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degrees) will decrease stability and traction in corners, but will increase high speed stability.

Shock Location: Leaning the top of the shocks inward on the tower will provide less forward traction and more rotation in a corner. Mov-

ing the top of the shocks outward on the tower will provide less rotation in a corner and the car will become more responsive with increased

forward traction. Moving the bottom of the shock to the inside of the arm will result in more forward and side traction (side bite). Running

the shocks in the outside hole in the arm will provide more on-power steering with less forward traction. In general, when changing shock

locations on the arm, it will be necessary to go up one spring rate when moving in on the arm and vice-versa.

Anti/Pro-Squat: In the stock conﬁ guration, the JRX-S has no squat. Anti-squat is generated by raising the inner pivot blocks, relative to the

outer pivot. This will increase initial steering and forward traction. Pro-squat is generated by raising the outer rear pivot relative to the inner

pivots. This will decrease forward traction and initial steering, but provide more on-power steering. Either pro-squat or anti-squat can be

increased in 1 degree increments using .035” roll center shims, supplied in the kit.

Rear Droop: This is adjusted and measured in the same fashion as the front droop, but use the bottom of the hub carrier, instead of the set

screw boss, for a reference. Testing has shown that 4mm of rear droop is a good starting point. More droop will result in smoother chassis

reaction and more rear grip. Less droop will react faster and possibly become a little abrupt.

Rear Hub Location: The

JRX-S comes standard with a long rear arm setting. Testing has shown this to offer the best, and most consistent,

setup from track to track. The optional offset hubs, short rear arm setting, (LOSA9854 (0-Degree), LOSA9855 (½-Degree), and LOSA9856

(1-Degree)) offer more steering and have been extremely useful on carpet/foam tire racing.

Tuning the Chassis of the JRX-S

Center Drive: The JRX-S comes with the option of a center one-way or a spool center drive. Similar to using an optional front one-way, brak-

ing will only occur with rear wheels. A center one-way will enhance the off-power affects of a front one-way by providing more total steering.

A spool center drive will give you less total steering and greater braking ability. Generally, the center one-way is used in combination with a

front one-way or front diff setup, when a lot of steering is desired. In the same respect, a spool center drive is generally used in combination

with a front spool, both used commonly with foam tire/carpet racing.

Arm Spacing: The JRX-S has options for changing the wheelbase by moving the front and/or rear suspension arms forward and back. Mov-

ing the .0625” shims in front or behind the arms changes the wheelbase. A longer wheelbase will provide a smooth feeling setup. A shorter

wheelbase will provide an aggressive steering setup. Additionally, moving the rear arms forward/back will increase/decrease rear traction.

Roll Center: The roll centers of the JRX-S can be easily adjusted by ﬂ ipping the pivot blocks (that came with the kit) and/or by adding equal

shims under the inner and outer pivots. The stock setup utilizes high roll centers without shims. Testing has shown that high roll centers were

the best suited for rubber tire racing. A higher roll center will keep the car from rolling (leaning), making the car react faster and have more

traction. A low roll center allows the car to roll more and react slower, reducing responsiveness in and out of turns. Testing has also shown

that low roll centers are best suited for carpet/foam tire racing. There is a .110” of pin height difference between high and low roll center. The

front and rear can be adjusted unequally to obtain the best overall balance at your track.

Diff Height: Caution! When adjusting the differential heights, rotate the acentrics as to loosen the belts, rotating in the opposite

direction, with the belts installed can severely damage the belts. Diff heights in the JRX-S are also adjustable by rotating the acentrics

that positions them. The diffs can be adjusted from a full low position to a full high position. The low position will allow the car to roll more

and keep the car in a turn longer, increasing on-power steering. The high diff position will give the car a ﬂ atter and more responsive feel. It is

also possible to change the balance of the car quite drastically by offsetting the height of the diffs from front to rear. Testing has shown that

maximum total steering can be obtained by running the front diff low and the rear diff high. For less total steering do the opposite. For less

overall traction run the front and rear diffs in the low position. For more overall traction, do the opposite.

Belt Tension: The acentrics have multiple adjustment positions. Testing has shown that the best setting for the belt tension is to have is 3mm

of vertical play. Simply move the belt up and down with your ﬁ ngers and adjust the diff acentrics to get the desired setting. Be careful to only

insert the screw where the holes in the bulkhead and the acentric are aligned, after setting the tension (per vertical play).

Shock Tower Height: The shock tower heights are vertically adjustable by .140”, providing a low (stock) and a high position. The lower

position is most often run since it offers the best overall balance. Running the tower in the raised position offers different shock and camber

locations to obtain less camber gain and change the shock mounting geometry. This adjustment can be used when raising and lowering the

roll center, to keep the camber links and shock mounting locations consistent from high to low.

Ride Height: This is the height of the chassis in relation to the surface of the track. A higher (stock is 5mm) ride height may be used on

bumpy or slick surfaces, improving overall handling by generating more weight transfer and chassis roll. A lower ride height will make the

car change direction quicker and should be helpful on high traction surfaces such as carpet. Testing has also shown that offsetting the ride

height, front to rear (running the rear ride height ½ mm higher than the front) will increase steering entering a turn.

Over/Under-Drive: The JRX-S is capable of utilizing overdrive (make the front tires turn faster than the rear) or under-drive (make the front

tires turn slower than the rear). Using a 41T pulley in the front of the car will give it overdrive. This will give the car more steering. Using the

41T pulley in the back of the car will give it under-drive. We have found this to be useful when less steering is needed. Under-drive will also

help the car accelerate through bumps better. It is also possible to run a 41T pulley in the front and back, but it is not recommended. *Note:

If the pulleys become mixed up, they can be distinguished by a ridge, located in the ﬂ ange on the 42T pulley. The 41T pulley does not have

any type of marking on the ﬂ ange area.

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