On Sep 15, 12:24*pm, Alan Baker > wrote:
> In article >, Don Q wrote:
> > On 2010-09-09 20:50:12 -0400, Arye > said:
>
> > > My thinking is to go up one size (from 185/60R14 to 195/60R14), to
> > > compensate for the slightly too-slow speedometer
>
> > Is there a typo here?
>
> > I'm no expert but my understanding is that 185 and 195 indicate the
> > tread width in millimeters. In other words, you are getting a tire that
> > is about 2/5 of an inch wider. This may provide slightly better grip in
> > cornering, everything else being equal. (Tread pattern, compound
> > hardness, tire pressure, slip angles...)
>
> > But since they are both 60 profile I think the diameter will be exactly
> > the same, hence the speedo/odo will not be affected.
>
> Ummmm... ...no.
>
> The "60" indicates that the section height of the tire is 60% of the
> section width of the tire (the "185" or "195" in the size; which is not
> tread width, BTW), and both of these figures are nominal and not
> necessarily completely precise.
>
> So a 185/60R14 tire is (nominally!) 185mm wide at its widest point (the
> tread is narrower and (nominally!) 2 * (185 * .6)/25.4 + 14 = 22.74"
> tall.

In fact, there is a great variance from manufacturer to manufacturer
and from tire model to tire model. On the company "Tire Rack"'s site,
you can compare the specifications of tires, and see that some tires
two full metric sizes apart (typically 20mm, or about 4/5's of an
inch) will have the same tread width, and the smaller section width
tire may even have greater tread width in some rare instances.