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# Re: Tires

```A little math may help your descion on tire size.

Overall diameter of tire = (wheel diameter in inches)(2.54) + (2)(tire width
in mm)(aspect ratio)

This will give you the overall diameter of the mounted tire, which is what
you want to match.
1.) The factor of 2.54 conterts your wheel size, in inches, to millimeters.
2.) The aspect ration is the decimal equivalent of the aspect ratio in the
tire size.  For example, use 0.5 for the aspect ratio of a 195/50/15 tise.

Beginning of example:

Original D = (14)(2.54) + (2)(195)(0.6) = 36 + 234 = 270 mm

or.....*drum roll*

New D = (18)(2.54) + (2)(225)(0.5) = 46 + 225 = 266 mm

Another thought.  This is a good opportunity to corrrect any inhrent
speedometer error, as I did when switching to 205/55/15's.

In the states one can usually find a deserted section afo roadway to test a
speedometer.  The mile post on the intrstate highway sytem are located one
mile apart.  Driving at sixty miles per hour, it should take you ten minutes
(600 seconds) to travel ten miles.  If it takes you only 630 seconds, you
have a 5% error in your speedometer. (630 sec./600 sec. = 1.05)

Now the fun part of the correction.  Your odometer "thinks" you have driven
ten miles based on the number of times the driveshaft "should" rotate to
travel that distance.  The reason it took you longer to travel the ten miles
ws because your odometer correlated distance traveled by each revolution of
the wheels with revolutions of the driveshaft.  In the example, With a
Speedo error of 1.05, you would need to find a wheeel/tire combination to
give you a 5% larger diameter, or (270)(1.05) = 283.5 mm

It's now 12:30 am and I give up.

- Doug
-----Original Message-----
From: Pat Martin <mardkins@email.msn.com>
To: Wm. Josiah Erikson <josiah@gsinet.net>; Audifan1@aol.com
<Audifan1@aol.com>
Cc: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
Date: Saturday, December 26, 1998 11:43 PM
Subject: Re: Tires

>Actually it is in between 50 and 55.  Closer to 55.  It depends alot on the
>tire.  Most tires you will find will be very close with a 195/55/15.
Really
>a 205/50/15 is the best tire in this app..
>
>Pat Martin
>864000csq turbo, 2 1/2 cat back, H&R-Boge, MC and loving it.  Drilled and
>stopping it. Koenig Cobra 16x7 with Yokohama A520's turning it,  K&N and
>uh..., Soon: Hella's lighting it.
>84 4000sq  AKA: The beater.
>95 subaru legacy
>Bothell, Wa
>
>
>
>>That's easy : )
>>50!
>>    -Josiah
>>    '84 GTI
>>    '86 Scirocco
>>    '87 QSW
>>    http://www.gsinet.net/~josiah
>>
>>Audifan1@aol.com wrote:
>>
>>> QList-
>>> 84 4ks stock tires are 185/60/14, want to go to 15" rims in spring,
>>> 195/??/15.  Please help and fill in the blank!?
>>>
>>> Thanks, Happy Holidays and safe traveling out on the roads!
>>> Ron
>>>
>>> Ron Roth   Ithaca, NY  USA    84 4ks "Heidi"  audifan1@aol.com
>>> http://www.geocities.com/MotorCity/Garage/8793/index.html
>>
>>
>
>
>

```