700/23 vs 700/25 tires ?

On Thu, 29 Jan 2009 17:17:50 -0800 (PST), Chalo
wrote:

And more to the point, do people trying to go fast care about a little
extra shock absorbtion?

Why wouldn't they? Every watt of muscle power they spend absorbing
bumps is a watt that doesn't make them go any faster.

http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm
http://davesbikeblog.squarespace.com...ge/Speed04.jpg
http://www.fredrompelberg.com/upload...cord_fiets.JPG

Interesting. And all the bike racers who do well around the world on
fairly narrow tires are choosing the wrong equipment I suppose?

On Thu, 29 Jan 2009 13:31:29 -0700, wrote:

At 20 mph, a rider hits a chunk of gravel (oops!) with an impact of
20^2 whomps, or 400 whomps.

At 25 mph, the same rider hits the same chunk of gravel at 25^2
whomps, or 625 whomps.

At 30 mph, he hits it at 30^2 whomps, or 900 whomps, more than twice
as hard.

Interesting. I would have thought there woudl be some vertical
componenent in many pinch flats regardless of speed, but then I don't
know much about physics and you clearly do.

On Jan 29, 6:17*pm, Chalo wrote:
John Forrest Tomlinson wrote:

Chalo wrote:

The faster you ride, the more you need in terms of rim protection,
shock absorption, wear resistance, pinch flat resistance, and
traction. *So the faster you go, the more you can benefit from a wider
tire.

I can see that for traction, though very few people go near the limits
of traction on moderatley narrow tires.

But why dod you need more for rim protection when going fast? *Or
shock absorbtion? *Or wear resistance?

Because the energy contained in bumps goes up as the square of the
speed. *It's four times easier to pinch flat or flat spot a rim at
30mph than at 15mph.

How do you know that likelihood of pinch flatting
goes up as the kinetic energy?

I'm not trying to get involved in flaming over tires.
You and JFT have opinions and are entitled to them.
But it drives me a little nuts when people on RBT
assert that something scales as such-and-such
without proof. In this case, it seems at least possible
to me that likelihood of pinch-flatting goes as the
momentum, linearly with velocity.

I have not worked it out in detail, but it seems plausible
that the compression of a tire hitting a bump or
edge is linear with the momentum and inversely
proportional to the tire pressure (and of course
the tire has to compress by roughly one diameter
to pinch flat, so larger tires resist better).

Ben

On Fri, 30 Jan 2009 01:37:27 GMT, John Forrest Tomlinson
wrote:

On Thu, 29 Jan 2009 13:31:29 -0700, wrote:

At 20 mph, a rider hits a chunk of gravel (oops!) with an impact of
20^2 whomps, or 400 whomps.

At 25 mph, the same rider hits the same chunk of gravel at 25^2
whomps, or 625 whomps.

At 30 mph, he hits it at 30^2 whomps, or 900 whomps, more than twice
as hard.

Interesting. I would have thought there woudl be some vertical
component in many pinch flats regardless of speed, but then I don't
know much about physics and you clearly do.

Dear John,

It's a tricky situation to model.

There's always a vertical component.

The simplest example is something that sticks up vertically, like a
chunk of gravel, a stone, the lip of a nasty crack, a jutting
cobble-stone, a small branch, or a piece of automotive debris. The
faster you go, the harder you hit these things, the more likely you
are to pinch-flat or damage a rim.

The opposite example is a hole of some kind--a wide crack or a
pothole. They provide the kind of vertical component and complication
that you may be thinking of, namely how far the wheel drops down.

At a really slow speed with a big enough hole, the wheel just rolls
down one side, across the bottom, and up the other side, without much
trouble.

At a faster speed with a wide enough hole, you start to fly off the
near edge of the hole and land on the bottom. There's more impact
here, but a smooth landing isn't likely to damage things.

Go a little faster into a narrower hole, and you fly off the edge,
drop toward the bottom, and slam into the base of the far side of the
hole as if it's a wall--ouch! Damage is much more likely.

At higher speeds, the good thing is that you don't drop as far down
into the hole, so you hit higher up on the far side, effectively
reducing the height of the obstacle and making things more gentle.

The bad thing is that you're hitting higher up, but much harder--the
higher speed that reduced how far you dropped raises the impact with
the square of the velocity. Ouch!

Every year, the cobblestones of Paris-Roubaix illustrate the problem.
The riders go like crazy over badly-mismatched chunks of stone and
pretty much expect to pinch-flat and crash.

Sometimes they talk about getting up enough speed to smooth things out
on certain stretches. If you go fast enough, you may skim over the
nasty cracks and avoid pinch flats.

Unfortunately, you also lose some control when the tire is in the air.
With dozens of cobblestones coming the riders at 30 to 40 feet per
second, crashes are routine in Paris-Roubaix, even for riders who can
do the whole Tour de France without any road rash.

One reason those pros like tubulars is that the rounded rim of a
tubular reduces the chance of a pinch flat, compared to the flange
sticking up on a clincher.

Pros have to worry more about pinch flats because they go faster and
thus hit things harder than slower ordinary riders.

Pros also can expect more pinch flats because they have less time to
react and avoid hitting things. Road hazards come at them faster, and
only the lead rider has a clear view of what's coming up. Anyone
drafting has to hope that the lead rider picks a smooth path--and pay
constant attention to the wheel a foot or so in front of him.

And pros naturally want the narrowest tires and thinnest tread and
tubes, which make pinch flats more likely. Road racing produces more
failures because the riders are going faster and insisting on lighter
components.

Of course, pros probably avoid many pinch flats that would victimize
ordinary riders because pros usually have better reflexes, pay more
attention, and have more experience. The rider who puts in 20,000
miles a year at high speeds next to other racers is probably better at
handling potholes than the guy who commutes 5,000 miles a year at
lower speeds, often daydreaming.

The other thing that helps the pro peloton avoid pinch flats is that
they usually race on good roads and can use the whole width of the
road, which is even swept nowadays for some events like the Tour de
France.

Cheers,

Carl Fogel

John Forrest Tomlinson wrote:

Chalo wrote:

JFT wrote:

And more to the point, do people trying to go fast care about a little
extra shock absorbtion?

Why wouldn't they? *Every watt of muscle power they spend absorbing
bumps is a watt that doesn't make them go any faster.

http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm
http://davesbikeblog.squarespace.com...ge/Speed04.jpg
http://www.fredrompelberg.com/upload...cord_fiets.JPG

Interesting. *And all the bike racers who do well around the world on
fairly narrow tires are choosing the wrong equipment I suppose?

How would one know whether they were using the optimum size? When was
the last time a pro road racer used 700x28s other than on
cobblestones?

Major Taylor used roughly 1.5" (38mm) tires. and he was racing on
highly groomed 'dromes and board tracks. I reckon he wanted to win
races too.

John Forrest Tomlinson wrote:

Chalo wrote:

JFT wrote:

But why dod you need more for rim protection when going fast? *Or
shock absorbtion? *Or wear resistance?

Because the energy contained in bumps goes up as the square of the
speed. *It's four times easier to pinch flat or flat spot a rim at
30mph than at 15mph.

Bumps have only a horizontal component? Interesting.

Do you think the speed of travel has nothing to do with the vertical
rate of acceleration of a bump?

John Forrest Tomlinson wrote:

Chalo wrote:

JFT wrote:

And Chalo - I have a couple friends who weigh 100-105 lbs. *In your
scheme of things, are they allowed to ride 23s or woudl you tell them
they'd be better off riding 25s or larger? *Not knowing them or their
riding goals.

If they ride on the streets I ride on, the smallest I could recommend
is 28mm. *That's what my wife uses, and she rides about as slowly and
sedately as any able-bodied person could.

OK I have to say it - you're a dogmatic idiot on tire size. To make
such a suggestion based on your wife, w/o knowing them. *The correct
answer to my question is some other questions: "What kind of riding
are they doing? On what roads? *What are their goals." Not some huge
boy dogma.

Why TF should people who weigh 100 pounds and compete in some of the
toughest bike races in the US use 28s? It's absurd. *It's saying "I
want to do worse than I can."

Why should they opt into a more punishing ride, sapping more of their
strength and inducing more fatigue than necessary, just to reap a few
grams of weight reduction? A larger tire provides a measure of
suspension that as any motorcyclist will attest is essential for going
fast.

Chalo

On Thu, 29 Jan 2009 22:48:29 -0800 (PST), Chalo
wrote:

John Forrest Tomlinson wrote:

Chalo wrote:

JFT wrote:

And more to the point, do people trying to go fast care about a little
extra shock absorbtion?

Why wouldn't they? *Every watt of muscle power they spend absorbing
bumps is a watt that doesn't make them go any faster.

http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm
http://davesbikeblog.squarespace.com...ge/Speed04.jpg
http://www.fredrompelberg.com/upload...cord_fiets.JPG

Interesting. *And all the bike racers who do well around the world on
fairly narrow tires are choosing the wrong equipment I suppose?

How would one know whether they were using the optimum size? When was
the last time a pro road racer used 700x28s other than on
cobblestones?

Major Taylor used roughly 1.5" (38mm) tires. and he was racing on
highly groomed 'dromes and board tracks. I reckon he wanted to win
races too.

Dear Chalo,

Unfortunately, citing racers' equipment is a double-edged sword.

All too often, we have no real evidence whether they won because or in
spite of their equipment.

Here's a nice 1898 photo of Major Taylor, a fearsome racer in events
around the world at the turn of the century, showing what would be
considered ridiculous balloon tires:
http://www.ltolman.org/chainless-b2.jpg

Racing tires of that era tended toward the notion that if a little is
good, a lot is better. The pneumatic tire had been invented only ten
years earlier, in 1889, and replaced the solid and hollow-cushion
tires in a year or so, partly because of the comfort and partly
because of Dunlop's original reason for trying inflation--they roll a
hell of a lot faster than solid tires.

But if you look at that photo again, you'll see that Major Taylor was
riding on a Sager roller-pin chainless shaft-drive bicycle, which has
a lower transmission efficiency than a chain. Taylor won races, as far
as anyone can tell, in spite of the handicap of a shaft drive.

Here's another photo of Taylor:
http://www.virginmedia.com/digital/g...kes.php?ssid=2

Don't worry about the tire size, which is hard to make out. Look at
the frame. That's a quad-stay Eagle design, with two chainstays.
Here's a page with lots of photos of a quad stay:
http://www.theracingbicycle.com/Eagle.html
http://www.theracingbicycle.com/imag...Quad_stays.jpg

Whatever slight stiffness might have been gained was probably more
than offset by the extra weight.

And here's Taylor with an even stranger bit of equipment, during his
triumphant tour down under:
http://i23.tinypic.com/jqqhcx.jpg

It's hard to see how that projecting front gear could do anything
except increase transmission losses and add weight.

Like many racers, Taylor was perfectly willing to try odd equipment,
partly in hopes of finding something that worked better and partly in
certainty that a sponsor would pay him.

Over the years, shaft drive was dropped for racing, extra chainstays
vanished, oddball projecting gears never appeared north of the
equator, and racing bicycle tires got narrower and narrower

Things are often more complicated than they seem. The wider, cushier
tire sounds like a good idea that would lose less power through better
suspension and lower rolling resistance. But the extra wind drag of
the wider tires (and frames) seems to outweigh such gains in
high-level racing.

Here's Sam Whittingham talking about the complications of the tires
used on the Varna Diablo:

"In 1998, in Montreal at the PMG test track we had the luxury of
testing many things over the few weeks we were there including
different tire configurations. John Tetz showed us how to do some low
speed roll down tests that transferred quite well to the higher speeds
(60mph)."

"At that time we found the best rolling tire to be a continental tempo
track tubular at 175psi ($100) we still use this on the back of
Diablo. Last year when I went 81mph we tried some Vittoria track
tubulars ($125) because they pumped up to 240psi. We gave up on them
because they were as much as 1/4 inch out of round!"

"The tire that performed almost as well and has been my front tire for
7 years is a panaracer technova clincher at 135psi ($11.99) very
cheap! This is also one of the roundest tires I have ever found.
Obviously cost has nothing to do with performance!"

"We also tested the tufo tires. They seemed like the perfect solution.
They could take ridiculous amounts of pressure. Because they are
rolled in there construction rather than sewed they are the most round
and uniform tire I've ever seen. They also have sturdy side walls and
are reasonably inexpensive. Seems perfect right? One big flaw, slow as
molasses. I was as much as 4 mph slower on these tires even at
200psi."

"I spent a few days trying to top 96km/h in Montreal. I switched to
the panaracers and immediately went 101km/h several times. This was
shown in our rolldown test as well when I rolled nearly 50% further on
the cheap panaracers. Even on my road racing bike I could feel that
the tufo's were sluggish."

"I soon realized that you could easily guess a tire's rolling
resistance by the suppleness of the sidewall. The lighter and more
flexible the faster it rolls. Problem is, it doesn't give you much
room for scrubbing the fairing. So to go fast you need a tire with an
inherently fragile sidewall and pray you don't knick it. Hence, my
80mph blow-out It was one of my beloved panaracers that gave out on
me. Several factors caused this:"

"First: the tire was old. We also found older tires roll better.
probably because the sidewalls have broken down a little. We had
checked it before every run and it was still good but not great. I
could see some threads starting to fray, but nothing I considered
dangerous."

"Second: The pressure on the side said 125psi we were running them at
175psi. We had tested several the panaracers at over 200psi for
several days with no bulging or any deterioration. We ran at 175psi
all week and the tires were fine after every run. Slightly larger but
still round."

http://www.recumbent-bikes-truth-for...ober-2003.html

I think that the 24" Panaracer Tecnova was 25 mm or even wider.

Cheers,

Carl Fogel

On Thu, 29 Jan 2009 21:36:31 -0700, wrote:

It's a tricky situation to model.

There's always a vertical component.

Dear Carl,

I was surpised that someone as good as physics left it out earlier but
I assume you did that to simplify the subject for simple people like
me.

Thank you.

On Thu, 29 Jan 2009 21:36:31 -0700, wrote:

The other thing that helps the pro peloton avoid pinch flats is that
they usually race on good roads and can use the whole width of the
road, which is even swept nowadays for some events like the Tour de
France.

Dear Carl.

You again demonstrate a lack of knowledge of bike racing.

Cheers,