[Mgs] Tires

[Richard Lindsay]

Mike, I recently did the same thing for my Land Rover. We like to think
we're smart but we still make mistakes. And speaking of mistakes, here's
what I would do...

Look up the original tire size for your car (or see if TireRack has that
info). Then calculate the circumference of that tire. For example if the
OEM tire is a 165r14 then the diameter is:

D = (165×.8×2)/25.4 + 14

The radius is:

R = D/2

The circumference is:

C = 2xRx3.14159

   This is the tire circumfrence, in inches, for which your speedometer is
calibrated. If you want to keep that calibration, just reverse the
equations above and start poking in numbers from available sizes. I do this
in an Excel spreadsheet. WAY easier.
   Just remember to include the new tire's aspect ratio. Old, unlabeled
radials have an aspect ratio of about 0.8, as used above.

Rick

On Thu, Jan 30, 2020, 12:11 AM Michael MacLean via Mgs <mgs at autox.team.net>
wrote:

> Well, I screwed up.  Reading the MG Experience forums I bought Douglas
> tires at a great price.  Taking off the old tires tonight I found they were
> Dunlop SP-20s made in 1999.  Wow!  The size on the tire was 165R15.
> Without looking and going by the recommendation of the MG Experience web
> site I bought 14 inch tires.  Crap.  Now I have to try to take them back.
> They have not been mounted so they are still just like I got them.  My
> question is, what the heck size tire should I get for a 15 inch wire wheel
> rim?  The MG Experience forum is saying 185/70 R15 is closest, (1/4 inch
> smaller) but not readily available for a decent price.  A 185/65 R15 is the
> next most popular tire, but smaller in diameter by an inch than the Dunlops
> I am taking off.  165R15 tires are 25.65 inches in diameter.  My head is
> about explode.
> Mike MacLean
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