Re: [MV] Directional tire directions - Further thoughts

Alan Bowes (inbox@todacosa.com)
Fri, 05 Jun 1998 23:15:08 -0600

Hi Geoff,

The tire that you pictured, which does rather resemble a tractor tread,
was often used in a rear-pointing direction on many British and
Commonwealth vehicles in WWII.

However, if you look at pictures of US WWII vehicles with what would be
considered a more typical "tractor" V-tread, I think you'll find that an
overwhelming majority were installed in a forward-pointing direction.
Just for kicks, I glanced through Vanderveen's WWII Observer's Fighting
Vehicles Directory. Of the dozens of US MVs with tractor-type treads,
the ONLY ones I saw pointing backwards were on a Bantam Mark II and a
Willys Quad, both pilot models. Perhaps I missed one or two in my quick
reconaissance of the book (someone will probably find them), but
certainly better than 95% of the US rigs with the V tread were forward
pointing.

However, I don't think that this reflects a different way of thinking
between the US and the UK/Commonwealth nations, since one important
practical deciding factor would have been the type of surface that a
vehicle was intended to operate upon.

On soft dirt and mud (or other compactible materials), a self-cleaning
tread direction (V pointing forward) is advisable for best traction,
because it clears the soft stuff out of the tread, allowing the lugs to
bite into more solid underlying material. HOWEVER, on something like
deep, dry sand, it may not be advantageous for two reasons: One is that
dry sand does not compact well, and as you dig deeper into the soft sand
deposits, you won't hit any solid underlying ground with significantly
improved shear strength, hence it wouldn't do much (if any) good to
clear the tread. Second, you don't want to sink down to the axles in
soft sand, and a rear-pointing tread would gather the sand toward the
center of the tread as the tires slip, helping prevent the tires from
digging in quite so deeply.

And, of course, many British vehicles were used in such gritty places as
Northern Africa, which has a VERY large sandpile called the Sahara.
While it is true that not all of the Sahara consists of soft sand, the
surface in that region most likely to frustrate a wheeled vehicle would
have been those areas of soft sand.

It would have been easy to reverse the tread direction if the vehicles
were transported to an area where dirt and mud would be the rule
(assuming that anyone even bothered to do this).

Vehicle handling, treadwear problems (such as cupping on front tires),
noise, etc. could also be factors that affected the decision regarding a
particular tread pattern.

Alan

Geoff Winnington-Ball wrote:
>
> Your theory sounds good. However, the URL below shows a pic out of a Canadian WW2
> vehicle handbook, indicating the "official" rotation direction. Maybe they were
> more concerned about stopping? :-)
>
> A great many pics I've seen show BOTH directions, on varied wheels. Perhaps the
> RCEME people simply put them on as they pleased. etc.

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