RCR GT40 BR. SUND. N

[Bjørn-Tore Rosenvinge]

It's been a while since I posted anything, but I thought I'd give it an update. It took a while before I got started, but I finally got started after the New Year.
Started by sanding down the chassis with coarse sandpaper. Put on etch primer and Raptor Bedliner. I think it turned out really well.View attachment 152024View attachment 152026View attachment 152027

 

[Randy V]

It looks great! Good to see your update!

 

[Bjørn-Tore Rosenvinge]

Ordered a Stancepart air lift from the Netherlands. As has been written about on these pages, there is no room for the cups for the air lifts against the chassis. You either have to order a smaller cup and shim out the attachment to the shock absorber or mount the air lift at the lower end of the shock absorber upside down. I decided to saw out a recess in the chassis to make room for the air cup.
I bought a 120mm aluminum tube that I welded into the recess.

 

[Bjørn-Tore Rosenvinge]

More pictures

 

[Bjørn-Tore Rosenvinge]

While I'm waiting for the suspension parts that are for anodizing, I'm working on rough fitting the spider and front clip as well as fitting the dash.

 

[Kevin B]

It's been a while since I posted anything, but I thought I'd give it an update. It took a while before I got started, but I finally got started after the New Year.
Started by sanding down the chassis with coarse sandpaper. Put on etch primer and Raptor Bedliner. I think it turned out really well.View attachment 152024View attachment 152025View attachment 152026View attachment 152027

Just curious, about how much Raptor liner did you use to cover the frame? It looks very nice.

 

[Bjørn-Tore Rosenvinge]

Just curious, about how much Raptor liner did you use to cover the frame? It looks very nice.

Yes, I am very happy with how the Raptor liner turned out. Under and in the areas around the wheels, I applied two coats of Raptor liner. I then used the included spray gun that came with the Raptor Bedliner set. This created a rough surface. On the rest I used a regular spray gun with a 1.8 nozzle. This resulted in a much finer surface, which is clearly visible in the one picture above.

 

[Bjørn-Tore Rosenvinge]

A little update. Now have the suspension parts from anodizing. Chose a golden color not unlike Steve's GT40. Very happy with the choice and the work that went into the anodizing process.
Finished adjusting the front suspension to recommended specifications. Camber - 0.9-1 and caster 5 degrees. Had problems, like most others, with reaching these recommended specifications while maintaining an acceptable distance from the rocker panels. I chose to have a ride height measured from the chassis underside and down to the ground of 13.3cm. This means that the lower control arm is not level, but has a slight slope of 1.5 degrees.
Can now turn the front wheels about 24 degrees before they hit the rocker panels/chassis.
Rear suspension is adjusted to Camber - 0.9-1 and caster 6 degrees.

 

[Jean-Marc]

Bjorn, thank you for sharing, I will compare with my data. But, I quick look at your data, and one of my friend is among the 8 test engineers in the world for Michelin and he pushed me to increase the camber to -2° -2.25° on the front. It is what they recommand for modern tires, the back camber is in the spec. But it is only a suggestion for race track.

 

[Bjørn-Tore Rosenvinge]

Bjorn, thank you for sharing, I will compare with my data. But, I quick look at your data, and one of my friend is among the 8 test engineers in the world for Michelin and he pushed me to increase the camber to -2° -2.25° on the front. It is what they recommand for modern tires, the back camber is in the spec. But it is only a suggestion for race track.

Hi Jean and thanks for the information. I will really consider increasing the camber to the specifications you have recommended. Thanks

 

[Chris Kouba]

Rear suspension is adjusted to Camber - 0.9-1 and caster 6 degrees.

How is the rear caster set? This is something I've never been able to figure out.

 

[Bjørn-Tore Rosenvinge]

How is the rear caster set? This is something I've never been able to figure out.

According to the build manual that came with the kit from RCR, the recommended setup for the rear wheels is: LR/RR. Toe -1/32, Camber -0.90 to -1.00, Caster + 5.00 to + 8.00

 

[Chris Kouba]

Thanks Bjorn. My next question is how is it set? I've not figured out how a radius rod rear suspension caster is measured.

 

[Morten]

Cut a 10degree wooden wedge, or whatever rear caster degree you want, place it under the upright lower the car onto it, adjust accordingly… check with digital degreeing tool….

 

[Jean-Marc]

Morten, could make a little sketch ?
Chris the only adjustment can be done by the 2 horizontal lings that hold the suspension to the front frame along the engine.

 

[Randy Folsom]

How is the rear caster set? This is something I've never been able to figure out.

The rear caster is determined by the position of the LCA inboard pivot and the lengths of the upper and lower four links.

The rear of these cars is quite challenging to set up. It takes multiple iterations because each adjustment has a ripple effect.

If I do it again, I am thinking to build a jig that holds the stripped down knuckle in the ideal position relative to the chassis (ride height, track width, wheel base, caster and camber) then attach the lower control arm, upper control arm, four links bars, etc.

 

[Clayton]

Maybe we should start a new thread for setting rear caster to stop deviating Bjorn’s build?
But while I’m here, sorry Bjorn
I think rear caster is a result of minimising roll steer on a reverse A arm suspension then a one size fits all.
The front caster is easy to measure and its effects on most replicas is consistent. Bigger numbers, more straight line stability etc.
Adding caster to the rear upright raises the lower trailing arm aft pivot, which in most cases reduces the arc of the arm pushing the rear upright backwards inducing toe out in bump. Not sure if that makes sense…
On my build (RF), I started at zero (both bottom pivots of the upright were parallel to the ground) and ran through roll steer / bump steer tests.
Added more caster at a time (lengthened the top and shortened the bottom trailing arms to keep wheel base the same) until the toe out was stopped in bump. This happened to be 3.5 degs and is easily measured across the rev A arm. I think originals were around the 7 deg mark.
As manufacturers have different front trailing arm pivot locations and different upright dimensions, one size caster won’t fit all.
That’s my thoughts anyway

Clayton

 

[Neil]

Maybe we should start a new thread for setting rear caster to stop deviating Bjorn’s build?
But while I’m here, sorry Bjorn
I think rear caster is a result of minimising roll steer on a reverse A arm suspension then a one size fits all.
The front caster is easy to measure and its effects on most replicas is consistent. Bigger numbers, more straight line stability etc.
Adding caster to the rear upright raises the lower trailing arm aft pivot, which in most cases reduces the arc of the arm pushing the rear upright backwards inducing toe out in bump. Not sure if that makes sense…
On my build (RF), I started at zero (both bottom pivots of the upright were parallel to the ground) and ran through roll steer / bump steer tests.
Added more caster at a time (lengthened the top and shortened the bottom trailing arms to keep wheel base the same) until the toe out was stopped in bump. This happened to be 3.5 degs and is easily measured across the rev A arm. I think originals were around the 7 deg mark.
As manufacturers have different front trailing arm pivot locations and different upright dimensions, one size caster won’t fit all.
That’s my thoughts anyway

Clayton

I mentioned before that John Horsman had asked how much front wheel caster I had designed into my black Mirage. "Seven degrees." "Sounds about right." I designed this car for a road course and for running at Bonneville. The high speed stability was excellent. The steering effort was not bad but there wasn't much weight on the front tires (it's a mid-engine layout).

 

[Bjørn-Tore Rosenvinge]

Thanks Bjorn. My next question is how is it set? I've not figured out how a radius rod rear suspension caster is measured.

As you can see from the posts from other builders, adjusting the rear wheels is a time-consuming task. As mentioned, all adjustments are interdependent. Adjusting the camber changes the caster and toe. Adjusting the caster changes the camber, toe and wheelbase, but eventually you should be able to get to the finish line. Just remember to set the wheels to ride height when you adjust.

 

[Bjørn-Tore Rosenvinge]

Had to move the rocker 7-8mm further back than recommended in the build manual. This was because the front wheels were touching, even though the front wheel is adjusted as far forward as possible. But now, after moving the rockers there is nice clearance from the front wheel at ride height. Had to make stops to put on the steering shaft. Used a 10mm thick aluminum plate that I sawed out a sleeve with a hole saw. Finally I threaded up to insert a set screw.