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Discussion Starter #1 (Edited)
Here's a quick "Jim's Chassis & Handling 101" course.

Disclaimer: The facts, figures and numbers used herein are for example and discussion purposes only.
If there are mistakes in math or explanations it's because I'm senile and have forgotten most of this stuff.
The information below is NOT a 'Real World' example of how to set up your chassis.
Your mileage may vary.

There is a LOT of 'chassis math' which I have skipped for this article.
(Mostly because I can't recall it and nobody wants to read big long formulas besides)
The examples are simple ones to help explain chassis adjustment, etc.


The sway bar works 'Cross Frame'. So, we need one on each end of the car.
Here's the 'magic' of sway bar operation:
It essentially adds part of the spring rate from the opposite side to the side bearing the greatest load.
It does this because as the chassis is 'LOADED' during a turn, one lower control arm is compressed and the other is uncompressed by natural forces acting on the chassis (dynamic weight transfer).
So the bar is twisted and the twisting of the sway bar addeds a percentage of the spring rate from the uncompressed side to the compressed side.
It is a 'Dynamic Spring Rate' adjustment device. It only works when the car is in a turn.
(After you think about this for awhile you will understand it)

Let's look at an example. (The numbers are solely for example purposes)
For this example we will ignore the geometry involved with the mounting of the sway bar ends ie; how close or how far out on the control arms the bar is anchored, the dynamic weight transfer and the spring compression.
For this example we will use just the spring rate and sway bar strength expressed as a percentage.
For example, let's say your Prelude has springs rated at 400 lbs per inch.
This means that for every 400 lbs applied to the spring it will compress 1 inch. We will also assume the spring rate is 'linear' which means it will compress equally for every 400 lbs applied to it.
Let's say the sway bar can transfer 15% from side to side for example purposes.

Now let's put our car in a high speed turn to the right.
In the RIGHT TURN, the LEFT SPRING is compressed and the RIGHT SPRING is uncompressed.
What we REALLY NEED is MORE spring rate on the LEFT FRONT in this high speed right turn.
The left spring is compressed,the right spring uncompressed, the chassis dynamically loaded and we're sailing thru the corner wishing we had a stronger spring on that LEFT FRONT.
Ok, let's take it back to the garage and install a SWAY BAR.
That will tie the LEFT FRONT suspension to the RIghT FRONT suspension with a spring steel bar.
Hmmmm, what will THAT do?
Let's try it out in that same hard RIGHT turn.
Now most of the same thing happens again.
The LEFT FRONT spring compresses and the RIGHT FRONT uncompresses.
Except we have tied the two together.
The sway bar twist and trys to COMPRESS the RIGHT FRONT spring.
Yes! That's what you wanted. When the sway bar twist and tries to compress the RIGHT spring, part of that SPRING RATE is added to the LEFT FRONT. Viola!! A Dynamic Spring Rate adjustment has taken place just when we wanted it, in the turn.

In this simple example we had two 400 Pound Per Inch springs on the front of the car.
We said the sway bar could transfer 15% of the rate from side to side.
So now as we are in the hard right turn, the spring rate on the LEFT
So here's what we have now with the sway bar:

400 * 15% = 60 lbs.per inch.

400 + 60 = 460 Lbs.per inch.

Our LEFT FRONT 400 lbs.per inch spring now thinks it is a 460 lbs per inch spring.
A higher spring rate on the LEFT FRONT was just what we needed to sail through the hard RIGHT TURN!
The sway bar works both right and left and the added bonus is we can run softer springs and handle much better with the sway bar than without.
This is a BACIC example of how the sway bar works.
Once you understand the sway bar you'll know more about chassis setup than about 95% of the prople you encounter at the track.

Note: Once you start 'PRELOADING" the chassis you will want to change to an adjustable sway bar links.The reason is you may not want to preload the sway bar. Or you may want to preload the sway bar only.
Adjustable links give you the option to do either. Subject for another article.


***The NUMBERS used in the illustrations are for explanation purposes ONLY!!***

Stiffer springs in rear will loosen up the rear of the car.
Spring rate can be 'adjusted' by placing spring rubbers between the coils.
The effect is to take part of the spring away and make the spring 'stiffer'.

The front springs are always heavier on a front engine car because:

1) The front of the car has a greater 'weight distribution' because the engine is in the front.
'Weight distribution' is expressed as a percentage of weight on the front vs. the weight on the rear in a 'STATIC' condition. Static just means the car is sitting still and not experiencing any cornering loads.
60/40 weight distribution would be 60% of the cars total weight sitting on the front wheels and 40% of the total weight sitting on the rear wheels.
"Ideal" weight distribution is 50/50 but not achieved very ofter due to design, construction and monetary concerns.
Example: C5 Corvettes are really close to 50/50 Weight Distribution. The transmission is mounted in the rear of the car to help achieve the 50/50 spec.

2) Weight transfers from the rear to the front in all braking manuevers so the front springs have to be stiffer to minimize 'DIVE'.
Dive is where weight transfers from the rear to the front when the brakes are applied while the car is moving.

"Cross Weight" or side to side weight (BIAS) is having more static weight on one side of the car than the other.

Let's use the 60/40 static weight as an example.
By adjusting the chassis (PRELOADING) you could have 35/25 'Cross Weight on the front. That means that there is 10% more weight on the left front than the right front but still the total weight is 60% on the front.

The extra weight on the left front has to come from somewhere and that somewhere is mostly the RIGHT REAR. Remember the "X".

Now the rear will also have a cross weight component because the chassis is 'PRELOADED".
Since the front cross weight has been changed, the rear will be changed aslo.
In practice, the rear will be the ADJUSTING POINT to accomplish the change wanted on the front of the car. Remember the chassis is like a big "X".
Because the left front has been 'preloaded' the weight on the rear will be
changed. Note: This change WILL INITIATE at the RIGHT REAR of the car.
That's the place to go to make a change to the LEFT FRONT. The Chassis works like an "X".
40% of the total weight WAS on the rear.
40% will still be on the rear but it is now 'redistributed' thusly:
25/15. 25% on the RIGHT REAR and 15% on the LEFT REAR.

So the total Front to Rear weight bias is still 60% on the front and 40% on the rear, the side to side or cross weight is now redistributed.

Front cross weight = 35% / 25% = 60%
Rear cross weight = 25% / 15% = 40%

Left side weight = 35% + 25% = 60%
Right side weight = 25% + 15 % = 40%

Let's now relate the percentages to the 'real world'.

To do this we need to know the total weight of the car.
For an example we'll use a number of 2500 lbs. which is probably close to our Preludes weight.

So we have a car that weighs 2500 lbs. sitting still with full fuel, oil and driver.

With a 60/40 weight distribution the front and rear weight will be:
Front Weight: 60% x 2500 = 1500 lbs.
Rear Weight: 40% x 2500 = 1000 lbs.

Here's the cross weight distribution:

Front: 35/25 Cross weight
Front Left: 2500 x 35% = 875 lbs.
Front Right: 2500 x 25% = 625 lbs.

Rear: 25/15 Cross weight
Rear Left: 2500 x 25% = 625 lbs.
Rear Right: 2500 x 15% = 375 lbs.

***The NUMBERS used in the illustrations are for explanation purposes ONLY!!***

From these number you can see the weight of the car didn't change but the distribution of the weight has changed drastically.

If we put a set of SCALES under each wheel, each scale would read the values in the example above.

The only way to know exactly the affect an adjustment has made to the static weight distribution is to measure the static weight at wach wheel using wheel scales.

It should now be obvious this car will 'handle' or turn better in one direction than the other.
Can you 'see' which way this car is 'Set Up' to handle best?

In AUtoCross, the car must be able to turn right and left equally.
Therefore CROSS WEIGHT should be 50/50 side to side.
That leaves working front to back with springs and sway bar size.

However if there are predominately more left (or right turns) at the course you typically run, the car 'could' be adjusted to transverse the turns in that direction better and achieve lower lap times.

***The NUMBERS used in the illustrations are for explanation purposes ONLY!!***

Dynamic weight distribution is the distribution of weight as the car is turning or braking.
To calculate dynamic weight the 'ROLL CENTER" and 'CENTER of GRAVITY" of the vehicle must be known along with the track conditions (banking), speed the car is expected to corner.
This is a subject for "Handling 110".


Shocks are selected to match the spring rates.Stiffer spring= stiffer shock.
Shocks affect the handling of the car less than any other suspension component. Their function 'in life' is to dampen spring 'REBOUND' and harmonics.
Rebound is the spring trying to return to it's unloaded static position after a chassis 'excursion'. Spring harmonics is the 'ringing' or vibration of the spring when it is affected by an external force.
Shocks are selected to match the condition of the track or running
surface and the installed spring weights.

Make small changes. An INCH anywhere is a LOT of change.
Keep a diary of what you had before the change, the change you made and the results of the change.
If you don't you'll get totally lost as to what worked for you (your driving style) and your car.

The above is a very BASIC explanation of chassis setup.
Understanding how the chassis works comes from thinking about it. The understanding will come, give it time.
If you understand 50% of the above, you will know more about chassis setup than 99.9% of the people you encounter at the track.

Hope this gives you a basic understand of how the chassis works..

1 Posts
Great Article

That was a great article. I read somewhere that for every 1.0 lb of weight you add unspringed (such as new wheels) it equals 1.4lb of springed weight. Is that true? Do you know anything about that?

Joey Molina

1,877 Posts
That was a great article. I read somewhere that for every 1.0 lb of weight you add unspringed (such as new wheels) it equals 1.4lb of springed weight. Is that true? Do you know anything about that?

Joey Molina
I know that replying to this 7 years later is all but pointless, but I've heard multiple figures for that number. I usually hear it's something like a 1 to ten ratio in terms of weight, but in fact that is a false myth. There isn't a real ratio. Yes, removing one is in someways better than removing the other, but it doesn't equate to removing more weight in another area. The best place to remove weight depends entirely on your application. Although, you never really want to add weight, you'd be better off most times just modifying spring rates.
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