Radius arm bush orientation

[Tom W]

I’m looking for opinions on which way to orient the
forward radius arm bushes. With the gaps fore/aft as Jaguar intended, or turned through 90 degrees as seemed to be recommended as an upgrade by some people? Is this a worthwhile change, or does it just cause the bushes and V mounts to wear out prematurely? Is it only really noticeable if you take the car on a racetrack?

The rear of my car has always felt a bit loose, but now I’ve stripped the IRS, I’ve found there were so many tired components, it’s no surprise things felt like that. So, I don’t really have a benchmark of what the standard orientation feels like to know whether to make the change or not.

[Heuer]

Rotating the bushes will stiffen the rear suspension and reduce rear axle steer. Common thing to do back in the day for a more sporting feel. You may or may not notice a difference depending on your driving style. Mine have been set at 90°'s since 1999 and I have covered 55,000 miles with problem.

[Tom W]

I would have thought rotating the radius arm bushes, thus stiffening the radius arms, would have increased rear wheel steer?

The rear suspension is geometrically imperfect, the radius arms and lower wishbones move through different arcs, so for it all to work something has to flex. With the bush orientation as per the factory, the radius arm is effectively able to change length slightly as the suspension moves. When set at 90 degrees, this effect is reduced, so the the next most flexible item in the chain has to move. Presumably this is the cage flexing around on the v-mount. In a corner, when the outside radius arm pushes the cage back and the inside arm pulls it forward, I could see this inducing some more rear wheel? I would also expect axle tramp to reduce with stiffer radius arms.

Maybe this is what makes it more sporting?

[rswaffie]

Or you could go for 45 degrees and have the best of both worlds!
viewtopic.php?f=3&t=11101

[Tom W]

Ah, but is 45 degrees in or out better?

[rswaffie]

It really depends on the track.
For Goodwood, clearly ‘in’ is the way to go.
For Le Mans, definitely ‘out’.
For driving from pub to pub in Northamptonshire, I’d go one side ‘in’, the other ‘out’.

Nurse, it’s time for my medication.

[Tom W]

I went for the slots fore and aft in the end. I’ll see how things are supposed to drive as Jaguar intended first. Anyway, the new OEM bushes look a lot stiffer than the pattern parts that they’re replacing, the cutouts are a lot smaller. They’re also a lot tighter fit in the radius arms. I was able to remove the old ones with a hammer and drift, the new ones gave the hydraulic press a workout.