S.A.E. proposals on tire simplification and the adoption of new wheel and tire sizes.
| Identifier | ExFiles\Box 158\1\ scan0048 | |
| Date | 6th February 1928 | |
| OY3.R.2.6.28 February 6th, 1928. TO Mr. Beaver cc - Mr. Nadin (England) Mr. Ross Mr. Burton Mr. Bailey (England) Mr. Hives (England) FROM Mr. Olley WHEELS AND TIRES The proposals of the S.A.E. on tire simplification are covered by attached table. The necessity of economy in sizes is such that this list will probably be adopted almost immediately. The list represents current American practice on about 98% of the cars in production. (Actually 77% of present production is covered by six sizes only.) The only well-base rim is the 30 x 4.50 used by Chevrolet and Ford. This is also the only tire on a 21" wheel. By agreement between these two companies it is proposed to replace this shortly by 30 x 5.00 on the 20" wheel. The convention that "Nominal outside dia. minus twice tire dia. equals wheel size," has been lost, of recent years, in the complication of sizes, and it is proposed to revise this standard nomenclature as shown in attached list under "New Name." The only course left open for us is to use the "32 x 6.75" (to be called "34 x 7.00") We propose to do this and adopt the well-base rim 3.75" between flanges at the same time, thus coming in line with England as regards tire mounting etc., but using the American standard 20" wheel. This will require some road-running and it is proposed to do this on three cars at works. This is the original "balloon" size tested on 102CX {Major Len W. Cox - Advertising Manager} and in those days(1924) reduced the road clearance unduly. The tire now is built larger and will stand about 15.800" from the road as against about 16.150" for 33 x 6.75 U.S. cord. Furthermore the bottom of the Phantom crankcase is inherently less liable to damage than the Silver Ghost1907 40/50 historic RAC 15,000 miles trial. The only danger points are our low running board and the bottom of the tool and battery box and front silencer, all of which can probably be moved up 3/4". (Continued) | ||
From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).