tyre pressure?

On 26/12/2007 18:12, Rob Morley said,

Quoted message said:

622-35 is 700C - is this a hybrid?

...or a 29er?

--
Paul Boyd
http://www.paul-boyd.co.uk/

Thanks everyone for the info,bought one of those track pumps and to prove
the point about tyres blowing off at higher pressue i misread the 85psi for
65psi on the gauge and the tyre started lifting(bulging)from the rim around
the area of the valve.Reduced down to 65psi and all is well on the front,a
little higher on the back because i carry panniers with clothes tools
etc.The tyres are 26x1 3/8 and it is my comfort/commuter bicycle.

Regards

Simon
"Paul Boyd" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On 26/12/2007 18:12, Rob Morley said,

Quoted message said:

622-35 is 700C - is this a hybrid?

..or a 29er?

--
Paul Boyd
http://www.paul-boyd.co.uk/

Simon Grant said:

Thanks everyone for the info,bought one of those track pumps and to
prove the point about tyres blowing off at higher pressue i misread
the 85psi for 65psi on the gauge and the tyre started
lifting(bulging)from the rim around the area of the valve.Reduced
down to 65psi and all is well on the front,a little higher on the
back because i carry panniers with clothes tools etc.The tyres are
26x1 3/8 and it is my comfort/commuter bicycle.

An overinflated tyre can start lifting anywhere - but at the valve is
suspicious. I would check the inner tube is not trapped - by deflating the
tyre and pushing the valve into the tyre a bit to make sure the tube is well
tucked in, before re-inflating. (The valve's locking would need to be
undone first if there is one).

~PB

In article <[email hidden]>, Simon Grant
[email hidden] says...

Quoted message said:

Thanks everyone for the info,bought one of those track pumps and to prove
the point about tyres blowing off at higher pressue i misread the 85psi for
65psi on the gauge and the tyre started lifting(bulging)from the rim around
the area of the valve.

Sounds like the tyre isn't seated properly on the rim. Take it off and
check that the rim tape isn't interfering with the bead, then when you
refit the tyre inflate it slightly and push the valve in to ensure the
tube isn't trapped before taking it up to full pressure. Then check
that the lines moulded in the sidewall are the same distance from the
rim all the way round.

Quoted message said:

622-35 is 700C - is this a hybrid?

No, sorry. Just me getting confused with the different units. I
meant 26x1.4 || 35-559. They're the Michelin XCR Road, (tyre-wall
markings don't specify whether they're 66 or 33 TPI), but the MAX is
actually 87psi, so 100psi doesn't stretch the +- 10% rule too far
(11.3% over, or an overall increase of 14.9%)

Quoted message said:

Quoted message said:

Maybe I'll take them down to 90 next time.

That should be plenty. OTTOMH: A tyre deforms until its footprint
matches the load it has to support, e.g. a tyre run at 100 PSI loaded
with 100lb. needs a square inch of contact. Rolling resistance on a
smooth flat surface is caused by this deformation, so the more flexible
the tyre casing, or the higher its pressure, the less rolling resistance
occurs. A wider (or larger diameter) tyre needs to deform less than a
narrow one because its tread surface has a shallower curve, and
inflating it to a higher pressure has the effect of reducing "suspension
travel" so that small road bumps are transmitted to the bike and rider,
effectively presenting you with a tiny hill that has to be climbed each
time you ride over a bump. A narrow flexible tyre at high pressure on a
smooth surface deforms less in the sidewall, relative to the contact
area, when compared with a wider tyre, so overall rolling resistance is
less, but the high pressure doesn't reduce the suspension effect as much
as with a wider tyre, so better contact/comfort is maintained.
(I expect someone from rec.bicycles.tech will be along in a bit to tell
me that Jobst says different, or something ...)

That's pretty interesting, thanks.

On Dec 27 2007, 9:21 am, "Simon Grant" <[email hidden]>

Quoted message said:

Thanks everyone for the info,bought one of those track pumps and to prove
the point about tyres blowing off at higher pressue i misread the 85psi for
65psi on the gauge and the tyre started lifting(bulging)from the rim around
the area of the valve.Reduced down to 65psi and all is well on the front,a
little higher on the back because i carry panniers with clothes tools
etc.The tyres are 26x1 3/8 and it is my comfort/commuter bicycle.

Shouldn't be lifting off like that. Happened to me once
(embarrassingly) while fitting a friends tyre, I just took the tube
and tyre off and started again - making sure everything was seated
nice and it didn't re-occur.

Regards,

Duncan