Tire size

[Ti Kan]

Ice Cat     ^. .^   ~ writes:
> The Bentley manual says 215 with a Z speed rating
> and the sticker on my cars says 205
> one tire place says that they can get either.
>
> Does anyone know the best sized tire to get for
> 89 Audi 200 Turbo (N Q)

Stay with the stock sized tires unless you know what you're doing.
Otherwise you will either have problems with speedometer/odometer
accurary issues, changes to the effective final drive gear ratio,
and worse, rubbing of tire on suspension or bodywork.  Also, a given
wheel width has only a limited range of tire widths that it could
accommodate without affecting handling.

The stock size on your car is 205/60-15

The first number is the tread width of the tire in millimeters.  The
higher the number, the wider the tire.

The second number is the side wall height of the tire, expressed as
a percentage of the tread width (known as "aspect ratio").  Thus, in
this case it's 205 * 60% = 123mm.  Since two times the side wall height
plus the wheel diameter is the rolling diameter, you'll want to preserve
the rolling diameter in order to keep your speedometer/odometer reading
correctly.  If you are staying with your stock wheels then you'll want
to keep the side wall height the same.  Since this is expressed as a
percentage of the width of the tire, if you go to a wider tire, you'll
need to reduce the aspect ratio to compensate.

The third number is the wheel diameter that the tire is designed to
mount on, expressed in inches.

> Right now there are 205s on there but the tire person said that 215s
> would ride better.

That is not strictly true.  If you simply went to a 215/60-15, then
it's possible that the ride may be improved somewhat due to increased
sidewall height, but this is at the expense of the accuracy of your
speedometer/odometer.  Also, a higher sidewall allows more flex and
squirm of the tire during cornering, which is bad for handling.

Also, the ride quality of a tire is also largely dependent on its
design and construction.  You'd be amazed at how much difference
there may be going from one make and model of tire to another, even
staying at the same size.

Finally, the speed rating of the tire.  Even you may not be driving
at the speeds the tire is rated at, it does provide some indication of
the tire's quality and durability under thermal stress.  A Z rated
tire is likely to have more stable construction than a V or H rated
tire, perhaps a stiffer sidewall which may affect the ride quality but
would provide better handling.

-Ti
2003 A4 1.8T multitronic
2001 S4 2.7T 6-sp
1984 5000S turbo
1980 4000 2.0 5-sp
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    ///  Ti Kan                Vorsprung durch Technik
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