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Tire pressure question

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Tire pressure question

Old 04-27-09, 08:53 PM
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chinarider
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Tire pressure question

I recall there was a thread a year or 2 ago about proper tire pressure. Kind of debunked the common wisdom that the highest pressure was always best. Included some graphs to determine proper pressure based on tire size & rider weight. I thought I saved a link, but can't find it. Anyone remember this & have the link? BTW I tried the search function, but couldn't find it.

Another question: my bike came with 700x 28s (standard bontragers). I need to replace them & am thinking of going to 25s. Will it make a difference in performance? Is the tradeoff in comfort worth it? The LBS has a pair of IRC Redstorms 700 x 25s someone ordered but didn't pick up. He'll sell them to me cheap. Are they better than the Bontragers?

Thanks for any help.

Dan
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Old 04-27-09, 09:08 PM
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psimet's tip of the day?

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Old 04-27-09, 09:12 PM
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Michelin has a cool chart of recommended bicycle tire pressures for different rider weights and tire widths. I think this same chart is printed on the box of new Michelin bicycle tires.
http://www.michelinbicycletire.com/m...rpressure.view
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Old 04-27-09, 09:17 PM
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Originally Posted by johnny99 View Post
Michelin has a cool chart of recommended bicycle tire pressures for different rider weights and tire widths. I think this same chart is printed on the box of new Michelin bicycle tires.
http://www.michelinbicycletire.com/m...rpressure.view
That is a useful chart.
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Old 04-27-09, 10:18 PM
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Originally Posted by AEO View Post
psimet's tip of the day?

use search with title only
That was a cool thread....
http://www.bikeforums.net/showthread.php?t=410701

Originally Posted by yours truly
Tip 1 - Inflate your tires before every single ride. Know what the proper inflation pressure should be for your tires. Inflation requirements will vary by rider, bike, tires, conditions, etc.

Below you will find equations that you can use to help determine an appropriate starting point using your weight and the tire's size. Adjust from these baselines to suit needs and conditions.

Proper inflation is the easiet way to avoid flats.

Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33

Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67


Example: You are 150lbs running 28's

Pressure (psi) = (0.33*150) +33.33 = 82.83psi (rear)
Front Pressure = .9*Rear Pressure = .9*82.83psi = 74.55psi front
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Old 04-27-09, 10:20 PM
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Originally Posted by AEO View Post
psimet's tip of the day?

use search with title only
I did (unsuccessfully).
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Old 04-27-09, 10:50 PM
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What doesn't make complete sense is the almost universal use of 700cx28 tires on road tandems. A 350 lb team (not unusual) would need 150 psi assuming equal weight on the front and rear axles. I'm assured that something around 110 psi will avoid pinch flats, but might be a bit high regards rolling resistance. Definitely something to think about.

I'm looking at a tandem and will consider 650 wheels since when I ride with one of my sons we'll be upward of 400 lbs.
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Old 04-28-09, 07:41 AM
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Originally Posted by Psimet2001 View Post
Thanks for the reply, but actually that's not the thread I was looking for. The one I was thinking of was older & had some different graphs.
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Old 04-28-09, 07:43 AM
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Here is another chart.
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Old 04-28-09, 09:11 AM
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Originally Posted by Psimet2001 View Post
If you want a useless, follow the tire pressure recommendation in that post. It is *wrong*. I love how all charts/formulas think they're the definitive answer to tyre pressure without adding a caveat that it's just a *starting point*.
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Old 04-28-09, 09:24 AM
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Ok, so following these chart's and calc's advice, they says I should run my pressure at 105 psi. Yet the tires I use, Vittoria Diamante Pro Lite's say use a minimum of 130 psi, up to 160. Obviously I will follow the tire's instructions, but then what is the use of the charts, etc.?
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Old 04-28-09, 10:05 AM
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Originally Posted by rdtompki View Post
What doesn't make complete sense is the almost universal use of 700cx28 tires on road tandems. A 350 lb team (not unusual) would need 150 psi assuming equal weight on the front and rear axles. I'm assured that something around 110 psi will avoid pinch flats, but might be a bit high regards rolling resistance. Definitely something to think about.

I'm looking at a tandem and will consider 650 wheels since when I ride with one of my sons we'll be upward of 400 lbs.
We run Conti GP 4 seasons that are rated at 116psi/8bar at max pressure front and rear.
Team + bike is around 400lbs. Haven't had a pinch flat so far. We can go close to 40mph, so rolling resistance doesn't seem to be much of an issue.
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Old 04-28-09, 10:08 AM
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Originally Posted by elros14 View Post
Ok, so following these chart's and calc's advice, they says I should run my pressure at 105 psi. Yet the tires I use, Vittoria Diamante Pro Lite's say use a minimum of 130 psi, up to 160. Obviously I will follow the tire's instructions, but then what is the use of the charts, etc.?
Putting a very high "minimum pressure" and an insanely high max pressure on a tire makes people think it is faster and better.
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Old 04-28-09, 10:16 AM
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Originally Posted by operator View Post
If you want a useless, follow the tire pressure recommendation in that post. It is *wrong*. I love how all charts/formulas think they're the definitive answer to tyre pressure without adding a caveat that it's just a *starting point*.
No it's not....and it does say that it's a starting point...like all recommendations are. Read the original thread.
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