At 02:24 15/12/2003, Robert E. Shlafer wrote:
>Mike....
>Snipped
>How the 155/80 stacks up against the 175/70 in terms of diameter I do NOT
>know. But a tire mfg. should.
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Guys,
Here is how to calculate the Overall Diameter of Radial Tyres/Tires:-
Standard Sprite size:= 145SR-13. Where no "/xx" is given, assume "/80".
So,where the tyre is145/80-13, you multiply the Thread Width of 145mm by
.80 = 116mm,
which is the height of the tyre from the rim to the thread.
Multiply this by 2 to allow for a Top and a Bottom = 232mm.
Convert this to Inches; divide by 25.4. = 9.13"
Add this to the Rim Diameter of 13"
So, Stock Overall Diameter is (9.13" + 13") = 22.13"
Now, to compare with a 175/70XR-13 tyre (the "X" is in place of a Letter
which denotes the Speed Rating)
Multiply the Thread Width of 175mm by .70 = 122.5.
Multiply by 2 to allow for Top and Bottom of Tyre = 245mm
Convert to Inches; divide by 25.4. = 9.65
Add this to Rim Diameter of 13".
New Overall Diameter is now 22.65"
This is an increase in Overall Diameter of just over 2.3%. Say 60 MPH on an
(accurate !!) Speedo would translate to just actual 61MPH. Be warned!
Hope this helps,
Ron, in Ireland.
'59 AN5 "Oggibip"
'64 Riley 1.5 NoNameYet
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