Mx 5 shaking at motorway speeds

[Loltraktor]

Hi, I'm currently looking at buying a NA mx-5. I've found a 1990 v spec model that I'm very interested in buying. The ran smooth and everything was good until I took it onto the motorway, I had the roof down and when I hit around 100 the car started to shake rather harshly, the steering wheel was not wobbling, the seller called this scuttle and said this is common. Is this actually a common problem with these cars and is it an easy fix?

[siren676]

Yeah its a pretty common occurrence in mx5's, chassis bracing or a hardtop tend to reduce it a lot. Mine had it around 105k's, Americans seem to have nicknamed it the 65mph shimmy

[Loltraktor]

Thanks, also could aligning and balancing the wheels help reduce this?

[Angreal]

Yeah that should also help it. My car used to do it when I first got the car but I haven't noticed it for a very long time now. Either the alignment, braces, suspension or some combination of these solved it

[BRM]

Factory wheels?

[Loltraktor]

No, some unknown aftermarket alloys which weren't balanced or aligned

[siren676]

Have a read through this article, you might find something which helps.
http://www.miata.net/garage/65_mph.html

[WideOpenThrottle]

Brand new wheels & tyres cured it for me.

[SLYDIT]

Very common. Fit a subframe brace. Fit quality tires and get an alignment. When I bought my car it had a bad shimmy because of the cheap Chinese tires. Fitted some quality toyo rubber and it all but disappeared.
If you look under the back of the car you will see the rear subframe hangs down to mount the lower suspension arms. Its like a big tuning fork that resonates at around 105kmh. Mazda actually added some bracing in the later models to cure it.