jaguar rear anti squat 1

[eddiewilbanks]

I want to use a Jag. XKE type rear suspension in a Cobra Kit car. I would like to design anti-sqwat properties into the mounting and geometry. I have some ideas, lets discuss it! Eddiewilbanks

 

[GregLocock]

Post your ideas and we'll discuss them. It would be nice if you could find a web link to a drawing so we can see what terminology you are using. Cheers

Greg Locock

 

[SWB]

The more the rear tires move rearward as the chassis squats, the more anti-squat you have. You will do this by pointing the pivot axis (in side view) upward at the front. You will have to be careful however, to make sure the radius arms do not pull the wheels forward as the car squats. They will have to also be angled upward at the front to accomplish this. I'll let Greg have the joy of explaining how to calculate the percentage.

Sean

 

[GregLocock]

I have a big and boring program to calculate this for me, but in principle it is fairly easy to work out. The idea is that the tractive force at the contact patch creates a couple around the CG of the body, tending to rotate the nose up. A cunning designer alters the effective line of force in the suspension so that an additional force pushes up as well as forward. This rotates the nose back down.

Imagine a pure trailing arm with a horizontal arm, pin jointed at both ends. The tractive force will be applied to the body at the height of the arm, which will be at the height of the wheel centre.

Now tilt the arm upwards at the body end. There will now be an additional vertical force at the body, becasue a pin jointed arm can only react forces along its length. This can be used to prop the rear of the body up, compensating for the nose up pitch due to the tractive force.

If that were all that was happening then life would be simple, but in practice the springs get compressed by this and have to be accounted for (although less as the squat gets reduced), and of course not many people use pin jointed pure trailing arms. Finding the effective line of action of the force for other geometries is just 2d geometry, if anybody can remember how to do that.

<eddie> what do you want to use the car for? road, track or both? What do you like about the XKE suspension - ie why did you choose it? What power and weight will your car be?

Here's a link

http://www.brownslane.com/diagrams/rear86.html

Here's another one, which I found later and is a bit clearer

http://www.erareplicas.com/427/rsusp.htm

So it has a single, wide, lower lateral arm, and uses the halfshaft as the upper arm, and has a separate pin jointed trailing arm. Toe compliance is mostly controlled by the lower arm bushes.

I don't like using the halfshaft as the upper arm, but it obviously works. The disadvantage is that your camber control is limited due to the close spacing of the two arms in front view. If you wanted to adjsut your toe compliance and camber compliance you'd be hard pushed since the same bushes are used for both.

Having an arm totally dedicated to reacting the longitudinal loads is a very good idea.

Castor is reacted by the vertical rate of the lower arm bushes, I can't get very excited by castor control, it looks fine. Cheers

Greg Locock

 

[SWB]

Here is how I visualize it.

Tire wants to go forward in a hurry.

Chassis has massive, inertial-based reasons to stay still.

If the tire moves forward in squat, it will allow the tire to move forward to an extent, while the chassis stays still (to an extent).

If the tire moves backwards in squat, it will tend to extend the suspension as it tries to go forward, which will tend to lift the back of the chassis.

I agree with Greg about the roll movement issues. However the wishbones have no compliance, pivots are all via roller bearings. The entire unit does move around however, where the &quot;cage&quot; is mounted to the body, they use rubber &quot;v-blocks&quot;
which are adequate for road use, but not so much for spirited driving. I think it would be impossible for anyone to say how the thing will jiggle around once you really get on it.

Sean

 

[eddiewilbanks]

I agree with your response about the Jag. rear suspension. I intend to use the car for everyday driving with occasional drag strip/track day adventures. I think the ERA concept with the top mount and lower links can be made to work. Think of the entire unit as a live axle mounted to apply torsional and thrust loads into the chassis. I need to consider your responses and respond accordingly. I cannot believe that I actually found a group of people who are willing to give input! I will talk ( e-mail ) with you later.

 

[BillyShope]

To achieve no squat/no rise, it is merely necessary that the instant center, when viewed from the side, is located on the &quot;no squat/no rise line.&quot; For an IRS, this line passes through the center of the rear wheel and is parallel to a line which passes through the rear tire patch and the intersection of two other lines, one a horizontal line through the center of gravity and the other a vertical line through the front tire patch.

The instant center is the intersection of lines through the trailing links.

Glad to hear you're taking this into consideration. I've seen street rods with IRS that exhibited an embarassing amount of squat on launch.