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,

Just to keep this thread updated - I moved my trucks forward about 1.5 metres yesterday. I had a look at the tyres fitted to each of the two trucks. One truck had three different approximate tyre lablels. 34 x 7; a 7.00 x 20 and a 7.50 x 20.

Due to the totally ruined nature of the tyres - very flat and square bottoms; I had to use a combination of 3 ton trolley jack and a mobile crane. The jack under the rear differential and the mobile crane via chains connected to the front leaf spring hangers, gave me ground clearance. Add in some locomotive force provided by a Yanmar diesel four wheel drive tractor. The battery went flat on the tractor so I called in the back-up. My late model Series 2A short-wheel base Land Rover. All the fun of the fair!

I moved the trucks forward so I could install three sets of pallet racking to store goodies on - like engines and gearboxes. Hopefully my lack of suitable, accessible storage has been resolved - finally after a decade!

I have gained a LOT of floor-space now and soon after I sort all the shelves and pallet racking out - I can find something when I go looking for it! Yes hope springs eternal.

Kind regards
Lionel

[Matthew P]

So is 7x34 referring to the rim width by overall diameter of the tire? I've not measured my 7.5-20 tires for my Ben Hur but to my eye they've looked about a yard across, or around about that 34 number.

Matt

[Lionelgee]

Originally Posted by Matthew P

So is 7x34 referring to the rim width by overall diameter of the tire? I've not measured my 7.5-20 tires for my Ben Hur but to my eye they've looked about a yard across, or around about that 34 number.

Matt

Hello Matt,

Thank you for the reply.

I got the measurements from one of the tyres off the truck that I took a photograph of and posted up (see link http://www.mapleleafup.net/forums/sh...15&postcount=1). The conversion down from 34 x 7 down to a 7.00 x 20 was via Hanno and a kindly linked tyre chart.... Commercial Motors article "Simplification of Giant Tyre Markings" from 1951. Seen in post http://www.mapleleafup.net/forums/sh...16&postcount=2.

Kind regards
Lionel

[Lionelgee]

Hello All,

Since posting the first message of the day at 23:18, I visited the Stovebolt Chevrolet forum. Back in a thread posted in 2005 they mention how the 7.50 x 20 tyres were getting hard to find and too expensive.

Subsequently, they swapped over to using more readily available and cheaper 8.25 x 20 tyres for the rims that were originally fitted with the 34 x 7 AKA in 1951 as the 7.00 x 20 tyres.

I checked in Australia - where I am from and the 8.25/R20 tyres are much more readily available and are quite reasonably priced.

Has anyone else fitted the 8.25 x 20 on your original Chevrolet truck rims? How successful was the swap over?


Kind regards
Lionel

[Tony Smith]

Be careful of the ply rating of the 8.25s. Most 7.50-20 were 8 or 10 ply tyres, while the 8.25s are usually 10, 12, or 14 ply. A rough ride will be the result, shaking you to bits.

Are you running duals on the rear axle? Unless your rims have the correct offset for 8.25s, when loaded the tyres will foul each other.

And check clearance around the front end, turning circle can be reduced if the tyres foul the springs or chassis.

I've no experience specifically with Chevs, but early Ford trucks were 6.00-20 and fitting 7.00 or 7.50 tyres led to all sorts of problems with gearing, braking, steering geometry and turning circle. But they were cheaper, carried a heavier load and more readily available than 6.00-20's. Sound familiar?

[Lionelgee]

Originally Posted by Tony Smith

Be careful of the ply rating of the 8.25s. Most 7.50-20 were 8 or 10 ply tyres, while the 8.25s are usually 10, 12, or 14 ply. A rough ride will be the result, shaking you to bits.

Are you running duals on the rear axle? Unless your rims have the correct offset for 8.25s, when loaded the tyres will foul each other.

And check clearance around the front end, turning circle can be reduced if the tyres foul the springs or chassis.

I've no experience specifically with Chevs, but early Ford trucks were 6.00-20 and fitting 7.00 or 7.50 tyres led to all sorts of problems with gearing, braking, steering geometry and turning circle. But they were cheaper, carried a heavier load and more readily available than 6.00-20's. Sound familiar?

Hello Tony,

Yes, both trucks run dual rear axles. The Chev had its front mudguards lifted in service. So hopefully this will solve the clearance issues.

Some further searching found that there are some Isuzu trucks that run the 8.25/R20 as standard. As the quality of my rims can only be stated as "dubious" I may be exploring the path of having a set of Isuzu rims getting their centres modified to fit the Chev bolt pattern. Not sure if this is an engineering option that would comply to the Department of Transport and Main Roads here in Queensland?

As far as the rim & tyre count goes I started off in the minus. Both trucks did not come with a full set of rims. Each truck only had singles on the dual rear axle and there were no spares for either truck. Plus I have some ring-ins. There are two almost solid steel faced rims. There are only the stud holes and then two squares cut out of the rim face. One is for access to the valve stem. The other square is directly opposite the valve. Perhaps these were dedicated internal dual rims for the REO Speed Wagon? They sure look like they should not normally be seen.

The interesting thing is that the 1940 Chevrolet rims are interchangeable with the REO stud pattern!

Kind regards
Lionel

[Lionelgee]

Hello All,

Well that was interesting. The Chev has one front rim with a plate welded to the face where the studs go through. This plate has 10 holes in it. The Chev's front axle has a 5 stud pattern. The other front rim has only 5 holes in it. The Chev's rear axle has a 10 stud pattern.

The REO Speed Wagon has a five stud pattern on both front and rear axles. I have had the trucks for years and never noticed the differences in stud patterns between axles before.

Oh and the oval shaped cut-outs in one of the Chev's rear rims is totally different than all the other rims on the truck - what a bonus.... Not

Photos are: (1) The welded plate with 10 stud pattern front wheel, (2) shape of cut-out on rim edge and circled removable single bead ring (3) 5 stud plate on passenger front. (4) rear rim cut-outs smaller and more numerous. (5) the REO 3 piece bead system. The first four photographs are off the Chev and the last photo is off the REO

Are either of the ring systems the notorious "suicide rims"?

Kind regards
Lionel

[Tony Smith]

Originally Posted by Lionelgee

Hello Tony,

The Chev had its front mudguards lifted in service. So hopefully this will solve the clearance issues.

Kind regards
Lionel

The clearance issue is not with the mudguards.

The 8.25 tyre is both wider and taller. As you turn the steering, a taller and wider tyre will contact the chassis and/or front spring sooner that the 7.50 tyre. This can be prevented from happening by adjusting any steering stops (if fitted) on the front hub, but in any case will increase your turning circle.

The other approach is to alter the centreline of the tyre by using a rim with less offset, or fitting a hub spacer with more offset. Tricky stuff to get right, dabble at your own risk.

[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.

[Paul Singleton]

In my opinion the most dangerous truck wheels were the centre split type used up to the early or mid 1960’s. I know that General Motors used them but I am not sure about other manufacturers. I hated working with them as they would blow apart regularly when on the truck especially if the truck was overloaded.
These rims split in the middle, there were two dimples marking where to start prying them apart. The locking part didn’t go all the way around as the rim needed a spot to allow disassembly. Also in the winter the sand and salt would collect in the rim at the split and cause rusting.

[Lionelgee]

Hello All,

I found a set of six 8.25 R20 tyres and rims for sale at a good price on an online free classified advertising site. The tyres were just about brand new when taken off a wrecked Mitsubishi truck.

It makes you wonder why people outlay the cost of a new set of six tyres, then not very long afterwards, they decide to take sell the truck to a wreckers?

I will shortly take the Mitsubishi wheels to one of the local tyre places and get the tyres stripped off the rims. Then to sand blast, then paint my Chevrolet 1940 rims. Once this work is done I will see if anyone local will fit the tyres to the rims.

Kind regards
Lionel