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PostPosted: Mon Feb 21, 2011 11:17 am 
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First off, a design process only, consider the discussion as a means to define why not to do it.

Honda, VW and Dodge have at some point all used them in production vehicles. Hollow torsion bars (splined on both ends) are readily available in a variety of lengths and wall thickness fairly cheaply. The adjusting bolt for the solid mount end can be accessible thru a small hole in the body allowing fast and easy adjustment and having a couple of mounting points on the linkage arms would provide additional fine tuning ability. They don't have to run parallel to vehicle centerline to fit but might project into the footwells, a common length is 30".

The biggest question I have is, how light can you make the shock linkage with no spring load on it?
Could you run it off of an arm projecting inward from a relatively light control arm since all of the load is dynamic?

I can think of a few ways to connect the torsion bar itself. (I'm assuming a longitudinal orientation)
A direct connection to the base of a control arm for example requires a stronger (heavier) arm to resist bending.
Kurt's testing shows that with his design for inboard coilovers.
Honda used this method in front on some cars, VW did the same with a transverse orientation on the rear of the Bug. Makes for a heavy control arm.
An actuating arm can be attached to the shock linkage on inboard shocks but does this really gain anything other than a bit of packaging? Its common to mount antisway bars in a similiar method so theres precedent and parts around.

If you used an appropriate upper ball joint, what would be the negatives of a pull rod suspension with linkage actuating the torsion spring?

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PostPosted: Tue Feb 22, 2011 9:48 pm 
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Well Jack, I thought you'd get some input from the guys and I've been watching to see what came up as I like the simplicity that T bars can bring to a design. So, just to see if we can stir the pot a bit, here's my 2ยข worth.

For years, T bars were SOP on American circle track cars (think "Indy"), and still are on the dirt circle racers like sprints and midgets. I believe this is primarily due to the ease of setting up the chassis and making changes. Also, a stack of bars will take up a lot less room in your transport than a pile of coils. In addition to the cars that you mentioned, IIRC the Jag E-type (and probably the D as well) used longitudinal T bars acting directly on the lower A arms of the front suspension, much like the Chrysler cars. You mentioned the heavy control arm to carry this load, but I think the Jag's A-arms were forged aluminum, much like the current crop of Corvettes. In place of the forged arms, how about arms machined from alum billet?

I don't know. Just a thought. anyone else have any ideas?

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PostPosted: Tue Feb 22, 2011 11:26 pm 
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I think coil-over shocks solve the same problem. Wrapping the spring around the shock and then providing for ride height adjustment is pretty convenient and it doesn't leave you with any other problems to solve. If you had an alternative to the shock too, things might be different. Taking the spring off the shock and then leaving the shock there doesn't move things forward much though.

Those oval track guys have all sorts of neat parts, it's just hard to find very many places we can or need to use them. I wondered the same thing about those torsion springs, but didn't come up with anything.

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PostPosted: Tue Feb 22, 2011 11:27 pm 
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I've researched this before and thought it was an idea worth pursuing, BUTT (and you knew there was one) it looked like redesigning parts of the suspension that seemed to work pretty well already.

Cost wasn't a big issue because there really wasn't that much difference although the Tbars were slightly more expensive.

Supply wasn't an issue, although I thought it would be, as you said there's lots of circle track cars and others that use/used them.

Flexibility wasn't as big an issue as I thought as there's quite a variety of bars available.

Another BUT is that coil springs can be found everywhere!

BUTT STILL I like it just due to the novelty & simplicity factor. How many builds have had space issues with the spring size?

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PostPosted: Wed Feb 23, 2011 8:45 am 
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My Isuzu donor had torsion bars as well.

Use of TB's not only requires more robust LCAs (unless you go with push-rods, which suggests that the 'rocker' could even be a lever on the end of the torsion bar - or still be a rocker with the shock still inboard), but a torsion bar itself will likely (certainly?) be heavier than the coil on a coil-over.

To really think wierdly, you could use a sprint car type torsion bar lever, like:

http://www.speedwaymotors.com/Aluminum- ... ,2136.html

bearing directly on a pad or roller on the LCA ..... which would allow use of current, or near current LCAs.

But when all is said and done, the AFTER end of the torsion bars on my Isuzu ended up on a rather robust cross-member which had to carry the springing loads. This would be a new bit of structure on the locost 7.

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PostPosted: Wed Feb 23, 2011 10:04 am 
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Warren Nethercote wrote:
(unless you go with push-rods, which suggests that the 'rocker' could even be a lever on the end of the torsion bar - or still be a rocker with the shock still inboard),


I recently read a torsion bar thread on here and someone mentioned that F1 uses torsion bars. Gobsmacked, I researched this and found that they pretty much do what you say above.

They have pushrods that actuate a rocker with its axis on a near vertical plane with the top being angled outboard slightly). The rocker is on the end of the torsion bar and it also acts as the link to the inboard shocks. It makes for a very elegant, compact, lightweight design and it should work well with existing lcas designed for coilovers.

However, (there is always a however) they use stubby hollow titanium torsion bars with a very tight lifespan tolerance. They would not be much use in much else unless you drove around with a supply of spare torsion bars for when they break.

We'd need to use steel ones for longevity and I suppose you cannot get long life stubby steel ones... (I have no idea)

Still, an interesting idea though.

Tom...


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PostPosted: Wed Feb 23, 2011 10:55 am 
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It was looking at the Redbull RB5 that got my thought process going.
Turns out hollow bars are available at 18" and 24"", more than short enough to fit inside a 7 engine bay and. ..
Sprint cars seem to frequently use a torsion arm of 8" to 14" in length. I would expect to use a shorter one :? even though 14" would allow a vertical downrod with the bar mounted on the inside of the frame upright I'm uncomfortable with that long of an unsupported arm. bars are available that would get into the desirable spring rate with a much shorter arm, maybe 2-5" would be more appropriate. A shock mounted vertically inline with the downrod could probably be tucked up into the bodywork with possibly small bump at the rear of the nose cone. No coil spring to surround so diameter is much smaller, might be able to fit inside the body but I don't think so.
(I robbed this from a Maserati fan site)
Attachment:
chubasco-10.gif
chubasco-10.gif [ 29.64 KiB | Viewed 2466 times ]

heres one from http://www.ukcar.com/features/tech/suspension/wishbone.htm
Attachment:
push_pull.jpg
push_pull.jpg [ 12.43 KiB | Viewed 2466 times ]

the one set of pics I found of a hollow bar in comparison to a solid bar (which I failed to save the link :BH: ) showed the hollow bar with a weight of 565 grams or ~20 oz (iirc it was a 30" bar).

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PostPosted: Thu Feb 24, 2011 1:28 am 
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oldejack wrote:

The biggest question I have is, how light can you make the shock linkage with no spring load on it?


Not much lighter at all, shocks, especially 'sports' ones, offer more resistance than it's partner spring does.


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PostPosted: Mon May 02, 2011 12:01 pm 
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For my first attempt at a home built car, I'm kicking around the idea of using a nissan truck torsion front end, pathfinder rear (triangulated 4 link and a locking diff), 240sx engine and trans. all available super cheap, and it eliminates me having to figure out how to make identical, quality control arms, link bars and such at home. the only downside is the ugly 6 lug wheel pattern. This way I can learn what works, what space I have, compromises made and I won't get frustrated by my limited fab skills on important parts.

I could even use my Frontier as a donor for it all, runs good and only cost $500.

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PostPosted: Wed May 04, 2011 7:31 am 
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It's your build, but I think you will regret putting truck suspension on such a light vehicle. Your unsprung wt ratio is going way to high. These builds typically takes years, so you will have more then enough time to improve you fab and welding skills.
Dave W


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PostPosted: Wed May 04, 2011 2:04 pm 
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A nissan frontier has a little lower control arm with a tension rod and upper a arm, sort of like a mustang II. the components are fairly light stuff, don't think of it as a truck, so much as a econo car with a big trunk. I imagine an inboard coil over could be adapted easily, as the lower arm has a stout area where the torsion spring bolts to.
I haven't even bought the book yet, just sitting back watching for now. I just sold my 53, I now have some cash, and a big empty space in the shop to fill. I might do a track-t first, get my confidence up and then knock it out without thinking my way out of it.

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PostPosted: Tue Jun 21, 2011 1:30 am 
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Hey guys, I think you're missing one of the main benefits of a torsion bar suspension.

When a spring compresses it creates a bending load on the damper, this creates friction inside the damper. All of this force that is going into your dampers is normal force that could have been at the contact patch.


This description says pretty much the same thing... to do all four dampers you would be looking at $1600... Most indy cars had these before dallara made the switch to torsion bar springing.. just like f1.


Quote:
These precision devices allow the spring end coils to tilt up to 4 degrees as the spring is compressed, reducing the bending loads on your shocks by as much as 96%. This reduction in side force and friction allows more force and energy to be directed to the car's mechanical grip while reducing wear on your shocks. This isn't just theory. Hydraulic perches have proven themselves on the track with rave reviews and reduced lap times. Having a hydraulic perch at one end of the spring will reduce shock bending loads significantly; however, hydraulic perches at both ends of the spring will provide optimum performance.
http://www.pegasusautoracing.com/productselection.asp?Product=1871



A far less effective option is to install torrington bearings on the perches... this at least gets rid of the axial bind and makes adjusting ride height much easier.

Image




ANYWAYS, what I'm getting at is torsion bar springs don't have these problems but running a pushrod setup is almost required.


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PostPosted: Tue Jun 21, 2011 2:47 pm 
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FYI here's a good pic of some DSSV F1 dampers and torsion bars: http://www.racecarsdirect.com/listing/3 ... mpers.html

No connection to seller, blah, blah, blah


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