Re: Tire Size

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Posted by David on August 19, 1999 at 06:58:45:

In Reply to: Tire Size posted by Bob on August 18, 1999 at 11:24:49:

Yes it is possible, no it is not an optical illusion!
Tire Guy is to a certian degree correct with the explaination that due to different design's - Tread & sidewall, some manf. have a squared shoulder and some have a rounded shoulder where the tread portion meets the sidewall that there can be visual difference from one brand to another, but it goes well beyond style.
The governing body of the tire industry sets peramiters & guidelines for sizing & nomenclature. There is also some latitude given to the manufacturer. There are exact dimensions/specifications for each numeric tire size. But there is also an approx. 10% variance allowed. Meaning the dimensions for a given tire size from a given manufacturer can be + / - 10% of the written specs for that size.
i.e.- a 205/60R15
205mm (8.07in) is the cross section width. This tire could actually have a measured cross section width of as little as 190mm (7.5in) or as much as 220mm(8.6in) and still be called a 205. The variance is usually not this extreem but could be possible. This same scenario hold true all other measurements of a tire as well - diameter, tread width, aspect ratio etc. (except rim diameter)
There can be many reasons a manufacturer decides to what specifications/dimensions a tire will measure out to be. It is actualy a high profile topic in the industry at this time due to all the traction control, 4wheel and all whell drive systems vehicle manufacturers are using today and problems this variance can have when not installing new tires in sets of four.

Hope this explains more acuratly what you are seeing with your new tires.

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