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suspension pickups on a main hoop?

Posted by Perry 
Perry
Perry Seaman
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suspension pickups on a main hoop?
November 18, 2015 11:49AM
Hello all.

Let's say your car was short and narrow like my old beetle, and you build a rear multilink suspension for it with some links that run forward at each wheel.
Picture something like the Volvo or merkur guys do where they build a box in the floor with a mount at the front and this longish trailing arm is bolted in to create a 4 link for a live axle car.

All this is legit in the rules and such and been done before.

On my beetle, I need to place the main hoop back a bit and could conceivably end up with the main hoop and the forward suspension pickups in about the same location... so I could just weld the pickups to the hoop for an upper and lower link on each side. I'm thinking a pair of plates with a bunch of holes for adjustment, like the circle track guys use, on each lower vertical of the main hoop.

for safety I'd probably offset the mounts a bit and weld a plate in to encourage the link to go outboard in a hard backwards impact so it didn't come towards an occupant.

Probably a NASA logbook, want to be RA legal too.

Legal? not legal? stupid idea? what say you.

The issues I see are:
1) is this becoming a tube chassis car with a body instead of "production based"
2) Someone may be concerned that main hoop integrity would be affected by the loading in a very serious accident. I think at the lower end it's braced a bunch anyhow by the door bars and the susp links would pull off before actually moving things around.



Perry

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Perry
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Re: suspension pickups on a main hoop?
November 20, 2015 12:16PM
Nuthin huh? I expected at least a catchy slap down or maybe at best contact with an actual scrutineer, but nuthin?

I suppose I'll plan for the safe route, which is to install the mount an inch or two behind the hoop and tab it to the hoop as a "main hoop support attachment to the shell"..



Perry

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john vanlandingham
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Re: suspension pickups on a main hoop?
November 20, 2015 12:35PM
Quote
Perry
Nuthin huh? I expected at least a catchy slap down or maybe at best contact with an actual scrutineer, but nuthin?

I suppose I'll plan for the safe route, which is to install the mount an inch or two behind the hoop and tab it to the hoop as a "main hoop support attachment to the shell"..

Myself been busy.. I cannot imagine any problems running a E/W bar between the feet of the main hoop and picking up mounts off of that if I understand whatchoo are saying.. Maybe piccies drawings would help..



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Re: suspension pickups on a main hoop?
November 23, 2015 03:50AM
Quote
john vanlandingham
Quote
Perry
Nuthin huh? I expected at least a catchy slap down or maybe at best contact with an actual scrutineer, but nuthin?

I suppose I'll plan for the safe route, which is to install the mount an inch or two behind the hoop and tab it to the hoop as a "main hoop support attachment to the shell"..

Myself been busy.. I cannot imagine any problems running a E/W bar between the feet of the main hoop and picking up mounts off of that if I understand whatchoo are saying.. Maybe piccies drawings would help..

The Mazda RX-3 that Michel Hoche-Mong now owns is done exactly this way.
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Perry
Perry Seaman
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Re: suspension pickups on a main hoop?
November 30, 2015 11:09AM
Thank you sir.

The more I look, I suppose that almost anything goes in the open class as long as you don't put a sharp spike on the steering wheel.



Perry

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hoche
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Re: suspension pickups on a main hoop?
December 08, 2015 01:16AM
Quote
john vanlandingham
I cannot imagine any problems running a E/W bar between the feet of the main hoop and picking up mounts off of that if I understand whatchoo are saying...

Ain't none. There you go - an official scrutineery OK.

Quote
Doivi Clarkinen
The Mazda RX-3 that Michel Hoche-Mong now owns is done exactly this way.

Yep. And that will be preserved, although I might change the links at both ends to Heims, depending on how much it binds when I get it all back together. We'll see. They may be far enough outboard that it's not a problem.

FWIW, the lower/outer front links just go to the stock brackets where the leaf springs went. They weren't reinforced. The car a hit (well, probably several) on the passenger side and the bracket held up fine, but the floor pan where it's attached buckled. It's tilted a degree or two. Summary: I think think leaf-spring brackets are pretty strong, but you may want to reinforce the area around them.



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Perry
Perry Seaman
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Re: suspension pickups on a main hoop?
December 09, 2015 10:52AM
Sorry all, I hassled you and then got super busy and ignored my own thread for a while..
I mean the suspension brackets/pickups are actually on the verticals of the main hoop. In the cheesy pic attached, the black is the approximate (measured with a micrometer of course) main hoop location and the yellow is two links of a 5 link independent rear suspension. We're talking about the pickups at the front of those links. Because the cabin of these cars is so narrow and the wheels stick out of the body, these links don't land on a bar that goes across the car, they end up right on the vertical lower part of the main hoop.

Hope this makes sense.



Perry

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KTM 950 ADV
74 Beetle turbo-efi etc..
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tdrrally
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Re: suspension pickups on a main hoop?
December 09, 2015 11:04AM
i favor a proper class 11 cage, check this out
http://www.thesamba.com/vw/forum/viewtopic.php?p=1819233



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