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JR Motorsports Technical Information - Chassis

Shock Dyno
Shock Tech
Understanding your Racecar


Shock Dyno
In-House Facility
Shocks are the “BRAINS” of your Suspension.

Racing has become more competitive every year! Maintaining your shocks is crucial for consistent performance race after race.

“Winning Races and Championships”

You ask “Why should I spend the money to have shocks tested?” Great Question, Here’s Why

• Regular maintenance on your shocks is vital. They are the most important performance-part of your suspension.

• Shocks are made with a cylinder, oil, shaft, seals, and valves. Much the same as an engine. For ultimate performance they both need to be maintained correctly and consistently. If not, they will wear out quickly.

• Imagine what can happen to a suspension item that is, caked with dirt, hit with rocks, moved at a rate of 5” to 13” per second at different angles, and mounted by an extremely hot brake rotor. After time, the rate will vary. Your racecars’ handling will change.

• Winning racers never run an engine for a full season without changing the oil and following a specific engine maintenance schedule for the season.

• Shocks should be dyno-tested when they are new, and then checked at least every 30 racing hours. This data will give you valuable handling information to compare.

• All major shock manufacturers do their best to give you a great product, along with an affordable price. To offer an affordably priced product, all parts need to be assembly-line manufactured. Keeping tolerances and cost in line are very important, however it allows for a standard deviation of a plus or minus valve variation. Each company has tolerance variation. This tolerance can be different on compression, or extension (rebound), or the rate overall.





Example Shock Rates
Compare these 2 shock set-ups with a 10% variation or change in rate.
• 4 valve shock         90#
• 5 valve shock       130#
• 6 valve Shock      170#
Rated at 5" of movement per
second for example.
Set up #1
5LF # 117    (-10%)
6RF # 187   (+10%)
4LR # 99     (+10%)
4RR # 81     (-10%)
Set up #2
5LF # 143   (+10%)
6RF # 153   (-10%)
4LR # 99     (-10%)
4RR # 81    (+10%)
Set up #1

LF to RF difference of 70#
LR Heavier 18#

Set up #2
LF to RF difference of 10#
LR Softer 18#

You’re a winning racer, you need to contact us today to design a specific maintenance schedule for your shocks.
Shock Tech
Shocks- What you need to know!
Timing is Everything
It’s important to understand what a shocks main purpose is. Shocks are a controlled suspension timing devise. They control what a spring does by dampening compression and controlling rebound, (the different rates of valving allow shocks to control
when the action happens), thus the length of time it takes for
each of the movements to occur.

Understanding today’s shock technology has proved to be the difference between winning or finishing second. Having the right shocks on your racecar is the suspension fine-tuning you need
for consistently winning races and championships.

Problem Solving
Will changing shocks solve a bad handling problem? NO!

Shocks only fine-tune your race car for improved handling performance. Changing a shock can cover up the real handing problem. When making a shock change, remember: What is the best compromise? A shock change will only help after you have removed the other variables such as, tire stagger, wheel spacers or offset, weight ballast, and the correct spring combination.

Utilizing our track diagram on pages 178 & 179 will help you pinpoint what change would give you to optimum performance.

What Shock Changes Affect.
Compression Rate - Front, has more affect on deceleration, or corner entry (B,C,D of Track Diagram).
Compression Rate - Rear, has more affect on acceleration, or corner exit (E,F,G of track diagram).
Rebound Rate - Front, has more affect on acceleration, or corner exit (E,F,G of track diagram).
Rebound Rate - Rear, has more affect on deceleration, or corner entry (B,C,D of Track Diagram).

Example Shock Change:
More traction is needed on corner exit (E,F,G of track diagram).

What change should you make?
Decreasing the rebound rate on the right front shock will increase the speed of weight transfer to the left rear tire.
Decreasing the compression rate on the left rear shock will also increase the speed of weight transfer to the left rear tire.

Weekly Shock Maintenance
It’s important to take the shocks off your race car every week to check for damage. Make sure the shaft isn’t bent. Check the shock body for dents and dings. This is extremely important on a mono tube shock. Look for tire rub marks (very important on a twin tube shock). Check the rod ends for any type of bind. Push the shock in and out to make sure it doesn’t have any slack in it. Look the shock over closely for any oil leaks around the seal or any signs of the gas bag bursting. If there is any signs of damage the shock needs to be rebuilt or replaced. If the shock is a rebuildable style it needs to be sent in for repair. If not it needs to be replaced. If any of this occurs, or you have any questions give our experienced technical staff a call.

Technical Support.
Our technical staff here at Karl Performance will recommend the right shock package for your specific type of racing. We will help you develop your standard shock base-line, along with other options you’ll need for each type of race condition. Our goal is to help you win more races and championships!


Understanding your Racecar  

what and where a handling problem is, and
where is actually starts is very important. In resolving a handling problem, it is imperative to begin at the start/finish line, follow the racecar through corner entry, mid corner apex, corner exit, and back to the start/finish line. Not taking the time to thoroughly diagnose the full racetrack will be a big mistake. An
adjustment will be made for one part of the racetrack, in turn, creating a larger problem somewhere else. Consistent laps will
be difficult to make, resulting in a slower lap time average.

Winning races and championships are not accidental. It’s done by making fast, but smooth consistent laps. Your racecar will be faster, more consistent, and easier on equipment, when the chassis set up allows the racecar to run freely through the
complete corner. Constantly loading and unloading the
suspension radically will work just the opposite and the racecar will become very difficult to drive.

Diagram the racetrack to pin point where the handling problems are and how large the problem. Use a highly visible mark on your steering wheel to help the crew and driver recognize where the front wheels are. Also marking left side tires can help
determine wheel spin and when it occurs. These are great driver tools to help with diagnosing where a handling problem is and exactly when it occurs.

Point to Remember
, the only thing your racecar has in common with the racetrack is the tire patch it is riding on. You want to use the whole tire, not just three of them or 75% of the four. Lap times will be the best with 100% all four tires in contact with the track, keeping the car straight, and using smooth throttle and brake applications. This applies to both dirt and asphalt races. If a handling problem occurs one of the four tires is being overloaded. Tire temperatures, air pressure gains, and shock travel will guide you in the area of a handling problem. This information needs to be obtained as soon as possible, or it will not be as valuable.

Communication between the driver and crew is very important. Understanding what the driver’s responses are in
relationship to what the racecar actually is doing becomes very crucial. A good driver will compensate for one handling problem, but possibly create a different one. You adjust the car, only in the wrong area needed for the most gain in performance. Example: The driver says the car is very loose off the corner, the crew say it’s tight into the corner. They are both right. The driver is shaking the car loose with the brakes, compensates for the tight corner entry. If you tighten the car as the driver says the problem will be worse, because you fixed the wrong problem. Answer these questions. Is the car loose or tight when the driver applies the brakes or the throttle? What would the car do if the car rolls into the corner freely off the throttle and before the brakes are applied? This answer is key, will it push or will it turn? Now you know where to start.

Use this track to pin point where the handling problems are and how large the problem is.


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