Miata Mailing List: August 1992, Message #26
sponsored by



     


   From: (none)
Subject: tires
   Date: (none)

>
>are really starting to show the 50,000+ miles, and are an absolute terror in
>the rain. =8^0  The rear tires show much more wear than the front, which makes
>sense because the rear end comes unglued before the front in hard cornering
My stock Bridgestones did this same thing, only they're shot at 27k miles.
>(oversteer).  A curious point is that the right rear is much more worn than
>the left -- to the point that a belt is peeking through the inboard side of
>the tread.  Perhaps this is because of the slow leak in the left rear, which
>makes me think that the tires should've been run at something *less* than the

I explained this wear pattern to myself thusly:  If you don't have a LSD (I don't)
then the right rear tire is the one which always receives power.  Hence, it's
always the one to slip under hard acceleration, causing more wear.  The inside
edge wearing is due to the negative camber which the miata runs on the rear by
factory spec.  This can be aggravated by extreme negative camber (like would be
beneficial for autocrossing) because there is a point around -2 degrees where
changes to camber begin to change the toe angle.

>recommended 26 psi.  (Lower pressure would've put less wear on the suspension,
>too.  Anyone care to comment?)  A less probable explanation for the left-right

My feeling is that less pressure (at least in the Bridgestones) would have caused
less sidewall stiffness, which would mean I would have worn the outside shoulder
into the cord a long time ago, because the tire would roll off the rim more.

>wear differential would be that the car is often driven solo (weight on left)
>or that it's usually driven on the right side of the road (crown to left,
>dropoff and gravel, etc., to the right.
>
>I'll be putting Yokohama AVS Intermediates, in either 185/60-14 size (stock)
>or 195/60-14 (slightly oversized), on it soon, but probably two at a time
>because of budget constraints.  Should I move the so-so Dunlops from the front
>to the rear and put the new tires on the front, or vice versa?  Would the

The miata gets really squirrely in the wet with poor tread in the rear.  Also,
you probably have a better chance of controlling a blowout if it occurs on the
front tires.

>width of the new tires (185 mm vs 195 mm) affect this choice?  Also, should

Might help reduce oversteer to have 195's in back.

>the Dunlops be switched left-for-right to compensate from outboard tread wear
>from understeer at the beginnings of corners?

Steve Grossman
Software Engineer