Myth of the week [Archive] - Classic Cougar Forums

: Myth of the week



cougarguy
November 12th, 2002, 09:29 AM
okay here is this weeks myth or truth. Weight distribution in a car should be 50/50.... true or false?

Gulf00
November 12th, 2002, 10:14 AM
True,
In an ideal situation the weight is devided equally over all four wheels so all wheels experience the same force on the ground, causing the tires to compress equally, resulting in an equal maximum drag coŽfficient for all tires. This causes the car to respond predictable in accellerating, braking and cornering, which is preferred.

Cheers!
Matthijs

cougarguy
November 12th, 2002, 10:43 AM
anyone else want to coment?

bowl
November 12th, 2002, 12:37 PM
i like em on the loose side

LiLWrink
November 12th, 2002, 12:39 PM
Weight distrubution depends upon the application, Same as was stated in the other thread, ex,drag raceing vs. circle track, ad the physics applied forces such as banking and it gets complex quickly.
Go easy on us bro, I'm no brain...:1poke:
Shane

cougarguy
November 12th, 2002, 01:03 PM
Okay buddy i will do an easier one next week. any other coments comon people dont be afraid to voice what ya think its for fun and learning whats your opinion.

72cat
November 12th, 2002, 01:05 PM
Maybe with me out the car the weight is 50/50, but once I am in, the weight is 75/25.

kent
November 12th, 2002, 01:11 PM
i want to know what to stop the water leak in a conv.header
its go under the trim and running down the inside of window.

texrep
November 12th, 2002, 01:22 PM
50/50 would be the ideal but in oour applicatiion its not very realistic. You would have tp have the motor sitting in the car with you .ala Pantera. agree that different apps require different loading of the tires. Most american cars are front heavy hence the large springs in the front and not so heavy springs on the back. You could always put a couple sacks of cement in the truck to help even hings out......my .02........ oh to answer the question...... False

Don

cougarguy
November 12th, 2002, 01:27 PM
okay thats 2 for against and one for the plus side and three nothing for or against?

greggieatthebat
November 12th, 2002, 02:24 PM
I say False to the blanket statement.
I agree with LilWrink that every application is different, and with Matthijs re: reducing drag (i.e. minimizing the weight at each wheel).
50/50 is ideal for the Shelby test (0mph-100mph-0mph) where the only measures are acceleration and braking.
For a drag-race car (i.e. pure acceleration) the ideal weight distribution is to be biased to the rear (i.e. more weight on the rear than on the front).
Just having a 50/50 setup is not enough for all cars; for example, roadrace cars go for 50/50 front to rear as well as 50/50 along the diagonals
(front-driver + rear-passenger = front-passenger + rear-driver)
Also, the suspension spring rates/shocks/sway bars/tires/etc have far more influence on the car's behavior than the weight distribution.

swamper
November 12th, 2002, 02:39 PM
I think most of this has already been said but for normal street use 50/50 is great as well as squiggly road. In a circle track 60/40 front to back maybe better plus 55/45 to bottom side of track. This to keep center of gravity lower and still swing rear.

Extreemly specific atipical use may require very odd distribution for optimal preformence in that application. I'm calling Myth.

bla bla.

cougarguy
November 12th, 2002, 02:49 PM
Aww its looking like the myths are running away with it were are the proponents?

Gulf00
November 12th, 2002, 05:24 PM
Oops yeah, I forgot to add my answer was based on cars that do accellerate, brake and steer left AND right. I remember an interview with a formula 1 driver who mentioned that they wanted the weight to be centralized...

Cheers!
Matthijs

cougarguy
November 13th, 2002, 04:29 PM
this is the truth about 50/50 as posted.
Here is a myth almost universally accepted by all of us in the automotive fraternity: the ideal weight distribution for a car is 50/50. WRONG!!! There is only one scenario for which this would be true: a car that steered equally with all four wheels, with equal sized tires, equal wheel rates, and equally-distributed four-wheel-drive, that is cornering at a constant speed. Unless your car fits this description (and Iím pretty sure it doesnít), then you should wish for a lot better weight distribution than 50/50. In general, the further rearward your weight bias the better for any rear-wheel-drive car. This will help evenly distribute weight under braking, and will help add as much downward force as possible to the rear under acceleration. Also, cars tend to understeer more at low speeds (and most autocrosses are low-speed events), and a rearward weight bias tends to reduce this effect. By the way, the more power our car has and/or the slower the corner out of which we are accelerating, the more we need the rearward bias. There are rules which limit the desirability of rearward weight distribution: 1) overall lightness is more desirable than a good distribution of weight, so we never add weight to achieve a good distribution; 2) we ideally want to have low polar moments in the car, so we really want the carís mass to be as centrally and compactly located as possible, too; and 3) way too much rearward weight bias makes it impossible to adequately adjust front roll stiffness to tune the suspension because the inside front tire will actually come off the ground. I have been told by a race car chassis engineer that in road racing applications a 42/58 distribution seems to be ideal independent of other variables, such as power. Rule #2 is the only thing making the Porsche 911ís layout a bad idea. The fact that it has the majority of its weight on the rear wheels is a big plus, but it has that motor hanging out behind the rear wheels, which increases its polar moment of inertia. Think of it this way: if rear weight bias were such a bad thing, why would Formula 1, CART, and all other series where the designer has leeway be dominated by mid-rear-engine cars with a rearward weight bias?

greggieatthebat
November 13th, 2002, 05:01 PM
Great information!

The most severe problem I can think of (in a street vehicle) of too much rear bias is the Corvair (Unsafe At Any Speed), wanting to swing that heavy rear around anytime it got just a little bit slippery (that's according to Dad's experience; I've never been in one)

One advantage of the cars you mention is the ability to tune a suspension for a very predictable environment (e.g. NOT on the street). They have very low Centers-of-gravity and have very little suspension travel and thus aren't as affected by the body-roll movements that we've been talking about in the previous Myth thread. They also don't have to worry about driver comfort (I'm always willing to sacrifice quite a bit of my own comfort for a little more performance... :D )

swamper
November 13th, 2002, 05:18 PM
cougarguy

I liked this one made me trist my brain around thinking about the problem. I can't do all the fancy physics stuff but its fun to think through how cars are setup for different things and how this applies to your question.

LiLWrink
November 14th, 2002, 03:34 PM
Hey man, I just dig ditches..........:1poke:
well sometimes they let me drive the truck!:D

mercury68
November 25th, 2002, 08:33 PM
Man I think with a little tutoring I could grasp this concept within a couple of weeks. I believe this discussion unravels the myth that car guys are just a bunch of adolescent grease monkeys who can't or won't grow up. Hope I didn't break everyone's concentration, but I was just dying to get involved.
Thanks,
Mercury68
I think this cougar forum is cool!!

LiLWrink
November 27th, 2002, 08:30 AM
Some info that may be useful to someone down the road; last spring I decided to add swaybars both front and rear to my beloved 55 Chevy. I contacted a company called Addco, who is a big producer of the bars foe all makes and models. They did all the math for me and told me how to set my car up for the type of street driveing that I do. I also found out that they will do the diagraming for you if you are useing thier products on a race car, dirt track or sprint, and have some local friends that have used the Addco setup to run, and have been consistently improving since they have enlisted the help of that company.
I seem to have missplaced the phone number, but I'm sure I can round it up if someone is ever interested. or call 800 info and ask for Addco...
I'm sure that just about any of the aftermarket companies that are in competition will be happy to help with the math/formulas that it takes to set up a competition car, which really helps some of us Dumb ol' country boys...:D

Shane