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Do underinflated tires increase the odds of getting a flat?

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Do underinflated tires increase the odds of getting a flat?

Old 05-02-09, 12:06 PM
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Digital Gee
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Do underinflated tires increase the odds of getting a flat?

Out cruising around the neighborhood this morning on my Globe, and noticed the tires were underinflated. No big deal, filled 'em when I got back home. The ride was slower and cushier, but on the errand bike, what's the rush.

Got to wondering, however, in terms of "for future reference." Do underinflated tires increase the odds of getting a flat?

The bike is black, if that matters.
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Old 05-02-09, 12:19 PM
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Grossly under inflated tires, especially when combined with rough roads, can lead to pinch flats when the tube gets caught between your rim and tire bead.

Riders of black bikes, though, seem to have a fine intuitive sense of when it's really time to haul out the pump.
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Old 05-02-09, 01:26 PM
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One has to strike a balance between too little air, which a gcottay says could increase the possibility of flats, and too much air which will make the tube/tire too heavy and could increase the possibility of flats. I haven't got a link, but I believe that this has been explored in depth at Goldielocks Bikes and has been postes on the web before.
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Old 05-02-09, 01:30 PM
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Originally Posted by Digital Gee View Post
Out cruising around the neighborhood this morning on my Globe, and noticed the tires were underinflated. No big deal, filled 'em when I got back home. The ride was slower and cushier, but on the errand bike, what's the rush.

Got to wondering, however, in terms of "for future reference." Do underinflated tires increase the odds of getting a flat?

The bike is black, if that matters.
White tubes have less flats.
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Old 05-02-09, 02:19 PM
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Never done the experimentation to find out if it is true but I do think you are right.

Whenever I have a puncture on a ride- The tyre is always flat.
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Old 05-02-09, 02:50 PM
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I'm not sure which Globe you have, you should state which one it is in your sig because there are 5 or 6 "Globe 2" models and they are all different.

If you have the Vienna 2, then you have 700x35 Nimbus anti-puncture tires, that probably inflate to around 80-90 PSI. Running those underinflated shouldn't make much different on getting flats. They won't roll as well, which would be particularly noticeable when going uphill. You probably wouldn't notice much of a difference until the pressure dropped below 60.

A road bike tire, like a 700x23 that runs at 110-120, will tend to get more pinch flats when underinflated. Very different beast than your Nimbus tires, much thinner width, height, and thinner rubber. It is hard to get a pinch flat on a wide, heavy hybrid-type of tire.
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Old 05-02-09, 04:19 PM
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A black bike you say.

Here's what you need to do, and you need to do this immediately. Ship the bike to me and I'll be sure to remove all the stale winter air from the tubes. I will then inflate each tire to the recomended pressure with fresh Great Lakes Region Summer air. Since it's for you, a venerable BF member of excellent standing I will also, at no charge, extensively test your bike over an extended period of time to ensure that the air performs to the high standards that you deserve.

I've cleared my schedule, my tools are clean and lubed and my repair stand and pump are at the ready.

I'm anxiously awaiting the arrival of my new, err, um I mean your venerable black bike.
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Old 05-02-09, 07:45 PM
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Cranky, don't you have enough bikes to ride already??!!

And weren't you the person who got a unicycle a little while back? How's that coming along?
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Old 05-02-09, 08:43 PM
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Originally Posted by Tom Bombadil View Post
Cranky, don't you have enough bikes to ride already??!!

And weren't you the person who got a unicycle a little while back? How's that coming along?
Never enough bikes. Buy! Buy! Buy!
I think I've got some kind of disease or something.

The unicycle's defective. Every time I try to ride it keeps tipping over!!
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Old 05-03-09, 05:35 PM
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Yes. Si. Ja. Da. Jawohl. Oui.
Affirmative in any language.
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Old 05-03-09, 08:18 PM
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Originally Posted by maddmaxx View Post
...and too much air which will make the tube/tire too heavy
say what?
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Old 05-03-09, 09:47 PM
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I have a great article on tire inflation and how to determine what is best for our tires and your weight, but it's PDF. I don't know how to upload it to this forum. Anyone?
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Old 05-03-09, 10:02 PM
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Originally Posted by Mojo Slim View Post
I have a great article on tire inflation and how to determine what is best for our tires and your weight, but it's PDF. I don't know how to upload it to this forum. Anyone?
Piece of cake. Open the PDF. Start a thread, and start typing everything that's in the PDF. In a matter of moments, you're good to go.
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Old 05-03-09, 10:33 PM
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Great suggestion, Deeg. I actually considered it, if it weren't for the charts and footnotes. Try this, everyone. Google "Jan Heine Tire Drop". The first entry that appears when I do it is, "Optimizing Your Tire Pressure for Your Weight". It takes me to the article. Good luck. I think you will all find it interesting.
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Old 05-03-09, 11:38 PM
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Originally Posted by Mojo Slim View Post
I have a great article on tire inflation and how to determine what is best for our tires and your weight, but it's PDF. I don't know how to upload it to this forum. Anyone?
If you go to "Manage Attachments"- you can add it as an attached file. I Have done it with Word documents but never tried a PDF file though.
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Old 05-04-09, 03:47 AM
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Originally Posted by maddmaxx View Post
too much air which will make the tube/tire too heavy and could increase the possibility of flats.
I'm sorry but I have to call BS on this one. More air will make the tire harder and less prone to pinch flats. Increasing air also reduces rolling resistance.

As far as increasing the weight, I just don't get that at all.
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Old 05-04-09, 04:07 AM
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Originally Posted by stapfam View Post
Never done the experimentation to find out if it is true but I do think you are right.

Whenever I have a puncture on a ride- The tyre is always flat.
I've experimented. Every time I had a flat readings were - zero pressure no air.
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Old 05-04-09, 04:10 AM
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Originally Posted by gear View Post
I'm sorry but I have to call BS on this one. More air will make the tire harder and less prone to pinch flats. Increasing air also reduces rolling resistance.

As far as increasing the weight, I just don't get that at all.
Partial BS. I agree on the weight thing, but most of my flats were at high pressure. Pot holes, small glass, even small chips of rock, etc. lower pressure allows 'give'. higher pressure causes high pressure points. just my $0.02
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Old 05-04-09, 10:07 AM
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Originally Posted by gear View Post
As far as increasing the weight, I just don't get that at all.
You haven't tried San Diego Air. As DG found out- Every spring you have to change from Winter to Summer Air- otherwise the bike gets sluggish.
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Old 05-04-09, 10:16 AM
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I have nothing scientific on which to base this, but, yes - under-inflated tires are more prone to flat.

I went through several years of riding before I broke down and bought myself a floor pump. Prior to that I used my frame pump and went to the gas station to use their air tower - practices that resulted in me riding on under-inflated tires more often than I should have. After buying my floor pump (and checking my pressure before every ride), I experienced a HUGE dropoff in the number of flats I get.
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Old 05-04-09, 10:30 AM
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Originally Posted by stapfam View Post
You haven't tried San Diego Air. As DG found out- Every spring you have to change from Winter to Summer Air- otherwise the bike gets sluggish.
Since I live at a relatively high elevation (~4000'), I always pump up my tires before leaving for an out of town ride (which is almost always at lower elevation). That way, my tires are filled with high-elevation air, which everyone knows is thinner and therefore lighter than lower-elevation air. Of course, if I'm headed some place like Denver (elev 5280'), I completely deflate my tires before leaving and pump them up when I get there, taking advantage of the even thinner air.

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Old 05-04-09, 10:38 AM
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Originally Posted by gear View Post
I'm sorry but I have to call BS on this one. More air will make the tire harder and less prone to pinch flats. Increasing air also reduces rolling resistance.

As far as increasing the weight, I just don't get that at all.
Increasing pressure reduces rolling resistance up to a point. Too high and the tires can't deform at all and wind up bouncing...it will actually slow you down.
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Old 05-04-09, 10:45 AM
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Originally Posted by Tom Bombadil View Post
A road bike tire, like a 700x23 that runs at 110-120, will tend to get more pinch flats when underinflated. Very different beast than your Nimbus tires, much thinner width, height, and thinner rubber. It is hard to get a pinch flat on a wide, heavy hybrid-type of tire.
I'm not sure about that...I can't speak about pinch flats from experience (I keep my tires properly inflated!) I know a lot of cyclocross racers prefer tubulars to clinchers precisely because they can run them at a lower pressure without worrying about pinch flats. And of course they're mostly running tires in the 34-35 mm range.

I keep the tires on my cross bike a little over 40 psi. Works pretty well.
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Old 05-04-09, 10:45 AM
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No, but it might ruin your knees...

Also, per a controversial post a few months ago, a cyclist from our club was killed about 6 months ago when her front tire blew out at the bottom of a very long mountain downhill. I have not heard what caused the blowout, but, from my own experience and being "raised in the sport" by former bicycle mechanics, it's very possible that the tires were inflated to their maximum (perhaps 140 psi), and, due to the constant braking of mountain roads, perhaps caused the rims to overheat and caused the fatal blowout, so, being underinflated can be dangerous, but, like car tires, being over-inflated is just as bad.

Best to get a gage or have a tire pump with one, and keep about 80-85% of the maximum rated pressure in the tires at all times - that will allow for a good ride but keep the tires within safe limits.

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Last edited by Glades2; 05-04-09 at 01:24 PM.
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Old 05-04-09, 10:59 AM
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Originally Posted by Glades2 View Post
No, but it might ruin your knees...

Also, per a controversial post a few months ago, a cyclist from our club was killed about 6 months ago when her front tire blew out at the bottom of a very long mountain downhill. I have not heard what caused the blowout, but, from my own experience and being "raised in the sport" by former bicycle mechincs, it's very possible that the tires were inflated to their maximum (perhaps 140 psi), and, due to the constant braking of mountain roads, perhaps caused the rims to overheat and caused the fatal blowout, so, being underinflated can be dangerous, but, like car tires, being over-inflated is just as bad.

Best to get a gage or have a tire pump with one, and keep about 80-85% of the maximum rated pressure in the tires at all times - that will allow for a good ride but keep the tires within safe limits.

Glades2
This quote is a small snip from a Velo News article about pressure ratings and rims. I might prove interesting.

"I believe that this will continue to be an issue for all manufacturers of clincher rims. To explain in greater detail, with a 23C tire each 10-degree increase in rim surface temperature above an ambient temperature of 70 degrees Fahrenheit will result in a corresponding increase in tire pressure of 1psi. On longer descents with accompanying heavy or near-continuous braking, the energy transferred by braking into the rim will routinely raise the surface temperature to well over 300 degrees Fahrenheit and can under extreme conditions reach over 400 degrees. Again assuming an ambient temperature of 70 degrees, a conservative 300-degree rim surface temperature means an air pressure increase of 23psi"
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