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I have this old bike, I assume it's Italian from what I've been told by the former owner, and a Google search, but some parts say "Made in France" and "Made is Switzerland", etc... The tires are very mysterious in the way they display pressure. "25-622 (7000)" is what the tire says, along with "25-622 700c Michelin —ELAN" I don't know the unit, and 622 psi seems wrong. Someone please tell me how much pressure is acceptable?

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look for some other text on the tyre, most likely containing the letters "psi" or "bar". Most tyres have both sets of numbers but could be that Michelin, being "foreign", only stamp the pressure in bars. Your pump will most likely be calibrated for both psi and bar but if not you'll have to hit Google for a conversion formula. –  PeteH Jun 28 '13 at 10:26
    
You should be able to feel the resistance coming out from the tube once you have inflated it to the optimum pressure. usually for MTBs, tyre pressure max is 45 psi. Hybrids - 55-60 psi, Road bike - 110 psi –  hagubear Jun 28 '13 at 11:22
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Be careful with "general guidelines" about tire pressures. My gatorskins (700x28) are max rated to 116 psi. The tires that came with my bike, Vittoria, also 700x28 say max pressure 80psi. I had an old road bike that had 25 mm width tires that were only rated to 80 psi, where as most road bikes today will probably be well over 100psi. –  Kibbee Jun 28 '13 at 14:08
    
in response to another question I have just posted a photo of the kind of text I am talking about. See here –  PeteH Jun 29 '13 at 10:40

2 Answers 2

25-622 and 700C are both ways of stating the size of the wheel, not the pressure. 25-622 is an ISO size: the tyre is 25 mm rim-to-rim, and 622 mm in diameter. 700C is a more traditional name for the diameter, which is more often known as 28 inch. ISO sizes are somewhat out of fashion these days, as there's less variation in wheel size. See the late Sheldon Brown's excellent tyre size guide for more information if you're interested.

According to VeloBase, Michelin Elan tyres are "rated to 100 psi" but shouldn't be inflated to more than 90.

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FWIW they're 700c in the US, too. –  WTHarper Jun 28 '13 at 12:21
    
Fine, I've rolled-back to my original wording. –  Dan Hulme Jun 28 '13 at 12:26

Tires that size (700c x 25mm) of good quality on decent rims should be able to hold 100 psi when new, but if they're more than maybe 5 years old you should downrate that a bit (especially if the bike has been stored where the tires would be exposed to sunlight). Plus you may find the ride at 100 psi a bit harsh. But they should be inflated to at least 60 psi, and probably 80. Below 60 you'll run a serious risk of "snake bite".

Note that if the bike has been sitting on flat tires for awhile the tires may not inflate evenly at first. Inflate to maybe 50 psi, ride the bike 50 feet or so, deflate and reinflate to your target pressure. While inflating watch the area of the tire adjacent to the rim to be sure that the tires are not off-center.

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Never thought about the lower inflation test first. Really good idea, as finding a split or unseated bead at 50psi is less damaging than it occurring at 90psi. –  mikes Jun 28 '13 at 13:33
    
@mikes - It's not so much a "test" as to "work the kinks out" of the tire -- flex it a bit so that it seats more uniformly. –  Daniel R Hicks Jun 28 '13 at 14:49

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