Tyre sizes: Is 700x28 and 700x30 basically the same?

Hi - I would really appreciate some help with tyre sizes as I am
totally confused!

My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish and I frequently get
punctures! This is mainly due to the fact they "retain" slivers of
stone in the tread that then gnaw into the inner tube as I ride.

I have seen some tyres that I think will be much better but they are
only available down to 700x30.

Does the 30 rather than the 28 mean that they are 2mm wider than the
originals width ways? 2mm greater diameter? 2mm greater
circumference? Any of these 2mm measurements would seem to be
insignificant, but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

Or maybe the whole 2mm thing is a red herring I just invented?

Any advice greatly recieved.

Thanks,

David

DrC wrote:

Hi - I would really appreciate some help with tyre sizes as I am
totally confused!

My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish and I frequently get
punctures! This is mainly due to the fact they "retain" slivers of
stone in the tread that then gnaw into the inner tube as I ride.

I have seen some tyres that I think will be much better but they are
only available down to 700x30.

Does the 30 rather than the 28 mean that they are 2mm wider than the
originals width ways? 2mm greater diameter? 2mm greater
circumference? Any of these 2mm measurements would seem to be
insignificant, but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

Or maybe the whole 2mm thing is a red herring I just invented?

Any advice greatly recieved.

Thanks,

David

The complete answer is on sheldon brown's site.
http://www.sheldonbrown.com/tire_sizing.html
The unambiguous tyre size is the E.T.R.T.O number, which specifies the
bead diameter and (still nominal) width. Sadly most bike shops will give
you a funny look if you quote it, although there are exceptions.

But the short answer is YES, they are not very different and one will
replace the other up to a point. If the tube was a bit fat for the 30mm
then it might be too big in the 28mm for instance.

Roger


--
Roger Thorpe

My email address is spamtrapped. You can work it out!

"DrC" wrote in message
ups.com...
SNIP
They are meant
to be puncture resistant but are, in fact, rubbish and I frequently get
punctures! This is mainly due to the fact they "retain" slivers of
stone in the tread that then gnaw into the inner tube as I ride.


I think the key word here is "resistant" and not "proof"

If you are picking up things that give punctures then you are still going to
pick them up - I guess that they need to be a bit thicker to stop the grit
in your case getting through.

SNIP
DaveB

DrC wrote:
My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish

Sounds like another opportunity to bang on about how great Schwalbe
Marathon Plus are

DrC wrote:
Hi - I would really appreciate some help with tyre sizes as I am
totally confused!

My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish and I frequently
get punctures! This is mainly due to the fact they "retain" slivers
of stone in the tread that then gnaw into the inner tube as I ride.

I have seen some tyres that I think will be much better but they are
only available down to 700x30.

Does the 30 rather than the 28 mean that they are 2mm wider than the
originals width ways? 2mm greater diameter? 2mm greater
circumference?

It's supposed to be 2mm higher above the rim (4mm greater diameter
altogether) and also 2mm wider. However, manufacturers are sometimes
inacurate or dishonest about sizes, so it could actually be the same size or
even smaller. Also, the width of your rim affects the shape of the inflated
tyre. The wider the rim, the wider but shallower the tyre will end up.

Any of these 2mm measurements would seem to be
insignificant,

Not /very/ significant for these sort of sizes, anyway

but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

No, they will fit.

30mm is a bit unusual though. 32mm is more of a common size.

~PB

in message . com, DrC
') wrote:

Hi - I would really appreciate some help with tyre sizes as I am
totally confused!

My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish and I frequently get
punctures! This is mainly due to the fact they "retain" slivers of
stone in the tread that then gnaw into the inner tube as I ride.

I have seen some tyres that I think will be much better but they are
only available down to 700x30.

Does the 30 rather than the 28 mean that they are 2mm wider than the
originals width ways? 2mm greater diameter? 2mm greater
circumference? Any of these 2mm measurements would seem to be
insignificant, but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

I /think/ (but may be wrong) that what's measured is the amount the tyre is
supposed to stand out from the bead on the rim when inflated, so a 700x30
tyre will be 4mm greater in overall diameter than a 700x28. But the
measurements are notoriously inaccurate and a 700x28 from one manufacturer
may in fact be bigger than a 700x30 from another. In practice I'm pretty
much certain your chosen tyre will fit.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/
;; First they came for the asylum seekers,
;; and I did not speak out because I was not an asylum seeker.
;; Then they came for the gypsies,
;; and I did not speak out because I was not a gypsy...
;; Pastor Martin Niemöller, translated by Michael Howard.

DrC wrote:

Any of these 2mm measurements would seem to be
insignificant, but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

The inner diameter (at the bead) is the same with all 700C tyres*, but
fatter 700C tyres have greater outer diameters and widths.

* Plus or minus a tiny bit, hence why some tyres of supposedly the same size
are easier to fit than others.

~PB

Simon Brooke wrote:
I /think/ (but may be wrong) that what's measured is the amount the tyre is
supposed to stand out from the bead on the rim when inflated, so a 700x30
tyre will be 4mm greater in overall diameter than a 700x28. But the
measurements are notoriously inaccurate and a 700x28 from one manufacturer
may in fact be bigger than a 700x30 from another. In practice I'm pretty
much certain your chosen tyre will fit.

I have some vague recollection that the stated measurement is supposed
to be the total width of the flattened carcass divided by 2.5...

Anthony

In article . com
DrC wrote:
Hi - I would really appreciate some help with tyre sizes as I am
totally confused!

My bike (Trek 1200) currently has 700x28 tyres fitted. They are meant
to be puncture resistant but are, in fact, rubbish and I frequently get
punctures! This is mainly due to the fact they "retain" slivers of
stone in the tread that then gnaw into the inner tube as I ride.

Are you sure you're pumping them up hard enough? If a tyre is run soft
it will flex more, and this tends to encourage bits of shrapnel to work
their way in.

"DrC" wrote

Does the 30 rather than the 28 mean that they are 2mm wider than the
originals width ways? 2mm greater diameter? 2mm greater
circumference? Any of these 2mm measurements would seem to be
insignificant, but maybe they need 2mm wider / longer / rounder wheels
and so wont fit at all?

I have a Schwalbe tyre on my utility bike and even the manufacturer can't
decide what size it is so it is marked 28/32.

The important thing is the bigger number, which might be 622 or 630, if it
is an older bike. Or 559 for a mountain bike (unlikely at this width though
narrow tyres do exist). Anything else is older, no longer mainstream and
may not have metric markings.