Know What Size Tire You Need - Dimension
Tires for standard adult bikes like mountain bikes, hybrids, etc. usually come in either 26 or 27 inch sizes, which is the measurement of the outside diameter of the tire. On today's road/racing bikes, the wheels are usually sized in metric, with either 650 mm or 700 mm being most common. BMX bikes usually have 20 inch wheels.
Your tire size will be stamped on the side of your present tires
Know What Size Tire You Need - Width
The next component of tire size is width. This is the second number of the tire's measurement. For instance, the "balloon" tires used on a beach cruiser type bike are labeled "26 x 2.125" This means the tires are 26 inches in diameter and a wide 2.125 inches across.
Most tires on mountain bikes and hybrids are in the range of 26 x 1.5, but the specific size you'll want will vary depending on the type of riding you do. We'll talk about that below.
Road bikes measurements also show diameter then width: 700 x 23 is common for high speed racing tires, meaning the tire is 700 mm in diameter and a skinny 23 mm wide.
The type of tread you want is tied to your normal riding surface. Completely smooth tires are best for racing or for riding on pavement; they intentionally have minimal contact with the road.
Knobby tires like you see on mountain bikes are at the other end of the spectrum. Those tires are great for wet or muddy trails, but they require more pedal power because there's more contact with the ground.
Most riders, especially those who ride mainly on pavement, will want tires with a smooth tread pattern. A little tread to hold the road is fine, but any more than that will slow down your ride and make you work harder.
Durability of the Tire
A major factor to consider is how durable you need your tire to be. If you are going to be a daily commuter or put on lots of miles on rough roads with glass, nails and other junk in your path, you definitely want to spend a few bucks more and get a tire that will last longer and be puncture resistant.
There are a number of good tires out on the market today with features like kevlar reinforcement for extra puncture resistance. The Ultra Gatorskins by Continential are just one example of these types of tire. I've used them on my road bike and they've worked well for me for about 2,000 miles so far.
Weight of the TireUnless you're competing at a very high level, and trying to shave off a couple of grams here and there wherever possible, the weight of your tires is not important. Basically, all tires that fit your bike will be within the same general weight range, and it's not really worth worrying about. Far more important, in my opinion, is the durability and performance.
What Width Do You Want?
Here's the basic formula related to bike tire width: skinny equals fast, because there is less contact with the road. But there's a trade-off: skinny tires need higher air pressure which gives a harder ride. They may also be more vulnerable to sidewall damage and wear out quicker.
Wider tires will make you feel more steady; they offer more contact with the road. They may offer better traction on irregular surfaces.
Tires that match the diameter of your rim - 26 or 27 inches for example - will generally fit fine in a range of widths. Where a wider tire may cause problems is in clearing your frame or brakes.
Determining Your Tire Size
If you don't know what size wheels you have, you can:
- Dig out the manual or paperwork for your bike if you have it
- Go to the manufacturer's website, which usually has specs for all of its bikes.
- Measure the rims yourself. Go rim-to-rim for the complete size, or else axle to rim, then double it.
- Easiest of all, show it to the pros at your local bike shop. They'll know just by looking at it. They'll also be able to recommend the best width for your type of riding and for your specific bike.