4 replies to this topic

[dirtstudent]

I got a ton of questions and there is a couple of ton's things that I do not know. I sure hope I can get information on here and don't have to resort to book learning. ___________________ You can put a car on the scales and add static weight to it and see the weight added on the scales. You can put a wing on the car and the air traveling across the wing can add down force. Those are two different ways of making the spindles and the axle push down harder on the tires. But there is also weight transfer. You will get weight transfer from acceleration and you will get weight transfer from braking. When you accelerate and weight transfers to the rear again the axle will push down harder on the rear tires. When you go around a turn centrifical force will transfer weight outward. And again the outside tires can have either the spindle or the axle push down harder on the tire depending on the direction to which the weight is transfered. All that is leading up to my question. For not know of a better way to ask i'm going to try the question this way. Are there two kinds of weight factors? One is the kind that occures when you just place static weight on the axle or you apply down force created by the car traveling thru the air. The second is when weight is transfered. Its the second kind of weight that i'm actually asking about. When weight transfers to the rear of the car because of acceleration do the actual parts of the car become heavier??? If the actual parts become heavier then I would think that the tires themselves become heavier. That would mean that weight transfer thru acceleration will actually make the rubber which makes up the tread of the tire become heavier???? Naturally if a corner of the car is heavier then the weight pushing down on the tires is also greater but repeating if the actual tires actually get heavier then I would think they would tend to grow more as the surface of the tire actually becomes heavier. ???? ???? If tires actually get heavier under acceleraion then tires will grow more when weight is transfered to them then when they are just rolling without major acceleraton or if the acceleration is removed. Also when weight is transfered to the outside during a turn that would tend to make the outside tire grow in diameter and the inside tire reduce in diameter. Yes I too see that the lr tire looks like it may grow more when weight is removed from it when the car is up and running on the outside tires. But that growth I think is because of the other kind of weight, real weight, leaving the tire and the tire just not being pushed down as hard by the axle. That would also mean that maby, just maby, air pressure consideations may have more to do with tire growth and the resulting stager much more than anything else.????? And all that leads me to this question. I and I think everyone else knows that an air pressure adjustment can do alot to the handling of the car. What are the different things that are effected by raising or lowering air pressure in a particular tire. And what is the primary thing in "YOUR" mind that you are effecting when you make an air pressure change at each of the corners of the car? I personally use to think mainly about how it would alter the contact patch of the tire and how I "felt" that would in turn change the grip at the tire that had the air pressure change. I now mainly think about how the tire diameter is going to be changed out on the track, and how the raising and lowering of that corner of the car is going to effect the handling. anyhow that's the question.... Do the physical tires actually get heavier and inturn lighter when weight is transfred to them and away from them. I sure hope to get some setup discussion started on here. It's going to be a long winter and once racing fever or the lack of racing sets in winters become long. Maby i'm just the only one that does not know answers to questions like this. In that case sorry, i'm just trying to learn and thru learning planning on being able to make a car go around the track ahead of you. ... someday

[dirtstudent]

And if anybody cares someone on another board was kind enough to send me information about my question. Here it is slightly re-worded and again I hope it might help someone in addition to helping me out. _________________________________________ "You are correct in assuming there are two types of weight (force is more correct), static and dynamic. Static weight is just that, the weight placed on each tire when the car is at rest with the driver in it. Dynamic load or Force (weight) is the result of the mass of the car and driver (weight) times the acceleration (g's) placed on that mass. From physics remember that Force= Mass x acceleration. Once we know what the acceleration forces and the mass of the car/driver is, we need to find the center of gravity so we can determine the resultant load on the component we are interested in. Knowing that, and the physical dimensions of where the loads are placed relative to the cg, we can determine the dynamic loads on the components of interest. Basically, (very basically) we add up the results of the dynamics load and the static load to get the total load on the component. Remember that the mass of the component does not change, (the wheel and tire's weight dont change,) but the load placed upon them does. I have calculated the weight transfer on cars and formula cars for my design projects. I will tell you that moving the cg has the the most dramatic overall effect of any change that you can do to the car. If you are interested running some of these calcs on your own, check into "How to make your car handle" by HP books, or if you'd rather do the hard work yourself, go get an engineering statics and dynamics book and dive in. The good news is that working these calculations will help you understand how a car works. The bad news is that these formulas while reasonably accurate, do not depict the whole story of chassis twist, tire dynamics, caster/dynamic camber change etc etc etc. At some point, calculations become just purely academic exercises to give us engineers confidence that we've designed components that won't fail under "normal" circumstances. Outside of that, there's no substitution for on track testing."

[Jon Banas]

The tires themselves do not increase in weight. They become loaded and carry more weight that causes deformation. Centrifugal force also deforms tires (makes them grow). Weight transfer under acceleration and cornering can be and is controlled by shocks. Different valvings will affect how quickly weight leaves or remains on a tire.

[dirtstudent2]

Thanks Jon Since I posted that back in october I have learned where I was going wrong. I really appreciate the input.

[dirtstudent2]

"Centrifugal force also deforms tires (makes them grow)."

Great thought Jon ... then it's probably Centripital force that squishes the lr down?

[This message has been edited by dirtstudent2 (edited 12-09-2001).]