Post by Admin on Mar 6, 2012 16:55:23 GMT -5
Coil over springs.
When we were starting out, we were sometimes going out on the track with the wrong choice of springs on our shocks. The Tobias springs are identified as follows: the 60 # spring has
more turns than the 80# and 100# springs. The 80# and 100# springs are identical
with the exception that the 100# spring is made with a thicker steel stock. That
is, the 80# spring has a steel thickness diameter of .222" and the 100# spring has
a steel thickness diameter of .235".
The formula for calculating the spring rate (60, 80, or 100) is as follows:
Spring Rate in Pounds = (1375000 * d^4) / ((D + d)^3 * N )
Where d = the stock steel diameter, D = Coil inner diameter. N = number
of active turns.
e.g. The tobias 100# spring = (1375000 X .235^4) / ((1.87 + .235)^3 X 4.5) =
(1375000 X .00305) / (9.33 X 4.5) = 4193 / 41.97 = 99.87 # .... well, close enough.
Now.....where do you put them ? You could write a book on this, but keep the following
in mind:
Since we are always turning left, the general tendency is to put stronger springs on
the right side of the car than the left side of the car.
For most dirt tracks, especially the shorter ones, go with the lighter springs. Perhaps
60s on the left and 80s on the right. Some prefer 60s all the way around.
For the larger tracks where the speeds into the turns are significant, stronger springs
on the right will handle the higher centrifugal force and keep the car from rolling over
to far.
The spring adjustability is made so that in most cases, all 4 wheels are loaded and in
contact with the track. (That is not to say the carrying the left front in the turns
is 'always' a bad thing ON DIRT)
Even with the adjustable collars, a spring swap is generally necessary between bigger
and smaller tracks since there is just not enough range to handle the changes with
spring loading alone.
Cross weight (which is a subject in of itself) is changed by putting differing springs
at an angle. i.e. LF = 60, RF = 80, LR = 80 and RR = 60. This would increase the
cross weight or as it is commonly refered to as adding wedge. More wedge generally tends
to cause the car to push going into the turn but allows the car to exit the turn better
since the left rear tire is loaded more.
Conversely, with LF = 80, RF = 60, LR = 60 and RR = 80. This negative cross weight tends
to loosen the car up and is done on tracks where the car is pushing like a freight train.
More on cross weight will be addressed in a future tech tip.
One of the biggest mistakes we made when we started racing was adjusting the spring collars
too much at a time. When we come in after hot laps now, it generally takes an
adjustment of only 1 or sometimes 2 springs; little more than a 1/2 inch or so.
A general rule of thumb is to have both the right side; front and rear wheels loaded with
the same weight in the turns. Easier said than done, particularly when you set up your
car on scales while it's sitting still.... all part of the art
When we were starting out, we were sometimes going out on the track with the wrong choice of springs on our shocks. The Tobias springs are identified as follows: the 60 # spring has
more turns than the 80# and 100# springs. The 80# and 100# springs are identical
with the exception that the 100# spring is made with a thicker steel stock. That
is, the 80# spring has a steel thickness diameter of .222" and the 100# spring has
a steel thickness diameter of .235".
The formula for calculating the spring rate (60, 80, or 100) is as follows:
Spring Rate in Pounds = (1375000 * d^4) / ((D + d)^3 * N )
Where d = the stock steel diameter, D = Coil inner diameter. N = number
of active turns.
e.g. The tobias 100# spring = (1375000 X .235^4) / ((1.87 + .235)^3 X 4.5) =
(1375000 X .00305) / (9.33 X 4.5) = 4193 / 41.97 = 99.87 # .... well, close enough.
Now.....where do you put them ? You could write a book on this, but keep the following
in mind:
Since we are always turning left, the general tendency is to put stronger springs on
the right side of the car than the left side of the car.
For most dirt tracks, especially the shorter ones, go with the lighter springs. Perhaps
60s on the left and 80s on the right. Some prefer 60s all the way around.
For the larger tracks where the speeds into the turns are significant, stronger springs
on the right will handle the higher centrifugal force and keep the car from rolling over
to far.
The spring adjustability is made so that in most cases, all 4 wheels are loaded and in
contact with the track. (That is not to say the carrying the left front in the turns
is 'always' a bad thing ON DIRT)
Even with the adjustable collars, a spring swap is generally necessary between bigger
and smaller tracks since there is just not enough range to handle the changes with
spring loading alone.
Cross weight (which is a subject in of itself) is changed by putting differing springs
at an angle. i.e. LF = 60, RF = 80, LR = 80 and RR = 60. This would increase the
cross weight or as it is commonly refered to as adding wedge. More wedge generally tends
to cause the car to push going into the turn but allows the car to exit the turn better
since the left rear tire is loaded more.
Conversely, with LF = 80, RF = 60, LR = 60 and RR = 80. This negative cross weight tends
to loosen the car up and is done on tracks where the car is pushing like a freight train.
More on cross weight will be addressed in a future tech tip.
One of the biggest mistakes we made when we started racing was adjusting the spring collars
too much at a time. When we come in after hot laps now, it generally takes an
adjustment of only 1 or sometimes 2 springs; little more than a 1/2 inch or so.
A general rule of thumb is to have both the right side; front and rear wheels loaded with
the same weight in the turns. Easier said than done, particularly when you set up your
car on scales while it's sitting still.... all part of the art