tilkens’ single-shock idea with Bolger’s rocker arm linkage and the rest is history. In time, every manufacturer had dropped its twin-shock design for a single shock, rising-rate linkage system (although Husqvarna resisted longer than anyone else).
Uni-Track, Pro-Link, dog bone and Full Floater became part of the vernacular, and the merry-go-round was in motion. Starting with the falling-rate (something that you definitely don’t want) of the first Kawasaki Uni-Trak, through the broken Corte Cossa shocks of the 1982 Maicos, to the sad demise of the Full Floater, all bikes soon became clones of each other. Copying, borrowing, rethinking and second-guessing have been the hallmarks of rising-rate shock theory.

BOLGER AND TILKENS’ ANTITHESIS

If Bolger and Tilkens were the proud parents of the suspension system that we have used for the last 20 years, who’s the progenitor of the no-link, single-sided suspension system? That’s a no-brainer! Horst Leitner, an Austrian-born American citizen, never believed in the rising-rate hullabaloo. When he penned the design for his first ATK four-stroke back in 1981, he mounted the single shock on the side and skipped the linkage. Honda even made copies of Horst’s frames for Ron Lechien and Johnny O’Mara to ride at the 1984 World Four-Stroke Championship. In 1990, KTM’s management paid Horst, who by then had sold ATK and gone into the mountain bike business, to build them a prototype motocross bike. The bike he delivered to the Austrian factory was a single-sided, no-link, perimeter-framed machine that was years ahead of its time. How many years ahead of its time? Six. Horst’s bike disappeared into the bowels of KTM’s Mattighoffen, Austria, factory, only to reappear in 1997 as the new no-link, single-sided PDS system.
The KTM PDS design was the first blow to rising-rate linkages. At first, it was only a superficial wound, largely because KTM’s shock valving was so far off the deep end that the rear suspension barely moved. But the damage was done.

NOT THAT LINKAGES WON’T WORK

Rising-rate linkages can be made to work. For 2000, Yamaha has the best showroom-stock suspension system. Not because Yamaha has a better rising-rate linkage than the other manufacturers, but for a more logical reason. Lack of action! In fact, Yamaha’s success is due to the fact that they haven’t changed their rising-rate in recent years (not that they haven’t changed it innumerable times in the past). How can not changing the rising rate result in improved suspension performance? It focused the available development time on the shock (where real gains can be made). Yamaha was able to make changes to their damping and spring rates that could actually be applied to a non-moving target. By not changing the rising rate, they didn’t shift all the variables and end up using guesswork on their damping. The lesson? Every time the engineers change a linkage’s rising-rate, they throw out all the previous testing, development and damping know-how. In essence, they start with a blank sheet of paper. Yamaha decided to work with what they had and make it better.

WHEN IS THE FUNERAL?

Honda, Yamaha, Suzuki and Kawasaki think they can make their rising-rate suspension systems work and 20 years of hit-and-miss failure hasn’t deterred their optimism. But the real question is, why persist with a system that puts the rest of the machine at a disadvantage? A no-link design can save valuable weight (especially important on four-strokes), make room for larger air boxes (engines are, in their basest form, air pumps), allow for perfectly straight intake tracts (eliminating the bugaboos of flow turbulence and scrubbing), improve maintenance (everything from preload adjustment to shock removal is simplified), lower production costs (which is why the incredible Full Floater was circular-filed 17 years ago), enable the press-release flacks to unveil a new flurry of adjectives (which is almost as good as real improvements) and offer better rear suspension performance in the long run (since suspension will become more shock dependent).
Rising-rate linkages are dead-please send flowers.