I've got a bit of a wobble!

[Agent L]

I'm looking for some MX5 experts that may be able to offer advice on this.

I've had a Mk2 1.8 S.E.Ltd for about 2 and a half months now. Noticed soon after I got it that it does a bit of a wobble at the rear at motorway speed, feel it through the back of the seats, makes you feel a bit queasy. The place where I bought it, although being recommended for their great warranty, refuse to believe there's anything wrong with it. All they've done to try and rectify it is to balance the wheels twice. I took it up to WIM yesterday and got it all checked out. Everything was out basically but nothing so much as to cause and handling issues. I also got them to balance all the wheels on their fancy stud mounted machine instead of the centre hole. All wheels were out of balance. Two have slight buckles (nothing much, had worse on other cars with no effect), the passenger side rear however has a pretty big buckle that was very noticeable when it was on the balance machine. Think it was about 1.2mm out of true on the rotation.

Strangely, the wobble goes away with the hardtop on. Do you think the wheel could be causing all the issues or could it be something more? Prop shaft, diff etc?

After sorting out the geometry etc the wobble is actually worse, but the turn in is great.

I thought I may put the suspect wheel on the front to see if that changes the wobble. Would that be a good indicator of what's causing the problem?

[MX-5 Lazza]

Well the first thing to try will obviously be some straight wheels.
The best way would be to find another '5 owner locally who is willing to let you try his wheels.
Due to the design of MX-5s they can suffer from "scuttle-shake" where the car will basically "twist" across the middle. On early cars this tends to happen if the alignment isn't quite right and usually manifests itself around 60mph. Later cars had a stiffer chassis so it's usually only noticeable over bumpy surfaces. If your wheels are bent it might well be inducing this scuttle-shake effect the same as if it was on a bumpy surface.

Where in Sussex are you?

[Agent L]

Thanks for the info, I'm in Brighton. Don't actually know anyone who's got a 5 so if anyone's local and up for it

I was under the impression that scuttle shake was only when you go over a bump and the car twists? Obviously not.

I really want to love the car but it's annoying me at the moment that no journey is comfortable.

[MX-5 Lazza]

Agent L said:

I was under the impression that scuttle shake was only when you go over a bump and the car twists? Obviously not.

It is - mostly. Thing is, if your wheels are bent then you are carrying your bumps with you everywhere you go. I'd guess that it manifests itself at certain speeds and 10mph or so higher or lower isn't as bad?

Try asking on MX-5 Nutz or (if you don't get any luck there) on MX-5 OC forums - you'll find someone local there.

[tootsnpurple]

Mine shakes around 60 if my tire pressures aren't spot on, your def right about the scuttle shape, still love it though.

[Agent L]

MX-5 Lazza said:

I'd guess that it manifests itself at certain speeds and 10mph or so higher or lower isn't as bad?

That's exactly right yes.

As for the tyre pressures, what is correct? I keep seeing 26 all round mentioned and that is what I run but I set them cold. Is that right?

[tootsnpurple]

Cold is right, & 26 is what it says in the book though i run mine at 28, seems to run smoother, & help with the shake.

[GravelBen]

I run mine at 30, really felt uncomfortably squidgy at 28. Guess different tyres like different pressures.

Edited by GravelBen on Thursday 23 October 21:12

[Evil Edna]

Agent L said:

I'm looking for some MX5 experts that may be able to offer advice on this.

I've had a Mk2 1.8 S.E.Ltd for about 2 and a half months now. Noticed soon after I got it that it does a bit of a wobble at the rear at motorway speed, feel it through the back of the seats, makes you feel a bit queasy. The place where I bought it, although being recommended for their great warranty, refuse to believe there's anything wrong with it. All they've done to try and rectify it is to balance the wheels twice. I took it up to WIM yesterday and got it all checked out. Everything was out basically but nothing so much as to cause and handling issues. I also got them to balance all the wheels on their fancy stud mounted machine instead of the centre hole. All wheels were out of balance. Two have slight buckles (nothing much, had worse on other cars with no effect), the passenger side rear however has a pretty big buckle that was very noticeable when it was on the balance machine. Think it was about 1.2mm out of true on the rotation.

Strangely, the wobble goes away with the hardtop on. Do you think the wheel could be causing all the issues or could it be something more? Prop shaft, diff etc?

After sorting out the geometry etc the wobble is actually worse, but the turn in is great.

I thought I may put the suspect wheel on the front to see if that changes the wobble. Would that be a good indicator of what's causing the problem?

Agent L

The good news is......there is nothing, inherently, wrong with your car. Not only are MX5s very sensitive to suspension geometry but, they are also very sensitive to wheel balance. I have EXACTLY the same problem as you.

My story:

I've had my mk2.5 VT-Sport for a year and a half. When I first bought the car it had ditch seeking Avon ZZ1s fitted to it. They were truly awful. I chose to replace them with GY F1 GSD3s, fitted by Event Mobile tyres. They really transformed the car and Event did a fantastic job balancing the wheels. No wobble, no shake, it was perfect.

A few weeks ago, I decided to get the alloys (16" 5-spoke) refurbed. I took them off the car, complete with tyres, and took them down to JP Polishing on Canvey Island. JP did an absolutely spiffing job on the wheels (tyres off, blasted back to metal, powder coated, lacquered, tyres then put back on and rebalanced - £170 all in), they really do look brand new.

However, when I refitted them to the car, I got the most horrendous shaking from the rear end at about 60-70mph. It was really bad, to the point where I could not sit at that speed range for any length of time.

I have taken the car to the "alleged" experts in Rainham, Essex, to get the wheels rebalanced. And, I must admit the rear end shake is much better but, it is still there. I know that my wheels are light and the tyres are heavy, and this makes them difficult to balance but, these people claim to be better than the rest.

I really need to take the car to someone that will take a bit of time to really do a good job, even if that means deflating the tyre and repositioning it on the rim several times, until it balances properly. If anyone can recommend anywhere within a 30 mile radius of Central London, I would be very grateful.

Anyway, I take some comfort in knowing that we are not alone. I had a dig around and found this:

http://forum.miata.net/vb/archive/index.php/t-24691.html

Regards,

EE

[Agent L]

Thanks for the info EE, I'm sorry you've got the same problem but I'm also glad it's not just me that's affected. That other forum actually makes for depressing reading as it seems many people suffer from it and finding a cure is less than easy.

Sounds like my best long term solution is to get a brand new set of wheels ( and tyres ) but I really like the ltd ed ones on my car and don't want to change the look, nor spend the money. Will converse with the garage I bought it from again today.

[MX-5 Lazza]

GravelBen said:

I run mine at 30, really felt uncomfortably squidgy at 28. Guess different tyres like different pressures.

Correct. MX-5s seem to be designed for tyres with fairly stiff sidewalls like Goodyear or Bridgestone. If you use something like Toyo which have soft sidewalls then you will probably need 28-30psi.

Agent L said:

Sounds like my best long term solution is to get a brand new set of wheels ( and tyres ) but I really like the ltd ed ones on my car and don't want to change the look, nor spend the money. Will converse with the garage I bought it from again today.

There is no reason you couldn't get your wheels straightened. I've had buckles taken out of my wheels before - on my old Mk1 I had 2 wheels that were quite badly bent - probably 10mm or more but they still managed to straighten them.