RE: The Brave Pill: TVR Chimaera
Discussion
carinaman said:
The comparisons with the Elan backbone structure suggests that with a bit of strategic bracing the TVR chassis could be improved?
Sportomotive offers an 'improved' chassis, but from what I can see they seem to be mainly suggesting that the improvements come from better specification (CDS) and beefing it up to heavier gauge tube, which is absolutely the wrong way to approach it (as the Elan's superior stiffness from a bit of 18 gauge folded sheet, at much less weight than even the standard TVR chassis proves).At risk of upsetting the TVR fanbois by using big words that they don't understand, all backbone chassis are fundamentally limited, because they suffer from a low second moment of area. But they can be made to work well by ensuring that their low second moment of area is at least a 'perfect' structure, with no discontinuities; whereas other chassis types for open cars offer a much higher second moment of area, but invariably have big, unbraced 'holes', to fit inconvenient things like people into them.
The TVR makes a fantastic job of getting it wrong on both counts. Whoever designed it clearly had a very weak understanding of structures.
What it needs is to be properly and fully triangulated and - more importantly - to have a proper fully stressed closure to the underside of the engine bay and transmission tunnel (not the half-arsed, laser-cut flat sheet that bolts in under the transmission areas and does f
k all).But torsional stiffness is only half it's problem. The other major limitation is the suspension geometry. Even setting aside the issue with rear roll centre, the decision to adapt Sierra front hub carriers (which were designed for MacPherson strut) left it with badly flawed steering geometry. It's possibly unfair to pick on the TVR for this, as it's a common problem with a lot of other kit cars of that era, which were trying to make do and mend with the cheapest and most readily available components that existed at the time. A few extra quid spent on bespoke hubs and uprights would have avoided the issue, but someone at Blackpool decided, rightly or wrongly, that cost was more important than competence.
This is all getting rather tedious, all this talk about geometries and stiffness.
I have had a Chimaera for 17 years now, and it is still a great car to take out for a drive around some winding country roads with the V8 burbling away. You don't have to drive it at 10/10ths to enjoy it.
Is the chassis as stiff as a Lotus or a cast iron gate?
Probably not, but really I don't care if the chassis flexes a bit, I am driving on public roads not on a race circuit. I don't feel that with driving on normal roads that I would ever get near to showing where there were any significant shortfalls in the chassis anyway.
People buy TVRs for the noise, the looks, the left-field details, and the fact you are driving a car that can bite back. It is a kind of 60's hairy chested sportscar reimagined for the 90's.
To try and think of them as a track going racer is missing the point.
I have had a Chimaera for 17 years now, and it is still a great car to take out for a drive around some winding country roads with the V8 burbling away. You don't have to drive it at 10/10ths to enjoy it.
Is the chassis as stiff as a Lotus or a cast iron gate?
Probably not, but really I don't care if the chassis flexes a bit, I am driving on public roads not on a race circuit. I don't feel that with driving on normal roads that I would ever get near to showing where there were any significant shortfalls in the chassis anyway.
People buy TVRs for the noise, the looks, the left-field details, and the fact you are driving a car that can bite back. It is a kind of 60's hairy chested sportscar reimagined for the 90's.
To try and think of them as a track going racer is missing the point.
Equus said:
You'll notice some very significant differences, too: the Elan chassis was designed by someone who understood structures, hence is a closed box section spine, not the (effectively) open inverted U shape of the Grimeara backbone. It also has competently designed (and very much more supple) suspension.
For reference:
I think I'd be embarrassed to admit that my 1990's sports car on 205/225 section tyres could only 'distinctly not be left behind' by a 1960's sports car on tall profile, 155 section tyres, on a smooth track...
The Elan's handling balance is fabulous, but its outright levels of grip are really very modest, by modern standards. Any even halfway competent modern sportscar ought to be able to leave it for dead on a racetrack - it's on bumpy backroads where the superior (and surprisingly soft) suspension means it can still hold its own, even these days.
Wow - someone clearly had a bad day in a TVR. For what it’s worth I have no doubt the Elan is a great car - shame you need to be a smurf to actually fit in one. I’ve just sold a Lotus Elise S - possibly one of the best handling cars in production - and I’ve traded it in for a Chimaera - just so much more character - both great cars but the TVR has the drama - I don’t care that it won’t lap Castle Coombe like the Lotus - for a B road trip around the Cotswolds or Lake District it’s the better car..and if you fancy a trip to Le Mans it’s perfect - plus you can fit more than a toothbrush in the boot!For reference:
- the torsional stiffness of a Grimaera chassis is about 2,650lb.ft/degree.
- the torsional stiffness of a bare Elan backbone chassis is about 4,500lb.ft/degree, despite being a lot lighter (it only weighs 45kg) and being fitted to a much lighter overall, lower powered, and more softly sprung car.
I think I'd be embarrassed to admit that my 1990's sports car on 205/225 section tyres could only 'distinctly not be left behind' by a 1960's sports car on tall profile, 155 section tyres, on a smooth track...
The Elan's handling balance is fabulous, but its outright levels of grip are really very modest, by modern standards. Any even halfway competent modern sportscar ought to be able to leave it for dead on a racetrack - it's on bumpy backroads where the superior (and surprisingly soft) suspension means it can still hold its own, even these days.
I'm with Equus on this one, last time I was at Snetterton I got overtaken going in to a corner by an MX5, and despite the shame of it, I clearly remember thinking as I blasted past it on the straight 'Jeez I wish I had more torsional stiffness, another 2,500lb.ft/degree would probably do it'
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