Tire width and RR

Thu, 09 Jun 2005 23:05:08 -0700, Mark Hickey skrev:

I
measured a "25mm" Conti Gatorskin this morning, and it was 23.4mm
wide.

I noticed that most tires are smaller than labeled, probably because
lightness is considered the most important parameter. My "25mm" Conti
4-Season measures 24 mm, and the "23 mm" labeled measures 22 mm. That
doesn´t affect my question, however.
Ivar

Thu, 09 Jun 2005 14:35:29 -0600, skrev:


You may be able to find some 23 vs 25 mm tires on this
chart, with different pressures:

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

All that I saw in a quick glance was near the bottom, where
a 23-622 Michelin Axial Supercomp at 110 psi had exactly the
same results as a 25-622 Nokian Roadie used at 100 psi
because they both were measured at a rolling resistance
coefficient of 0.0046. More than 2 significant digits may be
needed before any difference would show up.

Dear Carl
Thanks for the considerations and links. I've been there before some time
ago. This time I understand a bit more.
The beerdrinkers chart SEEMS to confirm, that a wider tire, even with a
lower pressure, will not produce more RR - maybe even less.

On the chart there are two Hutchinson tires of resp. 25 and 28 mm with
resp. 100
and 120 psi pressure.
And the 28 mm with 100 psi has a 15 pct. lower RR than the 25 mm with the
120 psi.
However I am not able to tell for sure, whether it is actually the same
model with the same casing, pattern and rubber compund or just the same
company.

All I can get out of the calculation of relative RR, is that higher
pressure in the same tire will result in (a slightly) lower RR. As you
note, that is not the way it works on real asphalt roads.

It may indicate, that the difference in RR is insignificant. That does not
satisfy my curiousity, however.

Now I have sent my original question to Continental Tires technical dept.
- they should know.


Ivar Hesselager
Denmark

9 Jun 2005 12:29:26 -0700, bfd skrev:

Does it matter? I say pump your 700x25 tires up to 100-110psi (what
that about 7 BAR) and ride! Riding is what's going to make you faster.


You are absolutely right: The difference in actual RR is not important.
Still I find it interesting. Discussing and researching the subject
doesn´t steal time from riding, but from other unimportant matters. ;-)

Ivar

Quoting Ivar Hesselager :
The tests that I have seen (referred to), however, compare 23 mm and 25 mm
with THE SAME pressure.
But how does a comparison between RR from a 23 mm and a 25 mm otherwise
identical tire come out, if they each have THE RECOMMENDED pressure, i.e.
7,5 and 6,5 BAR respectively? This will be the relevant comparison, I
think.

Not really.

There are two issues here; rolling resistance and comfort. Increased
pressure improves RR and decreases comfort (to a point - I know we've seen
the suggestions that very high trackie-style pressures are no good at all
on road); if you compare two tyres at different pressures you've also got
a difference in comfort which is unquantifiable.

We know from the identical pressure tests that for the same pressure, and
hence ride comfort, the fatter tyre has better RR. We can deduce from that
that we could make the RRs identical and the fatter tyre would offer
superior comfort (because it would be at a lower pressure).
--
David Damerell Distortion Field!
Today is First Chedday, June - a public holiday.

ahh comfort 80 mph on the snow to x country atb 20 degrees
down the rapids during flood mit swim trunks
mmm this is a good hurricane-lookit the &^%&(( gators!
must be the wrong group

anyway-the auto bike analogy has an inverse
the bike, gives an immediate notice of increased or decreased friciton-
pick a part- that's the sensation
but after a few miles-given a small increase or decrease-the rider
adapts and that new sensation submerges into total experince.
but the car going from 185mm to 235mm-that's unforgettable.
ahhh the beach boys...
hey watch those gators!!

Mark Hickey wrote:

"Ivar Hesselager" wrote:

I use Conti 4-Season tires in 25 mm on my road bike, because I have
read from several sources that 25 mm tires have less rolling
resistance than the 23 mm. (Plus better traction, puncture
resistance and comfort, but that is beside the point).

The tests that I have seen (referred to), however, compare 23 mm and
25 mm with THE SAME pressure.

Just to throw another spanner into these already suffering works, I
measured a "25mm" Conti Gatorskin this morning, and it was 23.4mm
wide.

If you want a fatter tire for its nominal width, try Vittoria. My 23mm were
actually over 24mm. They're some of the supplest tires around too.

Matt O.

Strayhorn wrote:
In article ,
"Matt O'Toole" wrote:


If you want a fatter tire for its nominal width, try Vittoria. My
23mm were actually over 24mm. They're some of the supplest tires
around too.

Strange - my Vittoria tires marked "25c" were actually around 24mm as
well. In fact, they are about the same width as the 23mm Panaracers
now on the bike (exact measurements are written down at home, alas).

Wonder if they just make the same width tired and slap different
stickers on them?

Probably. I've noticed this with various Vittorias too. They make a big deal
about the tread compound and design, and even give different specs for width,
among tires that are practically identical. They've proven to be excellent
tires anyway, in spite of the BS. Just too expensive...

Matt O.

On Fri, 10 Jun 2005 14:37:10 -0400, Strayhorn wrote:
In article ,
"Matt O'Toole" wrote:

If you want a fatter tire for its nominal width, try Vittoria. My 23mm were
actually over 24mm. They're some of the supplest tires around too.

Strange - my Vittoria tires marked "25c" were actually around 24mm as
well. In fact, they are about the same width as the 23mm Panaracers now
on the bike (exact measurements are written down at home, alas).

I seem to remember some posts claiming that Vittoria used to under-label
their tires, and switched labeling for a given type, so that your newer
25s may very well be the same tires as the older 23s.

Jasper

Jasper Janssen wrote:

On Fri, 10 Jun 2005 14:37:10 -0400, Strayhorn wrote:

In article ,
"Matt O'Toole" wrote:

If you want a fatter tire for its nominal width, try Vittoria. My
23mm were actually over 24mm. They're some of the supplest tires
around too.

Strange - my Vittoria tires marked "25c" were actually around 24mm as
well. In fact, they are about the same width as the 23mm Panaracers
now on the bike (exact measurements are written down at home, alas).

I seem to remember some posts claiming that Vittoria used to
under-label their tires, and switched labeling for a given type, so
that your newer 25s may very well be the same tires as the older 23s.

Well, one way to give people a smoother, more supple tire is to simply give them
a bigger one! Only so much can be done with exotic casings, and tread can only
be so thin.

Matt O.

In article ,
Strayhorn wrote:

In article ,
"Matt O'Toole" wrote:


If you want a fatter tire for its nominal width, try Vittoria. My 23mm were
actually over 24mm. They're some of the supplest tires around too.

Strange - my Vittoria tires marked "25c" were actually around 24mm as
well. In fact, they are about the same width as the 23mm Panaracers now
on the bike (exact measurements are written down at home, alas).

Wonder if they just make the same width tired and slap different
stickers on them?

I run Serfas wire bead trainers for their puncture resistance.
They ride well and corner well. Here are some measurements.

Nominal Actual width
STK-27.5 - 27"x 1.25" Wire Bead 1.25"
STK-23 700 x 23 Wire Bead 24 mm
STK-28 700 x 28 Wire Bead 27 mm

--
Michael Press