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tire PSI max's...whats the difference?

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tire PSI max's...whats the difference?

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Old 12-07-08, 08:51 PM
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iamthenoise
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tire PSI max's...whats the difference?

vittoria zaffiro pro's run a max psi of 60....

its my understanding that an underinflated tire is a slower tire (more rolling resistance), does that mean a maxxed out zaffiro at 60 psi is slower than a 140psi max tire run at 100psi? in other words, the higher the max psi, the faster the tire?

im a bigger guy (190, 6'0) and 60 psi max just seems....low.
enlighten me please.
....and yes im working on my weight. hah
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Old 12-07-08, 08:59 PM
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Zaffiros do not have a max PSI of 60. They have 60 tpi, threads per inch of tire casing.

And max PSI don't really provide information about the speed of the tire. The person riding the bike on which the tire is mounted provides information about the speed of the tire.
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Old 12-07-08, 09:03 PM
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you're working on your weight? that doesn't sound bad. I'm 4 inches shorter and 25 pounds heavier.
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Old 12-07-08, 09:24 PM
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Originally Posted by queerpunk View Post
Zaffiros do not have a max PSI of 60. They have 60 tpi, threads per inch of tire casing.

And max PSI don't really provide information about the speed of the tire. The person riding the bike on which the tire is mounted provides information about the speed of the tire.
i just looked at em again...you're absolutely right. and on both counts. im trying to figure out what the difference between max psi's mean in real world terms.
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Old 12-07-08, 09:29 PM
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Originally Posted by iamthenoise
...the higher the max psi, the faster the tire?
Yes and no.

Common sense and logic would tell us that the higher the pressure the faster the tire, but this doesn't always hold true, and especially so with modern tires.

In some cases, a lower pressure than the maximum allowed will actually produce less rolling resistance.

I think some manufacturers, such as Schwalbe, allow for higher pressures than optimum, for the sake of heavier riders.

I ride my Schwalbe Ultremos at their highest rated pressure, 145psi, because I weigh 235lbs with winter commute stuff.

Last night I hit a deep pothole that knocked my blinkie off my seatpost, but did not blow the tires nor damage the wheels.

I think I can thank the 145psi of the Ultremos and the toughness of my Cane Creek wheels for that.
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Old 12-07-08, 11:06 PM
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The other variable that effects rolling resistance is the texture of the road surface. Track tires are inflated to 190 PSI or higher, which is efficient because a bike track is perfectly smooth. However if you rode a 190 PSI tire on an average asphalt or grooved concrete surface, it would be less efficient than a 120 PSI tire (in general - this also depends on tire design)

The reason for this is that a properly inflated road tire absorbs the small textures in the road and rolls smoothly, whereas a track tire would bounce over each inconsistency in the asphalt, not only affording you less grip, but also eating up energy by vibrating you and the bike.

Generally tires are designed with a specific optimum pressure, which is at or near maximum inflation pressure. If you consistently ride on very rough asphalt surfaces, perhaps you should back off of max pressure by 10-15 PSI, or conversely, if your locality is blessed with perfectly smooth pavement, pump 'em up all the way to the max.

I usually ride tires rated at 120 PSI, and I inflate them to about 110 or 115 which i find to be a good balance (i'm 6'4" 200lbs).

For a while I used a pair of Tufo clincher tubulars that were rated for 145, however I preferred the ride quality with them closer to 120.

I can always tell when my tires are getting low because they start to feel like they want to pinch every time i hit a little ridge. This happens around 90 PSI, and i know that it's time to get out the pump
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Old 12-08-08, 06:11 AM
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Definitely +1 about road surface. If you're looking to achieve maximum speeds, you have to consider what and where you're riding. Maximum speed might be about cornering sharper and more precisely, which means you'd probably want to bleed a bit of air out of your tires to increase your contact point to not wash out on tight corners at high speeds.

But that's about racing.
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Old 12-08-08, 07:22 AM
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Originally Posted by queerpunk View Post
Zaffiros do not have a max PSI of 60. They have 60 tpi, threads per inch of tire casing.

And max PSI don't really provide information about the speed of the tire. The person riding the bike on which the tire is mounted provides information about the speed of the tire.
26 tpi actually.
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Old 12-08-08, 07:30 AM
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Oh dang, look at me doing no research. I assumed that the confusion was the one I was thinking of.
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Old 12-08-08, 07:34 AM
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Hah, the Pros are 60.
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Old 12-08-08, 08:20 AM
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vittoria zaffiros have a 60tpi peabody

to the OP, max PSI also has to do with the type of tire and the strength of the sidewall because i've had older tires (on my mtb) where i neglected to follow the instructions on max psi and bubbles started to form in the side wall (steel bead, i think) which then render the tire useless.

example
vittoria rando's have a "low"er psi rating than gatorskins, and i personally attribute this to the strength of the side wall and the different use of each tire as randos are more so hybrid cross tires than road tires. and tubular wheels has like a 200+ psi rating.

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Old 12-08-08, 09:04 AM
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Larger volume tires will also have a lower max PSI.
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Old 12-08-08, 11:22 AM
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Originally Posted by jdms mvp View Post
vittoria zaffiros have a 60tpi peabody

http://www.vittoria.com/index.php?op...719&Itemid=208

Vittoria would like to say otherwise.
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Old 12-08-08, 11:49 AM
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i think he's referring to this...



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Old 12-08-08, 12:42 PM
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http://www.michelinbicycletire.com/m...rpressure.view
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Old 12-08-08, 04:48 PM
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thanks!
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Old 12-08-08, 06:20 PM
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that's a good graph and shows exactly where I pump my tires without ever seeing that graph. I never go to 120 and anything less than 100 is just sluggish. 110 psi is my sweet spot for my weight and tire size and the math behind the chart agrees.

now, of course, when referencing a chart such as this, be sure to factor in true tire size. not all tires are what they are advertised to be (i.e. a 25mm can be a 23mm). Best to measure if you want accuracy.
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Old 12-08-08, 06:36 PM
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that chart doesn't do much for those of us over 180 lbs. Though I'd assume it means i should inflate to max pressure, which i do anyway.
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Old 12-08-08, 07:00 PM
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Originally Posted by dayvan cowboy View Post
that chart doesn't do much for those of us over 180 lbs. Though I'd assume it means i should inflate to max pressure, which i do anyway.
the chart does nothing, but the top line is "for riders above 180 pounds... ."
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