Tire pressure.
Kendall Wu
Hi, everyone.
Got a question about tire pressure. I know that you can pump up
tubulars a lot higher than clinchers, and this is supposed to make the
rolling resistance a lot less on tubulars than on clinchers. So, my
question is how high people have pumped up their clinchers? Most
conti's have a listed max of 120 psi, though I've seen one clincher that
can go as high as 150 psi. Has anyone tried pumping up a clincher
really high (like 170 psi)?
-Kendall
Stacy Hills
My conti GPs are rated max pressure 150 psi/11 bar. If you get anal and look up the conversion factor from atmospheres to psi in you handy "CRC Standard Mathematical Tables" by CRC press(doesn't everyone have one?) you'll find the number is 14.7059 psi/atmosphere. Take it one step further and convert 11 bars to 161.7647 psi.
Hmmm. Which rating do they want you to use?
NOTE: I'm only an EE and its been a long time since that required semester of thermodynamics so please go easy on me if I've screwed up and not accounted for something else.
For what its worth, I often put 160 psi in those same tires without a bit of trouble.
Furthermore, I just changed from my 120 psi(I think they were 650x23) Hutchinsons to 150 psi(650x3/4) conti GPs. I definitely noticed the difference in feel. Maybe its just psychological, but I think the contis felt quicker and less mushy.
Stacy Hills
SHi...@VCTInc.com
Reston, VA
Kendall Wu wrote in message <3536B8...@uthscsa.edu>...
Clive Jones
Kendall Wu wrote:
> Got a question about tire pressure. I know that you can pump up
> tubulars a lot higher than clinchers, and this is supposed to make the
> rolling resistance a lot less on tubulars than on clinchers. So, my
> question is how high people have pumped up their clinchers? Most
> conti's have a listed max of 120 psi, though I've seen one clincher
> that can go as high as 150 psi. Has anyone tried pumping up a
> clincher really high (like 170 psi)?
Some clinchers have dual ratings - you can go 20PSI or so higher on a
'hook bead rim', which tends to be a narrower rim with a more pronounced
groove inside that the tyre bead mates with.
Over-pressuring the tyre, in my experience either rapidly causes the
tyre to split on the sidewall, allowing the innertube to poke through
and burst, or the bead lets go of the rim and the tyre bulges.
Tyre manufacturers spend a lot of money testing to provide optimum
pressure ratings for their products, so it is probably not worth
exceeding them.
##################### CLIVE JONES #################################
SWINDON
UK
John Isgren
Not that this reallly matters, but some of us anal-engineer types have to
chime in when we can to spout off useless knowledge!!!
The difference con calcualted is due to the difference in aboslute pressure
and gauge presure. Gauge pressure subtracts the normal atmospheric
pressure from the system (tire) pressure. This way your pressure gauge
reads zero when the tire is flat and it is only reading atmoshperic
pressure (14.7 psia). Absolute pressure is the total pressure on the
system, ie the pressure in the tire plus the pressure do to the the weight
of our atmosphere. (The air exerts 14.7 lbs/sq inch at sea level. )
The 150 psi is actual 150 psig or gauge pressure, but the pressure in bar
is an absolute pressure. Therefor to convert you take the 11 bar * 14.7 to
get 162 psia (absolute pressure: Tire pressure on gauge + 14.7 psi for the
atmosphere) To get to gauge subtract 14.7 from 162 to get ~147 which is
close enough to 150!
I hope I have not confused this even more than its worth, and like I said,
nobody probably really cares!!
John Isgren
Matt Pope
John Isgren wrote:
>
> of our atmosphere. (The air exerts 14.7 lbs/sq inch at sea level. )
>
> The 150 psi is actual 150 psig or gauge pressure, but the pressure in bar
> is an absolute pressure. Therefor to convert you take the 11 bar * 14.7 to
> get 162 psia (absolute pressure: Tire pressure on gauge + 14.7 psi for the
> atmosphere) To get to gauge subtract 14.7 from 162 to get ~147 which is
> close enough to 150!
Psi and Bar are both valid pressure units and can be converted back and
forth using the factor Stacy cited. They can both be used to measure
EITHER absolute or gage pressure. A bike pump gage scaled to Bars is
going to be reading a "gage" pressure in Bars. So if you bike pump
reads 11 Bars gage pressure this does convert to 160 psig, or 174.7
psia. John is assuming Conti used gage pressure in one case and absolute
in another for their specifications. If so, they have added to the
confusion. Stacy, pump those tires to 150 psig and let's all throw away
our engineering reference books.
--
Regards,
Matt Pope
mailto:mp...@ricochet.net
Doug Fuller
Kendall Wu wrote:
>
> Hi, everyone.
>
> Got a question about tire pressure. I know that you can pump up
> tubulars a lot higher than clinchers, and this is supposed to make the
> rolling resistance a lot less on tubulars than on clinchers. So, my
> question is how high people have pumped up their clinchers? Most
> conti's have a listed max of 120 psi, though I've seen one clincher that
> can go as high as 150 psi. Has anyone tried pumping up a clincher
> really high (like 170 psi)?
>
I accidentally over-inflated my 100psi recommended, 110psi max, 650x23
Hutchinsons to 120 just before a race last season. Two minutes later
people were ducking for cover as it sounded like a gunshot when it let
go. The tube was shredded so I installed my only spare (foreshadowing
for the astute reader) and underinflated to about 90 or 95psi. I was
then amazed and thrilled that I was 4th out of the water heading into my
strong leg (the bike). About two miles into the bike I hit a bump on
the road and got a pinch flat. After patching the tube, I climbed back
aboard really bummed that I just lost about 8 minutes and, no doubt, the
best finish of my short and not very illustrious career.
Advice:
- Don't overinflate
- Don't use Hutchinsons
- Bring several spare tubes
- Bring extra tires
- Don't underinflate
These were my first foldables and I was wary from the start. I always
thought that the flexible bead couldn't be as strong as a rigid bead,
but maybe I'm drawing an illogical conclusion (won't be the first time).
Good luck,
Doug
Rick Denney
Okay, guys, let's keep our eye on the ball. The pressure of the tire
directly affects rolling resistance. Rolling resistance provides a
small amount of drag compared with aerodynamic drag, so even a
significant improvement in rolling resistance will have a small effect
on total drag.
But, every little bit helps. Remember that riding a bicycle is
achieving a dynamic balance between drag and power. Reducing drag is
like adding power, and adding power is why we all spend so many hours
training, at least between Overwaitea feeding frenzies.
Matt's right: both the bar and psi ratings are gauge ratings. But it's
the gauge rating that counts. A tire inflated to 150 psi absolute will
will fall off the rim if you put it in a hyperbaric chamber set at 150
psi. It's the difference between the pressure inside and outside the
tire that counts.
Good tires can be inflated to much higher values than their ratings,
especially for races. The ratings provide a margin to accommodate a
host of errors, not least of which is the notorious inaccuracy of most
pump gauges.
Vittoria Open Extremes are rated to 12 psi, even in the 23 mm size.
I'd feel perfectly safe (except for the longevity of my fillings) with
200 psi in them.
The difference between the 150 psi and 11 bar rating of Conti GP 3000
tires is probably just rounding convenience. Not to mention that a
conventional bar in Europe is not the exact same thing as a bar as
defined in scientific circles.
On Thu, 16 Apr 1998 17:16:54 +0100, Clive Jones
<jon...@ecid.cig.mot.com> wrote:
>Kendall Wu wrote:
>> Got a question about tire pressure. I know that you can pump up
>> tubulars a lot higher than clinchers, and this is supposed to make the
>> rolling resistance a lot less on tubulars than on clinchers. So, my
>> question is how high people have pumped up their clinchers? Most
>> conti's have a listed max of 120 psi, though I've seen one clincher
>> that can go as high as 150 psi. Has anyone tried pumping up a
>> clincher really high (like 170 psi)?
>
>Some clinchers have dual ratings - you can go 20PSI or so higher on a
>'hook bead rim', which tends to be a narrower rim with a more pronounced
>groove inside that the tyre bead mates with.
>
>Over-pressuring the tyre, in my experience either rapidly causes the
>tyre to split on the sidewall, allowing the innertube to poke through
>and burst, or the bead lets go of the rim and the tyre bulges.
>
>Tyre manufacturers spend a lot of money testing to provide optimum
>pressure ratings for their products, so it is probably not worth
>exceeding them.
>
>##################### CLIVE JONES #################################
>SWINDON
>UK
Rick Denney
Take what you want and leave the rest.
Rick Denney
>
>I accidentally over-inflated my 100psi recommended, 110psi max, 650x23
>Hutchinsons to 120 just before a race last season. Two minutes later
>people were ducking for cover as it sounded like a gunshot when it let
>go. The tube was shredded so I installed my only spare (foreshadowing
>for the astute reader) and underinflated to about 90 or 95psi. I was
>then amazed and thrilled that I was 4th out of the water heading into my
>strong leg (the bike). About two miles into the bike I hit a bump on
>the road and got a pinch flat. After patching the tube, I climbed back
>aboard really bummed that I just lost about 8 minutes and, no doubt, the
>best finish of my short and not very illustrious career.
>
>Advice:
> - Don't overinflate
> - Don't use Hutchinsons
> - Bring several spare tubes
> - Bring extra tires
> - Don't underinflate
>
>These were my first foldables and I was wary from the start. I always
>thought that the flexible bead couldn't be as strong as a rigid bead,
>but maybe I'm drawing an illogical conclusion (won't be the first time).
>
>Good luck,
>Doug
With a hooked-bead rim, such a mishap is almost always attributed to
the tire not being on the bead properly in the first place. I've done
the same thing. Anytime your tire blows a rim within minutes of
inflation, it is just about guaranteed to be a mounting problem.
So, if you remove that variable, then you have to remove the "don't
overinflate" instruction from your list. But you can add "make sure
the bead is properly seated before adding full pressure."
Bottom line: Overinflation, up to a point, is mostly safe. It reduces
rolling resistance. One down side is that it reduces the size of the
contact patch, and therefore reduces traction. The other down side is
that it makes for a much harsher ride.
Lynne Fonda-Kosorek
<listening to the sound of tires popping like firecrackers at Wildflower>
Rick Denney
>Vittoria Open Extremes are rated to 12 psi, even in the 23 mm size.
>I'd feel perfectly safe (except for the longevity of my fillings) with
>200 psi in them.
>
Speaking of not keeping my eye on the ball! The vitts are rated at 12
_bar_. 12 psi would be an unfortunate tire indeed.
BPSullivan
> - Don't use Hutchinsons
I wouldn't take this advice, at least not regarding blowouts. I rode
Hutchinsons in training and racing for a year on some rough roads and never had
a single flat. They were the most comfortable tires I ever had. But I felt that
at 100psi they were just too mushy for my 6', 180lb frame, and so I went to a
Vredestein (never could spell that) on the front and a Conti GP on the rear.
I'm much happier with the 120-140 psi they'll take.
Brian Sullivan
bpsul...@aol.com
Tridog
In article <199804261336...@ladder03.news.aol.com>,
bpsul...@aol.com says...
Humm. I am riding on Specialized Transition Armadillo tires,
rated to 105 psi, and I fill them to 125-130 without hesitation.
And yes, I too and 6'1" and 180ish.
Rob
--
Rob Blomquist aka TriDog
Seattle, WA
tri...@jps.net
http://www2.jps.net/~robbo
dco...@dial.pipex.com
In article <MPG.fad59f06...@209.63.114.134>,
tri...@jps.net (Tridog) wrote:
> Humm. I am riding on Specialized Transition Armadillo tires,
> rated to 105 psi, and I fill them to 125-130 without hesitation.
> And yes, I too and 6'1" and 180ish.
Yes, also being in this height & weight category, I'm using Continental Grand
Prix's which I pump to 120. I always pump to the max allowed pressure as
indicated on the sidewall. A cycle shop owner assured me that the tyres are
often tested to well beyond this recommendation. However I wouldn't try 160 !
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