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Tire Pressure Question

Old 04-05-09, 07:10 AM
  #1  
degnaw
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Tire Pressure Question

I don't have a pump with a working pressure gauge, nor do I have a presta compatible tire gauge.

At 85 psi, with 700x32 tires, how firm should the tires be when I lean on them? I weigh 110, and currently they flex outwards about 1mm, but I'm afraid to put more air in when I can't accurately see what the pressure is.

Sorry for the stupid question; I could buy a new pump or a gauge, but my LBS is 20 miles away and this seemed easier.
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Old 04-05-09, 08:12 AM
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I heard that the tire manufacturers list the suggested pressure as half of the pressure it takes to blow the tire off of the rim. So it takes some doing to put too much pressure in a tire.

Rolling resistance decreases with pressure. But rolling resistance tends to not decrease much with increasing pressure above 90 PSI for 23 mm tires. Also you get the negative of getting a harsher ride when you put in a bunch of pressure. Why pay $$$ for that super compliant frame and then negate much of it by riding rock hard tires?

The major reason to add pressure to a tire is to prevent pinch flats when you go over a pebble or hit a small ridge or so on. I would think that with your stated 1 mm flex that you are probably safe from getting a pinch flat.
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Old 04-05-09, 08:39 AM
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Originally Posted by Pat View Post
I heard that the tire manufacturers list the suggested pressure as half of the pressure it takes to blow the tire off of the rim.
I've heard that statement from a number of sources none of whom had anything to do with manufacturing or marketing bicycle tires. I wonder if it's true.
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Old 04-05-09, 09:20 AM
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You can buy a good electronic guage in the automotive section of just about any store, for less than $10. Good up to 100#
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Old 04-05-09, 09:23 AM
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Originally Posted by Wanderer View Post
You can buy a good electronic guage in the automotive section of just about any store, for less than $10. Good up to 100#
do these work with presta valves?
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Old 04-05-09, 09:28 AM
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If you have a schrader pressure gauge, you can get a presta to schrader adapter for around $3. It's worth the trip. Buy a couple they are cheap.

Originally Posted by Retro Grouch
I've heard that statement from a number of sources none of whom had anything to do with manufacturing or marketing bicycle tires. I wonder if it's true.
I wonder what rim?
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Old 04-05-09, 10:14 AM
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Since you obviously have access to the internet, and since USPS, UPS, and FedEx deliver to your door, 20 miles to the LBS is irrelevant, I'd say.
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Old 04-05-09, 10:47 AM
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Originally Posted by 2manybikes View Post
If you have a schrader pressure gauge, you can get a presta to schrader adapter for around $3. It's worth the trip. Buy a couple they are cheap.
Will an ordinary Schrader pressure gauge and an adapter work with a presta tube? I'm thinking the little Schrader finger won't go down far enough to push the poppet valve open.
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Old 04-05-09, 11:58 AM
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If you weigh 110, it's not going to be super critical.

Air your tires up until they feel right, ride to the bike store, buy a gauge.
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Old 04-05-09, 01:12 PM
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On tyre pressure as recommended. I ride my Michelin PR2's at 140 psi--recommended max is 116psi.

Tandems take a lot of weight so I always go 20% over the max recommended to stop Pinch Flats.

Only problem with High pressure is that it will give you a harsh ride- but the bike rolls better.

Unless you do have a high pressure floor pump- you will not be able to get above the max on a tyre with a frame pump- unless you have a lot more strength than I have. Low pressures as run on MTB's are the exception.
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Old 04-05-09, 01:58 PM
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My Bontrager 700 X 32C tires say 110 psi Max. I would think 90 would be fine for around-the-town cruising. But I don't use them. They came stock on a Trek 7.5 FX. I swapped 'em for some 700 X 28C tires - with a Max. of 100 psi!
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Old 04-06-09, 09:10 AM
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Now that you have the answer to your question - go buy a "patented" tire pressure gauge in the range for bikes. DO NOT buy a gauge that is not "PATENTED" it will just be a waste of money.
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Old 04-06-09, 09:46 AM
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at 110lbs, does one even need to inflate their tires?
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Old 04-06-09, 09:51 AM
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be nice
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Old 04-06-09, 10:04 AM
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Originally Posted by Retro Grouch View Post
Will an ordinary Schrader pressure gauge and an adapter work with a presta tube? I'm thinking the little Schrader finger won't go down far enough to push the poppet valve open.
Typically it works, however, there is a lot of room for error. One needs to screw the adapter on far enough. Some valve stems have lousy threads and don't thread down far enough to make it work. Also, different brands of Schrader adapters and even ones from the same batch can be different lengths. At the house I always use the same ones, it works fine. But at a shop some might not work right out of the jar, it has happened to me a few times. If the rider bends the interior stem on the presta valve sometimes they hit the side of the adapter and don't go down smoothly, even though one can thread on the adapter. A bent interior valve stem can spin the presta button down the treaded shaft as the adapter goes on too. It always works for me, but I don't mind messing around with it, and I learned not to bend the presta treaded rods. I learned all this mainly because I have a compressor at home and a compressor at the LBS with a Schrader head. It was worth the trouble for me learn to make it work to use the compressors, and then use the Schrader pressure gauge.

I'm sure you know plenty of people who don't get it, or don't care. At a shop with a presta pump with a gauge, who cares?
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Old 04-06-09, 10:31 AM
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Originally Posted by grimace308 View Post
at 110lbs, does one even need to inflate their tires?
I recall that when I was 12 years old and 110 lbs I never checked my tire pressure so the answer. obviously is NO.
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