Bushings are an interesting subject. Rubber is softer and more pliable
than polyurethane and deflects more. So what does this mean in the real
world?
1. Rubber bushings absorb higher frequency vibrations much better than
polyurethane, which helps make the ride smoother. Springs & socks work
mainly on the higher amplitude low frequency vibrations. The higher
frequency shocks get attenuated by rubber bushings and your seat
springs. Polyurethane, being harder and less pliant tends to pass those
vibration along. Some polyurethane bushing manufacturers use a
soft-poly formula to try to absorb more vibrations. Both metal and
driver fatigue are more common when poly bushings are used.
2. Polyurethane bushings do not stand up to heat well and deteriorate in
an accelerated manner when hot. Since they have less give, they move
more as the parts they separate move in relation to one another.
Friction between the bush and part that is moving creates heat. So the
smoother and more polished the contacting metal parts the less friction
is created and the longer the polyurethane bushing will survive. Of
course if you don't put many miles on your vehicle you will never notice
this.
Polyurethane bushings are popular with the Land Rover folks.
Polyurethane bushings used on a Land Rover that travels wash board roads
often do not last a year because the movement generates heat that
destroys the bushings. The hot set up is lubricated polyurethane
bushings. The polyurethane bushings have a grove along the inside
surface. The pivot bolt gets a grease channel and a grease fitting on
the bolt head. So the bushing becomes one more thing to grease but they
last longer and the common polyurethane squeak goes away.
3. Polyurethane bushings are easier to replace than rubber ones which
often seem to bind to the metal around them. This is why they are so
popular with the Land Rover crowd other than them looking cool. Land
Rover folks put up with the short life of poly bushes because you can
swap them all out in an easy afternoon. The rubber ones often require a
torch, saws all, many choice words and a full weekend. Of course the
rubber ones last for several years on wash board surface driving.
4. Because polyurethane deflect less steering and cornering becomes more
crisp and the vehicle handles better going through corners. And that's
where its at for much of the sports car crowd.
Getting back to Triumphs I think the best bushing depends upon how you
drive and what handling attributes are most important to you. Both will
probably hold up as well for the infrequent short distance driver.
Rubber is probably best if you do concourse and mostly club touring or
long distance touring style driving. Polyurethane bushings provide
flatter cornering when you are driving closer to the edge. If you
autocross or just love to throw your Triumph through sharp curves you
will appreciate the lack of flexibility of polyurethane bushings. Even
if your fillings do get vibrated loose.
Both bushings appreciate a smooth riding surface and poly bushings
require it if you expect them to hold up under long use.
TeriAnn
www.tjwakeman.net/TR/index.html
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