Severe vibration/shake at 100km/h

Moto · Postby **Moto** » Fri Jul 30, 2010 3:10 pm

Hi Guys,

I have a problem with my car, at about 100km/h it has this severe vibration/shake, it's strong enough to distort the rear view mirrors! The vibration goes away above about 108km/h and anything under 100km/h is smooth as silk.

I've had two lots of wheels on the car, one set with 8 inch wheels and 195 tyres (stretched) and my track wheels which are the standard NB8A wheels with 205 tyres. Both sets of wheels have been balanced. With the NB8A wheels the problem seems to be worse.

The car has a Brown Davis rollbar and a Whiteline front strut brace, it's also on BC coilovers. It hasn't had a wheel alignment for a while.

Any idea's what could be causing this? I want to take it on a road trip soon but it's horrible to drive at 100km/h!

:NB8A:

AJ · Postby AJ » Fri Jul 30, 2010 4:58 pm

could be a shot wheel bearing.............the NB8A rims are a bigger rim, the 205's are not only bigger but wider, which would contribute to the problem if it is a wheel bearing :?:

Moto · Postby **Moto** » Fri Jul 30, 2010 6:01 pm

I was thinking it could be a bearing. How do you test it? Jack the car up and try and wobble the wheel?

charlie_91 · Postby **charlie_91** » Fri Jul 30, 2010 6:25 pm

yep .. jack it up.. grab the wheel from top and bottom and push back forth to feel any movement..

It shouldnt be the wheel bearing because u would be able to hear a grinding sorta noise when the wheel is under load in corners and what not.

My suggestion is wheel alignment and wheel balance again. I had the same sorta vibration last week and i thought it was weird because i had just had my wheels balanced. I took it to another shop and rebalanced them and they were way out.. now no vibration.

good luck

JBT · Postby **JBT** » Fri Jul 30, 2010 9:41 pm

I doubt it would be wheel bearing. Agree with charlie_91 re alignment and balance - most likely the latter. There could also be some "out of round" issue happening too.

charlie_91 · Postby **charlie_91** » Fri Jul 30, 2010 10:20 pm

just had another thought.. have u got hubrings ? or are both the wheels 54.1mm centre bore ?

NMX516 · Postby **NMX516** » Sun Aug 01, 2010 10:56 am

Tyre placement on the rim can also sometimes cause problems. Tyres have a "heavy spot" marked on the sidewall, which is the heaviest part of the tyre, and is meant to be located opposite the valve on the rim. From memory it is a red spot painted on the sidewall, but not 100% certain on the colour of it. It will take some trial and error by an obliging tyre fitter, but doing this solved the problem for me on my NA...

de Bounce · Postby **de Bounce** » Sun Aug 01, 2010 11:14 am

NMX516 wrote:Tyre placement on the rim can also sometimes cause problems. Tyres have a "heavy spot" marked on the sidewall, which is the heaviest part of the tyre, and is meant to be located opposite the valve on the rim. From memory it is a red spot painted on the sidewall, but not 100% certain on the colour of it. It will take some trial and error by an obliging tyre fitter, but doing this solved the problem for me on my NA...

Agree it can be a tyre placement on the rim.
For clarification - According to the Tyre Bible (about 2/3 down the page)
A coloured dot is put on the sidewall of the tyre corresponding to the light spot, typically a yellow dot. The yellow dot should end up aligned to the valve stem on your wheel and tyre combo.
A tyre's high spot is mark with a red dot on the tyre sidewall and is called the uniformity mark.
Some tyres have them, others don't

A method to isolate the problem is to swap wheels with another MX5 and see if that solves or minimises the vibration.
There is also an article in the Garage Section on the Big Forum titled The 65 mph Shimmy

Mr Morlock · Postby **Mr Morlock** » Sun Aug 01, 2010 7:30 pm

I would be taking it to a tyre fitter and have it checked. They will be able to get the car on a hoist and check all of the usual reasons. Another forumite struggled for a long time to find a vibration on his car and it was finally solved by a bracing addition- there was a recent post on this. Check for the obvious first.

Wivvix · Postby **Wivvix** » Mon Aug 09, 2010 12:13 am

Don't waste your time taking it to just any tyre shop though.

You'll want to find a tyre shop with a Hunter GSP 9700, as this shop, provided the technician has half a clue how to use the machine, will be able to give you the low-down on the quality of the tyres as well as the previous balance.

I suggest you read up on the 65mph shimmy and tyre balancing with regard to Hunter GSP 9700's before pursuing this further. Been there done that. You'll want to know the ins and outs before you commit to spending any money, trust me.