Lotus Elan

Spyder Chassis

PostPost by: William2 » Sun Nov 03, 2013 10:06 am

Some experts would argue that the extra rigidity of the Spyder chassis isn't necessarily a good thing as regards road holding. The combination of the original body and chassis bolted together was designed to flex as a unit. At the end of the day there wasn't much that Chapman got wrong!!
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PostPost by: GrUmPyBoDgEr » Sun Nov 03, 2013 10:56 am

William2 wrote:Some experts would argue that the extra rigidity of the Spyder chassis isn't necessarily a good thing as regards road holding. The combination of the original body and chassis bolted together was designed to flex as a unit. At the end of the day there wasn't much that Chapman got wrong!!



Well I'm amazed; who was it that made that statement?

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PostPost by: Spyder fan » Mon Nov 11, 2013 8:04 pm

Elanintheforest wrote:Julian, I don't think that I would believe anybody who claimed that one chassis made an Elan handle better than another. I doubt that anybody has ever tested two cars back to back with identical tyres, shocks, springs, bushes, steering, geometry, weight and conditions, one with a Spyder chassis and one with a Lotus chassis, to be able to feel or quantify any difference.

I would love to see someone put forward that argument though!

Mark


Mark,
Given the choice between the two I would always choose the Spyder chassis just because of the advantages for maintenance and rust trap removal as already mentioned. I expect both chassis would handle exactly the same if fettled with the same equipment.
As I'm sure you are aware lot's of Spyder chassis cars have had the upgraded rear suspension system fitted (extra top wishbone basically) and other trick bits like adjustable toe wishbones, my S4 probably has their whole catalogue fitted and has amazingly sharp road manners, but I doubt I would notice any difference between the two if a folded metal chassis were adapted for the same setup.
"Enhanced torsional rigidity" is a nice phrase to use down the pub though!

I agree it's unlikely that 2 identical cars have ever been built side by side one with a Spyder and the other with a Gartrac to give an opportunity for comparison. It's a common mistake made by many to compare a tired out example with a freshly built example, the newly built car will feel sharper no matter whether it has a Gartrac, or Spyder and no conclusions can be made.

Pay yer money and make yer choice, but I would go for that nice shade of grey that Spyder use all day long.
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PostPost by: stevebroad » Mon Nov 11, 2013 8:52 pm

If you believe Tony Thompson, the Spyder chassis is rubbish. He reckons that the rear top wishbone angle is wrong so the outer wheel kicks out at the top on hard cornering - well, that is what he told me a few years ago.

This photo shows what he means. Even allowing for a little droop when body is attached, it appears to me that as the body rolls the wishbone will push the top of the wheel outwards rather than pull it inwards, which is what is required in order to keep the tyre vertical.

Image

After a lot of research, including talknig to many people and reading discussions on various forums, I went for a 26R+ setup spec'd for 600bhp with double wishbones at the rear set at the right angle :-) The proof of the pudding will be in the eating, hopefully next year.
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PostPost by: Spyder fan » Mon Nov 11, 2013 9:45 pm

stevebroad wrote:If you believe Tony Thompson, the Spyder chassis is rubbish. He reckons that the rear top wishbone angle is wrong so the outer wheel kicks out at the top on hard cornering - well, that is what he told me a few years ago.

This photo shows what he means. Even allowing for a little droop when body is attached, it appears to me that as the body rolls the wishbone will push the top of the wheel outwards rather than pull it inwards, which is what is required in order to keep the tyre vertical.

Image

After a lot of research, including talknig to many people and reading discussions on various forums, I went for a 26R+ setup spec'd for 600bhp with double wishbones at the rear set at the right angle :-) The proof of the pudding will be in the eating, hopefully next year.


Yes Steve,
Tony has been known to have an opinion about products produced and marketed by others especially when he is trying to sell you something produced and marketed by himself :lol:

Ask him about his special +2 radiator and mention my name :wink:
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PostPost by: stevebroad » Mon Nov 11, 2013 9:56 pm

Agreed, hence my first 5 words. However, the rear top wishbone still looks to me to be pointing in the wrong direction, ie down :-)

When the chassis drops the top of the wheel will lean out. Top wishbones need to be at least level at normal road height so, when chassis drops during cornering, the top of the wheel is pulled inwards helping to keep it upright.
Last edited by stevebroad on Mon Nov 11, 2013 10:17 pm, edited 1 time in total.
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PostPost by: Spyder fan » Mon Nov 11, 2013 10:16 pm

It was designed by someone much more knowledgeable than myself. I don't notice any unusual handling on either of my cars. I think some have had issues with wear on the top wishbone where it connects to the strut. Mine are the latest rose jointed adjustable items, possibly produced to overcome an issue with geometry.
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PostPost by: robertverhey » Mon Nov 11, 2013 10:17 pm

Always did wonder about that myself, but I assume Spyder have calculated the two arcs so that the wheel remains at the same vertical plane. The upper wishbone is more angled downwards than the lower in the pic, but as it is shorter than the lower arm, its arc would also result in less lateral movement as it swings up, wouldn't it??

Anyway, it's possible to have just the spyder chassis and leave the rear suspension as ACBC designed it.
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PostPost by: GrUmPyBoDgEr » Mon Nov 11, 2013 11:30 pm

A long time ago I bought Spyder's oval wishbones, CV joint/donut driveshafts & rear suspension to go with their very pretty tubular "space frame" frame/chassis. In fact the whole shooting match together with new brake bits fuel lines & all the bolts, springs & dampers to round off the job.
During the build up of the chassis & suspension I took a long look at the way things were shaping up & decided purely subjectively to ditch some of those sparkly bits.
Instead the original rear struts were refurbed with new damper inserts & fitted with 2 1/4" springs.
As has been mentioned here & I have held this opinion for all of these years & my gut feeling told me then that the very short top wishbones were "just wrong"
Not long after I found someone who bought those assemble but unused suspension bits from me & since that day I have regretted not having actually measuring those suspension bits along with their locations on the chassis.
With that information any draftsman can draw a simple layout & subsequently plot the suspension movement & its effect on the rear tyre camber changes; which would most likely show totally different characteristics to the Lotus design.
I would anticipate a more drastic camber change with the Spyder suspension, which I understand from vehicle suspension dynamics is not so desirable.

I have been reluctant to add this bit of blurb to this thread & was the reason for how I penned my first posting here on the subject.

So just to repeat myself, these are just subjective observations & have no scientific proof whatsoever.

Cheers
John
Last edited by GrUmPyBoDgEr on Tue Nov 12, 2013 12:18 am, edited 1 time in total.
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PostPost by: stevebroad » Mon Nov 11, 2013 11:45 pm

robertverhey wrote:Always did wonder about that myself, but I assume Spyder have calculated the two arcs so that the wheel remains at the same vertical plane. The upper wishbone is more angled downwards than the lower in the pic, but as it is shorter than the lower arm, its arc would also result in less lateral movement as it swings up, wouldn't it??

Anyway, it's possible to have just the spyder chassis and leave the rear suspension as ACBC designed it.


The exact opposite. The top wishbone is a lot shorter than the bottom one, so any movement is translated into greater effective change in length at the top. So, with the top wishbone angled down at rest, when the wheel moves up in relation to the chassis the top wishbone effectively gets longer thereby pushing the top of the wheel out, not a good idea.

I have no idea who designed this setup or their suspension design experience or qualifications but, on the face of it and IMO, they got it wrong. Not by much, so in normal road use I doubt that it matters, but at 10 tenths on the track I would take my set up anytime. Bottom bone level and top angled up:

Image
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PostPost by: robertverhey » Mon Nov 11, 2013 11:58 pm

Interesting, a bit hard to tell from the spyder photo how different the wishbone angles really are. Maybe they're both horizontal at normal ride height? If that were the case the top of the wheel would move inward under hard cornering, would it?
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PostPost by: bitsobrits » Tue Nov 12, 2013 12:54 am

Robert, you are right on that this helps the camber situation. Most sportscars that use A arm suspensions have a shorter top arm in order to provide neutral to negative camber on cornering. Here we are bashing a short/long arm suspension design, but just look at the front of the Elan, for goodness sake! The photo of the naked Spyder chassis tells you nothing about the normal ride height of the Spyder arms. You would need to see the installation fully laden to make a "visual" call, or better yet, as one poster mentioned: have all the dimensions and plot it out. In a short/long arm A frame installation the upper arm is typically lower at the inboard end so the top of the wheel will tend to lean "in" during roll. Lower arms are typically slightly higher inboard, tending towards level when fully laden. This shorter arc of the top arm, already somewhat rotated from level, creates more camber change per deflection than the longer arc of the lower arm. A simple paper model or drawing will help set you straight.
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PostPost by: twincamman » Tue Nov 12, 2013 2:24 am

Where in the spyder chassis or one close to that design was most Likely the original plan I would use one in a moment and originality counts zero as long as the car goes. Stops and is reliable.ed
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PostPost by: Spyder fan » Tue Nov 12, 2013 8:11 am

It's times like these when you realise you can never take too many photo's, here are some shots of my S4 chassis during various stages of it's long torturous build. I hope that it's clear that the rear wishbones are parallel on my car.
They were taken low resolution on Sean's dodgy old smartphone and emailed to me as a sort of weekly blog on progress.
s4 chassis side.jpg and

s4 chassis rear.jpg and

s4 chassis front.jpg and
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PostPost by: stevebroad » Tue Nov 12, 2013 9:30 am

If that is the case then that is a lot better. I need to look at a car fitted with this setup, maybe there will be one at the Classic Car Show this weekend. However, a slight upward angle would be better, IMO, in order to counter increased negative camber on the inside wheel when cornering :-)
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