The Lotus Cars Community banner

1 - 20 of 20 Posts

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #1 (Edited)
Many owners attempted changes to the spring rates. Others changed their shocks and springs with some mixed results. Ride quality is a function of the balance between understeer and oversteer and often does not respond well to random changes.
Therefore,
I'd like to start a discussion on the subject and compile collective knowledge in one place.
(DD required when using data below)

88-93 Esptit Turbo GEO
front:
camber -0°12' to - 0°42'
castor 2°55' to 4°05'
toe 0°00' to 0°09'

rear:
camber -0°20' to -0°50'
toe 0°21' to 0°30'

LOTUS ESPRIT S300 SUSPENSION GEO
FRONT
Camber -0°39’ to -0°51’
Caster 3°05’ to 3°35’
Toe -0°02’ to -0°06’

REAR:
Camber -0°52’ to -1° 08’
Toe 0°09’ to 0° 12’


SPRINGS:​
86/87/(and 88?) Turbo Esprit Wiki - Esprit.TechnicalData

Non-SE 89 (17% anti-dive), (is 88 Federal the same?)
Front: Rate– 22.8 N/mm / 130 Lb/in, Free Length–369mm (14.5”), Static Length– 203mm (10”), 585# preload, ride hgt 170mm
Rear: Rate– 27.5 N/mm / 157 Lb/in, Free Length–334mm (13.15”), Static Length– 205.7mm (8”), 808# preload, ride hgt 170mm
17 mm dia. front anti-sway bar

89+ SE (22% pro-dive)
Front: Rate– 29.1 N/mm /166 Lb/in, Free Length–372mm (14.6”), Static Length– 219mm (8.62”), 992# preload, ride hgt 190mm
Rear: Rate– 27.5 N/mm / 157 Lb/in, Free Length–347mm (13.7”), Static Length– 218mm (8.6”), 800# preload, ride hgt 170mm
17 mm dia. front anti-sway bar

S4/S4s
Front: Rate – 41 N/mm / 234 Lb/in, Free Length - N/A, Static Length– 214mm (8.43”)
Rear: Rate – 45 N/mm / 257 Lb/in, Free Length - N/A, Static Length– 227mm (8.93”)
15 ? mm dia. front anti-sway bar

The front damper platform height for each of these measurements is 59mm. The rear platform height is 115mm. The extended/compressed length for the front is 12in./10in., and the rear is 16in./12in.

About G-car rates
http://www.thelotusforums.com/forums/topic/14042-spring-rates/?p=518974



So, what rates have you used, why and what are the results?
 

·
Super Moderator
Joined
·
4,038 Posts
In your opinion, what effect would have an installation of 12% stiffer rear springs on 85-88 Esprit?
From my armchair, it would reduce understeer a bit. But in my limited street-only experience, I don't experience that much understeer on my 88 except in very low speed turns (despite the tail heavy weight distribution).

I would be concerned if the modification would have side effect of rougher ride. My 88 experiences some weird bouncing/porpoising on certain freeways with wavy surfaces (paving, not damaged roadway). If you tweak the front to back stiffness, it may affect behavior on certain surfaces.
 

·
Registered
Joined
·
1,505 Posts
One day I was going through Lotus Esprit videos on youtube. Came across one with Rodger Becker setting up the suspension through electronic servos whilst driving the car on the test track at Hethel.

Very cool video. I have to question people who want to mess with shear perfection designed by one of the most talented engineers in the automotive industry.

A little movie triva... 'The Spy Who Loved Me' The white Lotus S 1 Esprit in the chase scene was driven by Rodger. The director couldn't find anyone who could toss the car around as he wanted....
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #5 (Edited)
Nothing is perfect in this World!

Especially cars!

Car design is a compilation of compromises between the cost, reliability, performance and serviceability.
Eulogizing Lotus attributes without presenting test data is neither prudent nor wise.

Some folks repeat the same, over and over:
"The Lotus is the best handling car, so there is no room for improvement".
BUT, when you ask why they think so, they can't give you any details/data, except "because Mr. XX said so" or "everybody knows that".
Most of the owners accept such statements on faith and never ask any pertinent questions.
With an exception of a few, no one can even tell if his particular model/year car has understeer or oversteer tendency and why.
See#4 http://www.lotustalk.com/forums/f164/esprit-suspension-settings-209386/

In 80-s, cars were dialed in through trial and error methods. Up until the early 1990-s, there did not exist a method that could be used to accurately predict the handling of either an F1 car or Stock car. In early 1990-s a method was developed that represented an advancement related to vehicle dynamics modeling. It involved treating the vehicle as two separate masses, each with its own separate suspension system.

Ideally, both suspension systems (front axle and rr axle) are connected by a rigid chassis. What each system desires to do is influenced by what the other wants to do as the car negotiates turns.

Have you ever seen the circus act where two people are in a horse costume? The horse moves around fine as long as each end is in sync with the other. When the rear wants to go left and the front wants to go right, it gets comical.

In our cars, when the front moves/rolls differently from the rear, it is not so funny and performance suffers.
Considering Lotus back-bone low torsional stiffness, the handling could be less than perfect.

The key to creating a balanced setup is to change springs and moment center locations so that each end of the car will want to roll to the same angle. If that objective could be achieved, the softness of the esprit chassis would matter to the lesser degree. See for more info: http://www.thelotusforums.com/forums/topic/55159-chassis-torsional-stiffness-model-by-model/
and http://www.thelotusforums.com/forums/topic/5573-increase-the-torsenstiffnes-in-the-esprit/

A balanced chassis, where both ends are working in sync, is what engineers always tried to find by using trial and error setup techniques. In a well designed chassis, the roll angles would be the same.

IMHO, the 25 years old design always offers a room for an improvement.

P.S.:wave:
In 1981-88 Lotus was working on an active suspension system. These early attempts at active suspension were more ‘reactive’ – using hydraulic actuators to alter the car’s attitude in response to bumps in the road or particular inputs from the driver rather than actually preparing the car in advance for each specific change in the track. The first two iterations of the system (the second driven by Nigel Mansell occasionally in 1983), did not even use springs.

Oh, BTW, if Esprits were such marvelously handling cars from the get going, why Lotus initiated this retrofit programme in 2005?
http://www.lotusespritworld.com/EGuides/EModifications/Lotus_Suspension.html
"Lotus Ride & Handling Engineers then fitted special springs and dampers for development. Lotus looked to create new specifications based on the old set-up, but refining it. With the advancement in modern materials and design, they have developed a suspension package for the Esprit models of the past using today's know how.

Lotus have created new spings & dampers for each model retaining the 'feel' of each model, but improving the ride & handling without making all the models feel the same. Lotus have taken this project seriously and have investing a lot of money in it's development. The development has being done on both track and road and covers many different types of road surface, including motorway, A-roads, B-roads and the varying surfaces these can have. As you should know, Lotus is one of the leading companies in Ride & Handling and have years of experience in setting up road and track cars."
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #6 (Edited)
Lotus' Spring & Damper Programme was started in mid 2005 and covers Esprits from 1985 to 2004. Lotus tested and set-up each Esprit model with new springs and dampers doing a baseline appraisal on the current parts before beginning this development exercise.

It is interesting that they choose to use a common Billstein front damper on 85-87 HC, X180, SE, s4/s4s/GT3 and Sport 300, while changing only the spring rates for each model. V8 has different settings due to an extra engine weight.

Different damper was chosen for the rear, but again, it is common across all models (except V8). Common spring is used across 85-87HC, X180 and SE
whilst S4/S4s/GT3 and 300 received different parts/rates.

The original cost was £874 for set of 4 dampers and 4 springs.
 

·
Cal H
Joined
·
982 Posts
I would have to refer you to Dave Cammack (the current LOON prez). Not sure if he lurks on LT or is just on the list. He has 4 different Esprit models a N/A S1 and 85 G car, 89 SE, and X180R and an Elise (also non Lotus Panoz). He has played around with all sorts of combo's. He is an HPDE instructor and while many think not to change things on a Lotus suspension as that was what they were noted for, it is setup for street driving and not optimized for the track. So that is why he opted to change and play with the suspension for track use and robust street.
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #10 (Edited)
[...] while many think not to change things on a Lotus suspension as that was what they were noted for, it is setup for street driving and not optimized for the track. So that is why he opted to change and play with the suspension for track use and robust street.
I'm on the same page as DC.
"The best handling" can be always improved!
At the time our cars were put together, the best computer had less computing capability than my i-phone.

Someone has to say it: Emperor has no clothes!

IMO, it is difficult to achieve a balanced set up on our cars due to a "wet noodle" chassis.
 

·
Cal H
Joined
·
982 Posts
I'm on the same page as DC.
"The best handling" can be always improved!
At the time our cars were put together, the best computer had less computing capability than my i-phone.

Someone has to say it: Emperor has no clothes!

IMO, it is difficult to achieve a balanced set up on our cars due to a "wet noodle" chassis.
I have heard rumors that Griese has come up with or is very close to installing a stiffening brace similar to the ones found in the SP300 that looks like a bridge across the top of the cam gears. He is about an hour drive south of me and if he has one I must have a peek at it.

I just had a conversation with DC about tires and suspension yesterday. He was very precise in his wording and opinions. It centered around the Toyo RA1 which he termed the grip on the road surface as almost intoxicating. DC was the person who set up my suspension and alignment on my previous Esprit while I sat in the car and optimized the Esprit with 1 person 160 lbs in the drivers seat. The understeer went away and gained precise rear control using gas and brake pedals.
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #12
WOW!
God news
and...
another good news!

Please impress on Griese the importance of performing a simple, yet effective validation of improvements by testing the "before" & "after" torsional stiffness of the vehicle.

Here is the procedure:
First, place car/chassis on axle stands at the points corresponding to the suspension attachment points; wheels off the ground.
1. Level it on 4 stands.
2. Keep it on axle-stands; load the rr corners with ballast to keep it from jumping off.
If you’re testing fully dressed car the weight of the engine and transaxle will keep it pinned down.
3. Remove one (front driver side) stand and a wheel and measure the distance from the fixed chassis/suspension point to the ground.
If you’re to use a dial indicator, set it up and zero it.
4. Put known ballast on one corner that is not supported**, [F].
5. Now, measure how much the level on this corner drops down for a given ballast weight [D]
6. Measure the distance to the opposite side stand (closest to the measuring point), [L].

The torsional rigidity can be calculated by finding the torque applied to the frame and dividing by the
angular deflection.

K^2= FxL/tan(D/L)

This method of frame testing is relatively straightforward and the advantage is the frame stiffness can be determined without including the suspension components. The primary disadvantage is the artificially created load paths do not load the frame in the same manner as on the track.
Also, the choice of what rear nodes to fix and what front nodes to apply the load can affect the results significantly. For this reason a whole car (chassis with the body attached) torsion test is the preferred method for capturing the true vehicle stiffness.

Chassis testing, however, has very high non-linearity in the early stages. For small forces gaps in the suspension and compression of various bearing elements occurs. As these gaps are closed and bearing friction is overcome the slope of the load deflection curve becomes linear.
** For this reason, it is necessary to map the force displacement characteristic of the structure, rather than finding one stiffness value. To get better data small steps of load should be applied, and the corresponding displacement measured. It is also interesting to note that the force deflection curve has some hysteresis. To accurately gauge this characteristic, it is helpful to add or remove the load in finite steps and record the deflection. This will build a load deflection “path” that rises and then falls again. At high loads the deflection is linear. This represents the deformation of the elastic frame and suspension members after gaps are closed. Therefore one should start at loads higher than 40-50 lbs. Then, load it in 10 lbs increments.
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #13
DC was the person who set up my suspension and alignment on my previous Esprit while I sat in the car and optimized the Esprit with 1 person 160 lbs in the drivers seat. The understeer went away and gained precise rear control using gas and brake pedals.
Do you know how he did it? Did you have adjustable perches? Stock combos,or...?
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #16 (Edited)
I'd like to retract my post #10 "wet noodle chassis" comment.

Earlier this year, I measured the torsional stiffness of my car
and...
I was pleasantly surprised.

With bulkhead-to-chassis bolts removed and a body crack (discovered much later) at the rear LH bolt,
I arrived at the number comparable to Corvette C4, Viper Coupe and little bit below the Ferrari 360 Spider.
 

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #17 (Edited)
IF (!), we accept this statement at the face value: "Esprit has the best handling properties" and "Lotus engineers knew how to dial in the suspension",
the ratio of rear/front spring rates should give us some numerical idea about Lotus intended handling. We have two axle systems with two different motion centers and moments connected by torsionally soft back bone chassis, which adds an unknown parameter.
There are many factors other than spring rates (track width, tyre sizeand aspect, presence of spacers, wheel offset, chassis stiffneners), which should be considered.
If we analyze just spring rate ratios across all 4cyl models and compare to the empirical data, are we going to discover a trend?

88 Federal & non-SE 89: (17% anti-dive geometry); Ratio rr/frt= 157/130= 1.2
Front: Rate– 22.8 N/mm / 130 Lb/in,
Rear: Rate– 27.5 N/mm / 157 Lb/in,

89+ SE (22% pro-dive geometry); Ratio rr/frt=157/166=0.95
Front: Rate– 29.1 N/mm /166 Lb/in,
Rear: Rate– 27.5 N/mm / 157 Lb/in,

1990 X180R, Rigid roll cage, but no engine brace
Front: Rate- 40.3 N/mm /230 lb/in; Ratio rr/frt=177/230=0.77? That's odd. Shouldn't it be 177 front and 230 rear?
Rear: Rate- 31.0 N/mm 177 lb/in

S4
Front: Rate – 36 N/mm / 205 Lb/in; Ratio rr/frt=225/205 =1.098
Rear: Rate – 39 N/mm / 225 Lb/in
Lotus developed Bilstein/Eibach suspension for the S4 which uses lower rate front springs for the non stiffened backbone chassis than on the stiffened chassis.

S4s
Front: Rate – 41 N/mm / 234 Lb/in; Ratio rr/frt=257/234=1.098
Rear: Rate – 45 N/mm / 257 Lb/in,


Sport 300, Stiffer chassis+engine brace
Front: Rate – 43.2 N/mm / 280 Lb/mm; Ratio rr/frt=320/280 =1.143
Rear: Rate – 48.8 N/mm / 320 Lb/in

! Use of springs rated higher than OE on a SE chassis will lead to back bone cracking around gear lever aperture.

soft rear/hard front = understeer/push/tight - This is when the front tires are not getting enough grip on the racetrack. This causes the car to want to continue straight ahead when the driver turns the wheel.

hard rear/soft front = oversteer /loose - A condition that results when the front tires are getting a better grip on the racetrack than the rear tires. This causes the back end to want to come around in the turns making the nose of the car point towards the inside of the corner.

~~~~~~~~~~
What is interesting here, the ratio has a downward tendency for high performance models .
I assume the X180R had stiffened chassis... or not?

Your thoughts ?
 

Attachments

·
Integrator
Joined
·
2,863 Posts
Discussion Starter #18 (Edited)
Are the OE springs progressive?

It seems the S3 and early Stevens (non SE) front springs have a conical shape. Diameter at the top is smaller by1/2".
They are conical-for sure..., and pretty long in free state (14" !)
The successful use of the conical spring in an automobile application comes from its unique design. These springs comprise one tapered end while the radius of the other end is decreased to form a cone shape. The coils of the spring fold into each other, providing more axial space. Conical springs are seen as a good replacement for cylindrical compression springs, which have a limited axial space.

Load = max.shear stress x Pi x (wire dia)^3 divided by 8 x main coil diameter

Thus, if coil diam is large (like at the bottom), the Load, which spring can carry, is smaller.

Would conical spring have lower rate at the bottom and higher at the top?

Any thoughts or confirmation?
 

Attachments

·
Wingless Wonder
1988 Esprit Turbo
Joined
·
6,095 Posts
I couldn't tell you if the stock springs are progressive... but I DO know this:

When we toured the Hethel factory in 2002, Roger Becker (since retired Lotus suspension engineer) was asked about using progressive springs in a proposed Esprit racecar (an '85 to be exact).


He said NO, don't do it. With a progressive spring, you never know what rate you are encountering, so the suspension is difficult if not impossible to tune for predictive handling.

Think about it, every curve on a track would see a different rate depending on how much the suspension was compressed. If you use progressives both F&R, the variations are astronomical.

Roger (and Alistair McQueen) were the primo suspension developers in the 80s when the Esprit was developed.
 
1 - 20 of 20 Posts
Top