tire width, rim width, and pressure

I've got a 32mm tire on a rim that's a bit too narrow for it, as I
found when the bead lifted off and the tube blew out, shortly after
riding through a sharp curve downhill with a camping load on the bike.

Funny enough, the blowoff didn't happen in the turn, but about 100
yards after.

My question is, is such a blowoff more likely with higher or lower
pressures?

On the one hand, seems like because wide tires aren't 'hooked' in as
well where the tire bead meets the rim hook at an awkward angle, a
higher pressure might make it more likely to blow.

On the other hand, seems like a lower pressure would allow the tire to
squirm around more, esp. when side loaded, and might let the bead walk
off and blow.

I pumped to a somewhat lower pressure after replacing the tube, but
didn't encounter any more such turns, so I wonder if that was the
right move.

-pm

On May 15, 9:13*pm, pm wrote:
I've got a 32mm tire on a rim that's a bit too narrow for it, as I
found when the bead lifted off and the tube blew out, shortly after
riding through a sharp curve downhill with a camping load on the bike.

Funny enough, the blowoff didn't happen in the turn, but about 100
yards after.

My question is, is such a blowoff more likely with higher or lower
pressures?

On the one hand, seems like because wide tires aren't 'hooked' in as
well where the tire bead meets the rim hook at an awkward angle, a
higher pressure might make it more likely to blow.

On the other hand, seems like a lower pressure would allow the tire to
squirm around more, esp. when side loaded, and might let the bead walk
off and blow.

I pumped to a somewhat lower pressure after replacing the tube, but
didn't encounter any more such turns, so I wonder if that was the
right move.

-pm

I'd venture that the tire simply wasn't seated. You should be able to
safely run 32mm tires on virtually any rim short of wide downhill
models. I mean--xcrossers run 35mm knobbies on skinny rims all the
time.

On Fri, 15 May 2009 18:18:22 -0700 (PDT), landotter wrote:

On May 15, 9:13*pm, pm wrote:
I've got a 32mm tire on a rim that's a bit too narrow for it, as I
found when the bead lifted off and the tube blew out, shortly after
riding through a sharp curve downhill with a camping load on the bike.

Funny enough, the blowoff didn't happen in the turn, but about 100
yards after.

My question is, is such a blowoff more likely with higher or lower
pressures?

On the one hand, seems like because wide tires aren't 'hooked' in as
well where the tire bead meets the rim hook at an awkward angle, a
higher pressure might make it more likely to blow.

On the other hand, seems like a lower pressure would allow the tire to
squirm around more, esp. when side loaded, and might let the bead walk
off and blow.

I pumped to a somewhat lower pressure after replacing the tube, but
didn't encounter any more such turns, so I wonder if that was the
right move.

-pm

I'd venture that the tire simply wasn't seated. You should be able to
safely run 32mm tires on virtually any rim short of wide downhill
models. I mean--xcrossers run 35mm knobbies on skinny rims all the
time.

I'll agree, 32 isn't too wide for any of the more normal clincher rims. But then
my experience is with relatively low pressure, like 50-60 pounds at most and
much less for 'cross or off road.

pm wrote:
I've got a 32mm tire on a rim that's a bit too narrow for it, as I
found when the bead lifted off and the tube blew out, shortly after
riding through a sharp curve downhill with a camping load on the bike.

Funny enough, the blowoff didn't happen in the turn, but about 100
yards after.

My question is, is such a blowoff more likely with higher or lower
pressures?

On the one hand, seems like because wide tires aren't 'hooked' in as
well where the tire bead meets the rim hook at an awkward angle, a
higher pressure might make it more likely to blow.

On the other hand, seems like a lower pressure would allow the tire to
squirm around more, esp. when side loaded, and might let the bead walk
off and blow.

I pumped to a somewhat lower pressure after replacing the tube, but
didn't encounter any more such turns, so I wonder if that was the
right move.

If you habitually spin the wheel at eye level during
mounting (at half pressure and again at full pressure)
before installing it in your bicycle, you'll avoid the
overwhelming bulk of 'mystery' blowoffs.

Note each tire has a molded line just above the braking
surface. That molded line must be even and visible all the
way around. Where it disappears, the tire is below its
proper seat and hence can, and likely will, lift over the
top somewhere else. At an inconvenient time (c.f. 'Murphy')

Moreover, 'mystery' tire casing tear failures are frequently
attributable to brake shoe cuts just at the rim edge. These
torn areas will be visible before they are fatal. Noting
that damage early allows you to replace the tire and
properly adjust brake pad height at your convenience, rather
that just past the middle of nowhere. In the rain.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On May 16, 7:56*pm, AMuzi wrote:

torn areas will be visible before they are fatal. Noting
that damage early allows you to replace the tire and
properly adjust brake pad height at your convenience, rather
that just past the middle of nowhere. In the rain.

When in the phone you carry on the bike to call a taxi on days like
this the battery has run out of charge. -- Andre Jute

On 16 May, 05:13, wrote:
someone wrote:

Funny enough, the blow-off didn't happen in the turn, but about 100
yards after.

You probably had a combination heating and loading blowout, typical
for descents using a lot of braking because there are many curves that
do not allow higher speed that would more quickly cool the rim.

Nor do they correct a flexxy wheel.

Because pressure is a large part of blow-off, higher pressure is not a
protection against it.

Increasing a wheels rigidity reduces blow-off.

Not to worry, it squirms enough either way. *I just blew a 25mm tire
"Continental Gatorskin" off an MA-2 on a steep trail, causing a 10"
rip in the tube. *It was loud! *I put a spare tube in and continued
with more care to not overheat rims. *

After all these years, you should realise that the heating is only
partially the answer. The main reason your tyres blow off is because
they lack sufficient rigidity for you and your riding style. Buy a
pair of well built wheels whoose tyres do not blow off.

someone.

??? wrote:
On 16 May, 05:13, wrote:
someone wrote:

Funny enough, the blow-off didn't happen in the turn, but about 100
yards after.
You probably had a combination heating and loading blowout, typical
for descents using a lot of braking because there are many curves that
do not allow higher speed that would more quickly cool the rim.

Nor do they correct a flexxy wheel.

Because pressure is a large part of blow-off, higher pressure is not a
protection against it.

Increasing a wheels rigidity reduces blow-off.

Not to worry, it squirms enough either way. I just blew a 25mm tire
"Continental Gatorskin" off an MA-2 on a steep trail, causing a 10"
rip in the tube. It was loud! I put a spare tube in and continued
with more care to not overheat rims.

After all these years, you should realise that the heating is only
partially the answer. The main reason your tyres blow off is because
they lack sufficient rigidity for you and your riding style. Buy a
pair of well built wheels whoose tyres do not blow off.

someone.

Is that you Trevor?

--
Tom Sherman - 42.435731,-83.985007
LOCAL CACTUS EATS CYCLIST - datakoll

"Tom_Sherman" wrote in message
...
??? wrote:
On 16 May, 05:13, wrote:
someone wrote:

Funny enough, the blow-off didn't happen in the turn, but about 100
yards after.
You probably had a combination heating and loading blowout, typical
for descents using a lot of braking because there are many curves that
do not allow higher speed that would more quickly cool the rim.

Nor do they correct a flexxy wheel.

Because pressure is a large part of blow-off, higher pressure is not a
protection against it.

Increasing a wheels rigidity reduces blow-off.

Not to worry, it squirms enough either way. I just blew a 25mm tire
"Continental Gatorskin" off an MA-2 on a steep trail, causing a 10"
rip in the tube. It was loud! I put a spare tube in and continued
with more care to not overheat rims.

After all these years, you should realise that the heating is only
partially the answer. The main reason your tyres blow off is because
they lack sufficient rigidity for you and your riding style. Buy a
pair of well built wheels whoose tyres do not blow off.

someone.

Is that you Trevor?

--
Tom Sherman - 42.435731,-83.985007
LOCAL CACTUS EATS CYCLIST - datakoll

Tom,
It sure sounds like him.
Kerry

wrote:
snip
In passing, who are you that you offer vague but certain advice
anonymously, without credible explanation of how it works?

hey, jobst, who are you that offers utterly incorrect but certain advice
hoping borrowed your alma mater will stop you looking like a complete
fool? when you get stuff wrong, you get stuff wrong. anonymity has
nothing to do with it.

examples:
"van der waal's forces cause brake squeal"
"spokes fatigue from residual stress"
"anodizing causes rim cracking"
"wheels need spoke tension as high as the rim can bear"
"head set bearings do not brinell"
"bike wheel bearings are elasto-hydrodynamically separated"

it doesn't matter if the great and mighty jobst brandt graduated from
stanford or chico state - he's still an ignorant bull****ter if he's
posing as an engineer and making huge fundamental mistakes like these.

On 17 May 2009 14:06:47 GMT, wrote:

someone wrote:

After all these years, you should realise that the heating is only
partially the answer. The main reason your tyres blow off is
because they lack sufficient rigidity for you and your riding style.
Buy a pair of well built wheels whoose tyres do not blow off.

What is "wheel rigidity" to which you refer, and how does it affect
how well tire beads are held during high temperature brake heating?

In passing, who are you that you offer vague but certain advice
anonymously, without credible explanation of how it works?


Betcha it's "Nick L Plate"; I predict a flurry of unsupportable assertions
that tied-and-soldered spokes make stiffer wheels and that the majority of
cyclist have exceeded 60mph.