Nobody knows about RR

Benjamin Lewis wrote:

Depending on the smoothness of the road, you might actually be increasing
your rolling resistance by pumping that high.

Correct, and I'm sure on some roads that is the case. But typically the
roads here are pretty smooth and I'm sure on average the rolling
resistance is lower.

-as

Antti Salonen wrote:

Benjamin Lewis wrote:

Depending on the smoothness of the road, you might actually be
increasing your rolling resistance by pumping that high.

Correct, and I'm sure on some roads that is the case. But typically the
roads here are pretty smooth and I'm sure on average the rolling
resistance is lower.

It could well be. It's too bad there aren't more test results available for
this. For me, 7-7.5 bar feels pretty good, for bike+rider of about 80 kg.

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber

as a street rider never ridden a race bike - that chart tells me that a
racer can interpret it but that like it only raises more questions
without a solid foundation of race experience.
and surely conti isn't about to give its info away.

I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production.
Therefore I directed my question about rolling resistance to Continental
Tires
- and the production manager kindly sent me a reply that is surprisning as
well as interesing.

If you have access to a decent public library, you should be able to
locate many articles on testing rolling resistance. One in particular
deals with using coast-down tests to determine tire rolling resistance.
The article is "Tire Rolling Resistance Measurements From Coast-Down
Tests", SAE #760153. Yes, it is automotive related, but the procedure
should work fine. If you check SAE.org, there are many other papers on
this topic listed, such as "Determination of Vehicle Drag Contributions
From Coast-Down Tests", SAE #720099.

You'll probably find that air drag dominates tire rolling resistance at
higher speeds. But using coastdown tests, you should be able to figure
out if a 25mm tire has higher or lower rolling resistance than a 23mm
tire, assuming same rider, same bike, same environment (terrain, wind,
temp, etc.), recommended inflation pressures, and same type of tire.

My butt-gauge indicates that 25mm tires (Veloflex Roubaix - tubular)
grip better, and are more compliant than 23mm tires of the same
manufacturer. So, I believe I'm faster in turns, descents. I certainly
push harder. The tires are more compliant on rough surfaces, so it's
easier to go harder as the ride is smoother. They roll about the same.
The 25mm tire is somewhat harder to sprint or climb with since it is
heavier, and the diameter is slightly larger.

Regards,

Rob

On Wed, 15 Jun 2005 12:15:01 +0100, David Damerell wrote:

No, it's not. If you want to maximise speed, you should use in both tyres
the maximum pressure that does not cause the increase in RR we see with
track-style pressures (eg 170psi),

Um, what increase in RR is that?

produce an intolerably hard ride; that will be equal in both cases and
the 25mm tyre will have lower RR.

I don't think either of those conclusions are true. For one thing, a 25mm
tire may reach blow-off pressures before it is "intolerably hard", and at
that pressure I would assume the RR of the two sizes would be close to the
same.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems.
_`\(,_ | -- Paul Erdos
(_)/ (_) |

Thanks for a great variation of insights and interesting considerations.
But it still remains a mystery that there is no available messurements of
rolling resistance from 22 mm respectively 25 mm tires with their
recommended airpressure.

I do undertand that the answer to a simple question may be complicated
and will depend on numerous circumstances on the real road.
And I do understand that a reduced RR should be seen in relation to
higher wind drag and weight. And I do understand, that all these factors
have so little impact that it is tempting to end the discussion with the
conclusion: It don't mean ****.

But I am still curious and I still find the question relevant: In the
spring of 2003 the Belgian rider Van Petegem won the Tour of Flandern as
well as the Paris-Robaix on 25 mm Continental Competition tires. He must
have trusted, that those tires were faster than narrower ones. Did he
guess or did he know?
Whether you are racing to win or racing to make it through within the time
limit, you want the facts that will help you choose the right equipment.

The surprising conlusion, that the wider tire has lower rolling
resistance, is based on tests of tires of identical construction and
identical pressure. The explanation that is given is, that the two tires
have a contact area of exactly the same size, but the wider tire has a
shorter and wider one, which produces less RR than the narrower and longer
contact area.

If the result of that test is interesting, then it is even more
interesting to make a test of the same two tires with the recommended tire
pressure in each.

I think the Continental production manager was well aware, that I didn't
just want an advice on what tire to choose for my bike. I can´t think of
a reason not to give me an exact answer if he knew it. He would not
reveal production secrets by saying: �We have made the test, it shows that
the wider tire has a 10 pct. lower RR� – or the opposite. But that is at
matter of interpretation, I admit.

Ivar of Denmark

On Wed, 15 Jun 2005 11:19:17 -0700, Benjamin Lewis
wrote:

wrote:

http://w3.iac.net/~curta/bp/velocityN/velocity.html

Using the calculator above (the metric version offers
rolling resistance and frontal area), let's try a few values
and see what we get.

The default values predict a brisk 37.18 km/h.

Reduce the rolling resistance 5% from 0.0050 to 0.0045, and
the speed rises to 37.40 km/h, an increase of 0.22 km/h.

But if that 5% reduction in rolling resistance also
increased the frontal area from 0.4m^2 to 0.40544m^2, then
the speed drops to 37.24 km/h.

So the combination of a wider tire that rolls more easily is
predicted to increase a rider's speed only 0.06 km/h, or
sixty meters in an hour--a convenient 1 meter per minute.

I note that for these defaults, the two tires become equal at a little
below 44 km/h. (set the power to 473.5 watts)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

(This is assuming no wind and no drafting)

Dear Benjamin,

I found this memo stuck to your post in my newsreader:

# To: Captain Picard
#From: Commander G. La Forge, Chief Engineer
#
#I'd like to make it so, sir, but I left my 473.5 watt
#dilithium crystals in my other pants. Maybe that big
#Klingon sprinter can help you.

Naturally, I harnessed the big Klingon, told him that Lance
doubted that anyone with a forehead like a turtle could put
out a thousand watts for an hour, and found that the two
tires are still just about equal:

57.26 km/h wide (0.40544 25mm frontal) 0.0045 rr (imagined)
57.37 km/h thin (0.40000 23mm frontal) 0.0050 rr (default)

Of course, the 10% reduction in rolling resistance is just a
vague guess at the best that could be expected in reducing
rolling resistance by making the same tire 2mm wider, just
as the 0.0054m^2 increase is just a vague guess at the wind
drag increase for the wider tire.

But if adding 526.5 watts only lets the thinner tire pull
ahead 0.11 km/h, then we know why Commander Spock is leaving
the calculations to Commander Data. At low and therefore
plausible bicycle power levels, there isn't much difference
between the two tires. At outlandishly high levels, the tiny
differences make even less difference.

Which wasn't what I thought. I expected the wind drag to
matter more and more relative to the rolling resistance (it
does, since the thin tire pulls ahead), but overall it
matters less and less in terms of how much it affects the
actual speed as power increases.

That is, at 1000 watts, neither the tiny extra wind drag of
the wider tire nor the little bit of extra rolling
resistance of the thin tire can have much effect on the
speedometer reading.

So thanks for pointing out where the two imaginary tires
match--it made me think again.

Carl Fogel

15 Jun 2005 14:12:03 -0700, skrev:


My butt-gauge indicates that 25mm tires (Veloflex Roubaix - tubular)
grip better, and are more compliant than 23mm tires of the same
manufacturer. So, I believe I'm faster in turns, descents. I certainly
push harder. The tires are more compliant on rough surfaces, so it's
easier to go harder as the ride is smoother. They roll about the same.
The 25mm tire is somewhat harder to sprint or climb with since it is
heavier, and the diameter is slightly larger.

Regards,

Rob

I use 25 mm tires out of the same belief. Surpisingly the 25 mm Conti
4-Season only weighs 8 grm more than the 23 mm.

They are actually 24 mm wide and 25 mm high.

Kind regards
Ivar

15 Jun 2005 12:15:01 +0100 (BST), David Damerell
skrev:
If you want to maximise speed, you should use in both tyres
the maximum pressure that does not cause the increase in RR we see with
track-style pressures (eg 170psi), or the maximum pressure that does not
produce an intolerably hard ride; that will be equal in both cases and
the 25mm tyre will have lower RR.

Why would you use a lower pressure in the 25mm tyre if the aim is to
maximise speed?

Because overinflated tires are not faster: they jump too much, and have
too little grip.

Depending on the character of the road surface you might gain some speed
by increasing inflation TO A LIMIT. This would be true for 23 as well as
25 mm.
The ideal comparison would be between the two sizes of tires, each with
their ideal pressure (for road quality and rider weight). This should be
reflected in their "recommended pressure" - not in the same pressure.


But you did get a perfectly good explanation of why it is not a sensible
question to ask.

I still think the explanation was too much common sence and not as exact
as I want it.

Kind Regards
Ivar

Tue, 14 Jun 2005 17:24:24 -0600, skrev:


Reduce the watts from the impressive default 300 to a more
modest 150 watts, and the base speed is predicted to be
28.48 km/h, the pure rolling resistance reduced 5% raises
the speed to 28.76 km/h, and the final speed with the wider
tire's wind drag added drops back to 28.64 km/h--about 0.16
km/h faster, so rolling resistance does indeed matter more
at lower speeds, where wind drag isn't so important. It's
conveniently about 0.1 mph, or about nine extra feet per
minute at around 18 mph.

Carl Fogel


How I enjoyed this - and the following calculations. I so much want the
25 mm tire to be at least a tiny theoretical bit faster than the 23 mm -
and if the advangtage of the wider tire threatens to disappear completely,
I will only have to slow down till the reduction in RR again will give me
an advantage to those trationals, who ride on narower tires.

Regards
Ivar