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Old 12-06-01, 03:34 PM   #1
callbr549
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Tire (Tyre) pressure

I'm new to biking and have a question regarding tire pressure. I started into biking by purchasing a used road bike. I inflate the tires to the recommended pressure of 110psi, but when I check the pressure two or three days later it has dropped back to the 90-95psi range. Is this normal? Could the age or wear of the tubes or tires cause a slow leak? The tires appear OK except for a few small cracks along the sidewall, I suspect from the previous owner running underinflated.

If I have to top off tire pressure every few days I definitely need to invest in a better pump!
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Old 12-06-01, 04:40 PM   #2
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First, let me ask, is 110 psig the recommended tyre pressure, or the maximum tyre pressure? If it is the latter, why do you keep it so high?
As far as the leaking air, it is coming out in one of 3 ways:
1) through a leaky valve
2) through a small puncture
3) through the rubber itself
The first 2 are easy to fix, by either replacing the tube, or patching the puncture. Air leaking through the rubber, thoug, is natural, but different tubes leak down at different rates.
Latex tubes are notorious leakers, often losing 25-30% of their air overnight. The only reason they still exist at all is because they are quite light. Butyl rubber, on the other hand, is usually quite impermeable-until it gets old.
Chances are that the tube is toast, so you would do well to replace it.
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Old 12-06-01, 04:42 PM   #3
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Losing air is inevitable when you have to run high pressure in butyl tubes. Road tires are especially susceptable as they have relatively little volume and much higher pressure than MTB stuff. The reality is...you need to air them up when you are going riding. I would however check the tires out for dry-rot to make sure they ar still in fair shape. Cracking is usually from lack of use instead of too low a pressure. Good Luck
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Old 12-06-01, 09:22 PM   #4
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Callbr549,

Let me start by saying that as stated by Geronimo tires will lose pressure over time. 110 psi is not unheard of for road bike tires and you want to try to maintain tire pressure at that level so that you reduce rolling resistance. The downside to high pressure tires is that you get a hard ride. You probably should get yourself a good floor pump with a built-in pressure gauge that accepts both presta and schrader valves if you don’t already have one. Hope this helps.
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Old 12-07-01, 08:27 AM   #5
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Sheldon has a good article which relates recommended tyre pressure to tyre width and the rider's weight. I finally bought a new Nashbar floor pump with a dual head and a built-in pressure gauge, which makes it very easy to maintain ~100psi.
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Old 12-07-01, 08:52 AM   #6
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You should make a habbit of topping off the tires before every ride.

A good floor pump is a necessity.
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Old 12-07-01, 09:36 AM   #7
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Your pressure loss is normal.

I run my tires at max pressure always. Like Bobsled mentions, it reduces rolling resistance. It also goes a long way in preventing "pinch flats" or "snake bites". These are flats associated with hitting small rocks or other debris causing the tube to be smashed up (or sideways) into the rim. Thus catching the tube between the two and puncturing it.

If you had a problem with a slow leak, your tire would be flat or almost totally flat in less than a couple of days. Use a good floor pump and top off both tires before you ride.

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Old 12-07-01, 11:59 AM   #8
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Yup, I'm always at max. pressure, too.

But, you always will loose some air, that's normal. Just as long as when you come back to the bike they're not flat, you're good to put a little air in and ride off without a worry.

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Old 12-07-01, 03:53 PM   #9
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Lance Armstrong rides with his tyres (competition road tyres, probably all good for 140 psig, minimum) at 125 psig rear, 105 psig front.
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Old 12-07-01, 08:00 PM   #10
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Anyone who tends to wear out sidewalls before treads could probably benefit from more pressure. I like Lance's concept of carrying somewhat more pressure on the rear tyre, particularly if using a rear rack or panniers.
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Old 12-07-01, 08:30 PM   #11
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First, let me ask, is 110 psig the recommended tyre pressure, or the maximum tyre pressure? If it is the latter, why do you keep it so high?
Alex - I keep my Specialized Armadillos 700x25's at 120 - 125. It seems they go quite a bit faster, as they seem to be a slow tire anyway. I kept my Conti's 2000 Ultras at 120, at the strong recommendation of my LBS guy. I weigh about 230 lbs.

In 12,000 miles of riding (6,500 on mtn bike and 5,500 on road) I have never had any problems from either wheels or tires, except for the perfunctory flat from thorns and glass.

So, why do you not seem to recommend 120+ psi pressures for the road bike??
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Old 12-08-01, 08:45 AM   #12
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Well, this thread seems to be going astray!
On my road bike, which uses 21mm wide tubulars, I usually ride with 135 rear, 110 front. I will occasionally pump them up to 145/120 for speed, or run them at 125/100 for comfort on long rides. Both tyres are rated for a maximum of 175 psig.
On my touring bike, which uses 32mm wide clinchers (Armadillos), I generally ride with 90 rear/75 front, even though they are rated for 110 psig maximum. If I'm carrying a lot of weight in the panniers, I may increase the pressure to 100/85, but any higher makes the ride quite harsh.
There are some competition tubulars available which have a maximum pressure of 220psig, but I don't know anybody who actually rides with them at that pressure.
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Old 12-08-01, 09:13 AM   #13
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It actually depends on the shape/size of the tire and the composition of the rubber. I run my 23mm Conti GP3000s at the max -- 120 psi. I find the rubber a bit grippy and I find that I can have the best of both worlds -- grip and speed -- at high pressure. My Vrewdestein Fortezza Tri-Comps have a max rated pressure of 160 [or is it 145? I'll check]. But I find that they don't grip AT ALL at pressures above 120 psi. I normally run them 115 back and 105-110 front. I did jonce have them both at 135 on a group ride once, but it started to rain and the bike started getting mighty skittish.

[BTW... I like Vreds. I just can't afford to buy them often... and the sidewalls tend to shed threads like nobody's business.]
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Old 12-08-01, 10:36 AM   #14
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Originally posted by D*Alex
Well, this thread seems to be going astray!
Darn, and I thought this thread was about tire (tyre) pressure!!

Oops!! Well, what do you know. It IS about tire pressure.
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Old 12-08-01, 05:50 PM   #15
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One of my friends from the U.K. recommends reducing tyre pressure about 10 percent when cycling (or driving) in wet weather, to improve traction.
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Old 12-10-01, 05:39 AM   #16
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One of my friends from the U.K. recommends reducing tyre pressure about 10 percent when cycling (or driving) in wet weather, to improve traction.
I see the logic but I'm sure I read somewhere that for an average width bicycle tyre to aqua plane you'd have to be doing around 250 mph.

In which case on the road does tread have any practical use?

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Old 12-10-01, 08:39 AM   #17
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Sheldon claims that bicycle road tyre tread is worthless, and my experience supports this. Although your logic about aquaplaning and pressure makes perfect sense, I feel much more secure on 28mm or wider tyres when the road is wet, and consider my Bianchi, with its 23mm Contis, to be a fair-weather friend.
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Old 12-10-01, 09:41 AM   #18
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I seem to recall D*Alex pointing out that narrower tyres should give better traction because of the greater psi (I hope I'm paraphrasing him reasonably accurately ) and again I see the logic but I like the idea of the extra contact area.

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Old 12-10-01, 02:13 PM   #19
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I want to thank everyone for their replies to my original post. While I seem to have touched off a lively debate about tire pressure, tread, etc, I also got my basic question answered. There seems to be a consensus that my experience of losing 10-15 psi every few days is probably normal. Thanks for sharing your experience.
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