Tire Sizes - Help for the math impaired

[AlfaNeely@domain.elided]

Doug, Alex and all,
       I agree with Doug's calculations as far as they go.  The problem is, 
the manufacturers have not figured out that that is how they are supposed to 
build the tires.  Not all 185 70 14 tires are created equal.
       I once measured a bunch of tires just to see how they compared.  For 
ease of measurement, I measured the circumference with a cloth tape.  They 
were not all the same, even if marked the same size.
       For all intents and purposes, the 165 14 (165 80 14), the 185 70 14, 
the 195 65 14, the 205 60 14, the 195 60 15 and the 225 50 15 are ALL close 
enough to the same diameter to work on our Alfas.  The variation in diameter 
is probably less than the error in the speedometer anyway.
       You do time Interstate mileage markers to re-calibrate the brain to 
speedometer interface every time you buy new tires don't you?  I do.

Ciao,
Russ Neely
Oklahoma City



In a message dated 02/23/2002 10:44:25 PM Central Standard Time, 
owner-alfa-digest@domain.elided writes:



> 
> Date: Sat, 23 Feb 2002 18:32:22 -0500
> From: dsedon@domain.elided
> Subject: re:Tire Sizes - Help for the math impaired
> 
> alex, it really is easier to cure yer math impairment than using a web 
> calculator - faster to yust do it on a regular calculator.  :>)
> 
> multiply the width of the tire by the aspect ratio w/a decimal point in 
> front, to get the height of the sidewall.  ie:  my 225-50-15 has a width of 
> 225mm. it has a sidewall height of 0.50 x 225mm, which is 112.5mm.  
> 
> as the total diameter of a tire includes *two* sidewall heights, yust 
> multiply that by two; then convert it to inches by dividing it by 25.4.  
> so, the 112.5 times 2 goes back to 225; divided by 25.4, it's 8.86".  add 
> this to the 15" diameter & ya get the total tire diameter of 23.86"
> 
> hth,
> 
> someone e.

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