(slalom trucks)
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On 3/14/2002 john gilmour wrote in from 151.204.xxx.xxx:
Free advice is worth what you paid for it...But IMHO- and I could be wrong......
The more a truck turns for the FIRST few degrees of inclination the less tilt you have to put into the truck to get it to START steering. (This can be a good or bad thing depending on your usage).
Conventional trucks will not have a linear tilt to steer ratio. That is to say that if a truck turns (these are aribrary figures) say through an arc of 5 degrees for 5 degrees of inclination from the zero starting point it will probably not turn 5 degrees more for 5 increased degrees of inclination near where the wheels are about to rub on your board.
There is a point where the tilt to steer ratio is nearly linear (though not necessarily one to one) for a good truck.
Most conventional trucks will not give you much steering for the tiny bit of inital imput as the cushions tend to deform a little at first without giving much steering input. Then the truck begins to steer more for a given amount of input. Near the end the truck is not steering as much but just tilting more.
Depending on the geometry of the truck (relation of the axle to kingpin, pivot length, height of axle relative to pivot, pivot angle etc.) Trucks will give you different steering.
The peak part of steering in a truck (lots of steering for each degree of lean) can occur near the zero point or in the middle, or near the point of near wheel rub. Or if the geometry is really extreme- it might not occur within the rangle of tilt a rider would use the truck.
In general Taller trucks with the axle hanging over or beyond the pivot pin with a small distance between the king pin and axle (so called tall trucks or quick geometry trucks)- steer very quickly and radically very soon after the zero point. Trucks with axles lower to the base plate- with axles that do not extend far over the pivot, that are raked back- tend to steer less immediately after the zero point. (Randals are an exception as they follow a different design)
An Indy truck will steer even if tight because for a small amount of tilt from the zero position you get incresaing amounts of steering very quickly. Even just a few degrees of tilt gives you lots of turning. Then with lots of tilt the steering starts to "decay" as more tilt seems to not reward you with as much steering as earlier. So the peak steering for an indy truck comes early. A truck that gets peak steering early- acts like an easily exciteable spring system and will have a resonant frequency that will be more prone to oscillation (speed wobbles) at a lower speed. Bennetts would also fall into this category as would the American Cycle System (ACS)-(but not the 650 model), Energy trucks, American Magnesium, and particularly Lazer trucks. You just don't have to crank the deck very far over to steer the same arc. For faster courses- this can lead to wobbles.
Some trucks will offer little steering input from the zero point and then slowly increase in steering and finally offer their peak steering near the area of most tilt. Such trucks will require much more tilting of the board as well as risers to prevent wheel rub. A Tracker full track will offer very little steering initally- and start to offer more steering gradually and give the bulk of its steering late. This allows a person to ride very fast with loose trucks as the truck will not tend to osscillate from early steering (wobble) even when relatively loose. If there comes a point in a slalom course where there is a particularly tight turn, the rider can just suddenly crank on the truck and make it. Such trucks work well for slalom mostly on shorter wheel base boards (under 22 inches inner holes). Other trucks that fall into this range are Megatrons, Invaders (sure grip).
The tracker Midtrack (narrower than a full track)and Ex-track
(wider than a full track) according to Larry Balma (If I remember
correctly) have a geopmetry in between that of the Indy 101 and
full track. They give very predictable steering response for a
rider input. Also not offering immediate steering off the zero
point, but much closer to the zero point than the full track. The
Midtrack offers good steering and stability. The Extrack offers
more stability than teh fulltrack because of its width- more
traction, but it is harder to hustle the wide extrack truck
through tighter cones. The Tracker Six track shares the same
geometry as the full track. This however means that the truck
will never really turn a lot as you would experience wheel rub
very early due to its increades width. Adding lots of risers will
not help as they will rob you of
stability and traction. These trucks are best suited to riding
vert at ridiculously high speeds or for downhill courses that are
not very turny (and a Randall would be likely be better suited
for that). I personally have ridden sixtracks with a good deal of
confidence- but according to others who race like Chaput and lots
of other guys it is a safe bet to say that the Randalls won't
give you wobbles as much as a Tracker six track and the Randalls
could be ridden looser at speed. The Randalls never seem to hit
their peak steering as I think it occurs beyond the regular use
range of tilt.
For many European riders the Midtrack offers excellent stability and lots of turning sooner than the full track. For straight cones- the amount of steering needed is reduced by the narrow width which is good for the tighter European courses. The Narrow width however puts a limit on the amount of traction the truck can offer. Across the fall line offsets at high speed 25+ mph would be bad for this truck. However lower speed offsets are no problem and even eaier due to the amount of quick steering and narrow track that does not require as much steering to round the cones.
The Seismic offers linear turning throughout its useable turning range thanks to Dan's geometry and no slop design. It begins to steer immediately after the zero point- and it is a spring loaded truck with much less dampening than other trucks so it tends to store energy. This is great for straight tight (around 6 foot) cones at riduiculously high speeds (motorized tow ins for example)It allows you instant steering response and return to center for the next cone. But for bombing hills the Seismic will steer immediatelyfor even a little input so hittig a small pebble at speed will introduce steering. It is also ever so slightly harder to stop a seismic from wobbleing after it starts to wobble as there is almost no dampening action from the springs (you can't have it both ways). These trucks offer such a wide range of turning for the amount of tilt that they can be pumped to the highest speeds when set up properly (wedged- wheelbase- type of deck). They are easy to pump at low speeds and at very high speeds- exceeding other conventional trucks in this respect.
So why did your Indy's wobble and not your Seismics? Because
the Indy's turn a lot for very little input from teh zero point.
If you make your Indy's tighter you may find you have similar
steering to the Seismics and reduce wobble. The Seismics are self
stabilizing at lower speeds as they want to stay centered- but
get going too fast and the springs will store oscillation.
That is fine since a lot of people would never go that fast
through a course anyhow to induce the wobbles.