A Note From Bobby G.-Each month supermodified driver Bob Bogwicz will be contributing a column dealing with the technical aspects of the supermodified division. He is also a monthly guest on Wailing with Wing Side Up and you will be able to hear it before you read it. Please feel free to comment or ask Bob further questions either here or when you Hit the Wailbag. If there’s anything in particular that you would like to hear him talk about on the show, we encourage you to let us know.
Wing Side Up Tech Talk with The Bogwan 3/19/010
by Bob Bogwicz
On the March 1st webcast of Wailing with Wing Side Up, I spoke to you about weight and how it affects a race car. We touched upon the type of weight that most oval track racing fans are familiar with: total weight and left side weight.
Total weight is, of course the weight of the entire race car. Every sanctioning body in the world has a minimum weight that race teams need to adhere to in order to not have a competitive advantage, nor be unsafe.
Left side weight is the weight on the two left side tires in relation to the overall weight of a car. In general, the more left side weight, the faster a race car can go in the turns. Thus, sanctioning bodies will place a maximum left side weight on the competitors in order to level the playing field.
Usually, an infraction of the either the left side/total weight rule is worthy of a disqualification and egg on ones face!
There are additional types of weight that a race team must be concerned with (and are not directly controlled by the rule book) in order for them to be competitive. These weights are call “un-sprung” and “sprung” weight.
“Un-spung” weight is the mass of the race car that is NOT suspended by the springs. Components that are considered un-sprung weight are the axles, tires, wheels, brake rotors and calipers and the rear end center section. Since the forces that act on, and are generated by these masses do not go through the action of the springs, the result of these forces and actions cannot be “fine tuned” with a spring change or chassis adjustment. As far as the chassis is concerned, it’s almost dead weight. The best a race team can do is to choose components that are as light as possible but still meet the rules (i.e., a team cannot use aluminum to save weight when the rules require steel).
The sprung weight of a race car is the rest of the car that is not un-sprung weight and, as one can guess, this mass is suspended by the springs and shocks. Its action around the track can be controlled with any number of chassis adjustments to ultimately optimize the grip of the tires. A race team has plenty of leeway in where they place the sprung weight of a car. Obviously, some components can only go in certain places but many others are at the discretion of the car builder such as oil and fuel tank placement. “Low, light and left” is the rule of thumb.
There is a subset of sprung and un-sprung weight called rotating weight. Examples of rotating weight are the wheel/tire combination, the brake rotor and the drive-shaft. It takes additional horsepower to overcome inertia to get a component to rotate (let alone propel it down the track). It also takes energy (like braking) to slow a rotating part down.
This type of acceleration/deceleration will occur at least twice a lap, so controlling the weight of a component that rotates is vital. Again, lighter is better as long as it is within the rules. A race team will want to run aluminum wheels, lightened brake rotors and lightened drive-shaft components.
I recently purchased a set of brake rotors that weigh three pounds less per rotor than what I ran last season. Twelve pounds of rotating (and un-sprung!) weight removed from a race car is like removing fifty pounds of dead weight (like the driver going from 200 pounds to 150 pounds. It will make a measurable difference in how the car handles.
Sprung and un-sprung weight: what a concept!
I count just a little over 30 days until we hit the track at Oswego. Thank goodness burnt methanol is a legal drug!
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Great article on the benefits of reducing your your sprung and un-sprung weight.