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The following information is a general discussion regarding shock and spring selection. It is intended to offer a technical base from which to design, redesign or troubleshoot suspensions. These principles will offer insight to all forms of motor sports, from drag racing to street rodding. Valving recommendations have to be very generalized and are only intended to provide an approximate baseline to start fine-tuning. Every car is different, no matter how much you think your car is like your buddy's car. There will always exist differences in geometry, weight, torque, horsepower and more. Selecting the best shock and spring combination is dependent on many variables. In some cases the recommendations made could be very close, but we are not striving for mediocrity... we want you to win!
The best place to start any fine-tuning process is literally by the seat of your pants. Drivers have to become aware of what the car is actually going through, be it on the track or the road. On the track, he has to know if it is hooking initially and then spins, or doesn't hook at all initially and then hooks. For the rode, it is definitely by the seat of the pants. There is no reason a street rod has to have a bad ride. If the car is uncomfortable, then something was missed or overlooked when it was set up originally. In both situations you should begin by experimenting with different shock valvings and spring combinations until you find a set-up that works for the widest range of conditions. Once you have a good baseline overall set-up you can adjust for different conditions whether it is at the track or on the road.
In order to make the correct adjustments you first need to consider what the function is of the shock and spring. The spring is there to insulate the chassis from forces applied through the wheel generated by irregularities in the track and road surface. A spring that is too stiff can allow the chassis to accept too much of the force. The chassis movements cause unwanted weight movement and geometry changes. In drag race applications, springs with too much rate typically cause the car to hit the tire and rebound off too quickly. In street rodding, the ride quality and handling are less than desirable. Springs that are too soft allow the cars in both situations to become lazy, possibly allowing the cars' suspension to bottom out thereby causing a whole new set of problems, including safety. Both of the above examples are typically worst case scenarios. When the correct range of spring rate is established, the spring can then begin its job of controlling weight transfer. The spring determines how much weight is transferred to each wheel. When you have arrived at the proper baseline spring set-up, you should then try to fine-tune the hit on the tire or the ride quality with shocks and other adjustments.
Now, let's move on to the shocks' role in chassis tuning. One of the functions of the shock is to control the kinetic energy stored in the spring as the spring compresses and rebounds. That is a very simplistic statement; but it Is in fact one of the shocks' functions. The other, and most important shock function in a race car, is controlling when weight is transferred. The different valve settings offered in QA 1 shocks allow you to get the seat of the pants feel you desire. In drag racing, you can tailor the weight transfer in the front end and the hit of the rear tire depending on specific track conditions. In street use, the shock will allow the fine-tuning of the ride quality by setting the valving to what is needed to control the spring that has been selected for your application. This style of valving offered by QA1 for street use is specific by type of vehicle. Valving for a street rod will be different than valving for a muscle car. Each will be designed to offer superior control of the suspension.
I am
running exactly the same set-up as the track champion. I have driven his
car and it is much faster than mine. What's wrong with my car?
It is quite possible that
there is nothing actually wrong with your car. Building two cars exactly
alike does not happen very often. There can be variances in chassis rigidity
that make each car react differently to the same set-up. For instance,
a chassis with a lot of flex in it may need more spring rate to compensate
for the flex in the chassis. There can also be minor differences in geometry
that you may not have thought about. You may be running a different wheel
and tire combination, or the spring and shock mounts may be at different
locations. You will need to keep experimenting with your set-up to find
the right combination for your car.
Does
raising the spring seat increase spring rate?
No. Once the weight of the
car is set down on the shock and spring combination, raising and lowering
the spring seat will only serve to change the shocks eye-to-eye measurement
and also the car ride height. The compressed length of the spring
at that point will not change unless it has something more than the weight
of the car to work against, such as the shock is topped out or bottomed
out.
Is
there a difference between shock ride height and chassis ride height?
Yes. Chassis ride height
in racing will have to do with class regulations and chassis set up for
weight transfer and distribution. In the street world it often comes down
to the look. Does it have the stance to make it "cool"? Shock ride height
is a specified range that is measured from mounting point to mounting point
that the shock is designed to work within under normal operating conditions.
This measurement is taken or set with the chassis ride set where it needs
to be for the specific application. It is designed to allow the shock enough
travel in both directions So that the shock will not top or bottom out.
Suspension Clearance - Always check the clearance on all suspension arms, shocks and springs through the entire range of travel. The extra clearance through the entire range of travel could mean the difference in being competitive or not and, for the street buffs, whether or not it handles and rides correctly. This includes shock mounting locations and configurations.
Bearing Maintenance - The shock bearings should operate smoothly. Check them for wear and fit. QA1 Teflon@ lined bearings will offer smooth but firm operation. If metal-to-metal bearings are used, have penetrating oil applied and then worked in by hand for regular maintenance. Wipe the excess oil from the bearing when finished so that it does not collect dirt.
Binding
- Check the entire suspension without springs and socks for binding.
If the suspension binds in the normal operating range, fix or replace the
problem area. Binding and then freeing up in the typical suspension travel
range will, in effect, be adding spring rate at times and not adding it
at others, thereby making the chassis inconsistent.
We hope that this information
will get you on your way to quicker sets and/or a better ride from the
start.
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EXAMPLE:
Straight Mounted Spring
= 200 Ibs.
Spring Mounted at 30°
= 200/.75 = 266 Ibs.
The 266 Ibs. represents the spring rate needed when mounted at a 30° angle to equal the desired spring rate of 200 lbs. when standing straight up.
SHOCK ABSORBER CONFIGURATIONS
AND DIMENSIONING
Compressed and extended mounting lengths are measured from the center of loops and/or shock shaft/stud shoulders. If the measurements are taken from mounting surface to mounting surface, subtract 5/8" for each shaft/stud end. The preferred measurement in most cases is taken with car sitting on the ground as ready to go. If initially setting up the chassis, simulate the approximate ride height (stance) before measuring.
Front Springs - QA1 7" x 2.5" I.D.
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Rear Springs - QA1 12" x 2.5" I.D.
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Note:
This
quick reference chart is set up as a basic start for drag racing applications.