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Anti roll bars, do they age ?


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  • Gold FFM

Nearly there with the suspension refresh and wondered if it’s worth buying a new ARB or just getting mine blasted and coated.  Do they age and lose torsion etc or does the rust eat away at the diameter thus making it thinner?  Just wondered people’s thoughts?

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Don’t wire it too hard - any slight surface scratches may impede of the rebound flexibility compound refractionary curves 

I just made a simulation of a uniform thickness loss of a realistic anti-roll bar (not Esprit or even Lotus related though, just a random but realistic anti-roll bar). It's the first bar I found so it

I'd suspect that any minute difference in ARB effectiveness from blasting, would easily be less than (for example) fitting new tires...

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  • Gold FFM

Depends on the wear of the arb into the bush. The wear is normally obvious and the bar will rattle in the bush.

Only here once

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I just made a simulation of a uniform thickness loss of a realistic anti-roll bar (not Esprit or even Lotus related though, just a random but realistic anti-roll bar). It's the first bar I found so it's a tube but anyway.

The reference one (=new) is 26.5mm in external diameter and 17.5mm internal diameter. Its stiffness is 42.449 N/mm (~55754.828 N.m/rad)
I then reduced its external diameter to 26.3mm (0.1mm loss on the external surface), kept all the rest unchanged (id=17.5mm). Its stiffness is 40.841 N/mm (~53643.121 N.m/rad)

So I am afraid I don't agree too much with @drdoom, I would suggest to not sand blast any elastic suspension component (coil spring or anti-roll bar) as the external diameter is quite significant.

And that is for the diameter alone, whereas some (most?) bars are actually quenched so a hardened surface removal may have an even greater impact.

And then there are the steel fatigue which may change the bar stiffness too, and so on. I don't know too well to be honest.

=> Anyway, keep your suspension rust clean and rust free!

Now, in real life on the open road at legal speed, will that make any real difference? I suspect not so much — still, I changed mine since it had been scrapped by something on the road before I bought the car!

Edited by Giniw
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I believe that surface rust loss on the sort of component discussed here will be found to be minute, minimal change of dimension. It is correct to note the significance of material OD in parts stressed in torsion, so meaningful loss would entail reduction in rate and, more importantly, increased risk of failure. Like I said, rust OK if not atrocious. As to temper I'm confident that the A-R bars are through treated and tempered adequately to avoid brittleness so cleaning and painting are not to be avoided. Steel fatigue is unlikely to manifest in the bars, IMO. The fatigue life of correctly spec'd and treated steel is enormous, and the typical Lotus is used much less than other cars. Not much lost if cleaned up oldie proves disappointing, not so hard to switch over to a new bar.

The calculations offered seem misleading in my experience. How long was the reference bar where in torsion?

I do not advise sand blasting. Not only is it rather destructive but is broadly prohibited due to silicosis hazard. I use a glass bead cabinet for work on compact pieces, have jobbed out large piece prep to professionals using mix of walnut shell and crushed soft stone.

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11 hours ago, Giniw said:

The reference one (=new) is 26.5mm in external diameter and 17.5mm internal diameter. Its stiffness is 42.449 N/mm (~55754.828 N.m/rad)
I then reduced its external diameter to 26.3mm (0.1mm loss on the external surface), kept all the rest unchanged (id=17.5mm). Its stiffness is 40.841 N/mm (~53643.121 N.m/rad)

That's a reduction of N/mm of less than 4%, which i would be surprised to find changed the ARB from safe, to unsafe.

Disclaimer: these are just calculations from the figures given, which i have not even checked , and i am not certifying your ARB as safe, or unsafe, or anything at all. I'd be more concerned with the joins/welds/bolt fixings than the tubes.

Edited by LotuStuart
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6 hours ago, drdoom said:

The calculations offered seem misleading in my experience. How long was the reference bar where in torsion?

Both the reference bar and the reduced diameter bar are virtual: I got these results with a finite element analysis software (thanks to a spring and anti-roll bars dedicated simulation platform)

Edited by Giniw
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9 minutes ago, LotuStuart said:

That's a reduction of N/mm of less than 4%, which i would be surprised to find changed the ARB from safe, to unsafe.

Yes I agree it's not huge but still not negligible. I wouldn't say it becomes unsafe, although if I am not wrong a reduced rate would increase the car tendency to oversteer. But again, as I said on the open road at legal speed it's probably not a real problem ... ^^

9 minutes ago, LotuStuart said:

which i have not even checked

You couldn't indeed as you don't have the full data of the bar I checked ^^ (which is not an Esprit anti-roll bar I could do it as well but I don't have its measurements here)

Edited by Giniw
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I'd suspect that any minute difference in ARB effectiveness from blasting, would easily be less than (for example) fitting new tires...

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Atwell Haines

'88 Esprit

Succasunna, NJ USA

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I think I read about a broken front arb once.

Apart from that, and that the difference in the simulation is not overly much, personally, I'd look at it a bit differently, as I see it as a sum of many small differences. Like with tuning and optimising, the opposite can come into effect. It goes both ways.

So, 4% from the front arb,  some % from brake discs and pads, a littel from old fluid (or much), some from old rubber brake lines, a little from worn bushings, some from dampers and springs, some from a worn steering rack, a bit from ball joints here and there, incorrect tyre pressure, bad or old and bad tyres, luggage and stuff being placed inside the cabin and so on.

All in all I belive this may, in certain cases, lead to a potentially much more dangerous result, possible accident, even though the driver does not drive too fast or with lack of care taken for say a  wet road surface, as it's a sum of many small areas that is not up to the task. In such a case, the car may skid out, be less controllable and hit something or someone. We all want to avoid that.

I have experienced some of this in a friends old Volvo Amazone, which had to be driven very slowly because of it's owners neglect to suspension, which in effect made the car woble about and have enourmous braking distance, because of bad kept brakes and worn out springs and dampers, just to mention a few. The car was outright dangerous, which I told the owner/driver and to which he reponded: "Oh, but I do look ater the car regularely". I responded with a mix of explanation such as "when did you last service all bushings, brakes, suspension etc? He said never... Oh, I said, so the good looking over the car was just a polish of the paint and an oil change? Yes, and the interrior is still the original red nylon he replied. Being a really old car, and registred as a veteran car, the MOT is only every 8'th year, which in this case is dangerous, as you as the owner neglects your responsability, I commented. He replied that he only drives very slow. I said "Let's go for a drive in my Esprit, which we then did. Apart from the speed potential, he was in a state of deep shock of how well the car handled, braked, steered. He said, but that's a new modern car. No, I said, it's 29 years old. You wouldn't stand a chance driving 110 km/h on the freeway and then suddenly having to brake and avoid, I said. But I only drive it once in a while, he said. Yes, exactly so, as you won't even have the experience build up to handle the car in such situations, I kept on replying. We finally agreed.

Leasson learned.

Kind regards,

jacques

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Nobody does it better - than Lotus ;)

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3 hours ago, CarBuff said:

I'd suspect that any minute difference in ARB effectiveness from blasting, would easily be less than (for example) fitting new tires...

Well maybe (I honestly don't know) but aren't you happier with new tyres than with old dry ones? As @Jacques just said everything counts (keeping in mind that the parts can't be new for ever obviously so a little wear or loss in performance is inevitable indeed)

 

19 minutes ago, Jacques said:

So, 4% from the front arb

It's not the Esprit one so the actual numbers for us could be different. I will have to check with the real measurement of an Esprit AR bar. Anyone has its dimensions? I have two of them taken appart but not here with me.

Edited by Giniw
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Ambient temperature also comes into play. The action of an arb would have to be designed well inside the elastic limit of the material, so ideally an arb would not deteriorate over time. Too many variables for a layperson to work it out. 

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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I correctly designed a tubular A-R bar for my Elan, .065 wall 4130 steel heat treated to optimal temper, 38 Rockwell C as I recall. It worked beautifully and endured heavy work without strain. So a studious layperson can figure this out. A-R bars typically are not stressed close to the yield or fatigue limits of the steel. Dan Gurney, in sorting work trackside on one of his early Eagle Indycar chassis, went off to the nearest hardware shop for something to supplement the front bar. He settled on some galvanised plumbing piece and had it welded on, making good his assessment of the needed change of setup. The lauded and highly successful BRE racing team in America used a high silicon steel, trade named Stressproof, which required no heat treatment after bending to form A-R bars for their TransAm Datsuns.  I just love anecdotes of this sort!

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  • Gold FFM

Just either buy a new one - or clean and paint the old one.

powdercoating will cause you an issue refitting due to the thickness of the powder

Only here once

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  • Gold FFM

Out of interest @Mightymetro since your car is a bit of a factory special, do you have the standard ARB or the Sport 350 ARB, I believe they are 16mm and 17mm diameter respectively (but not positive on the dimensions)?

If it's badly corroded you may have a hybrid depending on where you measure it. 🤣

cheers

-Chris

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  • Gold FFM
5 hours ago, cweeden said:

Out of interest @Mightymetro since your car is a bit of a factory special, do you have the standard ARB or the Sport 350 ARB, I believe they are 16mm and 17mm diameter respectively (but not positive on the dimensions)?

If it's badly corroded you may have a hybrid depending on where you measure it. 🤣

cheers

-Chris

I’ll get the wire brush out and see how it looks 😂

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  • 2 weeks later...
  • Gold FFM

Chance to upgrade to a Sport 350 one, but you would need more new bushes as well. You are not having an easy ride with this one but you are doing a fantastic job, keep going, not long now.

BTW with the newly refreshed suspension bits and exposed hub castings are you considering any anti-corrosion coatings like ACF50 for example?

cheers

-Chris

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  • Gold FFM

I don’t think the sport 350 would be right for the car as I specced the shocks and springs to standard v8 settings rather than the 350 settings.  Guess I’ll have to bite the bullet and get a new one from SJ.

 

the hub castings have also had the zinc nickel plating 🤭

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  • Gold FFM
1 hour ago, Mightymetro said:

the hub castings have also had the zinc nickel plating 🤭

Oh nice, I had assumed you would only plate the steel items. 

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