Thanks Dan I will call them next week. It seems strange it fits with no pre-load in any of the links at 15.5.
I wanted to offer some observations on the GEN II (ERA) rear assy.
Though Bob and I will probably never agree a Jag rear cannot be solidly mounted, we now both agree you cannot mount the rear upright of the Gen II with solid bushings without risk.
Since ant-squat is built in, the rear upright swings aft and inward as it swings vertical. The longitudinal and vertical axes are controlled with the pivot bushings at the upright and the rod ends at the cradle, but there is no freedom of articulation in the transverse (inboard) direction using solid bushings because the bushing cannot give in that direction.
If the bushings are solid, that force has to go somewhere and the upright and pivot are quite rigid, so the radius rod most likely accepts the bending load which it is not designed to do. This is the job of the compliant bushings. By using compliant bushings, the bushings are more willing to accept the load than the radius rod, thus protecting the rod from bending.
In order to solid mount, we need spherical bearings at the upright pivots such that we have freedom of articulation in all three axes. Perhaps rod ends, but for peace of mind, spherical bearings would be best. This will require new control arms.
There was a post some years ago where Rick Lake discussed compliance in the system and it's contribution to wheel hop. I think he was all over it.
Compliant bushings summarized
Cradle to Chassis Top - 2 ea
Cradle to Chassis Front - 2 ea
Lower Upright Pivots - 2 ea
Lower Trailing Link - 1 ea
All of this allows compliance with respect to uncontrolled forces. It acts as a fuse taking load off of critical components - none of it is good for control of the contact patch, which matters not, unless you want to drive one at the limit. In that case, the limit is limited.
Imagine the top cradle bushings when using the rear sta-bar at the limit. How does that translate to the contact patch? Under hard cornering does the wheel base skew i.e cradle rotates with respect to chassis? Most likely yes, but most likely it is predictable and the limit is reached. It will not corner any faster with this system.
We have our cradle mounted to the frame with Delrin. Miraculously the pivot mounts needed no modification what so ever because we cannot strong arm Delrin. It has to line up. We changed the rear trailing arm pivot to a rod end at the chassis.
We will be putting the compliant bushings back in the upright next week.
I have 2 IRS equipped cars and I would never drop the clutch on either one. I believe IRS is a mis-application for this use. (never mind the T5
) Corner exit is of interest.
In summary, the compliant pivot bushings provide freedom of articulation in the transverse direction. I still don't understand why the cradle needs to move around and I have given up trying
. It goes against every "How to Build a Race Car" book I have ever read. If it is critical to ERA design, I hope Bob will advise.
Side note => if you are running a GEN II - next time you are down there, check the rear pivot at the cradle. Make sure the rod end is not touching the cradle such that there is no longitudinal articulation thru the bearing. In that case you are needlessly stressing the upright pivot and or radius rod.
chr
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