article on tyre tread patterns

[Hanno Spoelstra]

As tyre tread patterns are often a subject for discussion, I quote an informative excerpt (including images) from an article on this subject that David Doyle did a year or so ago for Military Vehicles Magazine.

"While many types of tread patterns have been used on US military vehicles, including some quiet unusual patterns, most US military tactical vehicles during the WWII through Vietnam era used one of four tread patterns.

These were a directional chevron tread pattern, a non-directional cross country tactical tire, a non-directional mud and snow combat tire, and a non-directional Firestone tread tire. While the tread pattern of the directional tire makes it readily identifiable, the other three have similar tread patterns that make them easy to confuse.

As a rule the tire tread pattern is molded into the sidewall of the tire along with a wealth of other information, usually in abbreviated form. Non-directional cross-country is usually marked as NDCC, while the non-directional mud and snow tire is abbreviated NDMS or NDT.

The shoulders of the tread area of the NDCC tire are rounded, while the shoulders of the NDT tires have a more squared appearance.

Tires on most commonly collected US military vehicles are of bias-ply construction and are sized by rim width and diameter. These sizes are imprinted on the sidewall of the tire. As an example, a 9.00-20 (commonly referred to as a "nine hundred twenty) tire, fits a twenty inch diameter rim that is nine inches wide at the bead seat.

Also inscribed on the sidewall will be the tire size. Tires for classic military vehicles are usually sized using the numeric system shown here. Authors, including this one, often erroneously write these tire sizes in the format used for flotation tires, but as can be seen here, the tires described by the two systems are quiet different.

Other markings frequently found on the sidewalls of military tires are as follows:
- Manufacturer's name
- Ply rating-not necessarily the actual number of plies, but their equivalent.
- N-nylon cord"

[Hanno Spoelstra]

"Tread Patterns

Chevron tread

Early in WWII many vehicles were equipped with chevron tread pattern tires, as can be seen in figure one. The chevron-type tread is a directional tread, which made tire rotation and replacement more time consuming.

According to TM 31-200, Maintenance and Care of Pneumatic Tires and Rubber Treads, April 1942, these type tires were to be mounted with a specific orientation.

When mounted on the rear driving axles, the tires should be mounted such that the point of V touches the ground first. This orientation allows the tread to clean itself of mud, giving superior traction.

When this type tire is mounted on the front axle of a vehicle, the open end of the V should meet the ground first whether or not the axle is driven. This is because the tire tread will wear more slowly when in this position. This stands to reason since there is also less traction when mounted in this manner.

The next edition, April 1943, made an exception to the previous policy. Directional tires when mounted on the front axle of scout cars and halftracks should be mounted just like the rear axles, that is with the point of the V touching the ground first.

When mounted on trailers, these tires were to be mounted for maximum tread life; that is with the open end of the V touching first.

Reportedly, when driven on hard surface roads, chevron tread tires on the steering axle tend to increase tire "hunt," making driving laborious.

Non-directional treads

During WWII the most common tread pattern found on tactical vehicles was the NDT, the non-directional tread. Characteristic of these tires was a very squared intersection of the tread area and the tire sidewall, as can be seen in figure two.

The tread known as the Firestone tread was very similar to the NDT, only the tread lugs of these tires had a slight twist to them, as shown in figure three. Although not as widely used as the NDT, they nevertheless were found on such vehicles as the GPW, CCKW, etc.

Non-directional cross-country treads were developed a little later. While at a glance they appear to be identical to the NDT tires, they are in fact different. Unlike the square shoulder of the NDT, the NDCC has a rounded cross-section. This rounded shape is clearly visible in figures two and four."

[Hanno Spoelstra]

"Figure 2: this illustration, from TM 9-8000, January 1956, shows the four most common types of highway vehicle tires in use by the US armed forces at that time. Notice the difference in shoulders between the Cross-Country (NDCC) tread, and the similar Mud and Snow (NDT) tread."

[Hanno Spoelstra]

Originally written by David Doyle
As an example, a 9.00-20 (commonly referred to as a "nine hundred twenty) tire, fits a twenty inch diameter rim that is nine inches wide at the bead seat.

Actually, the 9.00 in this case denotes the nominal cross-section width of the tyre, not the width at the bead seat. As an example, the 9.00-16 tyres fitted to many CMP trucks are fitted on 6.00-16 wheels.

H.

[Hanno Spoelstra]

Nice period pic from Life showing various tyre treads and sizes:

A stack of huge earthmover and combat vehicle tires showing deep treads.

[Keith Orpin]

Hi Hanno,
Nice article, the British actually marked their Chevron pattern tyres with an arrow, to show the direction of rotation. This shows the open end of the V striking the ground first, which is completely opposite to the way the Canadians show it in their manuals. Having stated that, driving my Chev with the open end of the V striking the ground first, makes it slightly easier to handled, than with the closed end hitting the ground first. I was told years ago, that the reason for mounting the tyres with the V striking the ground first, was that if you became stuck, you could always back out of trouble, which is hardly going to affect us on todays roads !
Regards
Keith

[Lynn Eades]

The size of the tyre, 900x16, is a tyre that fits a 16 inch rim. The tyre having a 9 inch high side wall, which gives an overall nominal diameter of 9+16+9=34 inches. or in the case of a 10.50 x 16, 10.5+16+10.5= a nominal diameter of 37 inches.
I write this because I believe the article is misleading.

[Grant Bowker]

Originally Posted by Lynn Eades

The size of the tyre, 900x16, is a tyre that fits a 16 inch rim. The tyre having a 9 inch high side wall, which gives an overall nominal diameter of 9+16+9=34 inches. or in the case of a 10.50 x 16, 10.5+16+10.5= a nominal diameter of 37 inches.
I write this because I believe the article is misleading.

Period publications clearly state that the 900 in a 900x16 size tire is the "width of cross section". In most cases, tires of that period were close to being as wide as they were tall in cross section (in todays jargon a metric car tire might be 185/100-14 if it were in the same proportion). This makes the formula you gave a useful approximation of diameter but the 900 is not a specification of sidewall height.

[Lang]

Lynne,

I will go with Hanno and agree that the numbers refer to the section width not the height of the sidewall. Verification of this can be found on numerous tyre manufacturers sites.

In the early days they used to describe the tyres as "Standard" or "Balloon" to describe tall skinny ones compared to fat round ones and they often only gave the overall height not width so you only knew they were fat or skinny by the word description.

Of course that problem has now been solved by modern tyre descriptions giving the width, height (expressed as a percentage of width) and wheel diameter eg 205 X 75 X R16 Which equates to 205mm wide by 75% of that high (about 150mm), R for radial and 16 inch wheel. Nothing like mixing up Imperial and Metric measurements to help everything.


Lang

[Lang]

Originally Posted by Keith Orpin

Hi Hanno,
Nice article, the British actually marked their Chevron pattern tyres with an arrow, to show the direction of rotation. This shows the open end of the V striking the ground first, which is completely opposite to the way the Canadians show it in their manuals. Having stated that, driving my Chev with the open end of the V striking the ground first, makes it slightly easier to handled, than with the closed end hitting the ground first. I was told years ago, that the reason for mounting the tyres with the V striking the ground first, was that if you became stuck, you could always back out of trouble, which is hardly going to affect us on todays roads !
Regards
Keith

Keith,

Most of the original directional tyres I have seen actually had two arrows, "Driving" and "Rolling"

I have a 1944 Australian Army TM (which is just a reprint of a US Army TM with a different cover) on "Care and Maintenance of Rubber Tires". It says all tires should be fitted with open side of "V" striking the road for vehicles used on formed surfaces. Up to 20% greater life can be expected. For vehicles used off road the rear driving wheels should be fitted with the point of the "V" striking the road. A considerable increase in traction on soft surfaces has been demonstrated by this fitment. Only wheeled armoured vehicles should have all wheels with the point of the "V" striking first at all times.

Lang

[Mike K]

No, Im not asking tyres out on dates...

On today's tyres.. among other sidewall markings you'll see a date code .. typically 4 numbers like for example: [1307] this number = the tyre was manufactured during the 13th week of 2007 . I checked my MRF 900 - 13's, and they are dated 2002 . I also have a few OLYMPIC 900-13's dated the year 2000 .

Recently, there has been a few cases of tyre retailers selling tyres which are way past the 'use by' date ... Apparently, more than 6 years old , is considered to be a non-roadworthy tyre here - they reckon the compound dries out .. leaving it prone to disintegrating under high speed.

Mike

[Lang]

Originally Posted by Mike Kelly

No, Im not asking tyres out on dates...

leaving it prone to disintegrating under high speed.

Mike

A Morris or 8cwt blitz at high speed?

[Lang]

I found another manual "Maintenance and Care of Pneumatic Tires and Rubber Treads" TM31-200 April 1, 1943

Quite thick and has vehicle and aircraft tyres, half-track treads and tank tracks including detailed repair and fitting instructions. Big charts of tire pressures for each size and vehicle type etc.

Lang

[Alastair Thomas]

I have been reading "Design Record Canadian-Developed Military Vehicles World War II". This is a summary of the experiences and design decisions made during the CMP program. It is in 8 volumes and in volume 4 tyre production, size choices and wear considerations are discussed.
Firstly the loss of the major rubber producing areas is discussed. This was a serious enough situation for a number of hitherto rubber parts (including the windscreen blocks on the Jeep and motor bike twist grips) to be made of alternative materials. It may be that the transition from rubber boots round the levers in the CMP cab changed from rubber to canvass at this time for the same reason. Then the topic of which way round to mount the tyres is introduced. Though specific instructions were issued one is left with the feeling that they were not strictly adhered to.
Alastair
F60S

[Jacques Reed]

Good Day,

Here is a reprint from The Australian Monthly Motor Manual 1946 which may be of interest. It was reprinted in the VMVC Newsletter many years ago.

In the article fitting of "Chevron Tread" tyres goes with the open end contacting the ground first for better longevity but admits some loss of traction.

Cheers