Suspension Redesign & Optimisation - Spitfire, GT6 & Vitesse

[nmallia]

Hi

The attached article has been prepared to compare the suspension setup of the Spitfire Mk IV and that of the GT6 Mk2 to the suspension setup of the Lotus Elan that has been regarded as one of the best handing small sports cars ever produced. The similarities of the front suspension will be highlighted as well as the compromised solutions at the rear. Finally modifications are presented to bring a triumph small chassis suspension to perform remarkably close to that of the Lotus Elan.

I hope you find this interesting & useful.

Nicky

Triumph small chassis suspension optimisation..pdf

[Nick Jones]

Nicky,

That's a fine piece of work. It will take me a little while to fully digest it, but I reckon I'm going to be mostly agreeing with you as we produced something pretty similar for our Spitfire a couple of years back.  It didn't occur to us to try and control the deflection shape of the spring though and in fact we are still using the MkIV spring complete with centre pivot.  The car drives nicely and handles well but is purely a road car with a standard 1300 engine and not driven especially hard, so perhaps not a definitive test.

Have you actually built one to test yet?

Also a question about the MkIV/1500 examples shown - are they using the long or short driveshafts?  Not sure how much difference it makes?

 

Cheers

Nick

[JohnD]

NIce, Nicky!   Would be good to include some of your excellent drawings of the Lotus setup too.

Sometime ago, before CAD, I analysed the same thing.    Appeared in the TSSC's Courier, and is now repribted on this site.  Hope you're interested!   See: 

John

[nmallia]

Hi

The drawings are of an early Spit IV short axle (48inch track) The later cars with longer axles (50inch) have a 6mm lower Roll Center. Its a marginal improvement. I had seen the pics of your car before and they included in the 'case cars' folder i have compiled over the years

I should be testing the system at the end of september. I will naturally keep you posted.

Nicky

[nmallia]

Nice article John!. I had seen this before and had taken notes of it. As you said CAD drawings allows the designer to presenst a full picture, moreover as you draw stuff to scale you start making  discoveries of  things you had not thought of before.

 

Nicky

 

[yorkshire_spam]

Really interesting read, thanks for sharing Nicky - I love a bit of modeling in FEA.

[egret]

Really interesting stuff.

[nmallia]

Hi everyone. We have some good progress in the prototype build. Attached are some images. I have fitted everyting loosly and it all seems to add up (so far). Will keep u posted.

[JohnD]

Those dampers are acutely Angled even with the weight off the car.   As the suspension goes i to bump they willgomoreandmore horizontal, and ineffective.    Suggest you get, or fabricate your own version, of the brAckets that put the upper end three inches further out.

 

John

[Nick Jones]

Looks good to me Nicky - and somewhat familiar. Do wonder a bit what effect that spring stop, and the sudden change in spring rate it will bring, is going to feel like.

Dampers are pretty much as fitted to all swing axle cars John. Yes, a fairly steep angle and increasing with bump, giving a falling rate, but this was designed in by ST at the outset. It is, as you say, fairly straight forward to fabricate brackets to bring the dampers more upright and increase their effect rate, but if adjustable dampers are fitted, not perhaps necessary.

Nick

 

[Mark]

Just stumbled across this thread, must have read it first time around,  but very interesting.  I am still working on the mk3 Spitfire, I was going to replace the fixed spring with the later mk4, 1500, swing spring. But after reading this thread it's got me thinking.  Possibly got some Roto rear uprights somewhere, just everything else I need, but whilst I have a bare chassis infront of me, maybe it's something I should think about having a go at. 

Seen Nickys Spitfire on YouTube, one very quick,  excellent handling Spit.

[JohnD]

A most interesting thread, Mark!  Thanks for reviving.         

You have seen Nicky Mallia's Spitfire online?    Sad to say, he never followed up the above posts with actual handling reports.

John

[Escadrille Ecosse]

Don't remember seeing this so thanks for reviving it Mark.

I have seen a Cooper rear suspension in the flesh and the biggest, and I think most significant, difference in the mounting arrangement is that the load is taken into the chassis only at the the two points part way along the spring. The centre clamp bracket is only there to prevent the spring from moving side to side as the load sleeves have to allow the spring slide a little as it bends.

The Corvette C5 monoleaf composite spring is mounted in a very similar manner although that suspension uses top and bottom wishbones.

The centre portion of the spring is completely free to move up and down so it is not forced into the double curvature shown on Nicky's CAD model of his design. I suspect this would cause a rather harsh ride and maybe eventually overstress the spring.