Sidewall flex, intermediate axle/rear axle

[gary j zingle]

"Here is my theory or hypothesis... The leading bogie wheel
hit a bump and the side wall flexes. Milliseconds later, the
trailing bogie hit the same bump, and with a two bag system,
the leading bogie flexes again with the reflection of the
same bump."

While I agree that on a 2 bag system the tires on the intermediate
axle will share the flex when the tires on the rear axle hit a bump,
I see no reason to believe that the opposite would not also be true.
When the tires on the intermediate axle hit a bump the tires on the
rear axle would also share the flex via the shared suspension.

Therefore tire failures on the rear axle should be just as frequent
as on the intermediate axle if sharing of flex were the only
consideration.

I would certainly agree that the tire flex caused by tight low speed
turns does not create heat and therefore is responsible for
few/no tire failures.

There is one that I have not yet heard discussed that I believe could
be a cause for increases in failures of marginal tires on either rear
axle of the GMC

If the tires are out of balance or out of round then at speed they move
up and down causing tire flex. With the 2 bag system the movement
and the flex would be shared by both tires.

I developed this theory after driving my recently purchased coach with
old, out of round, unbalanced tires/wheels at speed.

The only visual I have had is the observation of large trucks with tandam=

axles, walking beam suspensions and out of round or out of balance
tires or wheels. The rear axle appears to be moving down when the
unbalanced front axle is moving up (the opposite also seems to be true).
This looks like what I feel when I drive my coach.

I suspect the increased frequency of the flexing caused by the use of out=

of round or out of balanced tires or wheels on tandam axles with shared
suspension could be a factor.

Please don't read this as an endorsement for the 4 bag suspension, but
rather for good/round/alanced tires.

Thoughts?

Regards

Gary Zingle
1973 26 foot (patiently sitting in the snow waiting for new "E"'s on
Alcoas)

 

[john dolan]

>Thoughts? Regards Gary Zingle

I can see you have been giving this some thought...

With regard to the rear bogie getting the reflection of the bump from the first
bogie, lets hear you thoughts on this possibility, that I decided not to put in
the first post:

The bump is absorbed first by the leading tire sidewall, then the air bag, then
the trailing bogie being forced down, and then ultimately by the coach moving
up as in oooggghhh. By the time the trailing bogie wheel hits the same bump
the coach is probably still moving up, and possibly the flexing of the rear
bogie sidewall is less. QED?

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[john dolan]

>If the tires are out of balance or out of round then at speed they
>move up and down causing tire flex.

I seen some stop motion imaging of that motion, and with a bad shock it can get
pretty violent (more than you can see on a passenger car wheel without the stop
or slomotion playback). This is the interesting part of your hypothesis
Gary... what if the leading bogie is more likely to lose its balancing weights
than the trailing bogie (for the reasons I hypothesized) and then it bounces
along as your hypothesis explains, but more so than any other wheel?

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[tom warner]

Emory I can add only one thing and that is the fact that underinflation of E
range all steel belted tires to 65# or so instead of 80# will lead to
premature sidewall failure. This fact was documented in the Cinnabar study
for General Motors.

The out of balance conditions, impacting of the sidewalls, and sloppy bogie
pins hastens the failures when added to the previous conditions.

>

>
>
>If the tires are out of balance or out of round then at speed they move
>
>up and down causing tire flex. >>
>
>Gary - This reply is not directed just to you. I think many are overlooking
>the fact that the tire is already flexing with every revolution. It doesn't
>matter if it is out of balance or going over rough ground or perfectly flat
>ground.
>
>As the tire rotates, every time a point on the tire goes to the bottom the
>sidewalls flex out. Just look at the tire when it is sitting still. The
>bottom sidewalls are bulged out from the weight. If your tire is rotating at
>about 700 times per mile and you are going 70 miles per hour, every spot on
>the entire sidewall is flexing in and out 49,000 times per hour, or 817 times
>per minute. That is why I have stated in the past that it is not the vehicle
>turning that causes the problems. It doesn't even matter whether you have
>one air bag or two on each side. This flexing is due to weight on the tires.
>
>Take a rubber band and stretch it a few time and then feel it. It will get
>warm. If you did it 817 times in a minute it would certainly break.
>Fortunately the sidewalls of tires are reinforced and the synthetic rubbers
>hold up to heat much better.
>
>I maintain that the blowouts are generally caused by heat buildup in the
>sidewall that cause the tire to delaminate. This can best be prevented by
>using a stronger sidewalls (Load Range E with steel belts) and keeping the
>air pressure up to prevent as much sidewall flexing as possible. That is why
>I use 80 psi in my G159 load range E tires.
>
>Now, hitting a curb, pothole or other road hazard can break cords and cause a
>tire to fail. It doesn't matter what kind of tire you have. Certainly some
>of the blowouts that Roger recorded were caused by that, but I would bet that
>most were due either to low tire pressure and subsequent heat buildup that
>the construction of the tire would not tolerate or to the use of a tire with
>an inherently weak sidewall. Some tires meeting Load Range D specifications
>have a two ply sidewall reinforced with Polyester cord. Compare this to an
>actual 4 ply sidewall with woven steel belt reinforcing.
>
>Several GMC netters are trying to make this way too complicated. It's just a
>matter of weight, stiffness of the sidewall, and composition of the tire.
>The more weight you have on the tire, the greater the flexing. Granted, the
>moving up and down of the vehicle will put additional loading on the tires to
>help compound the problem but the two Load Range D tires that I had fail were
>at highway speeds on straight and level interstate highways. No pot holes,
>curbs, etc.
>
>I would recommend that anyone really interested in tires should look at
>cut-aways of various manufacturers tires to see how they are constructed.
>There is a world of difference between manufacturers and between different
>models of the same company. Some of the bigger tire dealers have these
>cut-aways available.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>

 

[john dolan]

Well there are not too (or is it two) many of us here in this thread...

This is not directed just at Emery, but it seems that he (and possibly others)
has never seen how much flexing goes on with small bumps and out of balance
tires, since he seems to be saying it's just the rolling flexing stupid, due to
the weight. I also think he is trying to make this way to simple, when he says
some GMCnetters are trying to make this too complex and we should look at a
static display that tire manufacturers have of their construction.

Nothing he said, explained what we were talking about at this point in the
thread, which is the higher incidence of leading bogie failure. He restated
his explanation, and said its that simple.

Somehow I get the sense that he doesn't want any further discussion on this
since he has said over and over again; it's simple, its just the flexing due to
rolling. Pardon my paraphrasing but I've heard it more than once...

>That is why I have stated in the past that it is not the vehicle
>turning that causes the problems. It doesn't even matter
>whether you have one air bag or two on each side. This
>flexing is due to weight on the tires.

Well if it is so simple and all we GMCnetters have to do is ponder
static displays... both leading and trailing bogies bulge out about
the same on my GMC, why then, does the leading bogie fail the most
of any tire on the coach including the front?

This might seem irreverent to some, but I will say it anyway. It is not simple
and I don't feel it is appropriate to try to close off debate, just because
someone has explained it in simple terms more than once. In fact it galls me
as much as someone saying "I'll take two more questions..." after having
answered none.

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[john dolan]

Thanks again Emery...

But we heard your explanation over and over... Is it possible that there is
more to it, than your simple explanation? (again not addressing the
differences in leading and trailing bogie failure).

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[hdavis]

>Thanks again Emery...
>
>But we heard your explanation over and over... Is it possible that there is
>more to it, than your simple explanation? (again not addressing the
>differences in leading and trailing bogie failure).
>
>Regards... John 74 Glacier (now Custom) near Washington, DC

John,

Looking at the data that Roger has collected I don't see any statistical
difference between mid and rear axles. So, I don't see the causative
implications that you ascribe to the wheel/tire action.

The information that was collected is interesting, but ignores (rightfully)
the primary reported reason for premature tire failure - underinflation.
Also, we don't know the mileage of the tires etc. As a result, we can't
draw any meaningful conclusions about the failures other than to observe an
apparrant increasing failure rate as tires age.

Because of several questions that I have about my own tires, I've been
talking with Goodyear's Chief Engineer for materials, the QA engineer for
light truck tires, and the North Western regional manager.

The number one reason for premature wearout and/or tire failure is
underinflation according to these guys. The next reason for failure is road
hazards (nails, rocks, potholes etc). Their return rate due to materials
and/or manufacturing defects is vanishingly small. Even so they do a number
of warranty replacements for other than defects as good will.

According to Goodyear, the front axle on most motorhomes is the biggest
culprit when it comes to overloading tires. Goodyear reps go to some RV
rallyes specifically to interview drivers and weigh coaches. It isn't
unusual for them to find a 12,000 lb axle loaded 6,600 left and 5,400
right. At 12,000 lbs evenly distributed the tires are within spec, but the
when loaded at 6,600 lbs they are over the weight limit. (ever wonder why
you see a relatively large number of front tire failures on the expensive
bigger rigs as compared to the rears?)

Lastly, Goodyear and the other US tire manufacturers have a lot of
experience with the GMC's rear axle configuration. They worked with GM to
spec the tires for our motorhome and tires for the newer GM MH chassis (and
busses).

Henry

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com

 

[john dolan]

Henry...

>Looking at the data that Roger has collected I don't see any statistical
>difference between mid and rear axles. So, I don't see the causative
>implications that you ascribe to the wheel/tire action.

I'm happy to hear from you, but I'm a little surprised to see you drawing
conclusions before we have a valid sample... What I said was the mid axle was
suspect. I also said we can't draw any conclusions at this point. You seem to
be drawing a conclusion that there is no difference... Are you
saying the same thing as Emery? (it's just the weight causing the rolling
flexing/heating, so forget it?)

Left front 3
Left Mid 8
Left Rear 4

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[gary j zingle]

Emery & Tom.............Sorry if I failed to mention
the importance of normal forward motion flex
in the heating of the tire. If the coach is not
overloaded and "E"'s are used and properly
inflated these temperatures should however
be normal.

Also I hope I made it clear that I don't see low
speed tight turning as much of a factor in tire failure.

What I was writing about were those things that on
a tandam axle sharing an air bag might cause a
tire otherwise operating normally to overheat i.e.
the extra monkey motion caused by out of
balance/round

John I see your point (although I don't necessarily
agree as to the result) about the coach possibly being
raised due to the intermediate wheel hitting the bump
first.

I see the intermediate and rear axles
operating very much the same.

Also I have not commented regarding any theory
of more problems on the intermediate axle
since other than hitting curbs I don't really see any
significant additional problem that the intermediate
tire faces.

And, I know nothing that would allow me to offer an
opinion regarding whether the intermediate tire
or the rear tire is likely to be the first to go out
of balance or out of round.

But I am willing to bet that given the sharing through
the air bag many shocks have been worn out before
their time trying to control out of balance/round tires.

By the way found a web site today with some
information for care of tires.

www.dunlop.com

Regards

Gary Zingle

 

[john dolan]

Thanks for the info and the comments, I think where was value in that even
though some disagree with my hypotheses.

Does anyone have any experience or data with out of balance or out of round
tires running hotter?

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[john dolan]

...or maybe as Rick highlighted 'out of align tires running hotter'?

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[hdavis]

>Well there are not too (or is it two) many of us here in this thread...
>
>This is not directed just at Emery, but it seems that he (and possibly
others)
>has never seen how much flexing goes on with small bumps and out of balance
>tires, since he seems to be saying it's just the rolling flexing stupid,
due to
>the weight. I also think he is trying to make this way to simple, when he
says
>some GMCnetters are trying to make this too complex and we should look at a
>static display that tire manufacturers have of their construction.

Here's a short form review of simple dynamics applied to the rear tires as
configured in the OEM setup.

In John's question, we're concerned primarily with the load transfer to the
tire as a consequence of hitting a bump (or hole). The issue is whether or
not there is a greater dynamic load on the mid tire or rear tire.
Considering a level coach at correct ride height encountering a bump in the
road:

the leading tire rides over the bump. As it begins to roll up the incline
the upper arm increases pressure exerted on the airbag. The pressure
equalizes at the spring rate of the bag forcing the trailing tire to accept
the same amount of force as the leading tire EXCEPT FOR THAT DISSIPATED AS
HEAT in the leading tire. [The leading tire encountering the bump transfers
load upwward through the arm into the airbag and then down to the trailing
tire. Draw a simple force diagram and you will convince yourself that the
forces are equal except for friction losses.] As the leading tire rolls
down the incline it unloads the airbag which in turn causes a transfer of
load from teh trailing tire to the leading tire. The action is one of
maintaining near equal loading on the two tires at all times, with some
system lag based on the spring rate of the airbag.

Next the trailing tire encounters the bump. As it rolls up the incline
creating an impulse load, load is transfered to the airbag and to the
leading tire. AS the trailing tire rolls down the incline it unloads the
airbag which in turn transfers load from the leading tire to the trailing
tire. Because the two tires are connected through the airbag the system
will in general evenly divide the loads (static AND dynamic) between the
two tires.

Recapping the dynamic case of hitting a bump, the leading tire accelerates
upward accepting an increased dynamic load which in turn is transferred to
the trailing tire. The two tires see the same load - dynamic and static.
The leading tire rolls over the bump and begins down the other side -
experiencing a downward acceleration which unloads the airbag which in turn
causes load from the trailing tire to be shifted to the leading tire. When
the leading tire stops its downward acceleration there is an additional
dynamic load imposed by the "falling" weight of the coach. This load is
evenly divided between the two tires.

Diagrammatically, we have loads as follows;

- ------^-v-^--------- leading tire
.------^-v-^-------- trailing tire

Now let's consider the case of an out of balance tire. I'll use the leading
tire as the example but the analysis applies to either tire.

The leading tire is out of balance and/or round. Every rotation causes a
dynamic load that is a function of the angular velocity of the imbalance
center of mass and the radius of the axle center to the center of the
imbalance mass. The imbalance creates a dynamic load that is periodic and
in particluar is sinusoid. As in the case of hitting a bump, the load on
the leading tire is transferred to the trailing tire through the airbag.
The airbag will serve to time delay the transfer by some amount that is a
function of the spring rate of the bag. Consequently the two tires see the
same dynamic load, just separated by time and friction losses.

Effects of undamped spring action
If the airbag was and undamped sring then it is possible to create
oscillations that mulitply peak loads providing that the outside impulse
function is repeated at the fundamental frequency or some harmonic.
However, the airbag is NOT an undamped system since there are dual action
shock absorbers on each wheel. When I said earlier in the dyanmic analysis
that friction losses may occur, the shocks are one element that may
attenuate the impulse response of the airbag system. Since the shock
absorber action is to attenuate high frequency more than low frequency, the
shock absorber is generally more important to out of balance or out of
round conditions since the tires complete one oscillation every rotation -
where significant road conditions are usually spaced relatively far apart.
At 60 MPH the waveform is about 11 Hz on my G159s. To get the same
frequency from road conditions would require bumps about every 7.5 feet.
The damping action of the shocks also attenuates the high frequency
components of the impulse that happens when hitting a "square" obstacle (or
one that is square relative to the rolling characteristics of the tire).

How does this affect the dynamnic analysis? well, the shock load applied to
the trailing tire will be somewhat lower than the leading tire absorbs. But
this doesn't affect the total dynamic load seen by the trailing tire. The
trailing tire encounters the same shock load when it begins rolling up the
incline as did the leading tire. Likewise, when the trailing tire transfers
load to the airbag, there is friction loss due to the shock absorber.
Assuming both shock absorbers to be equal in capacity and response the
tires still see exactly the same dynamic loads.

Bottom line: The axles don't matter for dynamic loads. At best (or worst)
the out of round or out of balance tire will get hotter than its
counterpart. The temperature delta depends mostly on how fast you drive and
the kind/how good your shocks are.

Henry
I used to be an engineer once upon a time but no longer claim that title.

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com

 

[hdavis]

>Henry...
>
>>Looking at the data that Roger has collected I don't see any statistical
>>difference between mid and rear axles. So, I don't see the causative
>>implications that you ascribe to the wheel/tire action.
>
>I'm happy to hear from you, but I'm a little surprised to see you drawing
>conclusions before we have a valid sample...
Here's what I said:
"Looking at the data that Roger has collected I don't see any statistical
difference between mid and rear axles. So, I don't see the causative
implications that you ascribe to the wheel/tire action.
The information that was collected is interesting, but ignores (rightfully)
the primary reported reason for premature tire failure - underinflation.
Also, we don't know the mileage of the tires etc. As a result, we can't
draw any meaningful conclusions about the failures other than to observe an
apparrant increasing failure rate as tires age."

In other words we have anecdotal information (which may be valuable) but
nothing that we can draw conclusions from.

Actually we'll never have a statistically valid sample. To get a sample to
my satisfation we'd need to have 144 tires of the same manufacturer run
under the same conditions - and to complete failure. That would give us the
FITs as well as the intricnisc failure mechanisms under the test
conditions. The results would only have a 95% confidence, but that's good
enough for me. I guess we could create a design of experiements that would
give life curves of inflation vs weight limits etc and only use a few
hundred tires.

>What I said was the mid axle was
>suspect. I also said we can't draw any conclusions at this point. You
>seem to
>be drawing a conclusion that there is no difference... Are you
>saying the same thing as Emery? (it's just the weight causing the rolling
>flexing/heating, so forget it?)

Nope, I'm saying that the two tires see pretty nearly the same loads. And
on any road I know, they see exactly the same loads assuming shocks are the
same and the pins are in good shape.

If I were to guess about the predominant GMC MH tire failure mechanism, I'd
say that underinflation combined with poor alignment make up the root
causes. My reasons for saying this are based heavily on the published
information from the tire manufacturers and my conversations with
Goodyear's Chief Engineer. They do all of the tests to determine failure
mechanisms. Their results all point to inflation pressure as the first
order variable.

I discard ALL tires reports based on LRD tires since GM says they're
unacceptable and do NOT meet the GMC requirements.

On my coach the difference between 65 PSI and 80 PSI is nearly 1 MPG.
That's over 15% difference between mileage at the two pressures. [I know
the 65PSI numbers because the shop reduced my TP without telling me and I
drove 1200 miles at the lower pressure] The gas difference goes into heat
in the tires. I can't measure the difference in mileage that I get running
on a bumpy road or smooth road - the variance is within what I see as
normal gas milage. Since the road type translates into less than 2%
difference in mileage, I know that tire pressure is more important to fuel
economy by a factor of at least 5 than road bumps. [I drove many of the
same roads before and after repaving - big holes to no holes].

Other than inflation pressure, alignment is the other big known factor in
heat build up. Perhaps there's atendancy for folks to hit things only with
the mid axle and knock out the alignment. I guess we could survey the GMC
shops and see what they say.

Henry

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com

 

[john dolan]

My question is the following: is there anything about the mid wheel that would
increase the temperature or flexing of the side wall of the mid wheel tire as
compared to the trailing wheel. I think we are seeing some possibilities.
It might surprise a few, that I agree with the flexing heating as being the
major cause and agreed with Emery and Henry right up to the point where they
concluded there is no difference between the wheels and these posts are getting
tiring (there are now). but conveying knowledge, thanks.

The following was a restatement one of my of my questions, but please Henry,
don't give us the short form review of all of my questions!

>In John's question, we're concerned primarily with the load transfer
>to the tire as a consequence of hitting a bump (or hole). The issue is
>whether or not there is a greater dynamic load on the mid tire or rear tire.

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[tom warner]

John I honestly do not know what you are arguing for or against. The numbers
of failures as reported for different tire locations is at best close to
voodoo and certainly worthless as any kind of statistical data if we are
trying to draw any kind of conclusions. I am not all trying to belittle the
effort, but as an engineer I can tell you that the information has not been
obtained under any kind of a controlled condition. For example how old were
the tires, were any of the coaches overloaded, were any of the suspension
systems marginal or inoperative.

What am I talking about? If we really want to start gathering information
on tire failures for the GMC motorhome, and be able at the end to use the
data to either prove or disprove something, than we need to set up some
guidelines to use in the data gathering. Just some examples and in no case
complete:

1. All similar wheel locations should be carrying nearly identical weights.
2. All tires should be inflated cold to the manufacturers PSI for the
application and all parties should use calibrated pressure gauges.
3. Driven on similar surfaces
4. Driven at nearly identical speeds
5. Driven in similar manners, ie; no severe stops, jack rabbit starts etc.
6. Motorhomes should be identical in design, ie; do not compare 2 bagger and
4 bagger systems, the data would not correlate
7. All tires should be the same manufacturer and age

And lastly even if we had a thousand samples here what would it show?

>Henry...
>
>>Looking at the data that Roger has collected I don't see any statistical
>>difference between mid and rear axles. So, I don't see the causative
>>implications that you ascribe to the wheel/tire action.
>
>I'm happy to hear from you, but I'm a little surprised to see you drawing
>conclusions before we have a valid sample... What I said was the mid axle was
>suspect. I also said we can't draw any conclusions at this point. You seem to
>be drawing a conclusion that there is no difference... Are you
>saying the same thing as Emery? (it's just the weight causing the rolling
>flexing/heating, so forget it?)
>
>Left front 3
>Left Mid 8
>Left Rear 4
>
>Regards... John 74 Glacier (now Custom) near Washington, DC
>
>

 

[tom warner]

Gary my "gut" feeling is that the passenger side mid axel tire has the most
failures. And I have scientific evidence to prove it. The refrigerator on
most coaches is close to the mid axel tire. I notice that everywhere I go
and meet other GMC owners, the top comment I always hear is "My wife was
putting food in the fridge right up to my pulling out of the driveway".
Seems that everyone that goes on a weekend trip takes enough food to last a
month. I believe this extra weight overloads the mid axel tire and
contributes to its early demise.

>Emery & Tom.............Sorry if I failed to mention
>the importance of normal forward motion flex
>in the heating of the tire. If the coach is not
>overloaded and "E"'s are used and properly
>inflated these temperatures should however
>be normal.
>
>Also I hope I made it clear that I don't see low
>speed tight turning as much of a factor in tire failure.
>
>What I was writing about were those things that on
>a tandam axle sharing an air bag might cause a
>tire otherwise operating normally to overheat i.e.
>the extra monkey motion caused by out of
>balance/round
>
>John I see your point (although I don't necessarily
>agree as to the result) about the coach possibly being
>raised due to the intermediate wheel hitting the bump
>first.
>
>I see the intermediate and rear axles
>operating very much the same.
>
>Also I have not commented regarding any theory
>of more problems on the intermediate axle
>since other than hitting curbs I don't really see any
>significant additional problem that the intermediate
>tire faces.
>
>And, I know nothing that would allow me to offer an
>opinion regarding whether the intermediate tire
>or the rear tire is likely to be the first to go out
>of balance or out of round.
>
>But I am willing to bet that given the sharing through
>the air bag many shocks have been worn out before
>their time trying to control out of balance/round tires.
>
>By the way found a web site today with some
>information for care of tires.
>
>www.dunlop.com
>
>Regards
>
>Gary Zingle
>
>

 

[tom warner]

Henry even you are overlooking potentially important information when you
say "The information that was collected is interesting, but ignores
(rightfully)the primary reported reason for premature tire failure -
underinflation". If we are talking about the GMC motorhome that are other
factors that may be just as prevalent. How many GMC coaches have toads
attached to the rear? Every time you stop that several thousand pounds is
transferred to the mid axel (it carries more of the braking in the rear) and
thus overloads the mid axel tires. Furthermore in the Cinnabar study on the
causes of tire failure, overloading of the coach was found in as many cases
as under inflation of the tires. Just some more food for thought. We are
asking the GMC motorhome to do things it was not designed to do.

>>Henry...
>>
>>>Looking at the data that Roger has collected I don't see any statistical
>>>difference between mid and rear axles. So, I don't see the causative
>>>implications that you ascribe to the wheel/tire action.
>>
>>I'm happy to hear from you, but I'm a little surprised to see you drawing
>>conclusions before we have a valid sample...
>Here's what I said:
>"Looking at the data that Roger has collected I don't see any statistical
>difference between mid and rear axles. So, I don't see the causative
>implications that you ascribe to the wheel/tire action.
>The information that was collected is interesting, but ignores (rightfully)
>the primary reported reason for premature tire failure - underinflation.
>Also, we don't know the mileage of the tires etc. As a result, we can't
>draw any meaningful conclusions about the failures other than to observe an
>apparrant increasing failure rate as tires age."
>
>In other words we have anecdotal information (which may be valuable) but
>nothing that we can draw conclusions from.
>
>Actually we'll never have a statistically valid sample. To get a sample to
>my satisfation we'd need to have 144 tires of the same manufacturer run
>under the same conditions - and to complete failure. That would give us the
>FITs as well as the intricnisc failure mechanisms under the test
>conditions. The results would only have a 95% confidence, but that's good
>enough for me. I guess we could create a design of experiements that would
>give life curves of inflation vs weight limits etc and only use a few
>hundred tires.
>
>>What I said was the mid axle was
>>suspect. I also said we can't draw any conclusions at this point. You
>>seem to
>>be drawing a conclusion that there is no difference... Are you
>>saying the same thing as Emery? (it's just the weight causing the rolling
>>flexing/heating, so forget it?)
>
>Nope, I'm saying that the two tires see pretty nearly the same loads. And
>on any road I know, they see exactly the same loads assuming shocks are the
>same and the pins are in good shape.
>
>If I were to guess about the predominant GMC MH tire failure mechanism, I'd
>say that underinflation combined with poor alignment make up the root
>causes. My reasons for saying this are based heavily on the published
>information from the tire manufacturers and my conversations with
>Goodyear's Chief Engineer. They do all of the tests to determine failure
>mechanisms. Their results all point to inflation pressure as the first
>order variable.
>
>I discard ALL tires reports based on LRD tires since GM says they're
>unacceptable and do NOT meet the GMC requirements.
>
>On my coach the difference between 65 PSI and 80 PSI is nearly 1 MPG.
>That's over 15% difference between mileage at the two pressures. [I know
>the 65PSI numbers because the shop reduced my TP without telling me and I
>drove 1200 miles at the lower pressure] The gas difference goes into heat
>in the tires. I can't measure the difference in mileage that I get running
>on a bumpy road or smooth road - the variance is within what I see as
>normal gas milage. Since the road type translates into less than 2%
>difference in mileage, I know that tire pressure is more important to fuel
>economy by a factor of at least 5 than road bumps. [I drove many of the
>same roads before and after repaving - big holes to no holes].
>
>Other than inflation pressure, alignment is the other big known factor in
>heat build up. Perhaps there's atendancy for folks to hit things only with
>the mid axle and knock out the alignment. I guess we could survey the GMC
>shops and see what they say.
>
>Henry
>
>Henry Davis Consulting, Inc / new product consulting
>PO Box 1270 / product readiness reviews
>Soquel, Ca 95073 / IP reviews
>ph: (831) 462-5199 / full service marketing
>fax: (831) 462-5198
>http://www.henry-davis.com/ http://www.henry-davis.com
>
>

 

[john dolan]

Thanks Tom...

>>>>>>>>>>>>>>>>>
John I honestly do not know what you are arguing for or against. The
numbers of failures as reported for different tire locations is at best
close to voodoo and certainly worthless as any kind of statistical data
if we are trying to draw any kind of conclusions.
>>>>>>>>>>>>>>>>>

I agree... voodoo doodoo I just wasn't ready to stop talking about it yet!

And some interesting stuff did fall out of it over the last few hours.

Regards... John 74 Glacier (now Custom) near Washington, DC

 

[dave lowry]

OK Gary Z.,

I went to www.dunlop.com and I couldn't find a damned thing about
tires. I'll admit I haven't graduated from Arch's WEB101 course yet, but
how do I get to the good stuff?

TIA

Dave (& Dege), '76 Royale, Santa Barbara, CA

 

[john dolan]

Click on this for tire info...

http://www.dunloptire.com/

The place you went is a cybersquatter that if Dunlop really wanted it, they
could have it, but they probably don't care.

>I went to www.dunlop.com and I couldn't find a damned thing about
>tires.

Regards... John 74 Glacier (now Custom) near Washington, DC