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Decoding Tire Specs
With all the talk recently about 315/365 tires, I thought I’d remind myself on how the tire size coding works. For those who are interested, I thought I’d share it here. . I’ll use 315 & 365 sizes as a comparison as it makes sense.
365/70R22.5
22.5 is the wheel diameter in inches, hence 22.5″ rims
365 is the tread/tire width in millimetres (just to complicate things!). Approx. 14.3″
70 is actually 70%. That is the ratio of the tire wall height (from the outer edge of the tire to the rim) to the tire width. So in this case, 365mm x 70%=255 mm (10.04″)
So, using the same method, a 315/80R22.5 tire will have a tread width of 315 mm but this time, the wall height is 80% of 315mm, giving the same (near enough) wall height which in turn means the same overall tire/wheel diameter and therefore rolling circumference.
So those who have both size tires on their bus will know, the only difference between the two sizes is that 365’s are around 2″ wider than 315’s, hence the requirement for different rims.
Tomorrow we’ll be doing algebra!
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1 Reply
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Good job, well explained!
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