Re: Bicycle Quarterly Rolling Resistance Tests: No Surprises

Quoted message said:

41 said:

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?

Quoted message said:

Quoted message said:

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. If
suspension losses were really important, pressure surely would have
had an effect. Remember that the theoretical calculation, which does
not include suspension losses, shows hardly any effect as well, so
it's not a matter of compensation hiding an effect.

Quoted message said:

Quoted message said:

Perhaps a better one is the following:

There was at least one more factor not controlled for in the BQ tests.
Changing the diameter of the tire or the press ure changes the
("pneumatic"😉 trail, which, regardless of whether the bicycle had a
lot of trail to begin with, changes the handling characteristics

Agreed that this could be a significant issue.

Chriss

In article <[email hidden]>,

41 said:

Quoted message said:

41 said:

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.

Quoted message said:

Quoted message said:

Quoted message said:

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. What they found was
that inflation pressure did not affect rolling resistance as much as
tire construction (casing type, rubber thickness, tread design). They
did not find that inflation did not affect the results.

Quoted message said:

If suspension losses were really important, pressure surely would
have had an effect. Remember that the theoretical calculation, which
does not include suspension losses, shows hardly any effect as well,
so it's not a matter of compensation hiding an effect.

There would be no "suspension losses" in steel drum RR tests, as the
drums are smooth and concentric. 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.

Ca. 1934 Reyhand (Vol. 5, No. 1) in BQ's image archives has a
different spoke arrangement

the idea that increased inflation doesn't lower rolling resistance is
n utty?

width is related to load and surface, does't exist as an isolated
quantity?

why would an all kevlar carcass suck energy?

Quoted message said:

the idea that increased inflation doesn't lower rolling resistance is
n utty?

It does lower it, but after and up to a certain point, not by much.

Quoted message said:

width is related to load and surface, does't exist as an isolated
quantity?

That's width of the contact patch: pressure, surface, load,
deformability of the tire. The width referred to is instead just the
tire size width. One inflates the tire based on that size, and the
other major factors are roughly constants in the tests.

Quoted message said:

why would an all kevlar carcass suck energy?

Kevlar is a highly hysteretic material, to answer your question by
restating it. Seriously, check out a Specialized Armadillo, chock full
of Kevlar. It's stiff and inelastic, i.e. an energy sucker.

'That is to say, everybody says ...'

well, everyone else sez those guys tires are too narrow and a nice
round tire with grippy rubber are more fun

but a 'buttery ride'? yawl hanging around with loose women?

one can discern this, maybe but sometimes maybe not

anyway, testers gonna discuss spec armadillos gonna lose all
credibility

"It's stiff and inelastic, i.e. an energy sucker."
metal tires/wheels are energy suckers because metal wheels are
inelastic?
elastic tires are not energy suckers?

the entire (sorry) thrust (eeek) from the tyre industry since 1955
sumpthin is eliminating dragging the tyre's load induced elastic
bottom bulge from Monte Carlo to Paris.

Tim McNamara said:

I suspect ...

yeah but the idea was to stiffen the bottom bulge reducing bulge
friction induced by load then flex the sidewalls with the reduction of
friction from the stiffer contact area bottom. sensitive sidewalls
joined with stiff bottoms produce fast moments.
you get sensitive sdiewalls in part by reducing air pressure.
the beef with the conti TT seemed to be the TT had weak sidewalls with
low recommended pressure producing quick light touring tires-cafe-but
not haul beans down the road touring tires or sidewalls that could
take touring abuse with the recommended pressures. variable to needed
spec or cheating? positions varied...

i bring that forward as what i understand is a valid primitve and
probabbbly obsolete understanding of auto tires but how do or do not
cycle tires differ from auto tire design?

Quoted message said:

"It's stiff and inelastic, i.e. an energy sucker."
metal tires/wheels are energy suckers because metal wheels are
inelastic?

Metal is elastic, that's why springs are made of it and why a bell or
a tuning fork resonates for a long time after you ring it. However,
the spring constant is very high. Stiff and inelastic together means
an energy sucker: everything does have to deform when squeezed, but if
it is stiff it will take a lot of force to do that appreciably and if
it is inelastic you won't recover the energy.

Quoted message said:

elastic tires are not energy suckers?

Pretty much.