Re: Off-diameter tires

["Richard Klein" <rklein@cris.com>]

On 10 Dec 95 at 2:03, STEADIRIC@aol.com wrote:

> Whoa there Richard, ...

Points duly noted...

> has a OD of 24.68" So the 225/50 is too small, It will not fit in the 
> rear wheel wells anyway with out taking a Baseball bat to them and 
> flaring them, Carefully!  

OK, then, maybe you can suggest something for my 5000s (stock tires - 
185/70R14).  If I remember right, the OD is somewhere around 23.5" 
(should be 14" + 259mm, but I can't find my metric conversion 
tables...) (wait, I found them!  Apparently the OD is closer to 
24.2"...).  Anyhow, what's the widest tire you'd recommend on this 
car, at this OD, with the stock suspension, no tire/fender 
interference, and no body modifications, and is there anything I need 
to know about wheel offsets?

For those who are interested (and any corrections will be welcome), 
here's how I figured the OD of my wheel/tire combo:

First, I need to decode the tire size designator:  185/70R14

185 = width of the tire in millimeters
70 = half the difference between the tires OD and ID as a percentage of 
it's width, also known as the aspect ratio
R = radial (that's not important for this calculation, though)
14 = OD of the wheel, without a tire

2 * (185mm * 70%) gives me the difference between the tires OD and 
ID, in millimeters - 259mm

Then I have to convert this to inches by multiplying it by 0.03937 -
259mm * 0.03937 = 10.19683 inches

I then have to add this to the size of the wheel that'll be inside 
the tire - 14 inches
14" + 10.19683" = 24.19683" (which I round up to 24.2")

That gives me the theoretical OD of my tire/wheel combo, which may 
vary slightly from tire to tire.

   -Rich
   '85 Audi 5ks
   '85 El Camino
   '72 Suzuki GT380 w/ front disk retrofit
   '73 Suzuki GT550 in pieces
    member Teamsters local 486