QuestionQUESTION: I know about the unsprung weight and how at wheel needs to act as a suspension as much as possible by the wheel absorbing bumbs itself. But i watched the 24 Hours of LeMans this year and i notice that the wheels on the cars are pretty large and the tire has less sidewall. Why a larger wheel for more unsprung weight? A smaller wheel obviously weighs less. but a larger wheel? isnt that making it lose more handle?
ANSWER: I normally only take questions from race car teams about their technical problems, but this one is too good to pass up.
First the tire sidewall. Go out in your regular street car and drive (safely) through a few corners at higher than normal speed. You will notice that the car leans excessively, and as you initiate the turn, an uncomfortable swaying will take place toward the outside, and generally the car will feel a bit unstable. It is !
Race car suspensions have no rubber bushings anywhere, the wheels are firmly connected to the road, there is no swaying or excess movement. Also the springs and shock absorbers are much stiffer than road springs on a passenger car. By using tires with short, stiff sidewalls, called high aspect ratio, more lateral stiffness is added to the mix. This entirely removes that uncomfortable and unstable swaying tendency.
The larger tires you see (with the short sidewalls) are also slick, no tread (unless it's raining). This gives the tire a larger contact patch, more area on the ground to resist sliding , spinning and losing traction. Thus the car can negotiate corners at higher speeds, and accelerate faster than would be posible with regular tires. Some race tires get as wide as 16 inches on a 15" rim. Huge looking things.
The manufacturers tackle the unsprung weight problem by making the tread area fairly thin. In an endurance race such as LeMans, tires usually don't last more than two to four hours before they're worn out, so they're actually quite light.
Race car builders tackle the unsprung weight issue by using lightweight materials for the suspension arms, hubs, brake parts, and related stuff. Wheels of course, are either aluminum or perhaps magnesium. Cost is no object. And most have rocker arm suspensions anyway so the springs and shocks are mounted inboard in the center of the car, and operated by pushrods and rocker arms. The cars you see compepting in LeMans andthe American LeMans series cost in the range of $1 million or more to build, tires for a weekend of racing, $10,000.00 Fuel these days is $8.00 a gallon or more. So you can see that it gets expensive, but the pro teams have sponsors with very deep pockets.
I hope this clears up the question for you, If you really like racing, go to < www.scca.org > and look around for a district in your area, join in and go to the races. Within a couple of weeks you could be on a corner as a flag person, and part of the action !!
Good Luck
Dan Liddy
Sarasota, Florida
---------- FOLLOW-UP ----------
QUESTION: So with rocker arm suspensions it becomes sprung weight? and sorry i'm not a race team chief or something lol. i'm just a 17 year old boy who wants to get into racing but most likely will never get a chance to.
AnswerOK try to find some pictures of Formula cars or Indy type cars.. Open wheel racers. You will see that instead of a verticle spring and shock arrangement there is a "pushrod" that runs from the bottom outside of the suspension at the wheel, to the inside of the car. There they have mounted a rocker arm that pushes on a spring/shock combination that is mounted along the center of the car.
It's hard to describe but if you can find some pix it becomes clear. The spring and shock are sprung weight, so only the pushrod and the rest of the stuff are unsprung, but since there is no need to mount springs and shocks at or near the wheel, the weight can be moved to the center of the car. Try doing a google on 'rocker arm suspension', and I'll see what I can find too.
Now then. If you want to get involved in racing, the Sports Car Club of America is one very good place to start. Quite a few pro american sports car racers came up through SCCA including the announcer Dorsey Schrader, and Tommy Kendall, there are many others as well. The web address I gave you before will give you a start. it's < www.scca.org> Once you get that open, you'll be able to look around for the region in your area. I think the annual dues are $75.00 per year. Like I said, you CAN get involved within the next few weeks, depending on your budget and where you are, there's a lot of activity to be had. Many people start thinking they want to become drivers, and end up deciding that the excitement of flagging or emergency crew or fire crew is enough for them. Many others become drivers and work corners or something on weekends when they aren't racing. Another advantage is that you will start to make friends with racers, some of which can steer you in the right directions for successful careers related to racing.
As an example , I went to driver school 20-odd years ago with a nice man named Davis- - un-assuming guy, average looking, drove a Porsche. Later on I learned that his father founded the Wynn Dixie grocery chain. Literally worth hundreds of millions. People like that can HELP you! Mr. Davis sponsored Mark Martin in NASCAR for many years !
So if you really want to be around it , SCCA is a place to start, $75 is a big chunk out of a weekly pay check, but it only happens once a year, and you'll be glad you did it , I promise !!
Dan Liddy
PS. Here's one website I found on rocker suspension, not what I described but a start.<< http://www.jblmotor.com/JBLchassis.html>>
