Antisquat and Instant Center Location

[BillyShope]

As the result of a long thread in another forum, I've added a page (Page 38 ) to my site which demonstrates that the tire patch force vector ALWAYS passes through the instant center. The spreadsheet user is able to adjust link lengths, rear pivot locations, and spread. The effect of spread on link loads is also part of the output.
http://home.earthlink.net/~whshope
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[bigblockbill]

Newbie question here...

Thank you for all the great info on your web site. I am new here and struggling trying to fully understand Anti-squat and what you really want.

From what I read you want chassis separation (Anti-squat) and I can understand how that applies a downward force to the rear tires. I can also understand how the further forward you move the IC towards the front of the vehicle the more force you get in lifting the front end.

Now what I don't understand. As you move forward with the IC to something reasonable.. say 40-50" the anti-squat line naturally moves further up and hence with the bottom bar adjusted level or slightly pointed down it puts the IC well below the slope of the neutral line (100% anti-squat) and yields numbers for me in the 15-50% anti-squat. So with that being the case and from what I have read I am assuming the car should squat on launch, which is not what is desired. Maybe I have it all backwards?

I would like to have some light shed upon what type of anti-squat percents seem to work well, or what should be targeted and why.

Thanks in advance.
Bill

[BillyShope]

I can also understand how the further forward you move the IC towards the front of the vehicle the more force you get in lifting the front end.

While, intuitively, this might seem to be true, this is one of those instances when intuition fails. As I stated on Page 38, it's the percent antisquat that is important, NOT the location of the IC.

...with the bottom bar adjusted level or slightly pointed down....

Why? It is only necessary that the bars be adjusted so that they "point to" the point on the desired percent antisquat line. As you'll see with further experience with the spreadsheet, the bars can be located virtually anywhere and with virtually any angles and, so long as the IC location remains fixed, the chassis will "see" the same resultant force.
http://home.earthlink.net/~whshope
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[bracketracer]

I can also understand how the further forward you move the IC towards the front of the vehicle the more force you get in lifting the front end.

While, intuitively, this might seem to be true, this is one of those instances when intuition fails. As I stated on Page 38, it's the percent antisquat that is important, NOT the location of the IC.

...with the bottom bar adjusted level or slightly pointed down....

Why? It is only necessary that the bars be adjusted so that they "point to" the point on the desired percent antisquat line. As you'll see with further experience with the spreadsheet, the bars can be located virtually anywhere and with virtually any angles and, so long as the IC location remains fixed, the chassis will "see" the same resultant force.
http://home.earthlink.net/~whshope
over 140,000 page views

So your saying that if the IC stays the same length anywhere the result will be the same???????? If so That won't hold any water at all...A drag car will act totally different depending on how high the IC is off the ground....

Here we go with another long post

[mytmouz]

[BillyShope]

So your saying that if the IC stays the same length anywhere the result will be the same????????

Of course I'm not saying that!

Suppose you want a small amount of separation. You might then choose an antisquat value of 105%. The 105% antisquat line passes through the rear tire patch with a slope equal to 1.05 times the ratio of center of gravity height to wheelbase. So, all you need do is locate the instant center anywhere on that line. So, both distance forward AND height are significant for a specific point, but it must be remembered that the point is only one of an infinite number of points which constitute the 105% antisquat line. And, any one of those instant center points will provide exactly the same performance.

I would suggest that you go to Page 38 and read the more lengthy explanation there.
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[bracketracer]

Bill give us some info on your car...HP,trans,4 link??,weight,tire size,etc..

[BillyShope]

Bill give us some info on your car...HP,trans,4 link??,weight,tire size,etc..

I suppose that I could say that "my" car was the C/A record holder known as "The High and Mighty." But, the "my" is in quotation marks because I was but one member of the Original Ramchargers.

I'm 73 years old and so crippled with arthritis that I can barely get around. The last racing I did, I ended up on my head in a sprint car, and that was many years ago. In the years between the Ramchargers and retirement, I worked as an engineer, raised a family, and fought with the IRS.

So, I'm now a retired automotive engineer who enjoys passing on my knowledge and experience to those actively engaged in the sport. You'll note that I restrict my comments to matters involving the physics of the sport. While there have been great gains in tire development and aerodynamic applications, the chassis...and the understanding of its dynamics by the average racer...has remained essentially unchanged since the fifties.

And, I haven't remained back in the fifties. I was a guest speaker at an SAE Motorsports Conference in 2000 and my work in asymmetric suspension design was mentioned in the Millikens' recent book, "Chassis Design."
http://home.earthlink.net/~whshope
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[John_Heard]

Billy I'd bet you have some great input on tuning a leaf spring car... Care to comment about how to change IC and Antisquat on one of those suspension setups?

[bigblockbill]

Bill give us some info on your car...HP,trans,4 link??,weight,tire size,etc..

Info on my car:

800-1000 HP
Powerglide
4 link
2600 lbs with driver
32 x 16" tires
111" WB
46.6% weight on rear
4:30 gears
What am I forgetting?

4 link IC as I bought the car 46.7" forward and 1.9" high (~25% anti-squat)

4 link IC as I plan to try next 48-50" forward and 6-8" high. That will put me at 60-80% anti-squat unless I can get it to change by playing with ride heights, so in theory my car should squat instead of having chassis separation right? So in theory would I really want to try and get something greater than 100% anti-squat?

[BillyShope]

So in theory would I really want to try and get something greater than 100% anti-squat?

Yes, but it's not theory.
http://home.earthlink.net/~whshope
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