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Old 30-01-19, 13:13
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Hanno Spoelstra Hanno Spoelstra is offline
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Quote:
Originally Posted by Lionelgee View Post
As per the photographs the numbers 34 x 7 and the ply rating is 12. The tyres were made by Olympic.

Has the unit of measurement changed as I cannot find any reference to a 34 x 7 tyre? If it has changed what would the measurement now be referred to as?

The next obvious question is .... are they still made and who sells them?
Hello Lionel,

34 x 7 is an old designation for the tyre sizes 7.00-20 and 7.50-20 (depending on the source). This size was commonly used on trucks in the 1930-40-50's. See the quote from a Commercial Motors article "Simplification of Giant Tyre Markings" from 1951.

7.00-20 is not a common size, but they are still being made new for the historical vehicle market and can be found.

Military NDCC (bar grip) tyres 7.50-20 may be an option too, these are far more common (at least in Europe) as most US military trucks like the GMC CCKW used that size of tyre.

HTH,
Hanno

Quote:
Originally printed on the 9th march 1951

Simplification of Giant Tyre Markings

%URING the past few years the tyre industry, recognizing • the need for the simplification of giant-tyre size mark

3s, has taken certain sleps to achieve this end. Further nplification has been announced by the Society of Motor anufacturers and Traders, which says that by January I, 52, the new markings will be completed for tyres for iginal equipment and replacement purposes.

For many years the tyre industry has had high-pressure d low-pressure giant tyres, the former being marked, say, x 6, and the latter 7.00-20. To simplify the range of :h tyres, high-pressure equipment was made in moulds the same dimensions as those used for low-pressure tyres, Ilist the difference in construction, as related to the numrs of plies of fabric,was maintained.

Dual marking in some sizes was temporarily adopted. A it-marked cover is a high-pressure tyre made to low:ssure dimensions. As an example, a 7,50-20/34 x 7 tyre, a 34 x 7 tyre, so far as price, construction, load capacity I inflation pressure are concerned, but it is made to 0-20 dimensions.

ks a further means for identification, "ply rating" is led. The term is used to identify a given tyre with its ximum recommended load when employed in a specific

e of service. It is an index of tyre strength and does not :essarily represent the number of cord plies in the tyre. kt one time it was possible to determine the maximum d and inflation pressure for a tyre by reference to the nber of plies it contained. A modern tyre, however, may itain more ot fewer plies than is indicated by the ply [hg,' but, for a given size of tyre, the higher the ply rating greater the strength. The simplification of markings has now been completed by the elimination of high-pressure or dual marking. Thus, the 34 x 7 (high-pressure) and the 7.50-20/34 x 7 10-ply rating (dual marked) become identified as 7.50-20 10-ply rating. Thus, tyres will have a particular size marking but different ply and load ratings, such as 7.50-20 8-ply rating for a maximum load of 21 cwt. and an inflation pressure of 60 lb. per sq. in., and 7.50-20 10-ply rating for a maximum load of 27i cwt. at 85 lb. per sq. in.

The following table gives examples of the original, interim (dual marking) and simplified markings for tyres fitting 20-in. rims: Where vehicle clearance limits preclude the fitting of tyres having the simplified marking, tyre manufacturers will continue to supply for a limited period the old high-pressure tyres, such as 32 x 6, 36 x 8, and 40 x 8. The marking of tyres for low-loaders remains unchanged.
Source: http://archive.commercialmotor.com/a...-tyre-markings, accessed 30-jan-2019
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