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Newbie w/air pressure question
#1
I've been rebuilding a Raleigh Sprite. It's a 10 speed w/ 27 x 1-1/4 tires. In the first few weeks I went through a bunch of tires and tubes.

First it was rust on the rim. Fixed that.

Then it was poor installation technique. Fixed that (I hope).

I had purchased Bell tires from Wal-Mart (I know, I was in a hurry) rated up to 90 PSI. Blew out tire on bike stand somewhere between 80 and 90 PSI.

I recently purchased Bontragger tires rated to 100 PSI. Currently have about 85 PSI (compressor needs a little more oomph). I weigh about 250 lbs.

Should I try and get a little higher PSI?

Will I damage my tires and or tubes at 85?

Thanks in advance.
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#2
It is not true that higher pressure = more speed. That holds only on really smooth surfaces...
http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

It all depends how and where you ride. On a road bike I usually ride about 7.5 or 8 bar. On a cyclocross I go as low as I dare, you cannot substitute traction by anything.

The main danger in too low pressure is snakebites (pinch flats), considering your weight I'd probably increase the pressure a bit. What is the minimum rating of the tyre?
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#3
(08-05-2010, 03:20 PM)Joe_W Wrote:  It is not true that higher pressure = more speed. That holds only on really smooth surfaces...
http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

It all depends how and where you ride. On a road bike I usually ride about 7.5 or 8 bar. On a cyclocross I go as low as I dare, you cannot substitute traction by anything.

The main danger in too low pressure is snakebites (pinch flats), considering your weight I'd probably increase the pressure a bit. What is the minimum rating of the tyre?

Thanks for your response.

There was no minimum rating given.

I mostly ride on paved city streets.

What the heck is 7.5 or 8 bar?
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#4
(08-05-2010, 05:09 PM)Bikeshrink Wrote:  
(08-05-2010, 03:20 PM)Joe_W Wrote:  It is not true that higher pressure = more speed. That holds only on really smooth surfaces...
http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

It all depends how and where you ride. On a road bike I usually ride about 7.5 or 8 bar. On a cyclocross I go as low as I dare, you cannot substitute traction by anything.

The main danger in too low pressure is snakebites (pinch flats), considering your weight I'd probably increase the pressure a bit. What is the minimum rating of the tyre?

Thanks for your response.

There was no minimum rating given.

I mostly ride on paved city streets.

What the heck is 7.5 or 8 bar?

That is the another measurement of air pressure. I think there are four. To convert to psi which the US uses there should be different lines on every bicycle pump and air gauge these days. If not just type "convert 7.5 bar to psi" in google's search box.
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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#5
1 bar = 14.503773801 pounds/square inch

Handy site to bookmark: http://www.onlineconversion.com/
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#6
(08-05-2010, 03:10 PM)Bikeshrink Wrote:  I recently purchased Bontragger tires rated to 100 PSI. Currently have about 85 PSI (compressor needs a little more oomph). I weigh about 250 lbs.


I'm not sure why, but some tubes I bought yesterday for a buddy as a favor say on the instructions: "Inflate tire to proper pressure (marked on sidewall of tire) using bicycle pump or CO2 inflater. Do not use a compressor."

These are Summit Cycling Products, as manufactured by Kenda, "Premium Bicycle Tubes".

Get yourself a decent floor pump maybe?
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#7
(08-05-2010, 03:10 PM)Bikeshrink Wrote:  . . . Do not use a compressor. . .

Maybe someone can correct me if I am wrong here, but I think you can use a compressor when the regulated output is compatible to the tire's pressure.

In other words, if the compressor's pressure regulator is set to 85psi and that is where mine is set, and the rated psi for the tire is say 90psi, then the compressed air will fill until the proper psi is reached or 85psi.

I haven't tried that so I could be wrong. Smile

I think the problem with using a compressor is that most people don't know what the regulated output is set at, for example, riding a bike to an auto repair shop to use theirs. But even then most air tools require no more than 90psi and that's where most are set.

Steve
Junkyard Tools rescued from the junkyard!
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#8
(08-05-2010, 09:49 PM)KC-Steve Wrote:  
(08-05-2010, 03:10 PM)Bikeshrink Wrote:  . . . Do not use a compressor. . .

Maybe someone can correct me if I am wrong here, but I think you can use a compressor when the regulated output is compatible to the tire's pressure.

In other words, if the compressor's pressure regulator is set to 85psi and that is where mine is set, and the rated psi for the tire is say 90psi, then the compressed air will fill until the proper psi is reached or 85psi.

I haven't tried that so I could be wrong. Smile

I think the problem with using a compressor is that most people don't know what the regulated output is set at, for example, riding a bike to an auto repair shop to use theirs. But even then most air tools require no more than 90psi and that's where most are set.

Steve

Thanks Steve,

Yes. I have two compressors and the problem with my little one (the one I was using) is that the regulator is fixed at 100 PSI and so when the tire pressure is higher, the compressor just doesn't have enough ooomph to top off the tire.

My other compressor has an adjustable regulator and can go much higher but I need to bring it in and have it checked before I use it again because the last time I ran it the pressure gauge went way beyond what it was set for. I've since shelved it and dubbed it "The compressor of death" at least until I can get it in to the repair shop.
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