I'm not sure I understand you. Aren't the present standard of tires fully metric? For example, if you go to the factory where they are made, aren't all of the drawings and production done completely in metric? If you are referring to the rim diameter still given inches, does that carry more weight then the way it is produced?
If you have a so-called 15 inch tire that is made to a 380 mm dimension in the factory then can the tire be considered a metric dimension. What about the bolts and nuts that hold the wheel to the rim? What standard are they today? I say if a tire is metric in design and manufacture, then it is a metric tire no matter what name you put on it for the consumers. Jerry ________________________________ From: John M. Steele <jmsteele9...@sbcglobal.net> To: U.S. Metric Association <usma@colostate.edu> Sent: Monday, March 9, 2009 8:26:16 AM Subject: [USMA:43590] Re: Tyre (tire) sizes Pat, In fact the metric rim tires are an example of "just because it is metric doesn't mean it is wonderful." There are whole standards behind those tire labelling schemes; those standards dictate many dimensions on both tire and wheel (mostly to ensure it seats and seals properly). The metric rim tire had a new (novel?) bead seat design (there were also symmetric ones used in Europe). The bead seat design didn't work out so well, the tires gave VERY poor service, and were expensive. Owners were SO mad they generally mounted new (conventional) wheels and tires, causing sales to go to near zero, leading to withdrawal from the market. This does NOT mean that specifying a rim in millimeters would be bad. But someone would have to write a new standard behind the labelling scheme, using a more conventional bead seat design and sell the whole concept. The exercise apparently left a bad taste and no one has every written a new standard for metric rims. --- On Sun, 3/8/09, Pat Naughtin <pat.naugh...@metricationmatters.com> wrote: > From: Pat Naughtin <pat.naugh...@metricationmatters.com> > Subject: [USMA:43582] Tyre (tire) sizes > To: "U.S. Metric Association" <usma@colostate.edu> > Date: Sunday, March 8, 2009, 11:58 PM > Dear All, > > Apparently, engineers in the 1970s saw an opportunity, > through metrication, to rationalise some of the original > design faults in tyre design and construction. Here is a > quote from: > http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46 > Tires and wheels that have a rim diameter expressed in > millimeters (190/65R390, as well as, 365 and 415) are called > millimetric sizes. Michelin initiated millimetric sizes for > their TRX tires that saw limited use on many different car > models in the late 1970s and 1980s. > > Michelin PAX System run flat tires have been introduced as > an integrated wheel/tire system on a very limited basis as > Original Equipment (O.E.) in North America. An example PAX > System size of 235/710R460A 104T expresses tire and wheel > dimensions in millimeters (235 mm Section Width, tire > Overall Diameter of 710 mm and a 460A mm rim diameter, with > the "A" in 460A signifying these tires feature > "asymmetric" beads in which the outside bead (450 > mm) and inside bead (470 mm) are actually different > diameters. > > All of these "unique" tire/wheel diameters were > developed specifically because the tire and wheel design or > intended vehicle use required them to be different than > conventional tires and wheels. All of these tires and wheels > feature bead profiles that have a different shape than > traditional "inch rim" sizes. > > Although the millimetric sizes were later withdrawn from > the market, they left their legacy in the branding on the > side of the tyre. When you see something like: > > 225/50R16 > > You know that the tyre is 225 millimetres wide; 50 % of > this width (113 mm high from rime to outside diameter); it > is a radial tyre; and it is 16 inches (exactly 406.4 mm) in > diameter from rim to rim. > > By doing this only 2 of the 3 measurements are metric and > not hidden from the public; the third is also metric and > hidden from the public. Clearly the opportunity was lost to > rethink the design of wheels and tyres to allow for the > increased speeds that have occurred since Henry Ford's > days as chief engineer. For example, asymmetric beads on the > rims could be useful. > > Cheers, > > Pat Naughtin > > PO Box 305 Belmont 3216, > Geelong, Australia > Phone: 61 3 5241 2008 > > Metric system consultant, writer, and speaker, Pat > Naughtin, has helped thousands of people and hundreds of > companies upgrade to the modern metric system smoothly, > quickly, and so economically that they now save thousands > each year when buying, processing, or selling for their > businesses. Pat provides services and resources for many > different trades, crafts, and professions for commercial, > industrial and government metrication leaders in Asia, > Europe, and in the USA. Pat's clients include the > Australian Government, Google, NASA, NIST, and the metric > associations of Canada, the UK, and the USA. See > http://www.metricationmatters.com for more metrication > information, contact Pat at > pat.naugh...@metricationmatters.com or to get the free > 'Metrication matters' newsletter go to: > http://www.metricationmatters.com/newsletter to subscribe.
