Truck Tyres 34 x 7 as 12 ply Olympics

[Lionelgee]

Hello All,

It is time to shake this tree again and see if something falls out.

I have a 1940 Chevrolet MCP ex-Australia army 30 CWT truck. It just so happens to that the Chevy has the same size tyres as my 1935 REO Speed Wagon truck came fitted with.

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?

Enough of all the questions.....

Kind regards
Lionel

[Hanno Spoelstra]

Originally Posted by Lionelgee

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

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

[Lionelgee]

Hello Hanno,

Thank you very much for your very rapid and extremely thorough reply, Hanno. I greatly appreciate it.

Your response greatly assists in my quest to track down around 14 of them. Enough for two trucks with dual rear tyres and a spare for each of the trucks. Well, that is unless they required different rims for the front axle and the inside dual? One truck rim is almost a solid face with two rectangles cut into them. It is very ugly. It was probably made as a dedicated inside dual wheel as it was not readily seen because it was covered up by the outside dual wheel.

Kind regards
Lionel

[Barry Churcher]

https://www.universaltire.com/700-20...wall-tire.html

Here is an example available in the US. I bought a pair of these for a trailer and they work well. I am sure you could find a supplier closer to home.
Cheers,
Barry

[Lionelgee]

Hello Barry,

Thank you for posting the link. They had approximately 6 different varieties of 700 x 20 tyres. I think I will do without the white wall version.

Would these tyres need tubes and rust-band; aka tube protector sets as well?

Kind regards
Lionel

[Tony Smith]

Originally Posted by Lionelgee

Would these tyres need tubes and rust-band; aka tube protector sets as well?

Kind regards
Lionel

Irrespective of what type of tyre you find, ANY tyre will require tubes and rust bands to fit on your split rims and still hold air. The problem is not the tyre design, it's the rim.

[Lionelgee]

Hello All,

What are the tell-tale signs that an old steel rim is not safe and should not be restored?

I have taken some rims to local tyre places and the first thing they see is a rusty rim. It is condemned straight away.

I intend on getting some old rims sandblasted for rust, primed and have a number of coats of paint applied to them. Then taking it to the local tyre mob and seeing if they will fit a new 8.25 x R20,

However, I would like to be able to make a decision whether doing a lot of work on a rim is not worth it because the rim is unsafe to use.

Kind regards
Lionel

[Grant Bowker]

Three things that would scare me on a rim: deep rust pitting, particularly if they overlap to form lines where the rim is thin (also a badly rusted retaining groove for the ring), poorly done modifications like the welded on plate shown in the first photo of your post above, rims that are split along the centerline of the rim, (as opposed to at one edge, see Firestone RH-5 rims for the centerline split). If none of those are present, I like your idea of a light cleanup and paint to see what happens at the tyre shop. I am not suggesting use of Bondo or other schemes to hide damage, just making sure the rim looks sound and cosmetically good. Make sure they are a long-established heavy truck tyre shop and not your local car repair joint. The car repair types are rightly cautious to work on things they aren't trained to do and which if improperly done can hurt them. A 2 or 3 piece rim is most dangerous as it is being inflated (and also somewhat if deflated due to blow-out on the road). As a result, they should be inflated in a cage or at very least with chains to prevent the ring from flying if it slips off the rim.

Comment, the rim shown with a 5 stud attachment might be a 10 bolt rim with 5 hole reinforcement plate with studs in alternate holes in the rim (usually on the front axle).

[Tony Smith]

Another "fail" is any corrosion or lack of a sharp edge in the lock ring groove, or loss of tension in the lock ring itself.

Note that some types of abrasive blasting can change the temper of the spring of the lock ring, leading to a poor fit.

[Hanno Spoelstra]

Also, clean the rims of tyre remains and strike them like you would do a bell. If cracked or severely corroded, they will not sound like one.

[rob love]

The condition of the ring and the channel are the unique considerations to these type of rims. Channel should be clean and the edge reasonably square. The rings must not be "sprung" or distorted. That is to say, when fitted back onto the rim, they should spring back flat into the channel. On top of that are the regular considerations: cracks, weld repairs, elongated mounting holes, excessive rust....any of these are a reason for condemnation of the rim.

When I was in Kandahar, the tire guys were fixing a very large (about 6 feet in diameter by about 3 feet in width) heavy equipment tire. They had it laying on the ground, with one guy holding the air hose and filling the tire. Three other guys were all leaning over the tire (ring facing up) and one guy was hammering on it, trying to get the ring back in to the groove, as it was part way out. I put a stop to their work and had them deflate the tire, which they did after putting a very large set of forklift forks over the ring.

I will always feel like I saved three to four lives that day.