MX5Ireland

A couple of weeks ago I was on the motorway, it was busy with trucks and general traffic and very blustery and I probably didn't take much notice, but I've used the motorway since and there's a vibration that starts at 100kph and gets worse until I go over 120kph, the vibration is through the body but no noticeable steering shake, I got the 4 wheels balanced and now it seems worse. The balance weights used are the stick on type placed inside the face of the rims, originally the weights were the clip on type that attach to the outer lip, I'm also wondering if the 9 year old dunlops on the front might be a reason. I did swap the front to the rear and "drove" the car on tick over in 5th while on axle stands to check for any warped tyre or rim but all seems fine, and even swapping front to back made no difference,one thing is that I don't know which side each wheel came from so two or even all four might be running in the opposite direction than they have alwa done, I'm going back to the place that balanced them but was wondering if there might be anything else that might be the cause, in the 4 years I've had the car it's only been on a motorway a handful of times so I don't know if there's some other problem like bent drives etc

So while waiting for the paint to dry I had another look, it seems like one or even both of the 9 year old dunlops may be the cause, off the car the wheels don't stand up straight, they lean towards the outside, if anything I'd expect them to lean towards the inside due to the negative camber the steering has.
I did a few basic checks, this time I put each wheel on the right front, without any speed it's easier to check the runout, no side to side problems but one of the dunlops seems to be a bit square, checking the runout on the thread surface it would appear that one has either a flat spot or a high on the thread, it touches the test level in a couple of places, the biggest gap is app 1.5mm,


An idea how much the dunlops lean compared to the others


I think at this stage the only option is to get two new tyres

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Side by side
I'd say it looks like the thread may be weak and has bulged slightly


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It does look like that alright.
I did have a shimmy at 60mph but had to add bracing to remove it

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To go some way to stop the vibration I replaced the two ancient dunlops with nice new Kumho's, also as you mentioned, I tightened the front strut brace, vibration is as good as gone now, it was so much better on the trip around the Clare coast today, still slight variation on the motorway when I get to110kph but nowhere near as bad and its all good at 120.
Thoughts now are that I might replace the poly bushes with standard ones

Pops wrote:To go some way to stop the vibration I replaced the two ancient dunlops with nice new Kumho's, also as you mentioned, I tightened the front strut brace, vibration is as good as gone now, it was so much better on the trip around the Clare coast today, still slight variation on the motorway when I get to110kph but nowhere near as bad and its all good at 120.
Thoughts now are that I might replace the poly bushes with standard ones

Funny you should say that, I also went from poly back to rubber.

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Ya, the plan now is to see if the motor factor has a listing for any of them, I saw them on ebay or some website somewhere but I'd rather try getting them in the factors

K, yeah cool. Think I went to ilmotorsport at the time.

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