Author Topic: Controlling IRS Squat  (Read 2948 times)

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  • TBI Guy
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Controlling IRS Squat
« on: June 01, 2014, 10:07:59 AM »
I am just going to park this quote here so I do not lose And can look into it at a later time.



"An IRS car typically squats on launch. This is because the no squat/no rise line (otherwise known as the 100% antisquat line or the "neutral" line) for an IRS car, while at the same angle as for the beam axle car, does not pass through the tire patch, but, rather, passes through the wheel centerline (as viewed from the side). This makes it very difficult to place the IC (instant center) anywhere but well below it, causing the car to squat considerably.

As you know, a dragstrip ladder bar car exhibits an opposite, but similar, condition: It always rises on launch. This is because it's almost impossible to make the ladders long enough to contact the neutral line since it passes through the rear wheel tire patch. But, if we change those ladder bars to torque arms, we're able to change the IC position. Recall, the production torque arms slide at the forward end. This results in an unusual condition. With a sliding torque arm, we have an "invisible" link. This invisible link has direction, but no length. The direction is perpendicular to the sliding surface. The aftermarket torque arms use a small shackle (similar to the shackle at the rear of a leaf spring), so the link is no longer invisible. Torque arm cars normally have a single torque arm in the center and two symmetrically positioned links to control the forces which the sliding link can no longer control. So, though it's not normally thought of as such, we now have a 3link. And, as with every 3link, the intersection of the link lines (as pictured in side view) determines the location of the IC. If we then direct the link lines to a point on the neutral line directly below the sliding surface, we have a car with 100% antisquat.

Can this same principle be applied to an IRS car? Of course! Since the wheels move independently, we must work with 2 IRS torque arms. There are numerous IRS designs, but, if I'm not mistaken, some of the early Jaguar IRS designs had beefy leading arms solidly attached to the wheel bearing assemblies. I'm just going by the pictures on the Internet, but, if that's the case, we have an excellent starting point to discuss the change. The front end of those Jag arms were attached...probably through rubber the chassis. If, instead, shackles were attached to those front ends and two more fully pivotable links were added, we'd have a very strange looking 4link. And, as with any 4link, it's now possible to control the IC location by "aiming" those link lines.

The normal squat of am IRS car can not only be eliminated, you can actually substitute a bit of rise, if you like. That should shock a few people at the strip (and, incidentally, improve 60 foot times).  "