In addition to learning to drive first, i'd also like to understand why suspensions respond the way they do be fore I modify the suspension on my car.

Here are my thoughts:

I get the whole weight transfer thing. Basically a layman's term for a change in forces exerted on the road by the car to counteract the forces of intertia and centrifugal force.

What I DONT seem to really get is why the body of the car rolls and why it rolls in the direction that it does. For instance, if you were to drive clockwise in a circle, why does the right side of the car raise up?

There are clearly forces acting on the car in the outward direction of the circle's radius and the tires exert the exact opposite of that force (hopefully). But what forces are causing the car to pitch in the specific direction that it does?

If I'm reasoning correctly, the outer set of tires are exerting more forces (inwards) that the inner tires. But it seems to me that this is the "reaction" to the "action" of the car rolling, not the other way around.

Anyone care to enlighten me?

Or would a book like "Going Faster!" or something be the better route than a long drawn out explanation?

Thanks in advance to all that contribute.

 

https://honda-tech.com/zerothread?id=285747

 

Was that the correct link?

"If we examine kingpin inclination (the axis between the upper and lower balljoints in front view), we see that turning the steering wheel pushes the wheel downward equally whether turned left or right. Positive Ackerman (inside wheel turning more than outside) will result in the inside wheel being pushed downward more than the outside wheel.

If we examine positive caster, we see that the outside wheel moves upward and the inside wheel moves downward."

Thats the closest thing, I could find to an answer to my question. Do you think that the downward force produced my the inside wheel causes the car to roll to the outside?




[Modified by NB, 10:29 PM 3/3/2003]

 

??

 

Hey guys newbie here, but Ill take a stab at it. Forgive me if I stick my foot in my mouth.

The cars center of gravity is obviously above the point where it contacts the ground so that is what gives the body roll.

The front and rear suspension each have their own point that the body will roll around connecting these points gives you the cars roll center ie. the axis the cars body rotates around.

Q: why does the right side of the car raise up?

A: As weight is transfered from the inside wheels to the outside, the springs relax and compress, respectively. ie the inside springs with less weight on them push that side of the body up. The outside springs with more weight compress and lower that side of the body. That is the roll.

I hope that helps.

-toolbox

 

now i feel like a retard

 

search the archived topics by rr98itr. read. read again. try to digest, then read again. finally, read again. everything you've ever wanted to know about setting up a civic/teg chassis is in there. even some stuff you didn't want to know.

nate

 

The hardest part about understanding vehicle dynamics is keeping the concepts simple. I am afraid that if you do searches and read 1000 pages of people trying to explain concepts here as a primer in the physics of handling, you will get yourself even more confused.

The best way to really, really understand what's going on? Go audit a college physics 101 class at a local college. Be sure to be there for the section on free-body diagrams. Forces must FIRST be understood in the context of a free-body. Getting a good basic understanding allows one to immediately throw away any misconceptions about forces (like the whole action/reaction thing and thoughts about the ground "pushing back".

Then, armed with a good basic understanding, read Fred Puhn's book, "How to Make Your Car Handle". Or you could try to start with this book. But it is difficult enough to master these concepts with a good background, that I recommend some classical training first.

No one said that it is easy. But once you are armed with the right knowledge, the world becomes a much simpler place.

Now to try to answer your question. Walk up to a chair sitting on carpet. Push on it anywhere except right at the bottom. Does it fall over? You pushing is centrifugal force on the car. The friction at the base of the chair provides the "reaction force" just like the tires. Since the forces are not balanced, there is a torque. The chair falls over. Get it?

 

if you just want to understand the forces going on:

weight transfer is caused by the cornering force generated by your tires reacting on the cg of the vehicle. using the formula weight transfer=cornering force in g's*vehicle weight*cg height/track width.

from that formula you can see that to reduce weight transfer you have to a)reduce vehicle weight, b)reduce cg height, or c) increase track width. the final option we aren't really interested in and that is to generate less cornering force.

note also that the formula makes no provisions for your spring rates. this means that even with an incredibly stiff suspension and zero body roll weight transfer still happens and to the same degree as before.

understanding body roll requires the understanding of virtual roll centers and their interaction with the cg. i'm not good enough at explaining things to go into this topic with any sort of clarity. in all reality, an understanding of weight transfer is really all that is needed. if the car rolls too much for your taste, get some stiffer springs and swaybars.

nate

 

That is the best short answer I have ever seen to this question.

Bingo! This is the concept that a lot of people don't realize. The next obvious question one would ask, then, is "Why use stiff springs?" Answer: to minimize detrimental changes to the tire's alignment to the ground, namely camber (and toe on some cars). That's it, in terms of overall performance potential. There are "personal" reasons as well, mainly dealing with feel and sensation.

Another subtle concept going on here is - Why do we want to reduce weight transfer? If you believe Physics 101, the amount of frictional force is proportional to the normal force, or load, on a tire. F(f) = f * F(n), where F(f) is the friction force, f is the friction coefficient, and F(n) is the normal force or weight. That means that there would be 2x the grip at 2x the weight. Thus, even if we had 100% weight transfer, with a "classical" frictional surface the available cornering force does not change with weight transfer.

This argument would also point to wider tires being no better than skinny tires.

In reality, normal force is not proportional to friction force for a tire on pavement. f, the coefficient of friction, is a function of normal force and actually decreases as F(n) increases. There is a great graph in Puhn's book which demonstrates this falloff of friction. This subtle effect is the sole reason to lower a car and put on wider tires -- not weight transfer or any other phantom effects.

Fun subject! I think about this crap way too much