Miata Mailing List: June 1994, Message #107
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   From: dquara@encore.com (Doug Quara)
Subject: Re: Tire Size and wheels
   Date: Tue, 7 Jun 1994 07:20:20 -0400

Chuang@ecn.purdue.edu, Shyue-Hong  Subject: Tire Size and wheels
> 
> Now that you guys have so generously provided me with so much info on tires.
> I noticed that a good many of you mentioned that you are running sizes
> != 60R14 on the stock wheels. How do you guys do it? I always had the
> impression that I had to change my wheels along with a change in tire size!
> So what kind of tolerance does the stock miata alloys have in terms of
> tire sizes? And in the event that I change wheels + tires, what are the sizes
> to stay within?

Using the rule that the wheel width should not exceed 70% of the section width 
of the tire, the following section widths are listed with their minimum
wheel widths:
		Section			Min
		Width  			Wheel
		(mm)			Width 
					(in)
		185			5.09
		195			5.37
		205			5.65


For that extra bit of margin, I would recommend a 6" wheel for 205.
The 195 probably could go either way, on a 5.5" or a 6" with no problems.
I do know of some autocrossers who have tried 205 on the stock 90-93
alloys, and didn't have any problems to speak of.  Still, if I was
going to go that wide, I'd go with 6".

The aspect ratio (the "60" in your example above) affects the overall
diameter of the tire (said another way, the sidewall section height).
Theoretically, a 195/55 is as wide as a 195/60; the 195/60 would 
have a section height about .4" taller (.8" taller overall diameter).

Stating the obvious, the wheel diameter must be the same, that is,
a 14" tire should go on a 14" wheel.

Hope this helps,
Doug Q.
dquara@encore.com