Tim McNamara wrote:
In article . com,
"41" wrote:
wrote:
On Mar 23, 4:30 pm, "41" wrote:
There should be very little discrepancy in suspension losses
between different tire models of qualitatively similar design at
the same width and the same pressure, since it is the air volume
inside them that does the bulk of the bouncing and the shock
absorbing.
I think the above is indeed the core issue, but I'm unconvinced
that the variables are well understood. Do we really understand
the r oles that the casing and tread play?
Sure. Deflate the tire, and press or rap it in and out. How much
shock does it absorb, compared to when inflated?
That's only one parameter of the effects of the casing and the tread, of
course. The classic issue in rolling resistance is hysteresis- which
did seem to be the major- although certainly not only- factor in the
ordinal rankings of the tires in the original BQ test.
I took the question to mean, do we really understand the roles that
casing and tread play in shock absorption. ?
Thus the road surface was smooth enough that suspension losses
are doubtful as the explanation for whatever minor disc repancies
from the drum tests might have been observed.
I'm not sure I fo llow how you've arrived at the above conclusion,
whether or not it's correct.
I mean, they found inflation pressure to not affect the results.
That's an incorrect representation of the findings.
Yes, that's true. JH said
#higher tire pressure
#did results in slightly faster run times. But the differences were
too
#small to be statistically significant, much smaller than the drum
tests
#predict. The regression analysis looked at all the factors that
could
#explain a tire's speed, and tire pressure was not one of them
I note that in my original post I didn't abbreviate:
-It was claimed that the pressure results of the BQ tests, which
showed that at higher pressures, not much difference in rolling
resistance results from raising the pressure further, were
inconsistent with the IRC drum tests. But that is not correct:
Seņor Fogel already posted the results below, using the rolling
resistance figures from those IRC tests:
There would be no "suspension losses" in steel drum RR tests, as the
drums are smooth and concentric.
Exactly. Thus the effects of rolling resistance and suspension losses
can be disentangled.
In addition to inflation pressure, one
would expect the stiffness of the casing and tread to be a factor in the
ability of the tire to absorb bumps.
That gets back to the first question above. I suggest that, certainly
for good tires, those factors are very minor compared to the pneumatic
effect of the air. I suggest one can discern this by deflating the
tire fully, giving it a rap, and comparing the effect to that when
done with the tire inflated.
Another way to look at it is: if they really were significant factors,
then we would have smoother rides with stiffer, thicker, highly
hysteretic tires. The Specialized Armadillo, chock full of extruded
Kevlar, would give a buttery ride, instead of the wooden one that is
more often reported. That is to say, everybody says the ride is best
when the casing and tread are so silken as to effectively disappear.
So, it really is the pneumatic effect (spread impulse out over time,
don't suck it into the tire) that takes the edge off the bumps, not
the hysteresis.