Polar Moment What it is and How to Use it to Setup Your Race Car. We get many questions regarding adding weight when and where. In this article we are going to focus on finding and using polar moment to discover your minimum weight balance. This information is critical to having a well-balanced race car throughout an entire race. We have hopefully laid this information out for you in an easy to understand and apply manner so you can take it and start using it immediately. Polar Moment The dictionary definition is Center of all forces. The racing definition is Where weight & balance cross front to back, left to right at center of gravity height. Most race cars have a center of gravity height between 16 20 inches. This includes Stock Car, Modified, Late Model, and Sprint Car etc - Heavier cars like a hobby stock are closer to 20 inches because of heavier components like cast iron heads, intake etc - The lowest you will ever get your center of gravity is around 16 inches. You can only get this low if you are running aluminum heads, intake, dry sump etc - For every 1 inch you lower your center of gravity your race car will transfer 3% less weight. - When you have a lower center of gravity you won t need to run as much left side or rear weight. **NOTE** Running a low center of gravity race car on dirt can be a disadvantage because it won t transfer enough weight to get the side and rear bite the car needs.
Finding Polar Moment The first step you need to take is to find out exactly where the polar moment is in your race car. This process is actually much easier than you think 1) Measure the length of your race car. 2) If your car is 52% rear heavy, find where 52% of the length is (from the front). 3) Measure the width of your race car. 4) If your car is 52% left side heavy, measure 52% of the width (from the right side). 5) Where these 2 lines cross at center of gravity height is where your race cars polar moment is located. 6) This is where your race car thinks its center is. Yes, it s not actually the center of the car That s it; like I said before it s not as hard as you originally thought is it? Here is an illustration that shows you what we covered above.
How to Use Polar Moment to Your Advantage To explain how to use polar moment to your advantage we are going to use a few illustrations and list some important points after each one. This race car weighs 2800lbs with 700lbs on each wheel. This makes this race car what we call a 50/50 car (50% of the weight on left & right as well as 50% of the weight on the front and rear). - The farther you move weight away from polar moment the more weight it will give you (Left or Rear) - Add 200lbs (to make 3000lb minimum weight) at polar moment, the car gains 50lbs at each wheel and remains 50/50 - Add 200lbs in rear by fuel cell and car only gains rear weight - Add 200lbs on the left side near driver and car only gains left weight
- Add 200lbs to the rear and left sides, toward the left rear tire and you gain left and rear weight - With a 50/50 race car you want to go to the left and rear sides to gain on both. To meet minimum track weight you must add 200lbs to this race car - When adding only 200lbs the approximate maximum percentages you can gain are 53% left & 52% rear - In order to gain left and rear percentages you must move the weight away from polar moment towards the left rear tire Important Points about Rear Percentages - Asphalt Race Car - There is no such thing as too much left side weight
- Dirt Race Car Over 55% left side weight gives you NO major advantage. 55% should be your maximum left side percentage. - Rear Percentages 50% - 52% Asphalt Car 55% - 57% Dirt Car - When running alcohol (it burns twice as fast as racing fuel) you will want to start with more rear percentage knowing you will lose some of that weight as the fuel is used up. Now let s compare this same scenario using a lighter car that weighs a total of 400lbs This is a 400lbs car with 100lbs on each wheel. - This is a 50/50 car just as in illustration above - Must weigh 3000lbs - Need to add 2600lbs to make minimum track weight
- Adding 2600lbs at polar moment adds 650lbs on each wheel and keeps this car 50/50 - Weight added at polar moment does not affect springs, shocks and does not promote a lot of weight transfer. - This car does not know it has the additional weight - Race Cars do not know how much they weigh it just knows how it will react. - This race car thinks it still weighs 400lbs - When building a race car, build it as light as possible then add the weight at polar moment - Race car will think its lighter and react like a lighter race car.
- To get rear or left side weight you don t need to move weight all the way to rear or left side. - The weight only needs to move a little off of polar moment to get the effect. - The more weight you need to add the shorter the distance you need to move it from polar moment to gain your left and/or rear percentage - Moving the weight a short distance from polar moment helps avoid pendulum weight transfer causing a lose condition and aids in keeping your tire temperatures equal - When moving the weight you are actually moving the polar moment of your race car. Move the weight in the direction you want the race car polar moment to be.
- This lighter (to begin with) car requires less spring (than the 2800lbs car) even though they weigh the same when weight is added. - Lighter race cars require weight to be in the middle of the car advantage - Heavier race cars require weight to be at the outer extremities of the car - disadvantage Final Points about Polar Moment 1) There is no better combination for changing direction or going forward fast than equally loaded tires. - You want your tires equally loaded after the weight transfers and after applying the brakes. - You need to start with left rear weight so when you turn left the polar moment moves towards the center of the race car (centrifugal force) and plants in the middle of the car, planting all tires equally so you can corner at the highest rate of speed possible - Weight alongside the driver is the best place to add weight AFTER achieving minimum weight and balance. - Weight added in this area will keep the tire temperatures pretty close to the same throughout the entire race. - The less slinging or sliding your race car does the longer it will go fast. 2) A good polar moment car is: - Much lighter than the rules require - Has the extra weight needed at polar moment or as close as possible - The best place to add weight if you just need to carry it (meeting minimum requirement) is at polar moment - Weight can be taken away or added without changing springs. The only thing that will change is the horsepower to weight ratio. - A lighter car will always go the fastest however a heavier race car with a good polar moment and balance will go almost as fast.
Now that you have been educated on polar moment you should go out to the shop and spend some time: - Figuring out where your polar moment currently is - Deciding what you need to do to lighten up your race car as much as possible - Adding in the weight you need to make the minimum tack requirement at polar moment and then adjusting it to get the left side and rear weight percentages you want. - Go out race your car and adjust as needed. - WIN some races!! Now that you have read this article I m sure you are thinking where can I go to find more of this kind of information? Well, as luck would have it we have started a Racers Edge Racing Club where you can find all kinds of race car setup information and more! It is a member s only racing club so you only gain access by joining. It is and will continue to be a top resource for you in setting up your race car. We have a ton of great race car setup information already there and we are adding more each month! Check it out and join an elite group of racers that make up the Racers Edge Racing Club. We are currently running a Limited Time Special 30 Day FREE Trial Get signed up here - http://www.racersedgebooks.com/racing-club-30-day-free-trial.html Do the work off the track so you are fast on the track Jon Roetman Author of The Racers Edge Race Car Setup Books www.racersedgebooks.com jon@racersedgebooks.com Did you like this article? If so, join one or all of our pages below so you can stay up-to-date on all the new Racers Edge Race Car Tech Articles coming out. We publish them every 2 weeks
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