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

[ERA2076]

Our new arm - 11/16 longer (11.312) Motion Ratio = .88

What ever friction there is, is not discernible. It is very smooth. Attached to the chassis the arm under it's own weight repeats on a scale over and over @ 3.06.



Front track => 55.375 - Tread is inside the flare. Section width is a touch outside.



You can get an idea of how far out we are rotating the top of the shocks. We are working on a new UCA bearing housing trying to get an 80 degree shock angle. We have 77 with this setup. Minimum clearance is at full droop.

[ERA2076]

I had forgotten the 3 different back spacing's I have used to get here and mindlessly used the difference of the two arm lengths to guess track. That is incorrect. The drawing below shows how far out we have moved things. Our track is very close to 54 (8" rim 4" BS). The rotor hats are .280 thick so that puts us at 54.715. We cannot run anymore backspace as the calipers are within .020 of the spokes.

Scrub is still reasonable with the more vertical SAI because we were able to move the lower ball joint closer to the center of the wheel.

I sprung the car @ 2hz on paper some time back, because of the improved motion ratio and reduced shock angle, we are able to get 2hz with a 325 lb spring instead of 450.



I have been using a suspension analyzer on this suspension for the last couple of years and after a lot of hours I learned that if I move the upper pickup points 3.015 outboard, the front roll center does not migrate vertically or horizontally at 2 degrees of roll. I read somewhere that the UCA being 60% of the lower will typically achieve good timing between the two arcs. Moving the pivot outboard makes the new arm 63% the length of the lower. Seemed like a good sanity check. With this timing and static camber @ -1.5 the outer wheel is vertical at 2 deg roll.

This is the new upper pivot axle beam we are going to try. Also working on a new bearing housing out at the end. This will allow us to tip the shock out a little more. Thinking of running stress analysis on the cantilevered shock mount, the pivot axle, and the CA bearing housing.



Some pictures of the tire with respect to the flare.



No spacer, no extended ball joint, lower arm parallel to ground.

[ERA2076]

Time finally became available on the CNC. We had them hard anodized.



We bolted it all together and setup the front end with -1.5 camber and the tires are inside the flares - we gained 1.375 front track. I am happy about this since we are running a 225 front tire and I have been concerned some about tripping over the front. You can see we put the front leg in double shear. I had the stock arms measured on a CMM some time ago. Interestingly the new arms ended up 1" longer to one thousands of an inch. I was surprised by this because we did not approach from this view. Instead, maintaining the tires inside, we as-built to the best fit of the components.



We could not use our modified neck for the fuel cap. There was just no way to get the vent line connected. There is not enough clearance between the inner glass and the top of the tank. We pulled the tank and had a full length return line welded in on the driver side. We machined a new straight thru neck for the cap.



I am really happy to have the front arms done. We used the front cross member for datum and shimmed the displacement from the cross member to the center of the rod ends to the same spec as stock.

We set and reset the rear diff assembly more than several times. It is amazingly square to the chassis, but unfortunately rotated down 2 degrees with respect to engine level. We did not check the machining of the dif housing, but I have a feeling this is where it is. We made new "cradle to cross member" brackets which allowed us to rotate the cradle up 2 degrees. I realize this will reduce the anti-squat and I have not studied yet if there are other mechanical problems. If anyone can advise, please do.

I have given some thought to machining a new lower cradle tray with no anti-squat and adjustable pickup points. This would dictate that the rear upright rotates normal in the transverse plane and would allow optimization of the rear RC when changing ride heights.

I took some rough measurements and ran the rear thru a suspension analyzer and was very surprised how good the rear roll center looks. I still can't get the dimensions in the book to work on a 90" wheel base without binding the rear rod ends against the rear of the cradle. Now that the front is located we can really square and finalize the rear. The trailing rods will be what they will.

Lastly we bled the clutch - unbelievable

[DanEC]

So what's the ETA for when this featherweight, track-burner will hit the asphalt now?

[ERA2076]

A long ways to go - We are working on shortening the upper control arms by relocating them outboard. Another science project that ties front and rear roll center migration much closer together.

We have not taken the Mustang out of the trailer just so we can keep it on the rack.

chr

[ERA2076]

We spent all spring and half the summer working on squaring the suspension. A very tedious process.



We are only able to get 89 7/8" inch wheel base.



The rear cradle assembly is square within 1/32". With the radius rods normal to the cradle our trailing arms are short 1/2" from the manual. I would guess we had the rear cradle in and out at least 10 times.



The diagonals are within 1/8". The wheel base is out a little side to side which we will fix by shimming one of the FCA. This should help the diagonal.Would like to get diagonal <= 1/16"



We have the power and drive installed and level. This necessitated building a new top plate for the tunnel to get the shifter location correct (3550 to T5). The tunnel had already been powder coated and the aluminum panels really take a beating with all the heat so we just built a new top plate.



I opted to have Jim build a set for an FIA. It greatly simplifies my life. I took a look at the pedal box and realized the whole thing comes apart quite easily. We have a new vertical link modeled in CAD to replace the gas pedal. From there a horizontal link to the Tilton pedal will have it all connected. The Tilton gas pedal has a threaded stop built in so it should be quite simple to get the linkage and throttle plates calibrated.

I have a set from Red Line for sale - PM if interested.



Weighed it => 2047 Close to where I need to be, but a little heavier than I hoped for at this stage. The magnesium wheels are still good for 40 lbs and maybe 15 out of the exhaust - I was hoping to be at 2000 as it sits. Stuff missing - hood, rack, front stabar, water, cooling system panels, wiring.



Ride height, camber, caster, toe set. FCA are flat.



I can't believe it is back on its tires. Still a round of suspension left.



Lastly - installed the inertia switch

[ERA2076]

Here is a part we have been working on for a while. After many iterations in Circle Track Analyzer I noticed shortening the UCA limited roll center migration to .100 vertical and 0 horizontally at 2 degrees of roll. As it sits now the front roll center moves 13 inches laterally at 2 degrees of roll. I took some sanity checks on the rear and the rear did not appear to move at all. This part was modeled to push the upper pivot outboard 4".

We have not put it on the car yet and we will have to hack up the inner panel as it intersects that plane. We plotted camber curves for front and rear so next we will install and plot camber curve with this. If that looks good I will have FEA run on it.

I upgraded to Suspension Analyzer some time ago which is a 3 space modeler set up for IRS. It requires a lot of input data which is why we laid the suspension out on plywood.

[ERA2076]

Hello ERA Brethren,

My wheels finally showed up. I ordered them in September. They are very lite and very beautiful. Some risk because I could not get drawings. Front brake package will need some work, but it it looks like they will work. Have not fitted the rear yet. I want to say its a no-brainer, but you just never know. Pretty sure I have 80lb front un-sprung in the bag.



I turned 59 in October. 2 days later I owned this.



It's been on the rack since December. Just coming off so the Cobra can go back on. Fully ducted the brakes with sealed rotor ducts. Quite an exercise but now we know how to replicate on the FIA. Gutted the OEM intake tract and air boxes. Will run cold air into the fender liners.



Sitting on DA coil overs. Gets full exhaust from heads back. Should be just North of 400. It is heavy, but the balance is - wow. Want to run it in September.



Can hardly wait to get working on the FIA again.

chr

[ERA2076]

Originally Posted by a427sc

checkout Hoosier Street TD Hoosier Racing Tire - Tires Designed For Champions

45160 P225/45D-15 H 7.6" 23.0" 72.5" 6.5-8.5" 7.5" 8.5"

26.6 vs 23" bias ply, treaded, a little harder compound. there's 1.8" for ya.

hmm -

Hoosier R7

24.6 and 25.8 - not pretty, very low to the ground (cannot get a low profile jack under the rear cradle), very lite.

Front 245x50 on 8 inch rim = 36 lbs (-10 lbs Minlite/Avon)
Rear 275x50 on 10 inch rim = 37 lbs (-20 lbs Minilite/Avon)

60 lbs of un-sprung ( I had counted on 40, but could not get it all from the wheels.) I will have achieved 80 on the front.

The look is difficult, but if I think of turn 1 somewhere, it looks like it would handle like a go cart.

Thinking I would run the Mini/Avon for show.

Trying to bring myself to post pictures - a lot of details to check (the mono-ball studs will have to be swapped to maintain geometry). The 245 swings thru in both directions.

chr

[xb-60]

Originally Posted by ERA2076

...I turned 59 in October. 2 days later I owned this.

...

Belated 'happy birthday'!! The AM V8 Vantage has to be one of the best looking cars on the planet.
FIA Cobra's not too shabby either

Cheers,
Glen

[ERA2076]

Thanks - very fortunate to live in a time where beautiful things are not valued with money.

chr

[ERA2076]

You can get an idea of how low it sits to the ground. The side pipes are configured for a 351. They are being reconfigured and will be raised abd tucked up into the chassis - we'll get some out of it. The tire gaps are horrific, but there is a sense of purpose when sitting on the ground.



I need to cycle everything and check for clearance especially in bump and turning. If it all can be made to work we should get ground effect by sheeting the bottom. The difference in tire diameter will give us the rake.



Unfortunate the front is on an 8" rim (steering response), but the tread width is inspiring. I'd like to push the front tire inboard a little, but I am against constraints. I can see trying to drive it hard with this setup much more than I ever could with the 225. If we can get it to work, it should be able to run down all kinds of stuff. The pipes could prove challenging.

[ERA2076]

I weighed the car tonight with most piled into it. We are at 2015 lb and I feel like we are within 100 of final assembled weight with coolant.



We found .400 so with a deeper brake hat and I was able to move the front wheels in board with no spacer (caliper bracket and steering arm will need re-design ). I weighed the front un-sprung and we are at 81.88 lb. 80 is still within reach, but I am very pleased with this. We started at 102. I am still working on changing the camber timing on the front. That part is at FEA so if we can get it to work we will build new lite weight UCAs. I weighed the control arms with them attached to the car and the upper is as heavy as the lower i.e 3lbs swing weight with joints.



The frame is around 3.5 in the rear and 3.1 in the front. We have lowered the CG around 1.5 and front geometry is maintained. I plan to measure the cg height when we are a little further. We are going to change the pan to a Daytona. It is an inch shorter,will not drop below the rails, and will allow smooth sheeting front to rear.



The aesthetics are not as pleasing to me, but for the first time I can see driving it briskly.With it sitting on the ground, it really feels like it could be capable.



I have been hanging around some FFR guys that ran Can Am cars in the 70's.They are quite knowledgeable and its interesting see the different ways guys build them. A lot of discussion on learning how to drive it.

Really getting excited - a ton of detail left.

chr