Armoured Vehicle Road Wheels

[Robin Craig]

I appreciate the advice and I enjoyed reading the learned document and grasped what it was all about.

As a civilian we are having issues obtaining NOS road wheels. The original rubber could have been as old as 1985 and is well past it's best before date.

We have to re-cover the road wheels and not using rubber seems for our amount of use and or abuse to be a value option.

The Bv206 track is designed to flex and twist and has more than one contact point. Once the moulded edge of the road wheel breaks down and the steel guide horns of the track make contact with the aluminum wears very fast.

I have a few pictures to put up in a minute.

We were royally shafted by a major company in Winnerpeg who did the rubber re-life a few years ago and despite having an NOS example as a pattern part to follow decided for ease of manufacture to machine the edge off and leave no side protection. We were forced to pay up front and despite all kinds of efforts it was felt un-economic ( by higher) to lawyer up and get into a legal fight. We have smarted ever since.

This time I am treading very carefully

[Douglas Greville]

Robin

Your decision.

I will say, that the failure mode of synthetics is from the inside out. Likewise bad formulation rubber. So it is not a case of watching to see if rubber is failing. Case of "oh crap, we just shed a pad or tyre, but they all looked perfectly ok 1/2 hour ago".

Alternately, you could fabricate "wear disks" which is what the M113s use on the inner face of their road wheels. Makes a huge difference.

Regards
Doug

Originally Posted by Robin Craig

I appreciate the advice and I enjoyed reading the learned document and grasped what it was all about.

As a civilian we are having issues obtaining NOS road wheels. The original rubber could have been as old as 1985 and is well past it's best before date.

We have to re-cover the road wheels and not using rubber seems for our amount of use and or abuse to be a value option.

The Bv206 track is designed to flex and twist and has more than one contact point. Once the moulded edge of the road wheel breaks down and the steel guide horns of the track make contact with the aluminum wears very fast.

I have a few pictures to put up in a minute.

We were royally shafted by a major company in Winnerpeg who did the rubber re-life a few years ago and despite having an NOS example as a pattern part to follow decided for ease of manufacture to machine the edge off and leave no side protection. We were forced to pay up front and despite all kinds of efforts it was felt un-economic ( by higher) to lawyer up and get into a legal fight. We have smarted ever since.

This time I am treading very carefully

[Robin Craig]

Here are some pictures. Note how the master has a significant bulge to protect the aluminum wheel. This was the portion that was ignored by the last company and the picture shows how they machined the side face of the rubber and left no protection, the bright silver portion shows steel to aluminum wear.

[Douglas Greville]

Robin

Oh, yuk.

I hate the engineering. Those things weren't designed to last.

Can't see any easy way to add a wear disk.

Given the design, what is usual life before rubber is removed by guide
teeth?

Sorry.

Regards
Doug

[Robin Craig]

I will say that the data provided by 45jim and Doug Greville is very powerful and I will be drawing the polyurethane folks attention to it for comment and warranty.

I enjoy being educated here.

[Robin Craig]

Doug,

We have never had a brand new, made last week road wheel, ever.

I can tell you that the polyurethane wheel we have been trialing has not chipped in the side wall at all and this was the third winter of use.

I will show and report what we experience.

Please bear in mind the cost for us is more calculated in dollar per season than dollar per mile. I would suggest we do on average now less than 300 kilometers a year.

[Douglas Greville]

Robin

Ok.

You may get away with it then. My understanding is that Polyurethane has excellent wear properties and lousy thermal properties. Hysteresis is the enemy immediately any speed or flexing takes place - both generate internal heat.

Another way of putting it (to my understanding), is that poly is designed to take slide or direct loads of slow velocity/slow cycling. Not the case if you are hacking your vehicle around at 30 or more kph, doing turns and exerting
cyclic forces of many tons
(not vehicle weight, but dynamic force - think of it as force x velocity x time - I am not an engineer, so don't know correct calculation).

Thus if you have a track weighing say 100kg and it is trundling around at 5kph the forces aren't that much. Thrash it around at 30kph and
it becomes an exponential multiplier, you can be talking tons force.
I had an engineer give me a gut estimate of the apparent weight of one of
my Kettenkrad tracks when doing 50kph. He said roughly 1.5 tonne PER TRACK - er, um, that was sobering.

If you are driving your vehicle really slow, say 5 kph maybe 10 kph then this may be the reason you have had no problems. Plus if it is cold (for me, Canada is cold even in summer), would also explain your observations to date as the poly can heat dump sufficiently to stay within its operational parameters. Don't assume that touch test will tell you if things are getting
dicey. The internal temperature can be much higher than the external
temperature of the rubber. The outside can heat dump, the inside can't.

Regards
Doug

Originally Posted by Robin Craig

Doug,

We have never had a brand new, made last week road wheel, ever.

I can tell you that the polyurethane wheel we have been trialing has not chipped in the side wall at all and this was the third winter of use.

I will show and report what we experience.

Please bear in mind the cost for us is more calculated in dollar per season than dollar per mile. I would suggest we do on average now less than 300 kilometers a year.

[Stew Robertson]

Being in the plastics business for some year you gentlemen are going to have a problem convincing me that rubber is better
90 percent of all rubbers are a synthetic of plastic
One little note polyurethane is used to replace springs in punch press die and take millions of hits before replacements a natural rubber component would take about 10 hits and disintegrate
There is so many plastics out there for many uses and the right one being used makes the difference
finish your home work it is in the supplier

[Chris Suslowicz]

If polyurethane was better than rubber as a tyre compound the world would have switched to using that years ago. It's all down to the conditions of use.

(Bear in mind that my experience of the tyre industry is completely unrelated to the technical side (I was in Dunlop's computer operations area, but did have acquaintances in Tyre Technical who would have known more than you could possibly need about rubber compounds), but that was 30 years ago.)

Polyurethane replaced rubber in lots of places: printing press rollers, casters, and small wheels, cutting mats, and so on. It's suitable for those purposes because the amount of flexing is small (and in the case of a printing press the rollers are cooled by the ink and process fluids). It's not suitable for vehicle (pneumatic) tyres because of the continual (and substantial) flexing that takes place in everyday usage. Dunlop's test fleet ran a variety of vehicles under standard road conditions (with regular stops to check tyre temperatures, etc.) to make sure the compounds used were up to the job. If polyurethane was usable they'd have jumped at it with much rejoicing because it would have saved them a fortune in imported rubber and equivalent substitutes.

Solid tyres are a similar case: the rubber is being continually flexed where it's under load (i.e. in contact with the floor or inner face of the track), and that continual flexing raises the temperature of the tyre. PU gets used for things like factory forklift truck wheels because they're usually working indoors, on a smooth surface, and at low speeds. Outdoor forklifts, I think, use rubber tyres, with different tread patterns for added grip but they are still a low speed device. (Unless you talk to my friend who repairs the things after various lunatics have damaged them.)

Tracked vehicle road wheels are a high-speed, probably high-loading, and certainly high-flexing application: the ground force of the track may be quite small (because it's a rigid plate), but that's transferred to a much smaller contact surface on the road wheel, and I doubt that polyurethane is up to the task.

Chris.
(Fort Dunlop is long gone, but it used to be the biggest tyre factory in Europe, and the rifle club had a mix of members from all over the factory and admin, including a few from Tyre Technical (who were the compound and tread pattern development side of things, there were some amusing tales told).)