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.

[nmallia]

Hi Lads and Lasses

Its been a while since my last post. We have been refining the setup and i think we have hit a sweet spot where the car is now very competitive. In most hard corners the car lifts the inner front wheel...an indication of a good setup (see pic below).

So much to say.... i will try to be as factual as possible. The following is the setup:

1. Front

a. Lower wishbones: Standard, however with the pick up points have been modified as indicated in my article.

b. Upper wishbones: These are bespoke that started life as a set for a Lotus Elan+2  . https://www.spydercars.co.uk/lotus-elan-2-front-suspension/#iLightbox[gallery_image_1]/0. Lengths cut to suit original spitfire geometry. Rose jointed.  Camber and caster adjustable on car . See pic attached

c. Dampers: AVO coilovers modified to shorten the travel.

d. Springs: Faulkners Race Springs 2.5" Internal Diameter, Free Length 8.0 Inch/203.2mm, Rate: 650lbs/ins / 114N/mm. Purchased from Demon tweeks  SKU: FLK08P0650

e.  Antiroll bar: 1 inch thickness purchased from moss.

 

2. Rear

a. Lower wishbones: As per my article. These started life as adjustable GT6 radius arms. https://rimmerbros.com/Item--i-151092. Ends modified to suit geometry as indicated in article. 

b. Leaf spring: As per my article but slightly modified.  Lower two leafs came from  a Spitfire MK4 swing spring.   Top Aluminium bar with shims for incremental ride height adjustment. 

c. Rear dampers: Spax ride adjustable. Low ride variant. These are a huge improvement over the GAZ type i had before. Those used to bottom out after 50mm travel. https://rimmerbros.com/Item--i-GDA4011SPAXLOW

 

 3. General 

a. Chassis: Six point roll cage including stiffening struts connecting the front suspension turrets to roll cage.  (huge stiffness increase). See pic attached.

b. Brakes: Hispec ultralight 4. These gave me some trouble as the pistons had little clearance in the bore and would lead to permanent braking. We had the bores machined to the correct tolerance. 

c. Wheels: Split rims from Image wheels UK.  7.0 X 13" RM3 - Silver Centre ET25. These are very light. 

d. Tyres: Avon Semi slick, super soft compound. 

d. Alignment. See pic

e. Corner weight adjustment: See pic of results with driver of 73kg

This car has matured gradually over the last 10 years into a purposeful race car, however it is still comfortable on open roads,  I take pride in driving it to and from racing events. 

I have let all my secrets out . Certainly not for the puritans, however its been a thrill unlocking the potential of the small chassis Triumph. 

As the say the proof of the pudding is in the eating....This year at the Malta Classic 2024 races I was busy chasing a Jaguar D type driven by a local karting champion. 

Hope to see some you next October at the Malta Classic 2025 , i will do my best to keep you entertained during the events. https://www.maltaclassic.com/

Keep well

Nicky

 

 

 

[Nick Jones]

Wow! I think that video says it all. That is a quick car. And the driver is very skilled…….. and brave!. That track/course! 

[PeteStupps]

Aha excellent, thanks for dropping in Nicky - it was me that posted on your Youtube vid asking.

Really interesting to read / see the pics, the car seems to go so well in your videos I was very intrigued to know if the suspension mods from the article worked.

Pete

[andymcp]

11 hours ago, nmallia said:

Hope to see some you next October at the Malta Classic 2025 , i will do my best to keep you entertained during the events. https://www.maltaclassic.com/

I need to convince the wife we have to revisit Malta next October!  The event website is definitely worth a look... 

[zetecspit]

This has now got me thinking. Mainly about the forces on lower wishbones.

My thinking is that the front wishbones on the small chassis cars are not exactly chunky. And yet they cope perfectly well with the significnt forces from braking, even on the most uprated brakes etc. As a thought experiment, all the braking force must go through the wishbones, they are the only thing attaching teh wheels to the chassis.

Likewise the rear wheels are attached via the spring (acting as the upper wishbone) and on "rotoflex" cars the radius arm must transmit all the acceleration and braking forces to the outrigger/heelboard. Otherwise the wheel would flop about. A lot. The lower wishbone doesn't add any real stability with its single inner bush. 

It would (in my little brain) make sense to have a lower wishbone as wide as possible especially at the chassis end. Would it be better to have the lower wishbone made as a single piece, ensuring it stays flat. Or would that introduce significant extra stress for little if any benefit? The type shown above and used by Marcus seem to work nicely from what the owners are saying. An elegant solution. And something I really ought to consider when the Spit gets its next light refurb (this winter is written off, the Vitesse is first in the queue once the sprint is sorted)

Now off to finish a bit of work on the MX5 after its clean MoT pass yesterday...

 

If any of my ideas/ssumptions above are incorrect, please say! 

Edited Wednesday at 08:39 AM by zetecspit

[Nick Jones]

Torque reaction forces from acceleration are passed back to the diff and its mounts.  However, the opposite and sometimes larger braking torque forces are passed directly into the vertical link and must be resisted by the suspension links.

The proportions taken by the various parts varies from layout to layout, but quite a bit in all cases by the damper I think.  This especially true with roto style layouts using closely spaced  lower links with Rose joints at both ends. They do exist and appear to work just fine (evidence GT6Steves very successful red racer).

[JumpingFrog]

Since Clive mentioned the front wishbones...

Anecdotally, and not directly related to racing, when driving long distances on washboard gravel we noticed that the lower wishbone bushes took far more damage than the upper. I assume the reasons for this are that the upper wishbone is shorter (less leverage?) and probably more rigid due to the way the ball joint is clamped. The lower wishbone however only has just one thin riveted brace, and is longer.

I am curious if there would be any advantage in a replacement lower wishbone (tubular?), although the lower wishbone to chassis mounts aren't super rigid to begin with.

Edited Wednesday at 01:48 PM by JumpingFrog

[Escadrille Ecosse]

5 hours ago, zetecspit said:

Likewise the rear wheels are attached via the spring (acting as the upper wishbone) and on "rotoflex" cars the radius arm must transmit all the acceleration and braking forces to the outrigger/heelboard. Otherwise the wheel would flop about. A lot. The lower wishbone doesn't add any real stability with its single inner bush. 

It would (in my little brain) make sense to have a lower wishbone as wide as possible especially at the chassis end.

Roger, it in effect does. The rear 'wishbone' of the rotoflex design isn't really a wishbone, it's a lower link that happens to have a relatively wide double pivot at the outer end. The radius arms on the rotoflex design are positioned so as to form as near a lower wishbone as possible in combination with the lower link. Also with the single bush in the lower link you can have toe adjustment.

Not a perfect but I imagine done to minimise chassis/body mods while ensuring that torque/braking loads from the rear end were taken by the spring/diff and heelboard in the same way as the swing axle cars do - the inner mount of the lower link/wishbone takes very little in the way of loads other than holding the wheel out on cornering. Doing so would have avoided too much re-design and re-testing of addtional chassis mounts if a full lower wishbone mounted on the chassis was required. Remember production vehicles not home-mods.

And whilst they work OK as above and in Nick/Chris's mod in a Spit, the inner mounts of their rear wishbones are really a bit close. Ideally they should be a bit further apart, especially for a torquier engine in a heavier car (like a GT6). But with the existing chassis layout - curve at the front and cut off at the back - there isn't room.

Incidentally I know of a quite successfull hillclimp MkIV Spit that used front lower wishbones and brackets as rear lowers.

Don't know that's what Webster and his team were thinking at the time but I suspect very much along those lines.

Look at the Lotus Elan. The inner lower wishbone mounts on them are wider, as are the outers and just as importantly they have the very long vertical strut to stabilise things and help with torque reaction.

The rotoflex upper link - the spring - has to do a lot of work. Even more on the swing spring cars. Having experimented with making a rigid composite spring pivot like the Triumph swing spring I found that ANY slack in the spring location at the diff would lead to violent 'tramp' in the uprights on real hard acceleration with any significant tyre slip. To the point where it could be seen from outside. Accompanied by a truly daunting amount of noise and vibration.

34 minutes ago, JumpingFrog said:

Anecdotally, and not directly related to racing, when driving long distances on washboard gravel we noticed that the lower wishbone bushes took far more damage than the upper. I assume the reasons for this are that the upper wishbone is shorter and narrower (less leverage?) and probably more rigid due to the way the ball joint is clamped. The lower wishbone however only has just one thin riveted brace, and is wider and longer.

The geometry of the trunions, uprights and dampers is such that most of the dynamic loads, especially fore and aft from bumps, etc go into the lower wishbones. Having had a few shunts racing, the lower wishbones and brackets are actually pretty tough and it's the chassis that bends. And while adjustable upper wishbones make life a lot better for set-up I think that they are actually detrimental in a shunt and put crash loads into the towers, lower wishbones and chassis that would otherwise be absorbed by a relatively benign crumpling of the factory uppers. Again, practical experience.

[Mark]

The engine sounds more like a motorbike than a 1300 triumph lump, I bet 0 to 60 is rapid. Is the gearbox Triumph? Very well sorted Spitfire.