Antisquat and Instant Center Location

[BillyShope]

Of course the site is over quota and I cannot get the number.

Don't know whether to call that a "senior moment" or attribute it to the fact that my wife was hurrying me out the door. She'll get a laugh out of it, either way.

I'll email you.
http://home.earthlink.net/~whshope
over 150,000 page views

[Gigapunk]

Mr. Shope,

I was a little confused by your comments on how an IRS changes the "no force" line. In your picture below does the "no force" line still go from the wheel center to point "A" at the height of the CG? With an IRS should the percentage calculation still be taken relative to ground level at the frotn wheels contact patch? Or is it now measured relative to the front wheel's center?

[BillyShope]

I don't know what you mean by a "no force" line. The line angling up to point "B" is the 100% antisquat line. All lines of constant percent antisquat would pass through the ring gear centerline. Their values would depend on the relative slopes.
http://www.racetec.cc/shope

[Rick360]

Billy,
How does the anti-squat % and force lines work when there is no front suspension? It is my understanding that the anti-squat line is based on the suspended weight and COG of that weight and how the force and acceleration cause the sprung weight to "pitch" forward or backward. If there is no front suspension this can't happen. Will the rear always try to separate on launch with no front suspension or what is the difference with no front suspension such as a 4-link dragster?

Rick

[BillyShope]

Billy,
How does the anti-squat % and force lines work when there is no front suspension?

Makes no diference.

It is my understanding that the anti-squat line is based on the suspended weight and COG of that weight and how the force and acceleration cause the sprung weight to "pitch" forward or backward. If there is no front suspension this can't happen.

The percent antisquat value tells you how much of the weight transfer is carried through the links. At 70% antisquat, 70% of the weight transfer is carried through the links and 30% is carried through the suspension springs. This is true with or without a front suspension.

Will the rear always try to separate on launch with no front suspension or what is the difference with no front suspension such as a 4-link dragster?

Rick

"Separation" occurs only when the antisquat exceeds 100%. Again, this is true with or without a front suspension.

I'll be adding another page to my site...probably within the next couple of days...in which I'll discuss what can be done with dragsters, both hard tail and suspended.
http://www.racetec.cc/shope

[RCJ]

Billy are you familar with dirt late models or IMCA style modifieds?

[BillyShope]

Billy are you familar with dirt late models or IMCA style modifieds?

I've been on my head in a sprint car, but I can't honestly say that I'm fully familiar with all that's happening today.
http://www.racetec.cc/shope

[vee8]

Does the height of the tire as in air psi or diameter affect anti squat?

[BillyShope]

Does the height of the tire as in air psi or diameter affect anti squat?

Certainly, since both center of gravity height and instant center height are affected.
http://www.racetec.cc/shope

[Bubstr]

Billy are you familar with dirt late models or IMCA style modifieds?

If it's simple I may be able to help, but now days it is so complicated that your chassis manufacturer has car specific info. None of them like to see one of their cars do poorly, so they help anyway they can. Even if you bought it second hand. Might try www4m.net also.

One thing to remember is different chassis use different center of gravity locations and the stuff you hang on it can change that also. One of the most important things is Center of gravity locations relationship to the roll centers. This is very much like Instant centers on a drag car only from the side.

[BillyShope]

This is very much like Instant centers on a drag car only from the side.

Yes, and understanding this helps in understanding why adjusting in more antisquat on the right than on the left contributes to cancellation of the driveshaft torque's tendency to unload the right rear during launch.

Just as you'd increase the front roll center (or decrease the rear roll center) to load the right front in an oval track car, increasing the instant center height on the right side (and/or decreasing the instant center on the left side) loads the right rear on a drag car.
http://www.racetec.cc/shope

[RCJ]

Billy do a search on YOU TUBE for dirt late model or dirt modified.You will see some anti squat values that will make you scratch your head.

[Bubstr]

Billy do a search on YOU TUBE for dirt late model or dirt modified.You will see some anti squat values that will make you scratch your head.

Yes it is the same horse just a different color. You must remember one rule, The % of anti squat in Dirt circles is called being on the bar. What ever is not on the bar, has to be made up with spring/shock, to get desired effect. There are a lot of compromises going on, that very from track to track. Track / tire compliance and front to rear balance are the important things. Corner speed is king.

[vee8]

Does the height of the tire as in air psi or diameter affect anti squat?

Certainly, since both center of gravity height and instant center height are affected.
http://www.racetec.cc/shope

So to expand on this to set a car up correctly do I need to figure the expanded size of the tire?

If you have your ladder bars too high and you do wheel stands then you drop them 1 bolt hole (1 in ) and the tire speed goes up tooo much. How would I get right. Do you raise the whole car or just the front or back?

[Bubstr]

Does the height of the tire as in air psi or diameter affect anti squat?

Certainly, since both center of gravity height and instant center height are affected.
http://www.racetec.cc/shope

So to expand on this to set a car up correctly do I need to figure the expanded size of the tire?

If you have your ladder bars too high and you do wheel stands then you drop them 1 bolt hole (1 in ) and the tire speed goes up tooo much. How would I get right. Do you raise the whole car or just the front or back?

To be dead nuts on, with tire growth, you would have to get pictures of the car at rest and picture of car while tires are grown at launch, then measure your front suspension points difference from the ground. Since most just guess at center of gravity anyway, I just figure a little underground level for rear point of neutral line. Note It doesn't make any difference how much the tires grow down track other than gear change.

When raising or lowering a car, you change two things. The forward mounting point position of rear suspension and the center of gravity. Look where these are located and it will tell you which end to work on, up or down.Raising front will raise the COG more than IC line and raising rear will raise IC line more than COG. Simple rule is, if you want an IC change do it at the rear. If you want a COG change do it at the front or both. Note, these are smaller adjustments than changing a bolt hole or raising an engine. After all the experimenting you will find the COG, especially height, is way more important than the IC. It is the relationship of the two and how much power, that makes a car work. It gets a little more complicated than that but just to maintain compliance to track. If you get an anti squat a LITTLE below 100% and spring/shock it to eliminate squat, the rest is GOC placement, given you have good slicks. This will give you compliance for track bumps and the COG gives the weight transfer. The restricting or enabling of the front suspension regulates how fast and how much you get.