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Hello, fellow racers! My name is Gus. I work on the crew for a local racer, and like all of you, I want my driver to win as often as possible! Now, I must admit something right up front. I'm no racecar expert! In fact, I'm just getting started in my crewin' career. The other guys on the crew call me "The Rookie Wrencher".

Yeah, I've got a lot to learn. But I've been doing a lot of reading and studying on racecar setup, and I've already learned a lot to help make my driver much faster. We've even pulled off a win or two! But sometimes I get stumped and I have questions that I just can't get answered.

So I came up with an idea! What if I pick a technical magazine article, write a review on it for all of you to read, and then throw out some questions to get a good technical discussion going? The end result will hopefully be for all of us to learn something from each other! Then after the discussion tapers off, we'll start all over with a new article.

The first article I'd like to start with is in the inaugural issue of Dick Berggren's Speedway Illustrated magazine from last year. I hope you'll join in on the discussion!

Review #1
"Throwing Your Weight Around"

July 18, 2001

Iíve been told it is better to be informed than ignorant. So when the premiere issue of Speedway Illustrated (vol.1 no.1) arrived, I got comfortable in my recliner and begin reading Doug Goreís article "Throwing Your Weight Around." And wouldnít you know it, it began with a quiz! A test which would reveal my knowledge... or lack thereof.

Which chassis adjustments will change the total amount of weight transferred from the inside pair of tires to the outside pair as a car corners?

This was going to be easy!

a.Changing one or more springs.
b.Changing the air pressure in one or more tires.
c.Changing the stiffness of the anti-roll bar(s).
d.Changing one or more shocks.
e.Changing the diagonal weight distribution, or wedge.
f.Changing the height of the rear roll center by moving the track, or Panhard, bar height.
g.All of the above.

After a few seconds of reflection I decided on my answer - "G." And that was my "final answer!" Then I read on. "If your answer is anything from A to G, you are wrong." No way! I set out reading the rest of the article with a vengeance to prove that my answer was right and Doug Gore was mistaken. Below you will find some notes I took from my reading. Please understand this is what I gleaned from the article and I realize that I might have unintentionally misconstrued Goreís ideas. So I would encourage you to read Goreís article for yourself.

  • The amount of weight transferred from side to side during cornering is determined only by: (1) the carís weight, (2) the height of its center of mass, (3) its wheelbase, and (4) its radial acceleration.
  • As a car goes into a corner it is pulled in two opposing directions. A centrifugal force pulls it toward the wall and a lateral force developed by the carís tires pulls it toward the inside berm.
  • If the rear tires lose grip first the rear end will break loose creating a loose condition. If the front tires run out of grip first the car will push toward the wall. The ideal is for the car to be neutral throughout the turns.
  • What causes weight transfer? A torque created from the fact that the force pulling against the center of mass is higher than the lateral force pulling against the tires. This causes the car to rotate (roll) toward the outside of the turn. The load is transferred from the inside tires to the outer.
    The total lateral load transfer is a reaction to the overturning torque of the centrifugal force, and it will always balance that torque out until all of the weight on the inside tires has been transferred to the outside tires.
  • It is ideal for all four tires to be equally loaded at all times.
    The front and rear tires should be equally loaded as pairs.
  • Because weight is continually being transferred while the car is cornering, braking or accelerating, it is impossible for all four tires to be equally loaded at all times. What to do? Set up the chassis so when the weight is distributed it matches the grip requirements of each pair of tires.
  • The rear tires produce a torque at the carís center of mass that tries to rotate it clockwise. The front tires do just the opposite. The lateral force creates a torque that tries to turn the car counterclockwise. When these two forces are equal they cancel each other out. When they are unequal, the larger torque will cause the car to rotate in its direction. Stronger rear force will cause the car to be tight and if the front tires' torque exceeds that of the rear tires, the car will be loose.
  • While one may not be able to easily change the total amount of side-to-side load transfer in the turns, one can easily change the front-to-rear distribution of where the load transfer occurs. And this is where the items mentioned in answers A though G come into play. At the end of his article Gore shows how each of these affect this distribution. I would like to focus in on one - springs.
  • Changing springs alters the amount of vertical force necessary to deflect the affected tire. Because a stiffer spring is harder to compress, more force is required to push the tire upward through its suspension travel as the chassis rolls in the turn. Therefore, for the sake of argument, if a car has 600 lbs of static weight on the left front and 400 lbs on the right front, and during cornering the spring on the right front allows 200 lbs to transfer from the left front to the right front, this will result in the left front having 400 lbs of weight and the right front having 600 lbs of weight while cornering. This could make the car push due to the front tires not being very equally loaded. But if we change the right front spring to a softer rate, this will cause less weight to transfer to that corner, resulting in a more equally loaded pair of tires on the front, such as 500 lbs on each tire, for example. This more even distribution will result in the front tires sticking better, which would reduce the pushing tendencies, or loosen the car.

    After reading Goreís article I came away with a new understanding of the factors involved in weight transfer. However, it also raised some questions in my mind; questions which I hope may stimulate your thinking and encourage you to respond with your ideas.

    1.Is Gore addressing asphalt or dirt tracks? And do these principles apply equally to both types of tracks?
    2.Is it best to have an equal amount of weight distributed between the left and right side tires during cornering on dirt tracks? Or would more weight on the outside tires create more side bite? Would tacky and dry slick conditions require different distributions?
    3.Does Goreís argument that a stiffer spring causes more weight to shift to that particular tire hold water? I have overheard certain racers at the track say that a softer spring will allow more weight to roll over onto that corner. This seems to contradict Goreís idea that a softer spring actually causes less weight to transfer there. Could both ideas somehow be right?

    To help this Rookie Wrencher out,

    to share your ideas.

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    Gus, The Rookie Wrencher Articles
     March 27, 2002

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