First off, we’re going to skip rigid framed bikes, as they don’t count in the evolution of off-road motorcycle suspension. Sure, people rode rigid framed bikes in the dirt, because that’s all they had. But they don’t count, because no suspension is just that, no suspension.
The first dirt bikes came from Europe, of course, and were modified from street bikes of the time, most were light weight single or twin cylinder motorcycles. We can trace the first off-road bikes to places like Germany, England and Spain, who used the bikes first for courier duties in the military, then for competition purposes, and finally recreation.
1958 BMW ISDT bike. Note plunger rear suspension
The first bikes that had suspension after the rigid era used any number of new ideas thought up by designers of the time, like sprung hubs, plungers, hinged sub-frames and other ideas that while groundbreaking and innovative for the time, didn’t work all that well. Much like the venerable Chevrolet V8, the only designs that made it through this period were the ones that worked; the swing arm rear suspension, and hydraulically damped front forks. The other stuff didn’t hack it off road, and quickly disappeared from the manufacturer’s drafting boards.
England seemed to have the edge on handling after WWII, and produced some legendary good handling motorcycles with the formula of the time, that used the “straight line” geometry in frame design. And what was that? It was the design where a straight line could be drawn from the center of the rear axle, through the center of the crankshaft, to the center of the front axle of the motorcycle.
You can see this design in almost every English and European motorcycle from the beginnings of swing-arm rear suspension, to the end of European domination, around 1973. Bikes of this period had rear shock absorbers bolted right over the rear axle, up to the sub frame of the bike in a straight up-and-down configuration. 
1960 BSA A-10 Super Rocket. You can draw a straight line right through the axles and the center of the crankshaft.
Front forks were hydraulically damped, with the axle mounted at the bottom of the lower slider, or slightly off-set with a leading axle design. Some, like the AJS, seemed to have a forward mounted design, but it was more of a mistake, than an actual cognitive design theory.
This design went unchanged for 30 years, until the early nineteen seventies, where new ground-breaking designs made their way into dirt bikes, the first by Maico, with the forward mounted design that gave the Maico a clear advantage in all things handling. 
1974 AW440 Maico (Note FMS rear suspension)
It was wide open after that, with every manufacturer copying the Maico, or coming up with their own version of LTR (long travel rear suspension). Forward mounted, laid down, upside down, linked, even rear suspension that looked like smaller copes of front suspension went on the back of dirt bikes, to get the elusive twelve inches of travel so many clamored for. But it wasn’t until 1975-1976 that Yamaha produced the design that would set the industry on its ear: the single shock Monocross design. After that, everything else was antiquated junk. 
1976 YZ250 Monocross
After the Monocross design by Yamaha, four years later Suzuki came out with the “Full Floater” with Kawasaki‘s entry named “Dual Control” for the twin rods that made up the linkage system on the single shock design. Honda came up with the “Pro Link” system that remains pretty much unchanged to this day, and was the most successful of the bunch, if longevity and design copy by other manufacturers mean anything. 
1981 RM 250 "Full Floater"
Front forks had to keep up with the evolution of rear suspension design, and manufacturers found that a larger tube diameter gave the forks the ability to stave off twisting in the clamps, something the old 35 and 38mm forks did quite often.
Again, all sorts of designs were tried on the front forks, air forks that got rid of the springs, air assisted sprung forks, air/oil forks that used a diaphragm (like an old Citroen), cartridge forks, etc.etc. and still the search goes on for the best design, the latest being upside-down forks that use the tubes as the sliders, in the search for a more rigid design that resists twisting even better than a large diameter standard fork.
In my humble opinion the BEST forks ever produced for off-road work were the 43mm Showa Cartridge forks that graced my 1987 CR500 (the most expensive forks ever put on a Honda motorcycle by the way). These “standard” 43mm Showa forks are still used on the big Honda 650 air cooled XR, if that means anything.
Suspension technology seems to have stalled out lately, with the exception of diamond coated sliders and seals (how do they do that?). It seems to me suspension technology peaked around the late 1980’s, and with just a few minor modifications, is about the same stuff we have now.
So what’s the next big thing in dirt bike suspension technology? Maybe ground seeking radar that adjusts the spring rate/damped settings a nanosecond before you hit that next whoop, or road berm. Or maybe some kind of anti-gravity device that floats you over that big wash-out?
I really don’t know. But I do remember transitioning from a 1972 CZ250 to a 1976 YZ125 Yamaha, and the difference was so great, I wondered if I was really going as fast as I thought on the CZ, as the YZ just walked away from it in every situation. No contest.
I'd like to hear what you readers think will be the next big technology leap in dirt bike suspension? Giant rubber bands? Helium?
Comment on this article