I just got a set of stock steel wheels for my Series V and had them sand blasted and painted. Now for tyres. I re-read a thread from last May. Let me recap [no pun intended] what was on that and add some calculations of my own followed by a couple questions?
Per Jarrid the basic formula for computing diameter (in millimeters) is h=2x(aspect x tread width) + rim diameter x 25.4 so Jarrid's 185/80/13 computes: h=2x(.8 x 185) + 13 x 25.4 = 626 mm (did I do it right???)
That makes the following tyre diameters and tyre revolutions per mile:
Size diameter tyre revs per mile
165/80/13 = 594 mm 890 [according to Firestone]
175/70/13 = 575 mm 914 [according to Firestone]
185/70/13 = 589 mm 897 [my interpolation, i.e. SWAG]
According to Goodyear, the diameters in inches are
165/80/13 = 23.39 "
175/70/13 = 22.68
185/70/13 = 23.23
According to the shop manuel the original equipment Dunlop bias plys were 11.65 or 11.41 inches in diameter. The diameter was then, 22.82" and 23.3
Therefore the narrowest of the above 13 inch sizes is the largest in diameter and very slightly bigger than original. The widest is closest to the original but I doubt anyone could tell one from the other from 20 feet away.
My questions if you are still reading this: Does anyone use the 185/70/13? The Goodyear data shows it fits on 4.5 to 6.5 inch rims but it is clearly the maximum width. Would the tread sit flat or would it curl up? I saw an Alpine with this size on Saturday and the owner loves them (no problems in 4 years).
I am inclined to go with the 175/70/13 because the 165s seem skinny and I fear the 185s are really too wide for the stock rims. Any comments?
Rob Carpenter