Are my ARBs causing higher speeds jitters?

  1. My model of MX-5 is: ND Sport Recaro
  2. I’m based near: York
  3. I’m looking for technical help or recommendations on: ARB handling issues

Hello all

I’ve just bought my second Sport Recaro (having had to sell my first to fund Covid-created income interruption!) and the previous owner had enhanced it with some BBR ECU/exhaust upgrades as well as fitting the Eibach/Mazda lowering spring and the Eibach ARB kit. It’s a lovely car, that corners on B Roads like its on rails (almost Caterham levels of oversteer in fact) but on faster main roads (70mph) it is very jittery with the slightest of steering inputs causing it to dart about. It actually feels dangerous to me.

I’m not clued up on the finer points of suspension but wondered if those ARBs were at the root of the handling issues? Could they be fitted wrong, or set up too stiff/wrong?

Or is it something else entirely?

I would suggest that the arbs would not be the cause of your issue. It is more likely to be the direction that your wheels are pointing. If it really does feel ‘dangerous’ I suggest a trip down the M1 to Roddison Motorsport in Sheffield. MX5 Racing - Roddisons Motorsport (mx5-racing.co.uk)

As an educated guess it may be that you have some toe out on the front as this will give you quicker turn in at the expense of straight line stability. Do you have the ability to measure things and change them? Perhaps the previous owner has some readings that he could pass on so as to form a basis for change.
This is a black art that can be ‘interesting’ to dabble in but the easiest and cheapest way to get what YOU need from the car is to visit an acknowledged expert. Fortunately one such person is only a short trip down the motorway.
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Thanks for that reply; very much appreciated. The ‘black arts’ as you describe them are well beyond my level of dabbling!

I know Paul as he looked after my previous MX5, so I will drop him a line and arrange a visit to Sheffield

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Excellent decision. Please let us know how you get on.
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Obviously you have checked the tyre 🛞 pressure :white_check_mark::white_check_mark::white_check_mark:
condition of tyres :ok_hand:and matching make on each axle ( if not all tyres)

If not, RODDISONS is a good shout for alignment

I have an ND Sport Recaro that BBR just carried out extensive work on. It is a Super 200 with BBR’s exhaust, but more relevant to you I also have the Eibach ARBs and BBR’s performance springs. I stuck with the Bilstein shocks. My car is absolutely planted on bends and motorways. It has BBR’s alignment, which I could forward to you if you’re interested, but we do have different springs so keep that in mind.

It certainly won’t be the arbs that are giving you handling problems. Most likely tracking as mentioned or mismatched tyres.

assuming something is not broken and tyres are good, with same pressures and not over inflated - it is possible that the anti roll bars are actually (or contributing to) the issue.

with the wheel geometry alignment setup - if you have excessive toe out front / toe in on the back the car will behave like its on a knife edge. the how much you should use is the black arts bit…

However the anti roll bars stiffness do change the understeer/oversteer bias (it is the relationship of torsional stiffness of the front part of the car to to the rear part). Note that the suspension stiffness also influence how the car rolls thus it will contribute to the overall torsional stiffness bias of the car.

if the stiffness relationship of the front arb is softer to the rear arb = oversteer
if the stiffness relationship of the front arb is stiffer to the rear arb = understeer

if the wheel alignment is what’s generally recommended for road use and your car at the moment oversteer excessively - if you have adjustable arb’s make the front arb stiffer or make the rear arb softer from its current setting.

my recommendation is to change one thing at a time and see the effect just to make sure you are changing things and moving towards the right direction.

Hi C,
‘on faster main roads (70mph) it is very jittery with the slightest of steering inputs causing it to dart about’
What you have written is correct but I do not (along with others) think that antiroll bars will affect or cause the situation the OP has, particularly when he states that the car ‘corners on B Roads like its on rails’.
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I also think that in his case the steering geometry is setup with too aggressive toe out/ in on the front/ back wheels respectively. I adjusted my comment by above to make it more clear.

All i was saying that the anti roll bars do change the understeer/oversteer characteristics but the effect would also be related to the car springs. The understeer/oversteer characteristics would be different if you were using softer (stock) springs when compared to the stiffer springs you usually get with aftermarket coilovers.

So to try fix it, look at the alignment. If the car still oversteer then you really need to adjust the antiroll bars

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Many thanks for the comments; all well received and appreciated.

I have it booked in for a full four-wheel alignment check as a first step - hopefully that deals with the issues.

I have also checked tyre pressures and treads - and they are all fine - but it does have Potenza S001 on the front and Hankook S1 evo3 on the back. Any thoughts on that combo?

Interesting. If you have the time and inclination why not swap the wheels front to rear and see what transpires.
I think we are all too excited and impatient to see what the ‘expert’ has to say.
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Well… I wouldn’t run different make of tyres in my car so makes me wonder what other “shortcomings” you may find.

Having said that I think the hankook have great reviews and was considering buying a set but went with the michelin PS5 instead. I don’t really think your tyres is the primary reason for your issue but obviously it would not help my OCD.

Having the same set of tyres make the car predictable as the progression through the slip range is the same for all tyres.

I never said or implied I was an expert btw. I just learn what I need to learn when I’m doing/having work done on my car

Slightly confused!!! The ‘expert’ I refer to is Rodders.
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Sorry i misread that. Please accept my apologies

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So the car was with Paul Roddison yesterday and it has returned like a changed car.
A new set of Kumho 215 width tyres and a Rodders alignment have sorted 80% of the issues. It’s still a bit jittery under hard acceleration but I’m convinced that is connected to an over ‘firm’ rear anti roll bar.

I think you have to look elsewhere for the jittery rear end. I have the Eibach arbs and don’t suffer from the jitteryness that you describe.

Why not test your theory by disconnecting the rear antiroll bar. Just remove one of the drop arms and see how it affects the car. (you can just disconnect one end of one but you have to make sure the arm does not flap about and interfere with anything)
If you have the lsd fitted then this could be causing this feeling and is ‘normal’ under aggressive applications of throttle.
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IMHO, having recently experienced similar problems I’d strongly suggest you get the tracking checked asap, minor deviation from the standard set-up caused mine to change from feeling as though it was on rails round a bend on any surface to skittering all over the place if a straight road surface was anything other than smooth, unrutted and free from potholes - get the tracking reset to the norm - also it might be worth getting the camber angle checked and again reset to the normal parameters.

A visual check can tell you a lot - stand about 10m back from the front of the car if - you can see any of the inner or outer sides of the tyre walls they are not correctly tracked for your model - getting it corrected will not only reduce tyre wear but bring it back to the handling that you know and expect.