Wheel/Rim Creaking

On Thu, 20 Jan 2005 19:40:45 GMT, Joe Riel
wrote:

writes:

Any idea what "some problem" might be?

Is petroleum supposed to cause butyl inner tubes to
dissolve, grow brittle, ignite in spontaneous combustion,
discolor, shrink, expand, smell terrible, foul Presta
valves, crack at their seams, glue themselves to the tire
casing, cause valve stems to fall out, or what?

It appears to affect the tensile strength. A relevant document is
ASTM D 471 "STANDARD TEST METHOD FOR RUBBER PROPERTY-EFFECT OF LIQUIDS"
I can purchase it for $39, however, I suspect that the local university
has a copy. Can anyone out there summarizee the relevant sections?

From another document (EM 1110-1-4008) I found the following info:

In addition, standards for resistance to oil and gasoline exposure
have been developed by the Rubber Manufacturer's Association
(RMA). These standards are related to the effects of oil or gasoline
exposure for 70 hours at 100C (ASTM D 471) on the physical/mechanical
properties of the material. Table 6-4 summarizes the requirements of
the RMA oil and gasoline resistance classes.


Table 6-4
RMA Oil and Gasoline Resistance Classifications
RMA Designation Tensile Strength Retained
Class A (High oil resistance) 80%
Class B (Medium-High oil resistance) 50%
Class C (Medium oil resistance) 40%
Source: RMA, "The 1996 Hose Handbook," IP-2, p.52


Note that Isobutylene Isoprene, which is, I believe, the rubber used
in inner tubes, is classified as having poor oil resistance.
Presumably, then, its tensile strength is reduced by more than 60%;
how much more I have no idea.


Joe

Dear Joe,

So oil reduces the tensile strength of inner tube.

Hmmm . . .

But how much does tensile strength matter in an inner tube,
which is expands only slightly before being flattened
against the inside of the rim and tire?

That is, the inner tube isn't under much tension, just a
slight expansion before it suffers much higher compression
against the inside of the tire and rim.

This paradox might explain why some people are saying that
there's no problem, while others are saying that oil is bad
for butyl rubber.

Thanks for finding what actually happens.

Carl Fogel

writes:

So oil reduces the tensile strength of inner tube.

Hmmm . . .

But how much does tensile strength matter in an inner tube,
which is expands only slightly before being flattened
against the inside of the rim and tire?

That is, the inner tube isn't under much tension, just a
slight expansion before it suffers much higher compression
against the inside of the tire and rim.

So, how much smaller should the small diameter of a tube be, compared
to the inner diameter of a tire, so that, when fully inflated, the
hoop stress in the tube is zero? You have 10 minutes...


Joe

Joe Riel wrote:

writes:


Any idea what "some problem" might be?

Is petroleum supposed to cause butyl inner tubes to
dissolve, grow brittle, ignite in spontaneous combustion,
discolor, shrink, expand, smell terrible, foul Presta
valves, crack at their seams, glue themselves to the tire
casing, cause valve stems to fall out, or what?


It appears to affect the tensile strength. A relevant document is
ASTM D 471 "STANDARD TEST METHOD FOR RUBBER PROPERTY-EFFECT OF LIQUIDS"
I can purchase it for $39, however, I suspect that the local university
has a copy. Can anyone out there summarizee the relevant sections?...

If this standard is written like other ASTM standards, it will tell you
how to run the test, but will not provide any information about typical
results.

--
Tom Sherman - Near Rock Island

Tom Sherman writes:

Joe Riel wrote:

writes:

Any idea what "some problem" might be?

Is petroleum supposed to cause butyl inner tubes to
dissolve, grow brittle, ignite in spontaneous combustion,
discolor, shrink, expand, smell terrible, foul Presta
valves, crack at their seams, glue themselves to the tire
casing, cause valve stems to fall out, or what?
It appears to affect the tensile strength. A relevant document is
ASTM D 471 "STANDARD TEST METHOD FOR RUBBER PROPERTY-EFFECT OF LIQUIDS"
I can purchase it for $39, however, I suspect that the local university
has a copy. Can anyone out there summarizee the relevant sections?...

If this standard is written like other ASTM standards, it will tell
you how to run the test, but will not provide any information about
typical results.

Agreed. Possibly useful is ASTM D2000, which classifies rubbers (I
believe), however, my guess is that, because butyl rubber is not
recommended for use in an oil environment, it doesn't specify any
quantative values (i.e. % tensile strength retained) for it.


Joe

Joe Riel writes:

So, how much smaller should the small diameter of a tube be, compared
to the inner diameter of a tire, so that, when fully inflated, the
hoop stress in the tube is zero? You have 10 minutes...

Pencils down.

Assume the major diameter of the tube matches that of the tire.
Rubber is essentially incompressible, so the flattening due to
compression must match the minor diameter increase to achieve a zero
hoop stress. The elasticity of butyl rubber is about 600psi (4.5MPa).
A tire pumped to 105 psig has an absolute pressure of 105psi + 15psi =
120psi. So the rubber compression is 120/600 = 20%. The initial
diameter of the inner tube should be 20% less than the inner diameter
of the tire, assuming the final cross sectional shape is circular,
only a fair approximation for a clincher, but pretty good for a
tubular.


Joe