Goodbye Kansas

[ERA2076]

Originally Posted by RRRuiz

Wow, nice separation of the pedals. Real nice set up.

Thanks - it seems like short people would fit well - me - not so good.

chr

[ERA2076]

Can one of you ERA guy's advise me. We are working on final assembly of the rear into the car. The manual says to set the lower trailing link to 16.5". This causes all kinds of fitment issues for us, such as the rear radius arm inner pivot is reward past the mounting tabs on the cradle thus putting a bending moment in the link if we try to assemble.

15.5 " and it all goes together pretty smoothly and looks correct i.e. anti-squat at cradle, visually looks reasonable with anti-squat at lower edge of upright.

I need to make sure because of the relationship to the upper trailing link as well as several others.

I checked the latest manual and it too calls for 16.5"

What am I missing?

x-chr

[DanEC]

I see 16 inches in the 427 manual for the trailing arms. A couple of us ran into a little interference between the tire and the front of the wheel well and Doug advised extending the trailing arm link a little to swing the suspension assembly rearward slightly more, providing more clearance. I don't think a precise dimension for the trailing arm adjustment is critical to anything as long as the suspensions and tires cycle without issue and it's equal on both sides. But a quick call to Doug should get you an answer.

[ERA2076]

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

[ERA2076]

I wish I would have said -

1) in plan, the rear upright has to be able to rotate about it's vertical axis in both clockwise (anti-squat) and counter clockwise (toe) directions. Can't do it with hard bushings.

2) hard mounting the cradle requires that the assembly tolerances are quite good from ERA. Mine are - YMMV I can see how this could go bad - cradle not square to chassis.

We started final fit of the cradle and rear suspension. Next week we will square it to the front and try to understand the 16.5 trailing arm length and will know just how square the cradle is to the chassis.

Trying to understand the 16.5 dim with respect to the wheelbase. I will call ERA but would like to understand as much as I can before I call them.



Trailing link @ 15.5 Wheelbase @ 90. Top link in double shear.


Urethane bushings reinstalled at upright - Delrin @ top of cradle


This is the pivot we are concerned with. There is .100 total gap left after rod end is inserted. If trailing link is too long this link is pushed back against the cradle. Any reward motion and the un-tapered portion of the rod end hits the cradle. We are building spacers to center the rod end in the mount.This will allow the link to rotate thru the bearing and hopefully not kiss the cradle. We are going to relieve a little material at the cradle to assure the un-tapered portion of the rod end does not touch.



Fuel line passage - Delrin at cradle front. With the top secure the front mounts rested against the cross member with no load. Bolts were threaded by hand. Very impressive ERA.



We bump stopped the front and increased track .250 per side. Since we are fabbing new arms I took it. With the front control arms horizontal, ground clearance at front of chassis = 4.250
Bump = 1.625
Droop = 1.875.

So with the front geometry square we've dropped the CG .500.



Start milling link spacers next week.

[ERA2076]

I also wanted to show you guy's our stabar concept for the front. We are running the last iteration of FEA on the front arm so hopefully we will machine them next week.

We measured around 2.500 from the bottom of the frame rail to the bottom of the front rear pivot. Since I am going to sheet the bottom of the car and I plan to run it all the way to the back of the front spoiler we have that room to mount the sta-bar in that volume. This will help me with raising the rack and loads all of bar into the the front cross member.

[ERA2076]

We got the last iteration of the lower control arm back today. The rod ends are nearly SF 3. Our original goal was SF2. We will machine them in the next couple of days.



I read in Allen Staniforths book about Jaguar not using jam nuts, rather they used a clamping system to reduce stress in the threads. We added Keen certs and collars to the rod ends ends.





This represents all five iterations of the FEA