Pulled this very interesting essay from today's Airlist. Author is Tom Cutter whose Airhead history extends back to his days with Butler & Smith into his Airhead service business of today.
<<Konis were what we fitted back in the day and were in Europe at least
considered to be premium shocks! Ikons have continued in that
tradition.
>> This from another post leading to Tom's reply.The Koni 7610P series were outdated in design by 1970, yet Koni
continued to manufacture and sell them all the way into the 80's. When
they sold their tooling to the company that began producing the exact
same obsolete design under the Ikon name, nothing improved. The same
over-sprung, inconsistently-damped shocks are for sale from them today
as Koni sold 40+ years ago. If they sold for $75 a pair, I might
recommend them for guys who want to keep their wheel from rubbing in
the fender, but otherwise they are about the poorest choice for
motorcycle suspension available on the market today.
There is a wide variety of choice in the motorcycle replacement
suspension market today. We are fortunate that the technology only
available to racers twenty years ago is now available in budget-priced
shocks and springs today. Just as important is that manufacturers today
have the capability to manufacture shocks that fit and are correctly
valved to work on the intended make and model, unlike the day of
one-size-fits all approach used by Koni 40 years ago, when the size of
the bolt hole and the eye-to-eye length were the ONLY two variable
available.
In the simplest summation, vehicle stability on a two-wheel, single
tracked vehicle is largely dependent on correct chassis geometry, match
of spring and damping rates to vehicle mass and load characteristics,
and wheel alignment. For THIS discussion, about shock absorbers, the
affected factor is chassis geometry. This is not a fixed number, it is
a variable that changes during riding as the fork and swingarm move
through their respective ranges of travel. It is important that both
work in unison, that the vehicle not pitch fore and aft, each of which
will have adverse effect on the steering head angle and swingarm angle
of attack. All of this is covered in most basic books on motorcycle
suspension dynamics.
To the Airhead rider, the change in chassis geometry when we ride is
most evident as the "hinge in the middle" or "rubber cow" effect. It is
NOT caused by chassis flexibility, despite the many claims to the
contrary by the purveyors of silly chassis stiffening kits.
Good suspension for your Airhead will start with correct spring
selection to obtain the correct ride height front and rear. The shock
damper must control spring sompression, to allow those compression
forces to bleed away into the chassis harmlessly without upsetting
geometry. Then the damper units must be able to control the spring each
time it rebounds from a bump, to prevent secondary and tertiary pulses
or "pogoing."
There is a lot more than this to suspension design and selection, but
choosing cheap, poorly-matched suspension components is to choose to
throw out the opportunity to have a stable, safe vehicle. This is much
MORE true for road riders and tourers than for racers, because racers
KNOW their exact load, the exact conditions of every inch of the road
that they travel, and can adjust accordingly. The street rider must
have a suspension package that will allow adjustability across a wide
enough range to accommodate the variations in load and road
characteristics that will be encountered by the rider.
There are a LOT of really good shock absorbers available for your
Airhead currently, and many of them cost in the same price range as the
bad ones. Choose wisely. Your safety depends on it.
Tom Cutter
Yardley, PA
http://www.RubberChickenRacingGarage.com
