Tyre Sizing (again)

[Pete Biggs]

bob wrote:
> I know that tyre sizing can be a bit problematic but here is one that
> has me puzzled.
>
> My wife's old Raleigh Classic has 27" rims. She has for the last
> couple of years been running 27 x 1 1/8" Continental Ultrasport
> tyres. These were the tightest rim-tyre combination I've ever
> experienced. Even my LBS commented on it.
>
> To make things a bit comfier and punctures easier to fix, I bought a
> 27 x 1 1/4" Schwalbe Marathon as an experiment for her rear wheel. I
> was really pleased when it when on with fingers only, no tyre levers
> needed. I was not so pleased when after I pumped it up, the tyre came
> of the rim and the tube detonated. It seems that the tyre is slightly
> too big for the rim.
>
> So how is it that one 27" tyre barely fits and the other won't stay
> on? According to Sheldon 27" all rims are all ISO 630mm so its not a
> rim-tyre size mis-match (or is it?).
>
> Could the Schwalbe Marathon tyre be faulty? Are they known to be big?
> Should I return the tyre (bought online)?

First of all, check that the rims and all tyres are actually marked "630".
(I think they will be). Then have another go at fitting the Marathon,
making sure the beads seem properly fitted before fully inflating. If all
seems OK at normal pressure, give it an extra 10 PSI to test that you will
have some leeway. Don't forget your ear plugs!

Some tyres and rims just are bigger/smaller than others of supposedly the
same size for no apparent reason. It may be all of a certain model of rim
or tyre, or just a one-off from a manufacturing fault. Sometimes the
mismatch will be so great that the tyre will not stay on the rim. In this
case I would ask for a replacement tyre once, then if that failed too, use a
different model of tyre.

~PB

[bob]

I know that tyre sizing can be a bit problematic but here is one that
has me puzzled.

My wife's old Raleigh Classic has 27" rims. She has for the last couple
of years been running 27 x 1 1/8" Continental Ultrasport tyres. These
were the tightest rim-tyre combination I've ever experienced. Even my
LBS commented on it.

To make things a bit comfier and punctures easier to fix, I bought a 27
x 1 1/4" Schwalbe Marathon as an experiment for her rear wheel. I was
really pleased when it when on with fingers only, no tyre levers needed.
I was not so pleased when after I pumped it up, the tyre came of the rim
and the tube detonated. It seems that the tyre is slightly too big for
the rim.

So how is it that one 27" tyre barely fits and the other won't stay on?
According to Sheldon 27" all rims are all ISO 630mm so its not a
rim-tyre size mis-match (or is it?).

Could the Schwalbe Marathon tyre be faulty? Are they known to be big?
Should I return the tyre (bought online)?
--
geomannie

[Pete Biggs]

wrote:

> Maybe, don't know, maybe. It could be the rim (I assume you are
> confident that you installed the tyre correctly). Are they a nameless
> brand, and do they have a hook for the bead? Mine did not, and I
> suspect they were the prime culprit, along with the narrowness of the
> tyres I was trying.

That's a good point. A rim would have to be quite ancient not to have
hooks, but that should be checked.

I would not feel happy using a hookless rim with any high pressure tyre.

~PB

[[email protected]]

On Oct 23, 9:36*pm, bob >
wrote:
> I know that tyre sizing can be a bit problematic but here is one that
> has me puzzled.
>
> My wife's old Raleigh Classic has 27" rims. She has for the last couple
> of years been running 27 x 1 1/8" Continental Ultrasport tyres. These
> were the tightest rim-tyre combination I've ever experienced. Even my
> LBS commented on it.
>
> To make things a bit comfier and punctures easier to fix, I bought a 27
> x 1 1/4" Schwalbe Marathon as an experiment for her rear wheel. I was
> really pleased when it when on with fingers only, no tyre levers needed.
> I was not so pleased when after I pumped it up, the tyre came of the rim
> and the tube detonated. It seems that the tyre is slightly too big for
> the rim.
>
> So how is it that one 27" tyre barely fits and the other won't stay on?
> According to Sheldon 27" all rims are all ISO 630mm so its not a
> rim-tyre size mis-match (or is it?).

First, it should probably have the ISO number on it too just to be
certain. But some combinations of tyres and rims don't work very well
- i have had blow-offs with some tyres in the past (I forget which
model....maybe tioga city slicker). The tyre being an inappropriate
width for the rim doesn't help but that does not seem to be your
problem.


> Could the Schwalbe Marathon tyre be faulty? Are they known to be big?
> Should I return the tyre (bought online)?

Maybe, don't know, maybe. It could be the rim (I assume you are
confident that you installed the tyre correctly). Are they a nameless
brand, and do they have a hook for the bead? Mine did not, and I
suspect they were the prime culprit, along with the narrowness of the
tyres I was trying. I had no problems with various other tyres though.
The standards just don't seem to be precise enough to guarantee that
all rims and tyres will work together, but I don't know whose fault
that is.

James

[Rob Morley]

On Thu, 23 Oct 2008 13:36:30 +0100
bob > wrote:

> I know that tyre sizing can be a bit problematic but here is one that
> has me puzzled.
>
> My wife's old Raleigh Classic has 27" rims. She has for the last
> couple of years been running 27 x 1 1/8" Continental Ultrasport
> tyres. These were the tightest rim-tyre combination I've ever
> experienced. Even my LBS commented on it.
>
> To make things a bit comfier and punctures easier to fix, I bought a
> 27 x 1 1/4" Schwalbe Marathon as an experiment for her rear wheel. I
> was really pleased when it when on with fingers only, no tyre levers
> needed. I was not so pleased when after I pumped it up, the tyre came
> of the rim and the tube detonated. It seems that the tyre is slightly
> too big for the rim.
>
> So how is it that one 27" tyre barely fits and the other won't stay
> on? According to Sheldon 27" all rims are all ISO 630mm so its not a
> rim-tyre size mis-match (or is it?).
>
> Could the Schwalbe Marathon tyre be faulty? Are they known to be big?
> Should I return the tyre (bought online)?

Are you sure it was properly fitted? Did you partially inflate it and
check that the bead was evenly seated all the way around on both sides
before giving it full pressure? Is the rim tape the right width, and
properly seated?

[Alistair Gunn]

bob twisted the electrons to say:
> So how is it that one 27" tyre barely fits and the other won't stay on?

Not all tyres, or rims, of a given size are actually the same size. Even
apart from variations in production. I seem to recall some reviewer
(possibly it was www.bentrideronline.com but I couldn't swear to that)
having great difficulty getting some tyres made by Greenspeed onto a
trike made by some other manufacturer ...

It turned out that Greenspeed make their tyres slightly undersized (in
order to cope with the sideways loads a trike can generate), whilst the
other manufacturer was installing slightly oversized rims ... for
precisely the same reason!
--
These opinions might not even be mine ...
Let alone connected with my employer ...

[Pete Biggs]

bob wrote:
> Thanks for all suggestions. Sizes are both right at 630 tyre and rim.
> On close inspection I think that my problem is a crap tyre. I noticed
> it was a bit off-round when I fitted it. Now its off the bike I see
> that it is very un-round.
>
> So a loose-fitting tyre that is off-centre. No wonder the tube blew it
> off.
>
> So its return to sender (grumbles about hassle factor).
>
> Pictures
> http://www.downie-geo.demon.co.uk/Bike/DSC00210.JPG
> http://www.downie-geo.demon.co.uk/Bike/DSC00213.JPG

It doesn't matter if a tyre looks off-round when off the bike as it should
sort itself out once fitted and fully inflated.

I would give it another go - although another inner tube could be lost in
the process if you are unlucky.

~PB

[bob]

Thanks for all suggestions. Sizes are both right at 630 tyre and rim. On
close inspection I think that my problem is a crap tyre. I noticed it
was a bit off-round when I fitted it. Now its off the bike I see that it
is very un-round.

So a loose-fitting tyre that is off-centre. No wonder the tube blew it
off.

So its return to sender (grumbles about hassle factor).

Pictures
http://www.downie-geo.demon.co.uk/Bike/DSC00210.JPG
http://www.downie-geo.demon.co.uk/Bike/DSC00213.JPG
--
geomannie

[bob]

In message >, Pete Biggs
> writes
>
>It doesn't matter if a tyre looks off-round when off the bike as it should
>sort itself out once fitted and fully inflated.
That's what I thought and has been my experience in the past. If I put
it on the rim and inflate gently it does come into true but not
completely. That and the loose fit seems to make it US.
--
geomannie

[Rob Morley]

On Thu, 23 Oct 2008 19:49:59 +0100
bob > wrote:

> Thanks for all suggestions. Sizes are both right at 630 tyre and rim.
> On close inspection I think that my problem is a crap tyre. I noticed
> it was a bit off-round when I fitted it. Now its off the bike I see
> that it is very un-round.
>
> So a loose-fitting tyre that is off-centre. No wonder the tube blew
> it off.
>
> So its return to sender (grumbles about hassle factor).
>
> Pictures
> http://www.downie-geo.demon.co.uk/Bike/DSC00210.JPG
> http://www.downie-geo.demon.co.uk/Bike/DSC00213.JPG

That's just because it's been folded. As long as there aren't any
significant kinks in the bead it shouldn't matter. If the bead is
slightly kinked you should be able to ease it straight without too
much difficulty and try again.

[[email protected]]

On Oct 23, 10:25*pm, "Pete Biggs"
<p...@pomegranateremovehighlyimpracticalfruitbiggs. tc> wrote:
> wrote:
> > Maybe, don't know, maybe. It could be the rim (I assume you are
> > confident that you installed the tyre correctly). Are they a nameless
> > brand, and do they have a hook for the bead? Mine did not, and I
> > suspect they were the prime culprit, along with the narrowness of the
> > tyres I was trying.
>
> That's a good point. *A rim would have to be quite ancient not to have
> hooks, but that should be checked.
>
> I would not feel happy using a hookless rim with any high pressure tyre.

Well, in my case I think it was a ~1990 vintage low-end Raleigh
"MTB" (so not really *ancient*) but with fairly wide no-name rims
which were presumably never intended for the rather narrow high
pressure tyres I was trying out...

James