anti-squat in the 427 chassis

[Dominik]

Good morning,
I am building the 427 chassis from the Cobra Restorers blueprints.
anti-squat is a good thing to keep the rear wheels on the ground under acceleration and bumps.

here is the million-dollar question for the 427 chassis:

why did FORD design antisquat with an angle of 3.5 deg into the suspension (rear upper pedestal), but used a lower rear control arm bracket with 12.35 deg, which will cause the rubber bush to twist in the chassis more than needed?
(picture taken from a Kirkham in Germany)

why not angle the lwr crtl arm bracket 3.5 deg as well?

who knows how many per cent anti-squat that is? 20%?
who found the center of gravity of the 427?

and why can others live without anti-squat?
how much anti squat is designed in other Cobras, like ERA, BDR, JBL or Superformance?

dom

[mickmate]

Er that's 3 deg 30 mins (3.5 deg) and 12 deg 35 mins (12.583333 deg). You and that metric system. Oh well gets it to the top. Tacked the upper arms on about half hour ago, someone better give us some direction soon or I'll just have to follow the blueprint.....
Cheers Nick

[Dominik]

sure,

3.5° (deg) = 3 deg 30 min - half a degree equals 30 minutes...
but, yes could be misleading.
is that now degrees Fahrenheit or Celcius... ? ;-)

the disk I used before sits a bit deep for the caliper.
I must find another disk (see pic)

with a little luck I can roll a chassis on wheels to the show on sunday, but the old chassis without the support frame for the body.

here is a conclusion:
if you want to build a car based on the original chassis, get a body which is self-supporting.
I mean, ready to be bolted down to the "rocker panels" and rest on the scuttle hoop.

I still don't know where the original body will be supported, but I will find out soon when we slide it on.

dominik

[Dominik]

it gets worse and worse, now I cannot even attach pics anymore...

[mickmate]

Working on it Dom, I'm better at putting cars together than playing on these things!

[mickmate]

Looks good Dom !

[mr bruce]

Can't comment on the anti squat (too many opinions), but I am interested in the rear hub carrier and front spindle,where,how?

[mpbartlett]

Um, ... lets see, .. 3 degress 30 minutes, 12 degrees 30 minutes? Nigeria??!!

[Richard Hudgins]

dom,

I never design in anti-squat or anti dive into any racing type chassis.

You are introducing an uncontrollable dynamic with this sort of geometry. In essence you are putting a mechanical bind into the system.

I have never thought this was a correct thing to do.

You control the chassis with the dampers.

[Dominik]

nick,

thanks for posting my pics.

richard H,
thanks for the response.
the real benefit of anti-squat can only be felt when having ample of wheel travel anyway, which we won't have in racing car, I think.

(again I got no notification, but check from time to time)

uprights:
very close to the original one, with a FORD Granada bearing and spindles adapted into it.

there will be other hubs/spindles in the US, which may fit once the bearing pockets are turned to size.
if I was in the US I would make a plan to use existing racing parts (spindles, uprights&hubs) like mentioned by Herb Adams: Oldsmobile Toronado hubs or parts from his company VSE Eng.. in Carmel, CA.
(there are probably 117 more suppliers)

mp:
I like that, close but no cigar! maybe I should change the design to my location 34 deg south, 18 deg east... ;-)

[Dominik]

sometimes i can post pics, sometimes not.
I will next time to show how the upright idea developed.
measurements somewhere here:

http://www.clubcobra.com/forums/t509...-&pagenumber=2

so long,

dominik

[Dominik]

okay,

here is the preversion of the boxed metal upright.

Dom

[scratch]

Dominik,

I'm surprised at JBL's response...but then he is building unique frames (very fast albeit) with adjustable roll controls.

Get Carroll Smiths' book on chassis tuning and read the anti-dive, anti squat calculations for his race cars (1980 technology).

A chassis man once described to me that anti squat is basically similar to holding your arms (trailing links) out straight...holding a vertical bat (frame linkage).

The further apart your hands are (linkage distance attachments) the harder it is for the bat to move...of course, the same with your shoulder distance (other side of the linkage/rear end or irs).

But then you knew that.

scratch.

[Dominik]

JBL's response probably indicates that in order to achieve anti-squat, one needs plenty of suspension travel to force the wheel changing castor.

a typical race car does not travel much (in the suspension)

I got all of C.Smith's books!

dom

[427sharpe]

Dominik, I am still curious as to where you got that rear upright! I have had an on again/off again experiment going with my own home built frame, also based on the OE blueprints. Seeing your work has re-fired the urge to get it done. I have been working on training myself in aluminum work. Started small (hood scoop, etc) and am working with the wheel to build proficiency up to full panels....I stowed away the frame because I couldn't find an upright that I liked (or one that liked my budget!).

[Richard Hudgins]

Originally posted by scratch


Dominik,

I'm surprised at JBL's response...but then he is building unique frames (very fast albeit) with adjustable roll controls.

Get Carroll Smiths' book on chassis tuning and read the anti-dive, anti squat calculations for his race cars (1980 technology).

A chassis man once described to me that anti squat is basically similar to holding your arms (trailing links) out straight...holding a vertical bat (frame linkage).

The further apart your hands are (linkage distance attachments) the harder it is for the bat to move...of course, the same with your shoulder distance (other side of the linkage/rear end or irs).

But then you knew that.

scratch.

Scratch,

I recommend that you read Carroll Smith's "Engineer to Win" page 219, "AntiSquat and AntiDive" section.

Please note the last paragraph and then you should understand that my position on anti-squat and anti-dive is no different than Mr. Smith's.

[mylesdw]

According to Herb Adams, it is very difficult to build anti-squat into an IRS where the diff is bolted directly to the chassis and none of the torque reaction is transmitted through the suspension. Some anti-squat can be gained by the positioning of the rear suspension members but the practical limit is 25% (compared with 100% for a well set up live axle). He says:

"Because independant rear suspension systems do not have as much anti-squat, they are not as good as a live axle in getting the power to the ground on high performance cars. This problem is not too bad with a rear engined car because of the rear weight bias. On front engined cars however, it is a distinct disadvantage"

It seems like the word is: there is not a lot you can do about squat in a powerful front engined car using an IRS. Better I guess to optimise the rear geometry to minimise camber change under those conditions.

[wrm]

Originally posted by 427sharpe
Dominik, I am still curious as to where you got that rear upright!

Me two, thanks.

While I have many other suspension design books, I dont have Carrol Smiths, maybe someone can explain to me why Carrol Smith doesn't design anti-squat into an IRS. While I understand an IRS is limited to around 25%, surely 25% is better than none.

[strictlypersonl]

"Because independant rear suspension systems do not have as much anti-squat, they are not as good as a live axle in getting the power to the ground on high performance cars. This problem is not too bad with a rear engined car because of the rear weight bias. On front engined cars however, it is a distinct disadvantage"

No matter what kind of suspension you use, anti-squat is achieved by making the instaneous trailing arm axis be as high as possible. If it passes through the center of gravity (side projection), you acheive 100% anti-squat. The problem is that the wheel must follow a up-and-to-the-rear path as it moves under bump. It decreases basic braking and accelleration stability - it is essentially in a state of unstable equilibrium.

There is no way to change essential weight transfer under accelleration. The net force vector (weight+accelleration) will always create a moment that transfers weight. The front will always rise up, the only limitation being the front spring rate.

Drag cars, with their extreme (more than 100%) anti-squat, raise the center-of-gravity because both the front and rear rise, raising the CG, and therefore have more weight transfer under extreme accelleration. In addition, since the weight transfer occurs because of geometry rather that spring compression, it's nearly instaneous, avoiding the short delay that would occur waiting for the spring to load.

For a road-racing vehicle, you almost always want the lowest CG for cornering (and springs are very stiff), so anti-squat is not especially desirable.

Street cars are a little different. Their springs are much softer and their CG is usually higher. Sometimes some anti-squat comes in handy to maximize available wheel travel under accelleration and/or keep the camber from going too negative.

[mylesdw]

Originally posted by strictlypersonl


No matter what kind of suspension you use, anti-squat is achieved by making the instaneous trailing arm axis be as high as possible. If it passes through the center of gravity (side projection), you acheive 100% anti-squat. The problem is that the wheel must follow a up-and-to-the-rear path as it moves under bump. It decreases basic braking and accelleration stability - it is essentially in a state of unstable equilibrium.

There is no way to change essential weight transfer under accelleration. The net force vector (weight+accelleration) will always create a moment that transfers weight. The front will always rise up, the only limitation being the front spring rate.

Not according to my book. 100% anti-squat is achieved when the instantaneous trailing arm axis is anywhere on a line drawn between the rear tyre contact patch and a point directly above the front axle centreline at CofG height. The majority of anti-squat effect is caused by the torque reaction from a live axle being transmitted through the suspension and causing a jacking effect equal and opposite to the weight transfer. An IRS transmits no torque reaction through the suspension so ant-squat is severely limited.

As you say, there is no way to increase weight transfer but anti-squat DOES increase rear tyre loading and thus traction. For an IRS anti-squat also has the benefit of minimising any camber change due to suspension compression.