What you will know if you do a Weight Transfer Worksheet....

 
 

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You'll be able to do the following:

Assess the "ride stiffness" (spring frequency) of your car

Spring frequency is the frequency of the body moving up and down on the springs, expressed as c.p.m. (cycles per minute).  You can calculate it in the WTW and, where applicable, find it directly with the Racing Car Technology "bounce" test.

Spring frequency is directly comparable between all race and road performance cars.  You'll know how hard or soft the ride is on your car.  You'll know what opportunity you have to increase ride stiffness (often required in a performance set up to give the car sufficient "support" - not dive, roll and pitch excessively, and to increase "response" for the driver).   Or what set up changes are needed if you want to reduce ride stiffness. 

Unless there are pressing reasons to the contrary, you will want the spring frequency front vs  rear to be within 5%-15%.  This will generally be achievable for rear wheel drive cars - rear a bit softer than the front.  Not so for a race set up front wheel drive, where rear may be heaps stiffer than the front.

You will understand the relationship between spring frequency and suspension travel.  For instance, if your racing sedan or sports car has 120 cpm front suspension frequency, this implies a bump travel requirement of 2.5" (at the wheel).  If you decided to lower the spring frequency to 100 cpm, bump travel requirement is then 3.5".     

Assess the "roll stiffness" of your car.

The stiffness in roll is conveniently expressed as degrees of roll per unit of lateral acceleration (degrees/g).  The WTW calculates weight transfer for a one g cornering force.  So you can assess roll stiffness from the "roll angle of the chassis" calculation (shown at the bottom RH column of the WTW).

You will be able to calculate roll stiffness for your anti-roll bars, and look at their contribution to total roll stiffness.  For the types of cars we have currently racing, it is pretty clear that front anti-roll bars should contribute between 45% and 55% of total front roll stiffness.  Rear roll bars, around 30% for live rear axle.  IRS, can be more.

Understand Geometric vs Elastic Weight Transfer.

For definitions of geometric and elastic wt see  Origins of Weight Transfer Concepts, about two thirds down the page. 

The WTW is a simple tool to calculate weight transfers using "moments" (force x lever arm), and then use roll resistance calcs to distribute that weight transfer front to rear.  See Origins of Weight Transfer Concepts,
"How Does the WTW Work?" about one third down the page.

It's just that roll resistance is our number one tuning tool for suspension set up, and therefore demands our attention. 

The limitations of the WTW are that we need to assess separately issues with corner entry and corner exit.

Know how to try different set up options in the WTW.

The WTW allows you to experiment with very important set up changes and immediately see the effects.

Use either the "bounce" test or a given spring rate to determine  spring frequency. Work backwards from a given spring frequency to a required required spring. 

Look at what springs have been on the car, and any combination of front and rear springs you might like to try.  Or enter your preferred spring frequency front and rear and see the affect on the car.  You can come up with a preferred softer set up, and preferred harder set up. 

Select anti-roll bars to suit your chosen springs.  Choosing roll stiffness is relatively straight forward for any given ride stiffness.  You will be able to balance the car by looking at the  "Magic Number", and assess roll stiffness (degrees per g) by looking at the calculated chassis roll angle.

 

 

 

  

  

 


Topic ONE here

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To see exactly how roll stiffness influences the balance of the car see:
"Origins of Weight Transfer Concepts"

 

 

 

 

The "bicycle model" devised by Chevy R&D people in the 60's does describe actual car behavior.  It is the exact model used 25 years later to allow the calculations required for Stability Control Systems. 

 

 

If you are too stiff, the tyres will wear excessively - excessive "graining", a treaded tyre will be torn away at the main tread groove.  The car will be nervous.  If ride stiffness is just right the tyres will look great, and the driver will give feedback about how good the car is.  If you are too soft, the car will be slow, and you may not be able to see why.  "Just right" will be different for different tyres.


Topic TWO here


Topic THREE here


Topic FOUR here

Topic FIVE here