Chassis torsional stiffness model by model

[benjamincalleja]

Hey there has been alot of talk about the torsional stiffness/rigidity of the various esprits throughout the years but no one has ever mentioned a number....the only number i can find is a very shady and unreferenced 5850nm per degree for the Esprit turbo SE but that seems unlikely given its half that of the listed figure of the elise at 11000 nm per degree when various sources state that the 300 sport was only 20% stifness of the elise.   See the issue??  can anyone provide concrete numbers?

[rogerch]

Not much is the quick answer. The backbone chassis has it's limitation as a design, interestingly the Lotus30 & 40 the CanAm sports cars were of the same construction and were 2 of the least successful Lotus's, the reason given was always that they lacked torsional stiffness.

The greater the power, the greater the grip, the greater the problem becomes.

Even in a sub 300hp Esprit you can feel the frame starting to distort if get all the power down out of medium fast turn and that's on some fairly old Pirrellis

[Vulcan Grey]

I'm fairly certain the Esprit is less than half the torsional stiffness of the Elise. The X180-R with the bolted full rollcage is much less of a wet noodle than my 89SE chassis. The Sport 300, will be between those two.

[Bentzion]

I'm not sure how many of you have seen this facebook site: http://www.facebook.com/pages/F1-Motorsports-Lotus-Esprit-S3R/178516808826230

 

But this guy has decided that he's going the radical rout.  I'm not sure how successful he will be with the chassis but I would like to hear if anyone else had installed a cage in any esprit and how it effects the car's performance.  It would seem that Dave (changes) could benefit from a good cage with all the torque and HP he's making now....

[Bentzion]

It would seem as you suggest that that is true.  Ducati in Motogp made a point of trying to move away from the trellis frame because it contended that a welded frame had too many inconsistencies that were very hard to control. Whatever the case I would like to see how stiff one can get the Esprit to be with a cage

[Vulcan Grey]

Two of my friends own 1991 Esprit X180-R's with full factory rollcages. I've driven both, back to back with my 1989 SE on street and track, and the cage makes a huge difference! I've also been in a 1997 with a 10 point roll cage. I can feel my SE chassis twist through turns, especially cambered descending turns. The cages definitely eliminate chassis twist, and they also increase traction due to better controlled suspension. My car will lift tires at the local track.

Actually, if you read what Matt Becker said about the chassis stiffness in this article about the Sport 300 compared to the Sport 350, he basically says that the Esprit chassis is so soft that it'll only take so much spring rate for the dampers before the chassis twists, therefore reducing the effective suspension stiffness.

http://www.classicandperformancecar.com/features/octane_features/249580/lotus_esprit_sport_300_vs_sport_350.html

[CHANGES]

 I would like to hear if anyone else had installed a cage in any esprit and how it effects the car's performance.  It would seem that Dave (changes) could benefit from a good cage with all the torque and HP he's making now....

 

I think you may be right.... on the last test run with all the new torque, I could feel it flex in the wet just as the

wheel broke loose , in the dry this may be an issue which will lead to stress fractures and eventually chassis

failure... There is always a catch when you make changes...

I have previously thought about this using an alloy cage , what stopped me was the interior design will need

changing too along with other major body mods to facilitate..

The best option i think is for me to obtain another body and start from scratch... anyone know of a cheap

shell lying around....? 

[dodge1979]

Dave your an addict....although we have previously mentioned (and I thought you were joking) MK2 ....all those shutlines to remake to aerodynamic efficiency again... :*)

[CHANGES]

The next one is always better than the last... but still just in planning stage due to recent outlay's

on mk 1,  My trouble is the itch...eventually i just have to scratch it....ohhh so many itches..!

[Bibs]

TLF is the custodian of the Esprit Vari moulds you'd be able to use?

[CHANGES]

OOOHH  Light weight carbon to go on space frame.... That's always been an itch i wanted to scratch.

The last time i scratched a similar itch it cost me a wife... But that turned out a win win. Till her lawyers 

got hold of me.!!!!

[sailorbob]

I've occasionally wondered if there's any scope for running bracing tubes through the cills to tie the front and rear together in additional places.

[Bentzion]

A carbon on space frame may even surpass what even a lawyer couldn't get to on behalf of you wife....But a Twin Turbo Evora with a GTE or GT2 carbon body...Now were talking serious performance:  550BHP at 2700lbs? Torsional rigidity a plenty!!!

 

YOU CAN DO IT DAVE

[red vtec]

Dave,

 

Maybe a clam shell like a GT40?  that's what GG originally intended.

 

Chris

[benjamincalleja]

TLF is the custodian of the Esprit Vari moulds you'd be able to use?

 

dont suppose there is a roof mold there so i can get my fiberglass roof made.....

 

 

so the answer is no, we have no concrete numbers then.  Is it the same for the M100 Elan?  In its day everyone said how stiff it was but that was i guess by comparison, if i got in one now would i find that to also be pretty wet-noodle like?

 

bibs, can you ask someone at the factory?  Im dying to know, 5850nm is very obviously wrong.  see list below which seems to be floating around the web...that number for the mclaren f1 seems odd too but who knows...

 

Alfa 159 - 31.400Nm/degree

Aston Martin DB9 Coupe 27,000 Nm/deg

Aston Martin DB9 Convertible 15,500 Nm/deg

Aston Martin Vanquish 28,500 Nm/deg

Audi TT Coupe 19,000 Nm/deg

Bugatti EB110 - 19,000 Nm/degree

BMW E36 Touring 10,900 Nm/deg

BMW E36 Z3 5,600 Nm/deg

BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg

BMW E46 Sedan (w/folding seats) 13,000 Nm/deg

BMW E46 Wagon (w/folding seats) 14,000 Nm/deg

BMW E46 Coupe (w/folding seats) 12,500 Nm/deg

BMW E46 Convertible 10,500 Nm/deg

BMW X5 (2004) - 23,100 Nm/degree

BMW E90: 22,500 Nm/deg

BMW Z4 Coupe, 32,000Nm/degree

BMW Z4 Roadster: 14,500 Nm/deg

Bugatti Veyron - 60,000 Nm/degree

Chrysler Crossfire 20,140 Nm/deg

Chrysler Durango 6,800 Nm/deg

Chevrolet Corvette C5 9,100 Nm/deg

Dodge Viper Coupe 7,600 Nm/deg

Ferrari 360 Spider 8,500 Nm/deg

Ford GT: 27,100 Nm/deg

Ford GT40 MkI 17,000 Nm/deg

Ford Mustang 2003 16,000 Nm/deg

Ford Mustang 2005 21,000 Nm/deg

Ford Mustang Convertible (2003) 4,800 Nm/deg

Ford Mustang Convertible (2005) 9,500 Nm/deg

Jaguar X-Type Sedan 22,000 Nm/deg

Jaguar X-Type Estate 16,319 Nm/deg

Koenigsegg - 28.100 Nm/degree

Lambo Murcielago 20,000 Nm/deg

Lotus Elan 7,900 Nm/deg

Lotus Elan GRP body 8,900 Nm/deg

Lotus Elise 10,000 Nm/deg

Lotus Elise 111s 11,000 Nm/deg

Lotus Esprit SE Turbo 5,850 Nm/deg

Maserati QP - 18.000 nm/degree

McLaren F1 13,500 Nm/deg

Mercedes SL - With top down 17,000 Nm/deg, with top up 21,000 Nm/deg

Mini (2003) 24,500 Nm/deg

Pagani Zonda C12 S 26,300 Nm/deg

Pagani Zonda F - 27,000 Nm/degree

Porsche 911 Turbo (2000) 13,500 Nm/deg

Porsche 959 12,900 Nm/deg

Porsche Carrera GT - 26,000Nm/degree

Rolls-Royce Phantom - 40,500 Nm/degree

Volvo S60 20,000 Nm/deg

Audi A2: 11,900 Nm/deg

Audi A8: 25,000 Nm/deg

Audi TT: 10,000 Nm/deg (22Hz)

Golf V GTI: 25,000 Nm/deg

Chevrolet Cobalt: 28 Hz

Ferrari 360: 1,474 kgm/degree (bending: 1,032 kg/mm)

Ferrari 355: 1,024 kgm/degree (bending: 727 kg/mm)

Ferrari 430: supposedly 20% higher than 360

Renault Sport Spider: 10,000 Nm/degree

Volvo S80: 18,600 Nm/deg

Koenigsegg CC-8: 28,100 Nm/deg

Porsche 911 Turbo 996: 27,000 Nm/deg

Porsche 911 Turbo 996 Convertible: 11,600 Nm/deg

Porsche 911 Carrera Type 997: 33,000 Nm/deg

Lotus Elise S2 Exige (2004): 10,500 Nm/deg

Volkswagen Fox: 17,941 Nm/deg

VW Phaeton - 37,000 Nm/degree

VW Passat (2006) - 32,400 Nm/degree

Ferrari F50: 34,600 Nm/deg

Lambo Gallardo: 23000 Nm/deg

Mazda Rx-8: 30,000 Nm/deg

Mazda Rx-7: ~15,000 Nm/deg

Mazda RX8 - 30,000 Nm/degree

Saab 9-3 Sportcombi - 21,000 Nm/degree

Opel Astra - 12,000 Nm/degree

Land rover Freelander 2 - 28,000 Nm/degree

Lamborghini Countach 2,600 Nm/deg

Ford Focus 3d 19.600 Nm/deg

Ford Focus 5d 17.900 Nm/deg

[Günter]

McLaren F1 isn't so bad ..if you mention it -for the age and that it was the first (or one of the first?)  carbon fibre chassis for road use ..so why not see improvement on the later Carbon chassis cars, one full decade younger.

 

Can't specify if the 60K is right ..but the Veyron needs a stiff chassis, as for the mass of the car, this body mass needs to be compensated by the suspension/springs, as for such a heavy sportscar the springs to hold it on the road even with bumps on higher speeds need a notable rate  -and with a 'ordinary' chassis stiffness it would not work 

..just like it was said on the Esprit, where the springs are 'underrated', so not stress the chassis to much (we all notice from time to time that the suspension is a little soft on trackdays for the cars with factory setup ..and there is a lot of roll-characteristic in it)

 

the other point is that the Veyron does have a lot of power , the power can only be transfered to the road if the engine mount is stiff enough to compensate the momentum -so again, the chassis needs to be stiff to hold this kind of engine in it.

 

Something that is interesting, if you mention the Venom, with its Elise base chassis ..?  How much can the Elise chassis hold, especialy if the wheelbase and rear subframe is changed as well as the engine ..?

Edited January 22, 2013 by Günter

[lotusesprit1]

So my ford Mondeo Diesel estate is over 3 times stiffer than my esprit if the 5850 figure is any where near true.

 

It would be interesting to know the actual figure.

 

If you jack the front of an esprit up on the jacking point it alters the door shut quite a bit. So much in fact I checked the chassis for cracks,turned out all was well

 

I remember when the chassis cracked in my +2, that became very wobbly to drive with the front cross member only attached at the bottom.

 

We could measure it I suppose. 

[dodge1979]

There is an enormous amount of flex in the chassis...i discovered this when reinstalling my engine, I had everything up on stands...the rear bracing channel that bolts in over the gearbox wouldnt actually align the bolt holes until I took tye rear up in the air off the stands to allow the rear to splay out..just shows that bolt in section certainly does a.job!

[benjamincalleja]

It begs the question though - how does the esprit manage to handle so well with such a weak chassis (by comparison, in its day I'm sure it compared very favorably).

[Günter]

you can simply calculate the suspension points (four individual corners), ok so..

-but for a real mathematical calculation in engineering you also learn that each axis, front & rear end, can be seen as 'a square positioned spring with spring- & damper- characteristic' that is in contact just in the middle of the car  ..so the effects of roll-characteristic count into it for the overall handling

 

..if you allready know that the torsional stiffness of your main chassis isn't up to the required numbers of the competitors, design your car as if it is two individual axles of course, like a type of dumper truck with traight axles and no suspension arms on the hubs

-but try to calculate how much it needs to stiffen up the middle ..I think that's allready why the body is not only put in direct contact onto the front and rear end ..what would be enough in terms of load carring of the body wheight, no it is more so also fixed in the middle on two positions, what means there is some influence of the fibre body as well .. just a thought

 

-so anyone who is there in the process of restoring an Esprit up from the bare chassis -please put it on axle-stands on tree corners, load the corners with ballast to keep it from jumping of ..and put ballst also on one corner that is not supportet. Now measure with a 'straigt edge' or something usefull how much the level on this corner drops down for a given ballast wheight  ..should be interesting numbers !!

most cabriolets/roadster versions of saloon cars have torsional stiffness problems, without the square/diagonal supports under the car  .

 

..just lift up a BMW 6series cabrio ..or equal cars -it needs to create a connection between both end, or at least most time the chassis base needs some bars there under the axis lines  (see the bars there on the model of a BMW chassis who are there to stiffen up the rear-end overhang on the real car)

 

 

 

 

(interesting point is if you need the opposite -a torsional flex, for road going characteristics ..think about trucks, and if a 'coachbuilder' wants to fit something on top of a truck chassis ..there are points he is not allowed to contact the main chassis, as a construction 'on top' can stiffen up the whole system in some cases)

*http://www.manted.de/manted/aufbaurichtlinien/d_l2000.html

Edited January 26, 2013 by Günter

[benjamincalleja]

 i asked directly and it appears the answer is yes we know, and no, you will never be allowed to know. 

Dear Ben, Engineering hold there own records, and this is commercially sensitive data that it was all held within engineering, not even published to us. Andy Graham - Technical Publications and Archives LOTUS AFTERSALES

Edited February 20, 2013 by Vulcan Grey
remove Andy's personal info.

[MrDangerUS]

Totally not cool!

What are they afraid of? Bad publicity?

If numbers were OK -no worries.  BUT, if numbers indicate that this frame has been a wet noodle from the get go…

That changes everything!

[ramjet]

Why does that change everything? Still outhandles a lot of stuff out there that is years younger.

[MrDangerUS]

 

 

Personally, I believe, Esprit stifness must be better than Viper, perhaps closer to Corvette C5.

I found this SAE Papers:

No. 983054, Design of a Twist Fixture to Measure the

Torsional Stiffness of a Winston Cup Chassis.

and

No. 2002-01-3300, Design, Analysis and Testing of a

Formula SAE Car Chassis.

This gave me an idea how to test stifness of the car in my shop within capability of my equipment.

Since my car did not have bulkhead anchor plates, I have to fabricate and promptly install them. Bulkhead joints are critical on our cars.

http://lotusespritworld.com/EGuides/EModifications/BulkheadPlate.html

Then, I'll be able to perform the test on my fully "dressed" car (I.E. complete chassis and body assembly w/engine, transaxle, etc,etc). I know the number will be at least 15-20% higher than the bare chassis.

I wish, I could find someone doing a complete restoration, so the bare bone chassis could be tested.

Any thoughts, pointers?

Edited November 9, 2013 by MrDangerUS

[ramjet]

But why? If you're not happy with it and you try to increase the stiffness, you will invariably add weight to do that. That weight increase will act directly against the stiffness that you are trying to improve. It would be like a case of diminishing return. I'd like to think that Lotus did all the math on this when they decided on the design.

 

If you're not happy with it, get an exige or an evora.