Zipp marketing...

Boyle M. Owl said:

Yes, I know, marketing is knowing how to make [censored] sound good,
but...

"All Zipp clincher rims are designed to work their best below 125 psi
tire pressure. Pressures above 125 psi (8.5 bars) can actually
increase rolling resistance."

_Increase_ rolling resistance? Uh, okay?

They're not saying that their clincher rims are weak, are they? No,
not at all.

"Finally, our bearings are smoother because they simply are rounder
than anything else that is currently available. The industry
standard allows for balls that are round to within 50/1000th of an
inch (which we think is laughable). Even "benchmark" hubs have
bearings that are round to only 25/1000th of an inch. We knew that
there was still room for improvement which is why our ball bearings
only vary 10/1000th of in inch in roundness. You certainly can't see
the difference, but you will defiantly feel it."

Did they /really/ write "defiantly", or is that your Freudian typo?

"Boyle M. Owl" <[email hidden]> wrote in news:9flfe.2619$Ay3.1046
@lakeread06:

Quoted message said:

"All Zipp clincher rims are designed to work their best below 125 psi
tire pressure. Pressures above 125 psi (8.5 bars) can actually increase
rolling resistance."

_Increase_ rolling resistance? Uh, okay?

Interesting. It's plausible that the marketing hacks of a ^tire^ company
might say that, but coming from a ^rim^ manufacturer? That's odd.

Or maybe the rolling resistance thing is a smokescreen to obscure what they
don't want to admit? As in maybe they are worried their rims might fail at
125 psi or higher?

Boyle M. Owl said:

Yes, I know, marketing is knowing how to make [censored] sound good,

but...

Quoted message said:

"All Zipp clincher rims are designed to work their best below 125 psi

Quoted message said:

tire pressure. Pressures above 125 psi (8.5 bars) can actually

increase

Quoted message said:

rolling resistance."

_Increase_ rolling resistance? Uh, okay?

This makes sense to me.

On any road that's not perfectly smooth, the surface will cause the
bike to vibrate. Vibration takes energy to happen, and that energy
needs to come from somewhere. That energy is taken from the rider &
bike's forward momentum. Thus, a rougher surface will require more
energy to traverse. This is what happens when you transition from
smooth pavement to rough chipseal- you'll slow down or start pedaling
harder (using more energy) to maintain your speed.

A pneumatic tire's purpose (among others) is to provide cushioning
between the rider/bike's mass and the road surface. At low pressure,
the tire's structure is flexing and twisting, dissipating energy as
heat (feel a car tire right after it's stopped- it'll be warm). At
normal pressure, the tire should not flex excessively, but it should
absorb the irregulaties of the road surface without passing them on to
the bike & rider. At high pressure, the tire becomes rigid and unable
to absorb these irregularities, passing the vibration on to the bike &
rider. Inflating tires to very high pressures has the same effect as
riding on chipseal: more energy is consumed vibrating the rider & bike,
thus slowing them down.

If extremely rigid tires were beneficial, we'd all be riding around on
non-pneumatic urethane tires or tubes. AFAIK, every attempt at
producing a non-pneumatic tire has been met with similar reviews:
harsh-riding and slow.

Example: Back in the late '70's, in the halcyon days of human-powered
vehicle competitions, one or two vehicles featured disc wheels that
used inside-out "V" belts as tires. Non-pneumatic, extremely narrow,
extremely rigid. Steve Ball's "Dragonfly" topped out at 49 mph one
year. The next year, with no other changes except a switch to
conventional tubular tires, he reached 52 mph- an enormous step,
considering that at those speeds the majority of drag is air
resistance, not rolling resistance.

I suspect, though, that Zipp's statement is a CYA on their part.
Extremely high pressures might fatigue the bond between the aluminum
rim and the carbon structure, and possibly the carbon itself.

Jeff

Boyle M. Owl said:

Yes, I know, marketing is knowing how to make [censored] sound good, but...

"All Zipp clincher rims are designed to work their best below 125 psi
tire pressure. Pressures above 125 psi (8.5 bars) can actually increase
rolling resistance."

_Increase_ rolling resistance? Uh, okay?

[snip]

Dear Owl,

Theory predicits and tests show that rolling resistance can
increase with higher pressures:

" . . . yes, there are lots of test numbers to back it up.
It is the same reason a suspension bike (or car) is faster
over rough ground - less mass must be accelerated when bumps
are encountered, thus saving energy and reducing momentum
loss. Every little bump that gets absorbed into your tire
(another reason that supple, handmade casings roll faster
than stiffer, low-thread-count casings) is a bump that does
not lift the entire weight of you and the bike.

You feel fast on a rock-hard tire for a similar reason that
people like the feel of stiff brakes (V-brakes with the
levers set on low leverage). The brake feels good and stiff
because you are doing more of the work. If you increase the
leverage, the brake feels spongy, because the extra
mechanical advantage allows a modest pull to squish the
pads.

When you ride a tire at 170psi, the bike feels really lively
and fast. That is because you are being bounced all over the
place by the surface roughness of the road. However, every
time you are bounced, energy you applied to the pedals to
get you up to speed is lost. Also, you have less control of
the bike, so it feels like it is going faster, even though
it isn't. Ever notice how driving down the highway at 75mph
in an old Jeep feels crazy fast, and you can cruise smoothly
along at 100mph in a nice Saab or BMW and feel like you are
going maybe 60mph unless you are looking at stationary
objects passing by?

There is simply no question about it; rolling resistance
tests conducted with bicycle tires rolling over surfaces
akin to normal road surfaces always indicate the lowest
rolling resistance at pressures a lot closer to 100psi than
to 170psi! Years ago, for example, I saw results like this
at the Continental tire factory. I was told of similar
results at a number of other tire factories I have visited.

--Lennard Zinn

http://www.ottawabicycleclub.ca/phpBB2/viewtopic.php?t=137&

Carl Fogel

Bill Sornson said:

Quoted message said:

only vary 10/1000th of in inch in roundness. You certainly can't see
the difference, but you will defiantly feel it."

Did they /really/ write "defiantly", or is that your Freudian typo?

HAHA

No, man, I just cut and pasted. It's there on the page.

--
BMO

Quoted message said:

There is simply no question about it; rolling resistance
tests conducted with bicycle tires rolling over surfaces
akin to normal road surfaces always indicate the lowest
rolling resistance at pressures a lot closer to 100psi than
to 170psi! Years ago, for example, I saw results like this
at the Continental tire factory. I was told of similar
results at a number of other tire factories I have visited.

--Lennard Zinn

http://www.ottawabicycleclub.ca/phpBB2/viewtopic.php?t=137&

Carl Fogel

Well, Zinn outvotes me. (I've got one of his books) I find it curious
though that track riders pump up their tires well over 100psi if that's
the case.

I'm a big fat guy, and I find that the higher pressure definitely helps,
though. The ride I get now is similar to when I used to be a teenager
and much thinner riding on 80psi tires. No, I don't get bounced around
at 125-145psi.

--
BMO

Quoted message said:

There is simply no question about it; rolling resistance
tests conducted with bicycle tires rolling over surfaces
akin to normal road surfaces always indicate the lowest
rolling resistance at pressures a lot closer to 100psi than
to 170psi! Years ago, for example, I saw results like this
at the Continental tire factory. I was told of similar
results at a number of other tire factories I have visited.

--Lennard Zinn

http://www.ottawabicycleclub.ca/phpBB2/viewtopic.php?t=137&

Carl Fogel

Well, Zinn outvotes me. (I've got one of his books) I find it curious
though that track riders pump up their tires well over 100psi if that's
the case.

I'm a big fat guy, and I find that the higher pressure definitely helps,
though. The ride I get now is similar to when I used to be a teenager
and much thinner riding on 80psi tires. No, I don't get bounced around
at 125-145psi.

--
BMO

"Boyle M. Owl" wrote

Quoted message said:

carlfogel said:

There is simply no question about it; rolling resistance
tests conducted with bicycle tires rolling over surfaces
akin to normal road surfaces always indicate the lowest
rolling resistance at pressures a lot closer to 100psi than
to 170psi! Years ago, for example, I saw results like this
at the Continental tire factory. I was told of similar
results at a number of other tire factories I have visited.

--Lennard Zinn

Carl Fogel

Well, Zinn outvotes me. (I've got one of his books) I find it curious
though that track riders pump up their tires well over 100psi if that's
the case.

I'm a big fat guy, and I find that the higher pressure definitely helps,
though. The ride I get now is similar to when I used to be a teenager
and much thinner riding on 80psi tires. No, I don't get bounced around
at 125-145psi.

BMO

I think the fact that the rolling resistance of a wheel depends to a great
extent upon the road surface is often overlooked. If the surface is really
smooth, such as the rail of a high-speed railway, then tire flex is the
energy absorber. You probably would be better off without a pneumatic tire.
However, with a rough surface, a wheel with a tire that absorbs some of the
roughness is probably more efficient. But I don't know how to calculate the
trade-off.

As a thought experiment, assume you were to glue a pencil to the road every
couple of feet and then ride over them at speed. If the tire has no "give",
then every time you hit a pencil, the whole bicycle and part of the rider
gets lifted into the air. Which takes a lot of energy and slows you down.
But a big balloon tire will absorb the bump without slowing you down. Of
course, the constant flexing of the big balloon tire absorbs energy. What
works best on a smooth track may not work best on chip-seal.

My guess is that I would go a touch faster with less pressure in my tires.
Some day I might try it.

Quoted message said:

In any case, we do in fact get bounced around at 125-145
psi, just as we get bounced around at 80 psi. It's just that
we have to be rolling fairly fast to notice the difference
on an ordinary road, something that Zinn's comment assumes.

The difference would not be something a rider would be
likely to notice, any more than a rider would notice a
change of 1 mph at 20 mph without a speedometer or stop
watch.

If we rolled along like snails at only 5 mph on the ordinary
road surface, then the 170 psi tire would probably have less
rolling resistance than the 100 psi tire--the bouncing
effect that confuses things at speeds of interest to racers
would be greatly reduced.

In other words....

"Get a tire and pressure that you find comfortable for your style of riding"

I'm not going to be telling anyone what Kg value I punched into the
calculator.

I'm currently running 700x28 Conti Ultra Gator Skins at 125 PSI. They
seem to be quick enough. Why such a heavy tire? Well, they still
haven't swept the streets around here.

I also tend to agree with Jobst's assertion that a larger tire at the
same pressure distorts less.

--
BMO

Pan Fan wrote:

<Interesting. It's plausible that the marketing hacks of a ^tire^
company
might say that, but coming from a ^rim^ manufacturer? That's odd.

<Or maybe the rolling resistance thing is a smokescreen to obscure what
they
don't want to admit? As in maybe they are worried their rims might fail
at
125 psi or higher?>

That might be better PR than publishing a list of "prohibited" tires
like HED, if blow-offs is the problem they're actually trying to
address here. --TP