Lotus Elan

Front Susp. Cross-Brace

PostPost by: cabc26b » Tue Oct 23, 2007 12:11 pm

I was at a race meeting sans car this past weekend and had time to check out a couple of elans I had not seen before. Both the cars were runnning a front cross brace - the devices were similar in purpose of design but not executed the same. both braces started in the center of the lower front cross member of the frame and ran 2 tubes up towards the top of vertical box section that holds the pins for the upper suspension arms and shock mount. One version ran out to the upper pin and attached with a rod-end. the other was mounted to the inboard flat surface of the boxsection ( around where the bobbin and plate meet) A single tube ran across the top tieing in the whole assembly as a triangle.

Questions to the forum -

Is flexing here a a known fault and how does it manifest its self on the track ?

Have any of you all run this set up ? If so was there an improvment and to what aspect of car behavior.

In the past I have just plated the bottom cross member (even for my road cars .. see photo) -

Employing this solution would require a relocation of the radiator and impact to other plumbing as I have both an oil cooler and remote mount oli filter up in the nose. So while they look cool ( esp the nickel pated on with rod ends) it would be very a very expensive image over substance move.
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PostPost by: Foxie » Tue Oct 23, 2007 4:34 pm

The original cantilevered front towers imho were not optimum design. My original chassis developed major cracks here. The Spyder chassis is a big improvement, but is still cantilever design. I've seen Stephen Doyle's extremely modified racing Elan (unknown type engine with reputed 290 bhp) has a cross brace fitted. Seems to be a simple and beneficial mod.

Sean Murray
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PostPost by: msd1107 » Tue Oct 23, 2007 4:50 pm

From the time the Elan was introduced, I wondered about the design of the front and rear chassis. Without proper cross-bracing and triangulation, the chassis is either weaker in torsion or heavier than necessary.

As you mentioned, twisting of the chassis can be decreased by putting in gussets. Theoretically, the stiffer the chassis, the better (or more predictable) the handling.

If you can free up space at the front (go to a front mounted radiator to clear space in this area), a cross brace across the top is the single most effective way to stiffen the front suspension chassis area. Triangulation improves the stiffness.

But check with your sanctioning organization as to the acceptability of these chassis modifications.

And if you do the front, the same stiffening should be done at the rear.

David
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PostPost by: cabc26b » Tue Oct 23, 2007 5:20 pm

Interesting points -

The rear is less of a concern because almost everybodies roll cage ties the two rear struts in.

On torsional rigidity I always thought that the majority of the work here was performent by the central box ( backbone) with the forks and the box acrross the front supporting the role.

Could it be that the brace keeps you from having to weld up the chassis ?

Would still like to hear from sombody who runs a car with the brace and speak to if it helps with performace , PM or does it help with both ?
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PostPost by: rgh0 » Wed Oct 24, 2007 11:04 am

I have contemplated this mod over the years and in the end not done anything for the following reasons.

1. I would have to move the radiator and this is not allowed in our regs
2. If I worked around the radiator it would be hard to make the braces stiff enough to be any good.
3. I do not observe any significant front end movement in practice versus the body shell. This is easy to judge via the tops of the front shocks which fit through a small hole in the body and any signficant morement would result in body cracking around these holes. The is certainly chassis twist between frort and back with the stiff front roll bar I run but bracing the front towers does not help this.

If running a heavily modified car with wide track and wide tyres then extra stiffness around the front end probably helps. For an historic Elan in similar to 26R specification with limited tyre width and grip I dont think its needed and is more show than go.

cheers
Rohan
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PostPost by: batfish » Wed Oct 24, 2007 8:17 pm

If you can make it out this a photograph of a cross brace that I took last year on an Elan racing in England, it is the only time I have seen one in 15 years of being around racing elans, I was told that it was a period modification and to get around the regs was described as a mounting for the cooling fan although in this case the fan was rad mounted. It consisted of two rods running diagonally from the top body mounts on the turrets down to the opposite end of the front cross member. I assumed that this brace is to prevent the top of the turrets from moving inwards under load and perhaps make up for any strength lost in using lightweight racing bodies.

regards

batfish
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PostPost by: Midlife » Wed Oct 24, 2007 9:20 pm

When spyder fitted my full cage, I had a good conversation with Andy Widnall about this, and come to the conclusion he was probably right that it would benefit from one. On my car this is now the weak area and would flex quite allot. One of my plans this winter is to get another rad (shorter and wider) and mount it further forward, then fit a cross brace. My event regs allow this though.

Cheers

Doug
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PostPost by: bill308 » Wed Oct 24, 2007 11:18 pm

I'm not sure there is any benefit in the rear because the rear is already tied to the cockpit to boot rear bulkhead by the turret attachment points. I previously had a Spyder roll bar and now am installing a Safety Devices roll bar. I don't believe either one imparts any real stiffness to the rear of the chassis as neither one fully triangulates the cross plane. The OEM fiberglass panel running between the rear turrets should be pretty stiff if the bolted connection is solid. This is one example were the body stiffenes the chassis.

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PostPost by: steveww » Thu Oct 25, 2007 11:11 am

This may not be standard but my S4 came with a brace across the rear turrets. Nothing on the front but it is something I have been giving some thought to.
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