Vibrations

[Phil Dyer]

I have just bought my red 91 MX 5 manual with 92000. Seemed to be the tidiest
around Christchurch yards with new hood, 15" mags and new low profile
195/50R15 Yokohama tyres - but paid $10999 for the privilege.
Did query wheel balancing after my first drive and the yard paid for all four
wheels to be balanced - had to push the tyre firm to balance the back ones
though - but still notice a moderate vibration that comes through the seat of
your pants and reminds me of unbalanced back wheels. It starts at 100ks
through to about 120ks. So if it is not the wheels - what else might it be?
Tyre pressure was 20psi and now is 32. The 15" mags may look good but you
notice the bumps in the road!
Phil

[my2cta]

On Tuesday, August 28, 2001 9:37 AM, Phil Dyer [SMTP:pdyer@inet.net.nz]
wrote:

I have just bought my red 91 MX 5 manual with 92000. Seemed to be the

tidiest around Christchurch yards with new hood, 15" mags and new low
profile 195/50R15 Yokohama tyres - but paid $10999 for the privilege.

Did query wheel balancing after my first drive and the yard paid for all

four wheels to be balanced - had to push the tyre firm to balance the back
ones though - but still notice a moderate vibration that comes through the
seat of your pants and reminds me of unbalanced back wheels. It starts at
100ks through to about 120ks. So if it is not the wheels - what else might
it be? Tyre pressure was 20psi and now is 32. The 15" mags may look good
but you notice the bumps in the road!

Phil
<< File: ATT00002.htm >>

Same size mag wheels on the 2000 Millennium model that we have. Factory
recommended pressures for these are 26 psi front and back. Can't see how
higher pressure would cause vibrations though and we have no problems.
Don't feel the bumps either.

Tim

[Richmond, Colin]

Have you considered that there might be flat spots on the tyres? Could
either be from good quality spin out, heavy braking, or just sitting
there for long periods underinflated.

I experienced this from a bad tyre batch (205/50 on 15x7 mags). Got rid
of the vibration by buying a new set of tyres - a bit extreme and
possibly costly, but it worked - I don't know how you can check this
though.

Might try moving tyres front to back to see if there is any difference.

Cheers
Colin

Phil Dyer wrote:

[...]

[Phil Dyer]

Thanks Tim - The yard suggested I ran them at 40psi! The tyre place said
below 32 will cause stability problems! But I think I will set them back to
26 - seems closer to what they were and they do give a hard ride.
Life is not simple is it?
Phil

[Scott Elder]

yea, I have a flat spot on 1 tyre and you can feel it when going over 110km/h.
It'll be replaced at the end of the month when I get my wof

[H & J Weir]

You are experiencing what the American Miata owners refer to as "... the 65
mph shimmy..."
There has been alot written on the subject at Miata.com and boils down to our
cars being very sensitive to some wheel/tyre combinations and alignment
issues.
The cure seems to be spot-on alignment, and trying another tyre type - sorry.

zorruno

[Gary Morrison]

Tim,

Try swapping wheels around, just front to back same side if they're
directional tyres, or any which way if they're not. See if it helps. If not
take the car to a GOOD tyre shop, someone who cares, tell them your problem
and that the MX-5 is VERY sensitive to any imbalance, and get them to
balance all 4 to the finest setting they can. This should solve the problem.
Its not uncommon on the earlier cars, and I've had it to some degree, off
and on with mine. The better the wheels are balanced though, the less you
will notice it.

There have been some claims that adding subframe braces, if they're not
already fitted to your car, will reduce this problem.

Gary