tires
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tires
i know this is a dumb question but i have a 1978 f-150 with 31" tires and need new ones...how do i figure out the codes on the tire sizes? what does 235/85/16 mean...could really use some help...does that mean its a 31" tire?
Posting Guru
Joined: Feb 2002
Posts: 2,404
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From: Cleveland, WI USA
Welcome to FTE!
235 is the width of the tire in milimeters.
85 is the sidewall height as a percentage of the width (85% of 235mm = 199.75mm)
16 is the rim diameter.
Tire Width: 235mm (9.25")
Sidewall Height: 199.75 (7.86")
Rim Size: 406.4mm (16")
Total Tire Height: 805.9mm (31.73")
Hope this helps.
Kevin K.
235 is the width of the tire in milimeters.
85 is the sidewall height as a percentage of the width (85% of 235mm = 199.75mm)
16 is the rim diameter.
Tire Width: 235mm (9.25")
Sidewall Height: 199.75 (7.86")
Rim Size: 406.4mm (16")
Total Tire Height: 805.9mm (31.73")
Hope this helps.
Kevin K.
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
Well, USUALLY it will. I've actually measured 3 or 4 of the same size tires from different manufacturers and they were all different. Most measure the tire width as the width of the tread on the flat surface of the tire. Where others measure the whole tread where it actually comes up the sidewall a little.
Either way, you're getting about 31".
Kevin K.
Either way, you're getting about 31".
Kevin K.
Senior User
Joined: Sep 2003
Posts: 213
Likes: 0
From: Northwest BC Canada
This formula has always worked for me.
2 x (width) X (aspect ratio) / 2540 + (rim diameter)= overall height in inches.
Width= first # in mm (millimeters) 265,285 etc.
aspect ratio = % of tire height from tread to rim based on width.
2540= conversion factor between mm's and inches
rim diameter= diameter in inches (15,16 16.5 etc.)
Therefore 235/85R 16=
((2 X 235 X 85) / 2540) + 16= 31.728" tall
This number is theoretical and may not be the same as the installed height on your truck as tire makers are allowed some variance of tolerances in manufacturing. Most tire makers will also tell you what rim width they used as this will affect your section width ( tire bulge) and thus overall height. Hope this helps.
2 x (width) X (aspect ratio) / 2540 + (rim diameter)= overall height in inches.
Width= first # in mm (millimeters) 265,285 etc.
aspect ratio = % of tire height from tread to rim based on width.
2540= conversion factor between mm's and inches
rim diameter= diameter in inches (15,16 16.5 etc.)
Therefore 235/85R 16=
((2 X 235 X 85) / 2540) + 16= 31.728" tall
This number is theoretical and may not be the same as the installed height on your truck as tire makers are allowed some variance of tolerances in manufacturing. Most tire makers will also tell you what rim width they used as this will affect your section width ( tire bulge) and thus overall height. Hope this helps.
