Tire width questions

I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?

1. What exactly does the width of a tire mean? Leaving aside the
question of whether the label is honest or not, what is actually
measured? In a 700C X (say) 25mm tire, which part is 25mm? Given that
the tire itself is flexible, I don't quite see how one could measure
the gap between the two beads, which is what width sounds like it
should mean.

2. In trying to judge whether a given tire will fit on my bike (i.e.,
under the rear brake bridge, inside the fork, and under the calipers),
if I measure the distance between the tires that are currently
installed and the bridge/calipers/fork, and if this distance is greater
than the difference between my current tire and a larger one, does this
mean that the larger tire will fit? E.g., if I have 25mm now, and I
measure 5 mm of clearance, can I safely assume a 28 mm tire will fit,
or is it more complicated than this (assuming either honest labels
across brands or consistent dishonesty within a brand)? It would be
nice to know before ordering tires.

TIA,
John

On 16 Aug 2006 08:13:12 -0700, "JBAFromNY" wrote:

I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?

1. What exactly does the width of a tire mean? Leaving aside the
question of whether the label is honest or not, what is actually
measured? In a 700C X (say) 25mm tire, which part is 25mm? Given that
the tire itself is flexible, I don't quite see how one could measure
the gap between the two beads, which is what width sounds like it
should mean.

But that is determined by the rim, so that would be (and is) a rim measurement.
The width of a tire is simply that, the overall width at its widest point.

2. In trying to judge whether a given tire will fit on my bike (i.e.,
under the rear brake bridge, inside the fork, and under the calipers),
if I measure the distance between the tires that are currently
installed and the bridge/calipers/fork, and if this distance is greater
than the difference between my current tire and a larger one, does this
mean that the larger tire will fit? E.g., if I have 25mm now, and I
measure 5 mm of clearance, can I safely assume a 28 mm tire will fit,
or is it more complicated than this (assuming either honest labels
across brands or consistent dishonesty within a brand)? It would be
nice to know before ordering tires.

Yeah, it is really just that simple. Fitting a 28 in a 30mm slot as in your
example is a bit tight. You do want some room for manufacturing tolerance,
rounded numbers, imperfect rims, etc.

Ron

JBAFromNY wrote:
I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?

1. What exactly does the width of a tire mean?

The width you would measure if you placed vernier calipers on tire when
it's fully inflated on the rim. Rim width will cause this measurement
vary slightly.

Art Harris

RonSonic wrote:
On 16 Aug 2006 08:13:12 -0700, "JBAFromNY" wrote:

I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?

1. What exactly does the width of a tire mean? Leaving aside the
question of whether the label is honest or not, what is actually
measured? In a 700C X (say) 25mm tire, which part is 25mm? Given that
the tire itself is flexible, I don't quite see how one could measure
the gap between the two beads, which is what width sounds like it
should mean.

But that is determined by the rim, so that would be (and is) a rim measurement.
The width of a tire is simply that, the overall width at its widest point.

Ah, that makes sense. I guess depending on the design/shape of the
tire, the "widest point" is in different places on different tires.

Thanks,
John

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In article ,
RonSonic wrote:
On 16 Aug 2006 08:13:12 -0700, "JBAFromNY" wrote:

I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?



2. In trying to judge whether a given tire will fit on my bike (i.e.,
under the rear brake bridge, inside the fork, and under the calipers),
if I measure the distance between the tires that are currently
installed and the bridge/calipers/fork, and if this distance is greater
than the difference between my current tire and a larger one, does this
mean that the larger tire will fit? E.g., if I have 25mm now, and I
measure 5 mm of clearance, can I safely assume a 28 mm tire will fit,
or is it more complicated than this (assuming either honest labels
across brands or consistent dishonesty within a brand)? It would be
nice to know before ordering tires.

If you bought a 28mm of exactly the same brand/model as your 25mm
you might be safe in this assumption otherwise all bets are off
in my experience. What you're really interested in is the height of
the tire when mounted and this varies quite a bit between "28mm"
tires. 5mm really isn't enough clearance to guarantee that any
28mm tire will fit.

_ Booker C. Bense





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"Art Harris" wrote in message
ps.com...
JBAFromNY wrote:
I'm a bit confused about tire widths. Perhaps someone can clarify
a
bit?

1. What exactly does the width of a tire mean?

The width you would measure if you placed vernier calipers on tire
when
it's fully inflated on the rim. Rim width will cause this
measurement
vary slightly.

Art Harris


I would say that rim width causes measured tire width to vary
considerably, not slightly. I purchased UltraGator 28 mm tires and
installed them on my Mavic racing rims, MA-40s I think (width about 14
mm bead to bead). The width measured out at 26 mm. I then installed
the same pair on a Breezer Liberty with a much wider rim, and they
measured a true 28 mm as advertised.

If width is what you want, it can matter. If air volume is what you
want, it doesn't matter, but what air volume are you getting? If you
are choosing tire size based on bike/rider weight with a "recommended"
pressure chart, who knows how you proceed?

Ken Freeman

JBAFromNY wrote:
I'm a bit confused about tire widths. Perhaps someone can clarify a
bit?

1. What exactly does the width of a tire mean? Leaving aside the
question of whether the label is honest or not, what is actually
measured? In a 700C X (say) 25mm tire, which part is 25mm? Given that
the tire itself is flexible, I don't quite see how one could measure
the gap between the two beads, which is what width sounds like it
should mean.


IIRC, tire "width" is a virtual measurement. Since actual outside width
depends on the rim that the tire is mounted on, there's no way to
determine this beforehand. Therefore, the "width" is the measurement
between the tire beads with the casing flattened out, divided by 2.5 .
That's the ETRTO standard, I think.

Jeff

Booker C. Bense wrote:

2. In trying to judge whether a given tire will fit on my bike (i.e.,
under the rear brake bridge, inside the fork, and under the calipers),
if I measure the distance between the tires that are currently
installed and the bridge/calipers/fork, and if this distance is greater
than the difference between my current tire and a larger one, does this
mean that the larger tire will fit? E.g., if I have 25mm now, and I
measure 5 mm of clearance, can I safely assume a 28 mm tire will fit,
or is it more complicated than this (assuming either honest labels
across brands or consistent dishonesty within a brand)? It would be
nice to know before ordering tires.

If you bought a 28mm of exactly the same brand/model as your 25mm
you might be safe in this assumption otherwise all bets are off
in my experience. What you're really interested in is the height of
the tire when mounted and this varies quite a bit between "28mm"
tires. 5mm really isn't enough clearance to guarantee that any
28mm tire will fit.

I guess that was part of the crux of my confusion -- what can one infer
about the "height" of a tire from its nominal width? I guess the
answer is "not much", and one has to rely on trial and error and/or
other people's experiences with particular tires. Speaking of which
.... in looking at the Rivendale site, they claim that their "ruffy
tuffy" and "roly poly" tires have "round" cross sections that make them
seem as wide as or wider than any nominal 28mm tire, but fit on bikes
that have very little clearance. Has anybody used these? Does
experience confirm the claim?

Thanks,
John

On 18 Aug 2006 06:15:09 -0700, "JBAFromNY" wrote:


Booker C. Bense wrote:

2. In trying to judge whether a given tire will fit on my bike (i.e.,
under the rear brake bridge, inside the fork, and under the calipers),
if I measure the distance between the tires that are currently
installed and the bridge/calipers/fork, and if this distance is greater
than the difference between my current tire and a larger one, does this
mean that the larger tire will fit? E.g., if I have 25mm now, and I
measure 5 mm of clearance, can I safely assume a 28 mm tire will fit,
or is it more complicated than this (assuming either honest labels
across brands or consistent dishonesty within a brand)? It would be
nice to know before ordering tires.

If you bought a 28mm of exactly the same brand/model as your 25mm
you might be safe in this assumption otherwise all bets are off
in my experience. What you're really interested in is the height of
the tire when mounted and this varies quite a bit between "28mm"
tires. 5mm really isn't enough clearance to guarantee that any
28mm tire will fit.

I guess that was part of the crux of my confusion -- what can one infer
about the "height" of a tire from its nominal width? I guess the
answer is "not much", and one has to rely on trial and error and/or
other people's experiences with particular tires.

Bicycle tires are all bias ply and will uniformly form a circular cross section.
The variation in rim width will affect this. But for a given rim width the
increase in overall diameter, heighth, is directly proportional to the increase
in tire width.

Ron

Speaking of which
... in looking at the Rivendale site, they claim that their "ruffy
tuffy" and "roly poly" tires have "round" cross sections that make them
seem as wide as or wider than any nominal 28mm tire, but fit on bikes
that have very little clearance. Has anybody used these? Does
experience confirm the claim?

Thanks,
John

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In article om,
JBAFromNY wrote:

Booker C. Bense wrote:


If you bought a 28mm of exactly the same brand/model as your 25mm
you might be safe in this assumption otherwise all bets are off
in my experience. What you're really interested in is the height of
the tire when mounted and this varies quite a bit between "28mm"
tires. 5mm really isn't enough clearance to guarantee that any
28mm tire will fit.

I guess that was part of the crux of my confusion -- what can one infer
about the "height" of a tire from its nominal width?

_ I think if the nominal width were accurate, most tires would
come to the same height, my experience is that the nominal width
isn't all that accurate between brands and that when you start
getting very close to the edge of what fits short reach brakes,
the tread design and lay up can make enough difference to matter.

I guess the
answer is "not much", and one has to rely on trial and error and/or
other people's experiences with particular tires. Speaking of which
... in looking at the Rivendale site, they claim that their "ruffy
tuffy" and "roly poly" tires have "round" cross sections that make them
seem as wide as or wider than any nominal 28mm tire, but fit on bikes
that have very little clearance. Has anybody used these? Does
experience confirm the claim?

_ My experience does. The rolly polly will just barely fit on my
Basso Gap, whereas the Avocet 28mm Duro will not. I have also
used Bontrager 28mm Race Lite[1] tires ( the race lites actually
measure to 26mm when mounted) on this bike. The Rolly Polly
measure 27mm wide and clear the brakes when mounted on the
same rims as the Avocet. The Avocets measure to a true 28mm
and that extra difference is enough to cause rub.

_ The Rolly Polly's are nice tires, but relatively expensive.
There is a difference between them and a good 25mm tire, but
is it a $20 difference?

Rivendell is just as hype-infested as the rest of the bicycle
industry, but there hype moves in a different direction.

_ Booker C. Bense


[1]- I can't recommend these tires if you're interested in
a smoother ride.

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