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6.50x13 Bias Tire to Radial Change?

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What tires do you guys run on the older GM Vehicles?

1962 Buick Special calls for 6.50" x 13" Tire. 


Can we switch to a modern tire?  Any tracking or steering issues?

Not looking to kill the bank so Coker Tires are not an option.


Found one site that said 175/80R13  and then another said 185/80R13.



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Whichever is the same outer diameter. The new ones will be slightly wider at the same outer diameter.


Going strictly by the marked sizes, and assuming pre-1965 tire sizing because the size ends in a "0", I am going to assume the aspect ratio to be 90.


6.50 x 13


6.5" (section width) x 0.9 (90%) = 5.85" (section height)


5.85" x 2 = 11.7


11.7 + 13 (rim size) = 24.7" overall diameter, in theory anyway. In practice this varied a lot between brands.


80 series (80% aspect ratio) tires are the tallest, or closest to 90% you are going to find in metric. Metric tires without the aspect ratio marked are usually either 80 or 82%.


175R13 or 175/80R13:


175 / 25.4 (convert to inch) = 6.89" section width


6.89" x 0.8 (80%) = 5.51" section height


5.51" x 2 = 11.02"


11.02 + 13 = 24.02" overall diameter


185R13 or 185/80R13:


185 / 25.4 (convert to inch) = 7.28" section width


7.28" x 0.8 (80%) = 5.82" section height


5.82" x 2 = 11.64"


11.64 + 13 = 24.64" overall diameter


I would go with the bigger ones if it looks like they aren't going to hit anything.


Also, get your front end checked and aligned. Always do that first. Radial tires can mask all sorts of front end problems, and you may not realize anything is wrong until you chewed up 2 brand new tires in a week.


Edited by Bloo (see edit history)

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If you have one of the 6.50x13 tires, you could inflate it to 30psi and measure the circumference with a cloth tape measure.  Then divide that length into 5280 feet to get "revs/mile".

Then go into and look for 13" tires.  Then look in the "specs" section of a 13" tire listing and seek to match the revs/mile number with available sizes.  Might need to do an individual search on many different tires to get there.  The tire you find will probably be wider than the one you have, which is to be expected.  Might even find some whitewalls!


In their search function, you can look for "sizes" and then look in the individual search results for the revs/mile spec you need to get close to.  Kind of a different way than above to find equivalent diameters/revs per mile tires that will look correct and good on the car.



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