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Safety
Officer’s Report:
Steve Coomer, Safety Officer From
HardTail to SofTail, the evolution of rear suspensions… In
each of the previous articles I discussed the development of front
suspensions, how they work, and how rake and trail affect the handling of
the motorcycle. This information built on my article covering tire sizes,
ratings, and general tire safety. Having covered the front end of the
bike, it is time to look at how the motorcycle rear suspension evolved
from the earliest days of no springs, to sprung seats, and finally to the
coil-over-hydraulic shock suspended pivoting rear fork that is commonplace
today. The
first motorcycles of the late 1880’s had outrigger wheels and tractor
seats mounted solid to the framework. Steam engines were the technology of
the times, and internal combustion engines were in their infancy. The
suspension and seat on these first machines were non-flexing and every
bump was felt, sometimes rather harshly, depending upon the speed at
impact. Bicycles of the period actually had sprung saddle seats that were
more comfortable than the first motorcycles. By
the late 1890’s, small, single cylinder engines were becoming more
readily available and a handful of companies were producing them (most
notably DeDion, Aurora/Thor, and Marsh) for the various bicycle
manufacturers (Schwinn, Hendee, and others) to experiment with. This laid
the groundwork for the appearance of nearly 300 motorcycle manufacturers
just in the United States by the early 1900’s. As reliable motors grew
smaller, it wasn’t long before bicycle frames became modified to fit the
driveline. In addition to accommodating the idler wheel control and
leather belt pulley, the frame was strengthened to handle the ‘mighty’
3 and 5 horsepower motors being produced. In addition to building
motorcycles beginning in 1903, Harley openly advertised their turnkey
motors starting in 1905. Starting
one of these beasts was accomplished by pedaling (as in bicycle) until
enough momentum was developed to fire the engine. Stopping was
accomplished by applying the coaster (as in bicycle) brake in the rear
wheel hub. There were no front brakes, but speeds were relatively slow due
to the rarity of smooth roads back then. During this early era, almost all
of the seats had small coil springs at the rear of the saddle and a
pivoting coil at the front, mounted on a base plate that bolted directly
to the frame downtube. The greatest single advance to this configuration
was the 1912 “Full Floeting” saddle offered by Harley on the X8A,
which was the standard sprung bicycle saddle now mounted on a
spring-loaded support inside of the downtube and secured with a pivot at
the upper back portion of the fuel tank. This configuration hung around
until the early 1980’s. Due
in part to their success and innovation on the racetrack, BMW was the
first company to offer a functional rear suspension in the mid-30’s.
This ‘plunger-type’ system was the predecessor to the present-day
motorcycle rear shock with coil springs. The frame was still rigid, but
the ‘shock’ had flanges to mount the axle through, allowing for almost
4 inches of independent travel of the rear wheel. In addition to this
breakthrough, the seat was still sprung as well, allowing for the most in
comfort and luxury at that time. Indian
and Harley each competed for the Army’s desert service motorcycle and
copied BMW’s suspension and shaft drive for the Indian 841 and the
Harley-Davidson XA. Less than 50 each of these models saw production due
to the African campaign ending prior to acceptance testing being
completed. In
1947, Triumph began offering an internally sprung rear hub. While this was
no match for the plunger-type rear suspension being used on BMW’s and
Indians, it was better than anything else offered on a motorcycle at the
time. Ironically, while Harley had been using the plunger-type suspension
for developing their desert bike, the rear suspension never made it onto
their street bikes. Harleys weren’t due for a rear suspension until the
introduction of the 750cc Model K in 1952. It might be of interest to
Sportster fans that ‘their’ bike’s predecessor had Harley’s best
suspension for 6 years before the ‘big twin’ finally received it. The
motorcycle suspension, as we know it today, began evolving in strides
during the fifties. Triumph still had their sprung hubs and some found
their way onto BSA’s. The companies of Indian, BMW, and Ariel were using
the plunger design on their bikes, but more importantly, Ariel was also
using the first coil-over shock swingarm on its 250cc scooters. Most
notably, Harley introduced its swingarm on the ’52 K-model and AJS
introduced their version in England on their 350cc street bikes. Other
notable changes during the era were the disappearance of sprung seats in
favor of frame-mounting and the development of the triangulated swingarm--invented
by Vincent and used on the 1951 Rapide. Finally, in 1958, Harley managed
to put a beefier version of the K-model swingarm on all of their big twins
with the introduction of the Duo-Glide. The
sixties and seventies saw nothing more than cosmetic variations of the
now-generic coil-over-shock swingarm frame. Some bikes covered the
springs, some had them chromed, some painted, and some shocks totally
encased in chromed or painted tubes. Swingarm lengths varied by
manufacturer in an attempt to optimize the ride and rear wheel geometry.
The plunger rear suspensions began reappearing at this time spliced onto
rigid wishbone frames and being marketed as ‘savior’ frames. Chopper
builders loved ‘em because now it was possible to ease the bumps in the
road while having a clean looking frame at the rear seat and sissy bar
area. The
early eighties saw the use of air shocks on the rear of big touring bikes.
At the same time, the Harley Comfort Flex seat utilized the sprung post
from the 1912 design in addition to a spring contraption something akin to
the fabled Mongolian Monster Trap. The seat had adjustable firmness and
damping beyond what was available through the shocks for ride comfort
control. While it is unknown how many monsters were actually caught by
this clunky spring-loaded mechanism, I know of a few sets of fingers that
hated the blasted paperweights. Thankfully (for many mechanics) that
contraption faded into history by 1984 with the advent of the FXR and
newer rubber-mounted frames. The final noteworthy suspension item of the
eighties was the marketing coup pulled-off by Harley with the introduction
of the 1984 SofTail. Remember the Vincent Rapide with its triangulated
swingarm? Thirty-three years after its introduction, Harley resurrected
and refined this configuration with the shocks being hidden under the
frame and becoming the SofTail. 1984 also saw the first of the Evo motors
wrapped in the frame that was reminiscent of the old hardtails. While the
SofTail suspension left much to be desired for 2-up long distance riding,
it was a great solo ride that was a throwback to a bygone era. The
nineties saw some frame enhancements to improve rigidity of the backbone
on the swingarm frames from the various manufacturers. BMW pioneered ABS
systems for motorcycles, introducing them in 1991. This led them to
re-tune their suspensions to control inertial reactions and resulted in
one of the smoothest, best handling tourers ever made. By the late 90’s
shock technology had improved to the point that SofTails finally rode
almost as good as they look. Harley
went to larger tubing and stronger box-sections on all of their frames by
2000 and further refined the SofTail by improving the rear suspension and
balancing the motor to reduce vibration. After 51 years the Sportster
swingarm geometry still provides for a nimble bike that handles well but
suffers from a higher center-of-gravity than the big twins. The Dynas and
FLH’s still have the best Harley suspension geometries for riding 2-up
and are among the best of what is available in the market. With
that said, I have witnessed long-distance 2-up riding on a Buell Blast!!!
As
always, Ride Alert…
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