Like a bumblebee taking flight, sportbike forks simply shouldn't work. That they do so well is a testament to design, development and perseverance (and the fact that there aren't many other devices to hold your front wheel).
SSB looks at this best worst solution.
Winston Churchill described democracy as: "The worst form of government - except for all those other forms that have been tried."
So what's the option? Bring back a monarchy? Nah. And if old Winston knew anything about bikes, he might well have bent his quotation to apply to front forks. Because in many ways, forks are the worst possible design for front suspension on a bike-except for all the other ones that have been tried.
The problems are pretty clear to anyone with an engineering degree. The front wheel takes care of two massively important jobs: braking and steering. That means there are often huge forces going through the front wheel and up into the frame. But on a bike with telescopic forks, that wheel is at the end of two very long levers. Having the wheel three-feet away connected to a pair of spindly hollow tubes doesn't seem to make a lot of sense-especially when the aluminum frame is so stiff. Every bump tries to bend the forks up and back, and building them sturdy enough to stop this from happening makes them heavier and pricier.
The other basic problem comes with heavy braking. All the stopping force that's generated travels through the wheel into the forks, and is then transferred to the bike's frame through the two long, skinny springs inside. That tends to slam the fork bottoms up pretty rapidly, using up the suspension travel just when you're likely to need all the help you can get from the suspension. Alternative designs try to separate the braking and suspension forces so that they don't interfere with each other.
Suzuki's GSX-R750 was introduced...
Suzuki's GSX-R750 was introduced in 1986, and set a new standard in performance. suspension back then still didn't work very well though, and front fork design evolved rapidly during subsequent models.
So why are we still using forks when they're so fundamentally "wrong?" Forks do have a lot of advantages too. They're pretty simple (especially compared with some of the other front end systems tried over the years), and relatively cheap to make. Combining the suspension and steering into one unit saves weight and complexity, and even the "diving" of a forked bike has some benefits. It increases weight transfer over the front wheel, which gives more grip, and also sharpens the steering geometry, making it easier to turn.
Best of all, there's been a series of clever developments that have largely worked around the problems of forks-at least well enough to keep them as the best choice. The earliest front forks used hydraulic damping mechanisms no more complex than a screen door controller. A damper rod inside the fork moved a piston through the damping oil as the fork moved. The drag created by the oil passing through holes in the piston absorbs energy from the suspension movement, giving a rudimentary damping effect.
They were remarkably unsophisticated though, and if you made the damping soft enough to absorb bumps they couldn't control the fork movement well enough under heavy braking and bottomed out. If made hard enough for braking, they stopped the forks from moving at all over bumps, giving a horrid ride and reducing grip on bumpy roads. On smooth racetracks they could be made to work well enough, but on the road several companies invented complex anti-dive setups to try and improve matters.
In the 1980s Kawasaki and Suzuki used hydraulic pressure from the brake circuits to close off some of the fork damping circuits, increasing the compression damping while braking. They weren't very successful though, and were soon dropped when basic fork design improved.