Your tires are one of the most important elements of your bike–they’re what connect you to the ground. It’s important that they be durable, grip well, and help you move along quickly. Whether you’re building up your bike for the first time or just need a new pair, this guide will help you figure out what you should be looking for when you pick out a tire.
The first step to figuring out what kind of tire to use is figuring out your tire size. The easiest way to do that is to look at the tires already on your wheels. Somewhere on the sidewall of the tires, the size should be listed. It will probably look something like “26 x 1.5” or “700 x 32” or “27 x 1 1/4.” After that number, there is (hopefully) another number in parantheses that will look something like “(38-559)” or “(32-622)” or “(32-630).” The three-digit number after the dash is the important part–its the ISO number. See, just to be confusing, there’s several different 26″ tires sizes and a host of other often confusing size designations as well. Sometimes 700C tires are called 28″. Sometimes they are even called 29″! Meanwhile, 27″ is something else altogether. ISO numbers, though, are specific and only designate one standard tire size each.
The two digit number is less important. It designates the tire’s width, and most wheel rims can take a wide range of widths.
Chances are, if you have a newer bike sold in the United States, it’ll take either ISO 559 or ISO 622 tires–that is, 26″ or 700C. If your bike takes one of these standard sizes, you don’t need to worry so much about the ISO size.
700C is a standard road bike size. 26″ wheels are found on mountain bikes, some touring bikes, and some hybrids. It’s always a good idea to doublecheck your tire size, though.
For information on older and less common sizes, check out this useful chart as well as the articles here and here.
Once you know your wheel size, figure out what width you want to use. Your width will be somewhat limited by your rim size–you can use the chart found here for an estimate of what widths your rim will allow–but you’ll probably be more limited by your frame, brakes, and fenders (if you have them). You might be able to guesstimate the maximum width you’ll be able to use by looking at how much clearance you’ve got with your current tires. Tire width is usually measured in millimeters or inches.
What tire width you choose will depend on what kind of riding you do regularly, and on your personal preferences. Narrower tires (23-25mm, say) are generally “zippier” than wider ones and also save some weight, so they’re preferred by road bike riders who like to go fast. Wider tires (up to 47mm wide) provide a little more cush and comfort (narrow tires require higher air pressure to avoid pinch flats), and are prefered by cyclists who habitually carry a lot of cargo–the weight is spread out over a larger contact patch. Wider tires are also better for riding over uneven terrain like dirt or gravel. If the streets in your neighborhood or city are rough and potholed, you might like wide tires better, too.
Another element to consider is tire tread. For most city riding, a slick tire is best. Too much tread will just slow you down. How well you grip the pavement has more to do with how much rubber is contacting the road than how much tread you’ve got, so slicks are best. If you don’t always ride on smooth surfaces, though, a little tread will help you grip uneven surfaces like hardpack dirt, gravel, or really badly paved road.
This cross-section shows the flat protection layers that are often included in city tires.
What is important on city streets is protection from all the debris that is often strewn in bike lines. Shattered glass, thorns, sharp pebbles… all of this will try to work its way past your tire and into your tube. Luckily, there are lots of tire manufacturers who’ve been working on this problem for a long time and have come up with all sorts of solutions with names like “DuraSkin” (Continental), “Protek” (Michelin), and “SmartGuard” (Schwalbe). Basically, these are extra-tough rubber compounds that are incorporated into the tires, where they provide a layer of protection against pointy things trying to pop your tubes. Some manufacturers also use Kevlar and other ultra-tough materials.
Others, like Soma Fabrications, makers of the Everwear tire, make the treads thicker than usual. Soma markets their tire as long-lasting, but the thicker treads also make it more puncture-resistant.
The unfortunate consequence of all the catchily-named rubber compounds mentioned above is that they tend to be stiff and rigid, which makes them a bad choice on wet or slippery surfaces. This effect can be mitigated by using a wider tire, which will have a bigger contact patch with the pavement, providing more grip. If you prefer narrow tires, look for ones marketed as “grippy” or “supple.” They will be a little less durable and more prone to flats, but you can improve their flat resistance with beefier tubes and maybe tire liners.