What does 'tire clearance' mean? Can you please explain with an illustration? Does it mean the distance between the tire and the fender?
Basically its the gap between the tyre and any non-wheel part of the bike frame.
Static clearance is almost exactly the same as the clearances you have while riding, as long as the wheel axle bearings aren't sloppy and the wheel doesn't move laterally.
The above picture is faked up but shows the approximate differences between a "normal road tyre" and a 40mm cyclocross tyre and a 2.1" MTB tyre. You can see that any smaller tyre will fit, but bigger tyres need more space.
That last bike might not even take the same size tyre from another brand, because tyres vary subtly, and that's not a lot of tolerance!
NOTE just to be clear - tyre clearance matters anywhere that the rotating tyre comes close to your bike frame. So that's
- Seat stays
- Brake Bridge
- Rim calipers if you have them.
- Seat post (pretty unlikely to cause problems)
- Rack supports (unlikely to be a prob)
- Trailer mounts
- Kickstands <-- ESPECIALLY loose ones!
Tire clearance is measured with respect to something(s) (by default, the frame in the rear and the fork in the front and the brakes if there are rim brakes; if anything between the frame/fork/brakes and the tire is there, such as fenders, this is included in the set of somethings). Note that this is a function of both the tire used and the somethings.
We can define tire clearance as the minimum of the distance(s) from the tire to the object(s) its being measured with respect to. That is, for each item in the set of objects, measure the distance between the closest point on the tire and the object. Then, take the minimum of these distances over the set of objects.
For example, if I wanted to measure the tire clearance in the front, I'd put the wheel in, and measure minimum distance from the tire to the brake caliper and to the fork and to the fender if I had one. The smallest of those distances would be my tire clearance.
Example 1 (from here):
The tire clearance in the front here is the distance from the top of the tire to the closest point on the fork, since thats where it comes closest to the brake caliper and fork.
Example 2 (from here):
The tire clearance to the chainstay here is the distance from the sidewall of the tire to the chainstays where the tire and chainstays are closest together.
There are various guidelines for how much tire clearance is necessary -- you don't want the tire to rub on anything as well as account for possible hazards. On a road bike, you'll typically see recommendations for 3-5+mm clearance in the front and rear. For mountain biking, you'll want something larger.
Sorry I can't add an illustration from my phone :-)
Tire clearance is the amount of air space between the tire and any other part of the bike (except the wheel of course).
So yes, that includes the distance between the tire and fender / mud guard.
The amount of clearance tells you how much larger you can make the tires, how much mud can accumulate before it impedes your riding, and how much tolerance the bike (especially the guard) has to flex.