The US standard rail gage was derived from the British standard gauge of 4ft 8½in (1435.1 mm). However the Irish works out in round numbers in both metric and imperial units - 1600 mm differs from 5ft 3in by 0.2 mm - well within tolerance limits.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John M. Steele Sent: 08 March 2009 16:34 To: U.S. Metric Association Subject: [USMA:43495] Re: Metric discussion on the railroad list (1) Assuming Wikipedia is correct, the tolerance of 1435 mm gauge track is 1423 mm to 1460 mm for track rated for 60 MPH travel. I assume lower grade (lower speed) track is allowed a wider tolerance. Thus, that 0.1 mm confusion in nominal is entirely negligible. I assume the tolerance is asymmetric because the width can not be narrower than maximum wheel flange spacing (the flanges are on the inside, and ideally do not touch) http://en.wikipedia.org/wiki/Rail_gauge --- On Sun, 3/8/09, Jeremiah MacGregor <[email protected]> wrote: > From: Jeremiah MacGregor <[email protected]> > Subject: [USMA:43489] Re: Metric discussion on the railroad list (1) > To: "U.S. Metric Association" <[email protected]> > Date: Sunday, March 8, 2009, 11:53 AM > Carleton, > > > Also in the design of railroad equipment, can you tell us > what the usual tolerance ranges usually are? You are > correct that in the world they don't get precise to > sub-millimeter precision unless they have to. They would > round everything to whole numbers if it wouldn't effect > the outcome or if it falls within acceptable tolerances. > > The standard rail gage in the US is 56.5 inches, which > equals 1435.1 mm. Everywhere else it is equal to exactly > 1435 mm. I don't know anything about railroads but I > bet that nowhere will one find the tracks consistently 1435 > mm due to many factors that distance will vary to some > degree. There is constant exposure to heat and cold. > There are movements in the earth which can shift tracks, > etc. Thus to worry about sub-millimeter lengths is > ridiculous.
