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OK to overinflate tires?



 
 
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  #11  
Old October 9th 05, 10:02 PM
Jasper Janssen
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Default OK to overinflate tires?

On Sun, 09 Oct 2005 14:53:17 GMT, "Dave Reckoning"
wrote:

(please forgive me the long URL, TINYURL is down!)


And that, ladies, is why shouldn't use tinyurl or similar services in the
first place. Well, one of the reasons.

a) Single point of failure
b) link target is 'hidden', which can be used for fraud, goatse, and other
shenanigans
c) privacy, tinyurl has massive datamining potential
and d) if they ever go bankrupt or lose all their systems without benefit
of backups, which is not that unlikely, not even archive services will be
able to help you see what the hell a post from yesteryear was pointing at.

And since there's no good reason to in fact stick to the 80 character
limit for things like urls, they don't even serve any purpose.

Jasper
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  #12  
Old October 10th 05, 01:59 AM
David Rees
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Default OK to overinflate tires?


"Dave Reckoning" wrote in message
news:x9a2f.228887$084.24624@attbi_s22...
"mort" wrote in message
ups.com...
I'm a lightweight, at 150 lbs, so I was wondering: what's the downside
of overinflating my tires somewhat? For instance, I am commuting on a
Schwalbe Marathon Slick that says it should be inflated to 85 psi.
What would happen if I routinely inflate it to 100? Tire explosions?
Rim damage? Earth crashes into Sun? Jobst admits that wheels hang
from their spokes? Any other bad effects?

I've ridden Conti tubulars that take 160lbs, and didn't notice any
difference in the time it took me to ride a known circuit, though the ride
was noticeably harsher. I prefer tubulars like Vittorias at ~115lbs for my
160lbs. This is unscientific testing under varying conditions, but I rode it
(timed and heart rate monitored) at least twice a week for years on
Vittoria, then a season on Contis (thought the higher pressure would be
faster), then back to Vittoria. The Contis -I forget the model- were
equivalent in price to Corsa CX/CG. It doesn't really answer your question
about overinflation since the Contis are designed for 160lbs, but I imagine
that factors others have explained negate any advantage derived from tire
pressure in this range.


  #13  
Old October 10th 05, 03:45 AM
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Default OK to overinflate tires?

Dave Reckoning writes:

I'm a lightweight, at 150 lbs, so I was wondering: what's the
downside of over inflating my tires somewhat? For instance, I am
commuting on a Schwalbe Marathon Slick that says it should be
inflated to 85 psi. What would happen if I routinely inflate it to
100? Tire explosions? Rim damage? Earth crashes into Sun? Jobst
admits that wheels hang from their spokes? Any other bad effects?


Bicycle wheels, like most machines, are systems which contain many
components. While the maximum pressure rating of the tire is
important I would be just as if not more concerned about the rating
of the rim to handle the tire size and pressure. Mavic shows
maximum inflation for their rim at:


http://tinyurl.com/8zskk

As you can see from this chart some of the strongest Mavic rims are
rated as low as 49 PSI for wide tires. I assume these are
conservative ratings but I would recommend that you pay attention to
them as you don't want to have a rim come apart on your front wheel
at speed!


It's not the rim that comes apart but the tire that blows off the rim,
something that can occur even at the recommended maximum inflation if
you use rim brakes on a long slow (much braking) descent. The
critical pressure results from the width of the inside-to-inside edge
of the rim bead (the area on which inflation pressure acts). Larger
tires have greater casing stress that could case a blowout but about
the same blow-off pressure.

That is what these pressures are about.

Jobst Brandt
  #14  
Old October 10th 05, 04:26 AM
jim beam
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Default OK to overinflate tires?

wrote:
Dave Reckoning writes:


I'm a lightweight, at 150 lbs, so I was wondering: what's the
downside of over inflating my tires somewhat? For instance, I am
commuting on a Schwalbe Marathon Slick that says it should be
inflated to 85 psi. What would happen if I routinely inflate it to
100? Tire explosions? Rim damage? Earth crashes into Sun? Jobst
admits that wheels hang from their spokes? Any other bad effects?



Bicycle wheels, like most machines, are systems which contain many
components. While the maximum pressure rating of the tire is
important I would be just as if not more concerned about the rating
of the rim to handle the tire size and pressure. Mavic shows
maximum inflation for their rim at:



http://tinyurl.com/8zskk


As you can see from this chart some of the strongest Mavic rims are
rated as low as 49 PSI for wide tires. I assume these are
conservative ratings but I would recommend that you pay attention to
them as you don't want to have a rim come apart on your front wheel
at speed!



It's not the rim that comes apart but the tire that blows off the rim,
something that can occur even at the recommended maximum inflation if
you use rim brakes on a long slow (much braking) descent. The
critical pressure results from the width of the inside-to-inside edge
of the rim bead (the area on which inflation pressure acts). Larger
tires have greater casing stress that could case a blowout but about
the same blow-off pressure.

That is what these pressures are about.

Jobst Brandt


but jobst, larger tires at higher pressures /do/ cause greater rim
stress. you know, fatigue, cracking, that kind of thing??? or is it
just anodizing - i forget which. whatever, mavic don't know a thing
about rims so we can ignore their tire pressure specs, just like we can
ignore their spoke tension specs.

  #16  
Old October 11th 05, 08:03 PM
Werehatrack
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Default OK to overinflate tires?

On 8 Oct 2005 13:32:59 -0700, "mort" wrote:

I'm a lightweight, at 150 lbs, so I was wondering: what's the downside
of overinflating my tires somewhat? For instance, I am commuting on a
Schwalbe Marathon Slick that says it should be inflated to 85 psi.
What would happen if I routinely inflate it to 100? Tire explosions?
Rim damage? Earth crashes into Sun? Jobst admits that wheels hang
from their spokes? Any other bad effects?


Rough ride. Increased fatigue due to vibration. Increased
possibility that the tire will unseat from the rim flange, allowing
the tube to blow out. Increased wear down the center of the tread
area. Slight reduction in the tendency to have pinch flats due to
road hazards. Increased probability of rim failure if the side
flanges of the rims are weak or badly worn.

For me, the first item is enough to make me lose enthusiasm for
overinflation. YMMV.


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  #17  
Old October 11th 05, 10:51 PM
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Default OK to overinflate tires?

the marathon's carcass is not the complex layup found on a conti tt is
it??
the TT at the rec pressure of 70 pounds flattens out on the bottom when
the bike is loaded with 50 pounds on the rear racks.
pumping to 85 pounds shapes the tire's contact area back toward the
form found when pumped to 70 pounds with a 160 pound rider. handles and
rides better at increased pressure for increased load-not slippery
the TT which is not normally slippery but grippppy gradually gets
slippreier with load but no increase in pressure
or at the high end of things that may be the focus here
the TT gets slippppreier under 70-80 pound loads even with the extra 15
pounds air
like glazee covered with water eeeeeyyahhhhh!!!
but maybe the layup prevents the tire from leaving the rim even at 110
pounds?? haven't tried it.

 




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