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Tire Pressure - The harder the better?

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Tire Pressure - The harder the better?

Old 04-13-11, 07:15 AM
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FasterNearGirls
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Tire Pressure - The harder the better?

Will the highest pressure possible give me the least rolling resistance and more speed however a rougher ride and less grip? That's what I always thought but I read somewhere that a harder tire is actually slower. (?)

On my 25C maximum recommended 130 psi, i usually inflate it to just over that; about 135 psi (I'm 163 lbs).

Same with my 23C Pro Race max = 116 and I go slightly over.

Thanks!
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Old 04-13-11, 07:23 AM
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With your weight and a 25mm tire, you're about 35 pounds higher than you need to be.

There are a number of tests that show that higher pressures do in fact increase rolling resistance on real world roads. There are links in various threads arround here.

The reason higher pressure increases rolling resistance is beacuse a rock hard tire bounces over imperfections in the road, rather than conforming to the imperfections and rolling over them. Leonard Zinn has done a couple of good pieces in Velonews explaining this.

Finally, the pressure on the side of the tire is a Maximum pressure not to be exceeded, it's not a recommendation that you fill them to that.
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Old 04-13-11, 07:25 AM
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I know I can go much lower, but I'm wondering if the higher = the faster?

I see you edited the above. Thanks.

Last edited by FasterNearGirls; 04-13-11 at 07:49 AM.
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Old 04-13-11, 07:26 AM
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After a certain point, more PSI = more rolling resistance. A harder tire is less able to conform to bumps in the road that it will otherwise smoothly roll right over. That actually slows you down. You are not doing yourself, or the life of your tires, any good by over inflating.
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Old 04-13-11, 07:26 AM
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I ride with 100psi front and back, realized it didn't changed much from 100 to 110. So at least I'll have some grip and some shock absorption. Btw I ride GP4000S, 700x23.
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Old 04-13-11, 07:27 AM
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On a theoretically perfectly flat and smooth surface the harder tire would roll better, but in reality the bumps and irregularities of a typical road will cause an overinflated tire to bounce up and down vertically instead of absorbing the bumps. That causes increased rolling resistance and also makes for a crappy ride.
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Old 04-13-11, 07:28 AM
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Over inflating your tires is NOT a good thing. your jsut asking for one to fail.
Also, higher pressure is not a solution to lower Crr unless you are on a track or very smooth surface. At your weight and that tire width I'd go not a lot higher than 105psi.

FWIW I'm 185 on a 22c tire (rated to 140psi) and ride at 110psi for everyday stuff. I'll ride 120psi for racing TTs and Tri
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Old 04-13-11, 07:32 AM
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Higher pressure means lower rolling resistance, at least on smooth surfaces. More recently, some argue that when rolling over typical pavement, there is some point where high pressure becomes counterproductive and increases rolling resistance due to bouncing and deflecting over the small irregularities rather than deforming and smoothly rolling over them. To be complete, the effect of the rough ride on the rider's power output should be included. Here's some data on smooth surface rolling resistance:

http://www.terrymorse.com/bike/rolres.html
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Old 04-13-11, 07:42 AM
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Originally Posted by MegaTom View Post
After a certain point, more PSI = more rolling resistance.
I'm from the Show-Me-State; where's the study that backs this up?
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Old 04-13-11, 07:52 AM
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Thanks everyone! I knew you'd clarify this for me. I understand it perfectly now and will start riding at 100 psi on the 25s and maybe 95 psi on the 23s. I'll see how it goes.

Thanks again.
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Old 04-13-11, 07:55 AM
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Originally Posted by FasterNearGirls View Post
Thanks everyone! I knew you'd clarify this for me. I understand it perfectly now and will start riding at 100 psi on the 25s and maybe 95 psi on the 23s. I'll see how it goes.

Thanks again.
Typically you need higher pressure in narrower tires.
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Old 04-13-11, 07:57 AM
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Originally Posted by canam73 View Post
Typically you need higher pressure in narrower tires.
Oh. I should disregard that the maximum on my michelin 23c pro race 3 is lower than the 25s . Again thats just a maximum, I see. I'll ride 100 with both then.
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Old 04-13-11, 08:06 AM
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Originally Posted by Phantoj View Post
I'm from the Show-Me-State; where's the study that backs this up?
http://velonews.competitor.com/2007/...ce-redux_13059

http://velonews.competitor.com/2010/...ressure_145969

http://velonews.competitor.com/2005/...sty-roads_7508

http://velonews.competitor.com/2010/...uipment_149851

Admittedly, these links don't give you actual test data, but they do reflect knowledge gained from tests done by Zipp and Continental, and Pro Tour experience.

More Data:

http://velochimp.com/2006/11/21/rolling-resistance/
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Last edited by merlinextraligh; 04-13-11 at 08:13 AM.
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Old 04-13-11, 08:12 AM
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The max pressure rating has to do with keeping the tire on the rim. The idea behind having higher pressure in a narrow tire is compensate for having a narrower contact patch and ultimately prevent pinch flats. Also, most people find it nice to run a little less pressure in the front to absorb pumps and keep your hands and wrists comfortable. This is not a problem as the rear tire supports more of your weight.
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Old 04-13-11, 09:26 AM
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i have been experimenting with 95 in the rear and 90 in front and am very happy with it...
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Old 04-13-11, 09:37 AM
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Originally Posted by FasterNearGirls View Post
I know I can go much lower, but I'm wondering if the higher = the faster?

I see you edited the above. Thanks.
In a nutshell, on a perfectly smooth track...yes. Out on the road, no. Higher pressure on the road will make the bike bounce, where a lower pressure will make you glide over all the bumps and imperfections on the road.
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Old 04-13-11, 10:06 AM
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I don't think I am misinterpreting the available data, but rolling resistance (Crr) will actually decrease with higher pressure, not increase...BUT, decreased rolling resistance does not translate into faster speed. I think this is what folks are trying to say here. See Al Morrison's extensive studies at http://biketechreview.com/tires/roll...75-roller-data

The drive tire has to be grippy to transfer the power from the engine (you) to the road. As has been said, high pressure is going to cause bounce and otherwise lessen the contact patch of rubber to the road. This reduces the grip between the road and tire, (and consequently the rolling resistance) but this is not a good thing if you want to go fast.

There is a happy medium between minimizing the Crr of your tire which is probably a very minor force in impeding your forward progress, and maximizing things such as tire/tube longevity, smoothness of ride, and more importantly grip for cornering, and grip for forward propulsion.
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Old 04-13-11, 10:16 AM
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Originally Posted by merlinextraligh View Post
Admittedly, these links don't give you actual test data, but they do reflect knowledge gained from tests done by Zipp and Continental, and Pro Tour experience.
http://forum.slowtwitch.com/cgi-bin/...engine#1909561
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Old 04-13-11, 10:23 AM
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dont forget the human factor too, too high or rather, pumped to the number on the side of the tire (which I tended to do) means a harsher ride (depending on road surface of course) and more beating up on you, hence a more tired you....so this works against things in the "big picture" side of it.
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Old 04-13-11, 10:36 AM
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That chart and accompanying discussion is very interesting, especially with respect to the marked dichotomy of Crr between testing on rollers (smooth or not) and actual road....at least for that rider at ~120 psi was his break pressure for riding on the road, and it got way worse from there.

Bears out what many have been saying and what many feel just from actual experience and long time perceptions.
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Old 04-13-11, 10:51 AM
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i have vittoria rubino pros. the range given on the tire is something like 100-140 or 105-145 psi, can't remember exactly. i weigh 145ish and could probably run low pressure, but i usually keep them at about 120. i find the low end of the range feels a little squishy on hard efforts, and the ride isn't too much harsher at 120. i also ride over some massive potholes/cracks (crappy NJ roads) and have only ever gotten one pinch flat when my rear wheel slammed directly into the sharp edge of a pothole. i think that impact would have flatted anything, and in general i think the high pressure helps.

obviously rolling resistance changes, but i bet the differences aren't huge within recommended ranges. don't go over the max. experiment with different pressures and just go with what feels good to you.
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Old 04-13-11, 11:06 AM
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Check PSIMET's tip of the day from way back then.
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Old 04-13-11, 11:44 AM
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The harder the better?

True for some things in life (why they invented little blue pills) but not for bike tires.
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Old 04-13-11, 12:26 PM
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I have25c Vredestein Fortezzas. They show a min-max of 115-165psi. The maximum I understand; the minimum I never did get. Anyway I weigh 135-150 lbs and run low 90s in the back & low 80s in the front. Over 3000 miles and no problems ( other than 1 flat about a week after I got them; the tube was torn by the valve--probably from when I put the tires on).
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Old 04-13-11, 01:00 PM
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I use 23's and ride them at 120.
I like em' like stones.

S
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