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During the initial 'wild-west' period of full suspension development,
brands devised innovative solutions to trump their competitors
and seduce the mountain biking public. The resultant imbroglio
of diverse designs was utterly confusing. Some worked quite well,
many were a disaster zone of flawed performance and high maintenance.
The dust has now settled on these turbulent times, with the main
players now evolving variations around two main threads: single
pivot and the four bar linkage. So here's an (over) simplified
summary of the generic full suspension designs. And to keep it
really simple I've restricted my musings to XC and lightweight
freeride bikes
Single Pivot
A basic swing arm attached to the frame at only one point.
Pros: A single grunty pivot for good reliability
and minimal maintenance, the stiff rear end and relatively light,
and you get good performance for modest price.
Cons: The pivot point placement determines its
behaviour. Above the chain line causes the rear wheel to dig in
as you pedal - better traction but locks out the suspension action.
A lower pivot point retains active suspension under power but pulls
the wheel away from the dirt - providing less traction. Choose
your poison. A lock-out switch with a low pivot position is a tidy
solution. Also, the single pivot and shock take the brunt of any
sideways or twisting force, so long travel bikes require a heavier
coil-spring shock.
Four Bar Linkage
A more sophisticated solution that includes 'horst link' and
Virtual Pivot Point (VPP) variations.
Pros: The suspension is always active, ie. doesn't
lock out under power and is less affected by braking.
Cons: All those pivots mean more maintenance
and more to potentially go wrong on the trail. Anticipate a minor
fiscal haemorrhage when replacing the multitude of sealed bearings
every couple of years.
Show me the money
Before you rush out and buy the 'editor's choice' full suspension
mount of your dreams take a moment to balance the ledger. Full
suspension delivers a plush ride and lets you raise the bar on
technical terrain. But you pay around a NZ$1000 premium over a
comparable hard tail. It will weigh about 20% more and demand additional
maintenance to keep the pivots good 'n' tight. That said, for most
riders in most conditions, a lightweight full suspension bike is
a good thing.
Travel, weight and price form an interdependent triangle. 100
to 125mm is the standard for cross country – and will weigh
between 24lbs and 32lbs. An 'XT' spec'ed all day riding/occasional
racing set-up should tip the scales at 28lb and lighten your wallet
by upwards of NZ$4000. All-Mountain bikes typically provide 160mm
travel with a weight range of 30-40lbs.
Platform shoes
The recent advent of stable platform rear shocks has revolutionised
full suspension designs. When set up correctly (best to read the
manual), these intelligent shocks provide a plush ride with minimal
pedal induced bob. Combining this technology with simple designs
has hugely reduced the price of full suspension bikes that really
work and don't weigh a tonne. The shocks are so hugely popular
that it is difficult to buy a bike with an old-school standard
shock.
No Free Lunch
The cost of using stable platform shocks is the loss of fully
active suspension. Dialling out pedal induced bob also prevents
your shock from responding to small bumps - both when climbing
and descending. Salvation comes in the form of the Virtual Pivot
Point (VPP) – used on most models from Santa Cruz and Intense.
They consistently rate at, or near, the top of gear tests conducted
by magazines around the globe. Two links enable the rear axle path
to follow a modified 'S' path. The mechanics are complex, but the
result is fully active suspension without pedal induced bob. Regretfully
VPP comes with caveats as well – a hefty price tag and extra
pivots that require additional care.
Zen Pedalling
While manufacturers promise an absence of pedal induced bob,
this will never be realised if you stomp on your pedals. The antidote
is to pedal in smooth circles Grasshopper, while keeping your upper
body nice and still. Check out Tech Tips: Lesson
Four, Climb Like a Billy Goat
Here piggy piggy
It's unlikely you'll end up with a lemon if you stick to the
established brands, but different models all have their relative
advantages and compromises. Check out reviews on mtbr.com and talk
to ya mates. Many shops and importers offer a test ride service.
So once you've got your short list, thrash a few around some familiar
track before breaking open the piggy bank.
May the force be with you.
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