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Giniw

S4s anti-roll bar diameter?!

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Hi Everyone,

I am refurbishing my S4s Esprit suspension and as my anti-roll bar was a bit scrapped/bent and I had an opportunity to buy one used cheap I thought it was the right time to change it as the car is on the lift.
I just checked the diameter and I am very surprised the old scrapped one diameter is only 15 mm and the new one 16mm!? (the new one is apparently from a 2003 FED V8)
As far as I know the S4/S4s/Sport300 and V8 share the same one and it's supposed to be 16mm if I am not wrong (and the Sport 350 17mm)
So, what is that 15mm bar I have on my car?!! Do you happen to know if it comes from a SE maybe?!

Do you confirm a S4s should have a 16mm diameter bar?

Thanks in advance!! :)

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I can measure the one I have fitted which was bought new from SJ a couple of years ago, if that helps?

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Well why not if it's an original one =)

Thanks Ian ^^

As far as I know the S4/S4s/Sport300 part number is D082C4222F from the S4 parts manual,
and the V8 is D082C4222F too (labelled explicitly to be a 16mm one) and the Sport 350 is A082C4254F (labelled 17mm).

So that would be some good news as the replacement I found is a 16mm one, it's just very strange that the one I have/had on the car is a 15mm one?!

 

v8 roll bar parts list.png

S4-S4s-Sport300 anti roll bar parts list.png

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The SE is a 17mm.

I've always heard the 88, 89, S4, S4s, V8 all had a smaller one, wasn't sure about the Sport 300.

The X180-R, and Sport 350 also have 17mm.

If I recall correctly

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So that would be from a S1-S3 maybe?! (not sure if it's the same front suspension, I think I have heard the early cars had a different setup, I am not sure when it changed for the *modern* setup -- probably changed along with the Peter Stevens restyling? The thing is, the 15mm one I have is the same as the 16mm one, except the diameter of course ^^)

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As can be seen on video, the Sport300 does roll some.

But having very wide tires both front and rear, these will affect some of the roll and also create a bit firmer suspension, because wider track means less weight transfer, and generally more stiffness could also be introduced by having a shorter bar, hence acting as if there were wider Wheels, but without having stiffer suspension movement regarding springs. I haven't measured those bars that Lotus use on Stevens Esprits for length, though. I suspect they have the same length, but I cannot tell for sure.

But since the Sport300 used lower springs, the center of gravity which also determins the body roll, will also act as a stiffer arb, hence the need for a thinner front arb on the Sport300 compared to higher cars.

It would be interesting for this debate to hear from someone WHO installed the 18 or 19mm front arb from fleabay, for how they actually feel the change, for example, does it induce more understeer in real World driving? Or did they do other adjustments in  the same time, to counteract this, for example by having stiffer rear springs?

Could someone calculate the percentage in stiffness increase in relation to increase of diameter, and make a curve, so more values can be viewed? (say 10-25mm)

So, in Giniw's example a thick'er front arb would induce more understeer, but if he installed stiffer rearsprings this would be counteracted, and if he installed lower springs, he would increase roll resistance, without having to thicken the front arb, and therefore not introduce more understeer, as the center of gravity would be lower. Installing a lower Sport300 seat as well as installing it in it's lowest position would also lower cg, Again increasing the resistance to roll in corners, which in turn would allow slightly more room for softer springs (small values).

I hope I am correct in this ;)

Kind regards,

Jacques

because wider track means less weight transfer.

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I measured my S4s anti-roll bar in the middle area and I am getting around 15.5mm - 15.6mm for the diameter.

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The SE 17mm bar actually is responsible for some of the understeer on that car.  Apparently the earlier cars had less understeer.

Though the 89SE= cars with the "Eagle chassis" also changed to a pro-dive & pro-squat geometry. 

It is possible to dial some of that out with alignment changes, adjustable suspension, adjustable damping, and tire pressure changes.

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On 25/02/2018 at 00:06, Jacques said:

Could someone calculate the percentage in stiffness increase in relation to increase of diameter, and make a curve, so more values can be viewed? (say 10-25mm)

I can do that, but I would need to take proper measurements of the bar (the shape of it, not just the diameter). Please do not hesitate to remind me if I forget — which is very likely, if I am being honest :D

Thanks @Seraph, mine is more around 15.2 so I suspected the extra 0.2 is the paint thickness and tolerances — welcome to thelotusforums by the way! :)

 

Steve from SJSportscar told me that according to him D082C4222F is a 15mm bar. He does know that there is a 16mm bar, but its origin remains unclear to him. Strange it contradicts the V8 parts manual ... ?!

 

33 minutes ago, Vulcan Grey said:

The SE 17mm bar actually is responsible for some of the understeer on that car. 

To my understanding a stiffer roll bar at the front has a tendency to make a car understeer more indeed, but I am faaaaar from a specialist in that subject.

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@Giniw Thanks for the greeting.  I thought I signed up a long time ago, but I couldn't find my login. I lurk most of the time anyways.  

Mine is getting rust and I was considering a replacement, but I had not decided what diameter to go with either.  I'll probably watch Ebay and see if maybe a good used 17mm shows up.

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As for me I would like to keep it stock but it's not that clear what is actually the proper diameter for the S4s — the parts manuals seems to contradict what we have on our cars ... ?!

("Joined: February 7, 2015" ooops yes indeed :D)

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I figure that if I start with a 17mm diameter bar now, then it will rust its way down to a proper 15-16mm in another 20 years :) 

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