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How to control front arb if cornerweighing?


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I am wondering how if it is possible to adjust the front arb if say, one is cornerweighing the Esprit. Or just changing the height on suspension. The model in question is a 1990 Turbo SE, but seems relevant to all models, if I am not mistaken.

Normally, after having adjusted the cornerweighing, one would adjust for example droplinks (where applicable) for the anti roll bar, to make sure that the arb is not affected when car is stationary and on perfectly level ground. But the Esprit's front arb is installed in the front track arms and two clamps in the middle on the chassis. How can I do this?

Kind regards,

jacques

Nobody does it better - than Lotus ;)

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Hello Jacques,

I would agree that having the A-R bar in a neutral state on a level surface when car is static is correct. Can its mountings be shimmed slightly on one side to achieve this?

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Perhaps my grasp of cornerweighting techniques is wanting. I figure the method amounts to shimming the spring at the front corner least loaded until balance is achieved across that end of car. If so, I would expect the bar would be displaced at the connection point to the lower wishbone in proportion to the increased distance between spring perches on the shimmed side, so putting the bar in torsion as if car in mild cornering state. If that is correct analysis then I imagine the method whereby the bar could be made neutral would be to loosen the pivot mountings on the chassis, importantly before resolving cornerweights so that the bar does not impart its function to the outcome. Then, once the weighting is sorted I would expect the bar mountings would show a gap to chassis above on the shimmed side, so indicating where and how much to shim.    

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I have read about this situation a few times on the internet about other types of cars (so i must be an expert?  :-0)

The solution in these stories was to set the corner weights with the center mounts on the bar to chassis disconnected so the bar would not effect the CW (as suggested above).  Next they would pray that the ARB mounts would bolt back up with no pre-load when the car was sitting level with the driver weight still in the drivers seat.  The shim idea above seems great if it wont bolt up with out pushing!  

To really do it right you need to change the ARB bar to a style with adjustable drop links because Lotus never designed the car to be properly CW.  I have never seen a kit for the Esprit for sale?

Another thought?  Just do the CW with drivers weight with the ARB connected and include any pre-load in the CW settings.  Might be fine for 90% of situations.  

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In my view, if the anti-roll bar doesn’t have adjustable links, then the car should be set up with it fitted. If it’s set up whilst disconnected, the settings will change once it’s reconnected again. Remember this is for a road car, not an F1 or track car where it may well be desirable to re-jig the roll bar system to include adjustable links. If the Factory saw fit not to make the roll bar adjustable, I suspect it might be for a reason because everything else suspension-wise is adjustable, at least on the later cars. Cost, perhaps? Who knows.

Margate Exotics.

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At first glance, the only way to go would be to somehow move the complete bar downwards. However, given the available space, I wonder whether the roll bar geometry could be maintained without some serious modifications. As I only use my car on the road it's not a project I want to waste my time on.

Margate Exotics.

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I will lower it very slightly, my goal is a few fun track days a year and suspension geometry is very important in my opinion for optimal camber characteristics etc.  With out major fab work or $$$ parts (drop spindles) most cars are difficult to lower substantially and maintain good geometry.  I think Lotus worked very hard to optimize the geometry and the compromises toward performance that would have to be made to improve much there would be beyond my pocket book and desire.

I just want to get to a higher end shock and slightly higher spring rates.  On top of all that the Esprit is pretty low to begin with and I dont want to be scraping off FG body parts 🙂.  

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On 26/11/2019 at 17:37, Jacques said:

Adjustable droplinks for the arb seems a smart to me. But as we know, this is not the case.

Any ideas?

Kind regards,

jacques

Personally I have always left it connected when corner weight is done .    I understand your logic but question the reasoning...    My take on this is that for the front of the Esprit or any car for that matter too sit flat at any pre-set ride height ,  the suspension links that the ARB connect to, will be in the same relation to the ground and the car on both sides.   As a result the ARB should have no tension.    The corner weight is balancing the car by pre-loading the springs on an adjustable platform , not altering the position of the lower link, that will stay constant..    So as long as your car sits flat the ARB should be neutral.    However as with all things mechanical there may be tolerances within designs that form a pre load on the ARB... As an ARB is fully floating any slight pre-load will be balanced between the two sides. If way out of spec due to damage to ARB frame mounts etc, the effects may be different.   

Should you feel this is not the case or would like to have independent adjustable ARB links , then you could fit up links ... This could be done by design/manufacture of mounting plate to top wishbone. Another mounting attachment could be made on the ARB to facilitate the link.    What you will need to also consider is where you are attaching to the ARB..  By leaving the ARB in its present position and shortening it to give relief from the lower link , you will have increased the ARB's roll tension.  You could develop frame mounts to move the ARB physically forward, this would maintain integrity and present roll tension.    By some subtle design inclusions you could make your ARB's roll tension adjustable at the same time .  If going down this route I would be looking at using the later spec ARB which is thinner..  This could be shortened and adapted using original mounts to give comparative roll characteristics to the earlier ARB.     All seems a lot of work for a road car, But would be very interesting to explore.    Hope this helps..             

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Dave all excellent points.  In my very limited experience the issue with cars like ours and Air cooled Porsche 911 that have very light front ends when you add in the drivers weight during the CB, it is such a large percentage of overall weight on the front that you will "activate" the front ARB.  Its unfortunate that the design is not conducive to an adjustable link, but I have to think Lotus knew what they were doing and figured out some way to minimize the effects (very light ARBs or some other wizardry).  It will be interesting to look at when I start the CB process.  

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This is no complicated matter, lads. An A-R bar is just a simple thing used to tie one side to the other and be inactive whenever the car is level on its suspension across that axle. I am correct in stating that leaving the bar properly attached whilst adjusting cornerweights is counterproductive, obviously. To reiterate my central point why not simply permit the bar to find its neutral position by loosening its chassis mounts whilst adjusting c/weight then shim the one side indicated before re-tightening. One should seek to preserve a no torsion, inactive state of the bar when the car is level. As a load transfer device by its nature the bar should be disabled during c/weight adjustment.

Just reviewed Prepare To Win, one of late, great race engineer Carroll Smith's highly instructive books and he states that cornerweights across the front are the ones to focus on, by the way.

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Yeah CW across the front are really sensitive in hard braking I have found and I am no Senna. 🙂

I would not be surprised to find different thickness shims under the chassis mounts from the factory for exactly this reason.  The floppy rubber bushings do provide a lot of leeway though, especially after worn.

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2 hours ago, drdoom said:

This is no complicated matter, lads. An A-R bar is just a simple thing used to tie one side to the other and be inactive whenever the car is level on its suspension across that axle.

This is a very true statement.

2 hours ago, drdoom said:

To reiterate my central point why not simply permit the bar to find its neutral position by loosening its chassis mounts whilst adjusting c/weight then shim the one side indicated before re-tightening.

This statement would assume that the chassis frame mounts are not in alignment with each other.   This should not be the case unless the chassis is twisted or out of spec.    When fitting up front suspensions I have always left the central mounts to the ARB loose until the suspension is loaded..  I do this as it is a lot easier to bolt up when its not hanging..  By doing it this way you also get to see the ARB mounts symptomatically align with the chassis .. If they did not I would be asking WHY !.   At this point the ARB is neutral so i see no reason to slacken off to do corner weight.  

2 hours ago, drdoom said:

One should seek to preserve a no torsion, inactive state of the bar when the car is level. As a load transfer device by its nature the bar should be disabled during c/weight adjustment.

The first sentence makes sense , the second confusing,  as it would only be influencing as a load transfer device if it was in an 'active' state when the car is level,  which is not the state you describe in first sentience...    If there were twists or errors which needed shimming out , then one would presume a neutral state then existed as a result, when sitting level,   So why disable it when adjusting corner weights if it is neutral when fitted ?..  

2 hours ago, Erikl said:

Yeah CW across the front are really sensitive in hard braking I have found and I am no Senna.

What you also have to consider is the type of corner weight or balancing you intend to use.   Left to right , front to back, or cross..      ...  But that you must decide what is correct or best for you .... 

I do think this thread is really over complicating a simple ARB set up ...   

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Mechanical visualization is not my strongest suit. Working through the process will perhaps help me get clarity. For example, to up the c/weight right front one raises spring load at the left rear, so jacking across the diagonal axis defined by the other two corners. Does this impart a change of chassis attitude, that is tilt side to side as if in cornering? If not then there is no deflection of the A-R bar to neutralize., as @Changes instructs. 

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24 minutes ago, drdoom said:

Mechanical visualization is not my strongest suit. Working through the process will perhaps help me get clarity. For example, to up the c/weight right front one raises spring load at the left rear, so jacking across the diagonal axis defined by the other two corners. Does this impart a change of chassis attitude, that is tilt side to side as if in cornering? If not then there is no deflection of the A-R bar to neutralize., as @Changes instructs. 

You are on the right track with this line of thought...     The chassis attitude or orientation should not change , to do so would have the body out of level, this would be /look wrong.. .    Once the ride heights are set , pre-loading various springs will balance the corner weight as required , This process should be done as to not change the ride heights or the level attitude of the body..  The two setting are all parts of a single package  

You would be amazed how many Esprit are not to spec from ride height and GEO point of view.   When they are they handle and feel fantastic..   The problem is things move as they wear/relax and owners don't annually check/adjust settings.  As a result they creep un-noticed out of spec and owners don't notice the gradual deterioration.   Its only when they drive a well sorted example or have theirs professionally set up after a full refurbish that they appreciate the difference.     

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When I did some work on my S4, I am pretty sure that there was some slight preload on the ARB after I had set the ride height.

As this preload exist on both sides, the difference across the front end would be no effect?

It might change front to rear weighting, but I would not think by much.

I really would not see much point to this unless you were going to race your car where every hundredth of a second counts. The cornerweights would change each month due to suspension bush wear/bedding, that more time would be spent sorting this out all the time versus driving. Fuel load, stuff in boot, passenger, no passenger, etc.

My vote is on driving. :driving:

I could also have no clue as to what I am talking about. :ermm:

  • Haha 1

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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David,

Are you saying that a CW car once the driver weight is removed would not be slightly higher on the drivers side?  I would think in a light weight car this would be the case.  I wish I could work with a pro to set it up once so I understood everything better.

The way I do it, 

  • Set ride height
  • Unbolt one link of sway bars
  • Jack up rear and remove rear wheels, the lower to approximate ride ht
  • Rear jack point is centered and I use a one inch piece pipe so it can rotate freely
  • I load 225 lbs of bags of horse feed and excersize weights in the drivers seat and floor board
  • adjust front so both sides of frame have same measurement from ground
  • Re-install rear wheels and jack up the front and adjust rear heights
  • Re attach swaybars adjusting so there is no load (the bolts just slide in).

Its sounds simple but its very time consuming and I have had good results.  Mostly street driving just a few fun track days.

The above was how I did it with Datsun's and Porsche 911's (old air cooled ones).  I am sure its no where near what a proper set of scales could deliver.

 

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If you set the car up for one particular set of circumstances, it won’t be correct for others. For example, carrying a passenger, carrying luggage, or any combination of those two. There is also a differential mass of fuel to take into account, from 16 gallons to tank empty. 

Ultimately, a decision has to be made whether it’s a race car, or a road car.

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Margate Exotics.

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16 hours ago, Erikl said:

David,

Are you saying that a CW car once the driver weight is removed would not be slightly higher on the drivers side?  I would think in a light weight car this would be the case.  I wish I could work with a pro to set it up once so I understood everything better.

The way I do it, 

  • Set ride height
  • Unbolt one link of sway bars
  • Jack up rear and remove rear wheels, the lower to approximate ride ht
  • Rear jack point is centered and I use a one inch piece pipe so it can rotate freely
  • I load 225 lbs of bags of horse feed and excersize weights in the drivers seat and floor board
  • adjust front so both sides of frame have same measurement from ground
  • Re-install rear wheels and jack up the front and adjust rear heights
  • Re attach swaybars adjusting so there is no load (the bolts just slide in).

Its sounds simple but its very time consuming and I have had good results.  Mostly street driving just a few fun track days.

The above was how I did it with Datsun's and Porsche 911's (old air cooled ones).  I am sure its no where near what a proper set of scales could deliver.

 

To answer your question , the weight distribution with no driver installed will be different , as a result the cars attitude will have changed very slightly.. ( not really that noticeable without measuring )

Not sure how the way you describe setting up your Esprit will get the desired results..  

Firstly, you need to set the ride heights on level ground with all four wheel planted , this will ensure full weight is distributed when ride height is set ....  doing it with a pivotal loading ( one end jacked up ) will give different figures. 

Secondly,  you can not check corner weight/balance or adjust without the car being on scales..   Also when balanced the weights recorded on each corner will be different.  Its the % at the balance point you are after..  Here is an example of cross balance set up i did on 300 sport ..   Note the different recorded corner weights to gain the balance requirement.  

370625803_S300cornerweights001.thumb.jpg.d31975d2d471c2b860ac8f2b9ba3f7ef.jpg

 

Lotus are very specific with their spec figure for compliance reasons... change one and they all react different.. What i mean here is,  if you go off spec you really need to know what you are about or it will end up as scrambled egg. 

I always make sure the set up suits the application and use top engineers with very accurate equipment to finalise results. its just not possible without the correct equipment.. 

IMG_20180405_105417773_HDR.thumb.jpg.36f95e8fd83f544ad2e26929e8070c48.jpg

 IMG_20180405_105442050_HDR.thumb.jpg.9b28c6ec584c41a5b315f69b764cef06.jpg         

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