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Chassis Set-Up

General Recommendation's
As the JBL Motorsports Competition chassis is intended as an ultra-high performance competition platform, it is therefore strongly suggested that the owner read and follow the recommendations contained in the manual completely and also fully understand the setup of, the maintenance of, and the general characteristics of the chassis.

Anti-Roll Bars - (cockpit adjustable-blade type)
Unlike the static changes that the driver can make to the chassis settings while in the garage or pits, operation of the anti-roll bar adjusters is done while in motion. This adjustment allows the driver to change and fine tune the chassis balance characteristics (IE. understeer/neutral/oversteer) to suit the road and track conditions at any given time.

If, for instance, the driver wishes the vehicle to understeer (push) a bit during high speed cornering, they would move the FRONT lever towards "FIRM" a notch to increase the roll stiffness and therein produce the effect. Conversely, the driver could elect to reduce the rear roll stiffness by moving the REAR lever towards "SOFT" and produce a similar effect.

Ideally, once set to driver preference for a given circuit or road condition, these adjustments will remain unchanged unless conditions change. (IE. The road surface becomes wet or oily.) In the instance of the above conditions, the driver would reduce the settings towards "SOFT" to allow greater lateral weight transfer to match the road conditions and driver preference.

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CAUTION!
It is extremely important that the driver make small changes to the anti-roll bar settings. It is highly recommended that the factory settings as noted on the adjustment plate be followed for all conditions. Remember that small changes in lever position make large changes in chassis handling characteristics.
NOTE: it is very important that no preload be on the Anti-roll bar ends.
CHECK AT RIDE HEIGHT WITH DRIVER ONBOARD AND ALL FLUIDS TOPPED. ADJUST AS REQUIRED AT THE ROD ENDS TO ELIMINATE PRELOAD.

Static Suspension Settings
Note: All settings are with driver in vehicle.

Setting Series One: Series Two: Series Three:
Front Ride Height 5 inches 5 inches 3.75 inches
Front Camber .5 deg. negative .5 deg. negative 1.0 deg. negative
Front Castor 2>3 deg. positive 2 deg. positive 2 deg. positive
Front toe-in 0.0625 (1/16 inch) 0.0625 (1/16 inch) -0.040
Rear Ride Height 5.75 inches 5.75 inches 4.5 inches
Rear Camber 0-.25 deg. negative 0-.25 deg. negative .25 -.75 deg. negative
Rear Castor 0>.5 deg. negative 0>.5 deg. negative 0>.5 deg. negative
Rear Toe-in 0>0.03125 (1/32 inch) 0>0.03125 (1/32 inch) 0>0.03125 (1/32 inch)

Cockpit Adjustable Brake Bias
The brake bias (front to rear balance) is adjustable by a dash mounted knob which is turned either clockwise or counterclockwise to vary front and rear brake line pressures.

The brakes and master cylinders on this chassis are sized to give a neutral bias when the adjustment is in the center position. (IE. all brakes lock at the same time.) As the loading in the vehicle changes due to passenger or fuel load changes the driver can fine tune the balance to maintain this bias under all conditions.

Also, many drivers wish to have a slight rearward bias, which would allow the rear brakes to lock first. This setting is quite useful on high speed circuits which have some very slow corners. With the chassis set for high speed understeer, it if often difficult to point the nose in at slow speed, therefore a rearward brake bias allows the driver to momentarily lock the rear brakes and tighten the arc into the corner.

CAUTION!
Over adjustment of the brake bias in either direction will cause severe imbalance in the braking and stability of the chassis. Small changes are all that should ever be made from neutral settings!


Setup Guidelines (Competition Only)

Circuit Type
The suspension settings will have a large effect on the basic handling of the chassis as it relates to either a low speed or high-speed circuit. Below please find some recommendations by circuit type.

  • LS Low Speed, most corners are below 70 mph.
  • HS High Speed, most corners are above 70 mph.

The static suspensions settings as shown in the proceeding chart are to be used as a guideline in your setup, they are a good starting point for all circuits.

  • (LS,HS) It is generally best to run the chassis at the lowest ride height possible without bottoming under braking or over bumps. (Note: bump rubbers on coil-over damper shafts can regulate this by allowing a firm stop at the correct point.) Corner weights should always be set equal side to side to within 2-5 pounds with driver on board and all fluids topped.
  • (LS,HS) Depending on track surface, banking, adverse camber and weather conditions the static front and rear cambers may have to be increased to maintain even tire temperatures and to insure balanced handling.
  • (LS) Traction while exiting a corner is typically of more importance on low speed circuits than any other factor. Therefore, rear camber should be maintained as close to vertical (0) as possible, without inducing oversteer, to insure maximum tire contact patch for best launch out of the corner.
  • (LS) Front and rear toe settings are extremely important on low speed circuits. Never run more than .0625 toe in on the front. You will find that some front toe out (.030-.060 max) will help the car turn in to the corner. If you still have a lot of understeer with some front toe out, a little bit of rear toe out (.030-.060 max) will often cure this condition.
  • (HS,LS) The standard competition spring rates are a compromise and work best on a smooth, clean, dry track surface. If time is available for testing at the track before you begin competition, testing various spring rates is recommended. The best method is to set front and rear anti-roll bars dead soft and then alter the spring rates until good chassis balance and the best tire temperatures are found. Then, the driver should begin increasing the roll rates one step at a time until the quickest times and most stable condition for consistent lap times are achieved.
  • Tire Stagger. One thing to remember, all racing tires as supplied vary in their circumference, therefore you must check each tire after mounting to determine the dimensions.
    • (LS) This is something to be avoided on short courses with a fairly equal number of both left and right turns. If there is a single long radius turn, which is a major part of the short course, a slight stagger can be helpful. However, stagger will typically hurt the acceleration off of slow corners.
    • (HS) On high-speed circuits, tire stagger becomes very important. The amount of stagger should always be very small on this chassis. If the circuit has, for instance, a predominance of high speed left hand corners, the right rear tire should be larger than the left rear. If the corners are right hand, the opposite would apply. It will be best to speak to the tire engineers present at the circuit for their recommendation and tire selection.
  • Aerodynamics. (HS) The COBRA body does not produce any downforce. It actually produces lift at any speed over about 80 MPH. There are few things that one can do to help this situation. Below are some suggestions:
    1. It is recommended that the front ride height be as low as you can possibly run it and the rear be set a maximum one (1) inch higher than the front. This will help minimize front lift. However, you must be extremely careful that you do not make the rear any higher than necessary, as this could induce high speed oversteer due a higher lift component on the rear Bodywork.
    2. The front radiator opening should be minimized to just enough area to cool the engine properly. The less air that enters the engine bay the better, as lift is created by underhood and underbody pressure. The components to achieve this are available from the factory on a per circuit specification.
    3. Front Air Dam. Depending on the class rules in your particular sanctioning body, a front air dam is of more help then any other single item in reducing overall lift and drag. A number of configurations are available from the factory on a per circuit basis.

CAMBER CHARTS
Below are camber curve charts for the front and rear suspension in both bump, droop and roll configurations. These will help you and your tire engineer to determine static suspension settings for a particular circuit.

Figures 5 and 6 are camber charts, which show camber change through a typical range of suspension movement under normal operating conditions.


Figure 5


Figure 6

These charts show the dynamic gain in camber angles of the front and rear suspensions. They are best used once you know the camber needs of your particular tire and compound. Your tire engineer should be able to give you this information.

If, for example, the particular front tire that you are using requires a total of three (3) degrees negative at a lateral load of 1.5 G, and you know that you are getting one inch of suspension travel due to roll, you would look at the chart and see that the camber gain is two (2) degrees. Therefore, you will need a static setting of one degree negative to give you the proper camber for your tire. Of course you must use tire temperatures to fine-tune your settings.

This ends the setup section. There is much more detail and many ways to make the car work better and be faster. For more assistance, please contact the factory.

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