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On my tire is printed the following:

25-622 (28 x 1.00 - 700x25c)
6.8-8.0 Bar, 85-115 psi

I think I know what some of this means but am not sure. BTW, this came standard on my 2012 Cannondale Synapse 600 Alloy bike.

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There was a thread just a few weeks back that covered tire sizing in detail. Unfortunately, I can't find it. –  Daniel R Hicks May 27 '12 at 20:48
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Here's one thread: bicycles.stackexchange.com/q/8469/1584 –  Daniel R Hicks May 27 '12 at 20:51
    
BTW, that means that you have a tire that's either a 622mm rim size, 25mm wide, a 28"x1" tire, or a "700C" tire 25mm wide. They're all the same tire, just different "standards". –  Daniel R Hicks May 27 '12 at 20:53
    
@DanielRHicks was it this one: bicycles.stackexchange.com/questions/9238/… –  Mac May 28 '12 at 4:03

2 Answers 2

up vote 5 down vote accepted

700x25c is the diameter x width (in millimeters) of the tire, and 25-622 (ISO) and 28x1.00 (decimal) refer to the size in two different systems (see Sheldon Brown's Tire Sizing Systems page for more detail). Buy tubes to fit as close to this size as possible. I sometimes have to use 25c on my 23c bike when I'm in an area with limited cycling supplies.

6.8-8.0 Bar is the recommended air pressure range, same as the 85-115 psi. Bar is a metric measure for pressure, while psi is pounds per square inch. PSI is more common in the US.

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700 millimeters diameter of the rim, the width across the rim rather than the circumference around it. This is a very common rim size, if not the most common. –  Brandon McKinney May 27 '12 at 20:28
    
Actually, 700 mm is the "nominal" tire diameter. The rim diameter is 622. –  Daniel R Hicks May 27 '12 at 20:42
    
25c isn't the width at the rim either. –  Mac May 27 '12 at 23:15
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I edited the question, so that 700x25 undoubtedly refers to the TIRE dimensions. 25 does NOT refer to the rim, but to the tire (that's why it's printed on the tire, not the rim). The rest of the answer is correct. –  heltonbiker May 28 '12 at 1:18
25-622 (28 x 1.00 - 700x25c)

The size of the tire. The way it's written here is kind of a mess, so no wonder you're confused.

The rim size is 700c (this designation is a relic of a sizing system that's no longer used. See the link to Sheldon Brown in the other answer). On a 700c wheel, the diameter of the bead is 622 millimeters. This size is sometimes referred to as "29 inch" when it's on a mountain bike. It can also (very rarely) be called "28 inch".

25 is the width of the tire in millimeters (writing it as "25c" actually makes no sense). I assume that 1.0 is supposed to be the equivalent in inches.

So what you have is a 700c 25 mm tire - pretty common size for road bikes.

6.8-8.0 Bar, 85-115 psi

Recommended tire pressure, but I'm sure you already figured this out.

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