Most high-performance road bikes come with skinny 23mm tires. Those used in pro racing have even narrower tires, as skinny as 18mm, even though fat tires are touted as both comfy and stable. So why do road bikes have narrow tires?
Join us for a detailed look at all these questions and more.
What Are Road Bikes for?
Road bikes are made for driving on super-smooth, paved urban roads. The operative term here, of course, is smooth and paved. Many urban streets are littered with glass debris and loose gravel, which affect speed and are just two of the many culprits that puncture narrow tires.
So Why Are Road-Bike Tires Narrow?
Road bikes generally come with 23mm or 25mm tires as the default width. Racers go even skinnier with 21mm tires or narrower. Here are the most important reasons for that.
Speed, Speed, Speed
Road bikes were designed to zoom by on smooth asphalt, and, even though not all road bikes are racing bikes, many are the choice for pro racing. These two reasons made speed a key point.
Consequently, narrow tires were the solution for the three issues that affect speed: Wind resistance, rolling resistance, and aerodynamics.
The first culprit behind drag is wind resistance. Even though cyclists wear tight clothes and use drop bars to help them cut through it, wind resistance only increases the faster they go. Narrow tires slice through wind resistance easily and faster than wider tires.
Keep in mind that the difference in speed can be mere fractions of a second. While this may not matter much to regular folk, it’s a vital consideration for racing pros.
Different tires roll with different smoothness levels. This happens because of rolling resistance, which is the energy necessary to flex the tire surface where it contacts the ground. It’s also the second reason for drag after wind resistance.
Here are some of the tire specifications that affect rolling resistance:
- Air pressure
- Casing thickness
- Tread thickness
Until recently, scientists and engineers agreed that thinner tires had better rolling resistance. In the last few years, however, we’ve seen a new argument: At the same pressure, thicker tires are faster because of tire deflection, which is the way tires distribute weight under a load.
When your tire flattens under your weight, part of it touches the road as a flat contact surface. At equal air pressure, a fat tire and a skinny tire will have the same contact surface. A fat tire has a wide but short contact area, while a skinny tire has a thin yet longer contact area.
Because a narrow tire’s flattened contact area is longer, it deforms more and loses more of its round shape while rotating. By contrast, a fat tire’s flattened contact area is shorter. This helps it keep more of its round shape, so it rolls better and faster.
A narrow tire’s smaller frontal area reduces rolling resistance, which means lower drag. In turn, this gives you improved aerodynamics, so you exert less effort pedaling. Ideally, you’ll get the best aerodynamic performance when the tire’s diameter is 2-4mm less than the brake track width.
Narrower tires have less bulk than their wider counterparts. This makes them lighter and consequently faster. This is particularly noticeable with carbon-frame bikes, compared to the heavier aluminum frames of the past.
Better Snow Traction
Because fat tires maintain contact with a wider surface area, they generally provide better traction. However, surface contact isn’t the only source of traction: There’s also pressure per square inch. The greater it is, the better the traction, and that’s where skinny tires are superior.
This can be readily seen cycling on snow-covered roads. Narrow tires cut deeper through the snow, providing better traction and greater speed.
Most skinny tires have bigger rims, which give cyclists a chance to install bigger braking parts. This can greatly reduce the braking distance, which is vital when you’re tearing through the streets and a congestion pops out of nowhere.
Disadvantages of Narrow Tires
Narrow tires come with two main drawbacks.
To avoid pinch flats, narrow tires must be pumped up to a high air pressure. This makes them super-stiff and reduces their contact area with the road, which severely limits their grip on the surface.
A fat tire, on the other hand, can run at lower pressures because it has a wider part touching the road. This means it can grip irregular parts of the road surface with more effectiveness. As a result, you have much more control when you take corners.
Because narrow tires are pumped up until they’re extremely hard, they have almost zero shock absorption. Unless you’re gliding over silky smooth roads, you’re going to feel every single bump, pothole cover, and crack. You’ll also need to exert more effort to maintain stability.
A fat tire at a lower pressure has excellent shock absorption. This lets you enjoy a more comfortable ride and feel less tired afterward.
Can You Fit Fat Tires on Your Road Bike?
Before you buy a wider tire for your road bike, check the tire clearance your frame has. The space between the frame and fork and your tires will show you the biggest tire size you can get.
Wider tires will provide a more comfortable ride and probably a better sense of stability. It’ll come at the expense of the aerodynamics, but wide-tire enthusiasts don’t mind going slower and exerting more effort for comfort and stability.
As long as your bike frame has sufficient clearance for the fat tires you want, you can absolutely go ahead and experiment with wider tires.
Can Your Road Bike Go Super-Wide?
If 25mm and 28mm tires are fine, why stop there? Why not go all the way up to 45mm tires even?
There are a few obstacles to that. First, most road bikes come with frames that can’t even fit 28mm tires. It would be downright impossible to fit 35mm and 45mm ones.
Second, you can sacrifice aerodynamic performance to a certain degree with 25mm and 28mm tires, but any bigger will be simply incompatible with your wheel rims.
Finally, while it’s still possible to go fast on wider tires, they’ll increase your wheels’ rotational weight, which slows down your acceleration.
Can You Fit Cross Tires on Your Road Bike?
You can’t. Cross tires may fit your wheels, but you won’t be able to put the wheels back onto your frame. Cross tires are exclusively made for cross-bike frames.
Can You Ride a Road Bike on Unpaved Trails?
Since road bikes are specifically designed for smooth tarmac, they’re not your best bet for unpaved trails. You may feel they’re not as stable or comfortable. You could also be risking punctures with every roll of your wheels.
Most dirt-trail enthusiasts need to pack provisions, but road bikes aren’t suitable for heavy loads either due to their lighter weight. You’re better off with a mountain bike for that tough off-road terrain.
Can You Race on a Road Bike?
You absolutely can; in fact, road bikes are often used for racing by professional racing cyclists. The trick here is to know the right tire width.
While bicycle tires come in a vast array of widths, race bikes usually have the skinniest tires. This reduces weight and makes for better aerodynamics. The default width used to be 23mm or less, sometimes as narrow as 19mm.
Lately, 25mm has slowly become the default tire width. Some newer race bikes can even take tires as wide as 28mm.
Puncture-Resistant Solutions for Narrow Tires
Keep in mind that regardless of the method you choose, you should always know how to fix a flat tire and have the necessary tools with you at all times.
Here are five ways to protect your narrow tires from punctures:
- Swap your tires for a pair of heavy-duty tires.
- If your rim bed has sharp edges sticking out, cover it with dedicated heavy-duty rim tape.
- Put latex sealant in your tubes, even if they’re not tubeless.
- Turn your old tires into lining for your new ones.
- If you have a rim-brake frame, attach a flint catcher to it.
Traction Solutions for Narrow Tires
Outfitting your road bike’s narrow tires with studs is an effective way of getting better traction on snow and slush.
The Bottom Line
Narrow tires give road bikes better wind resistance and aerodynamics, lighter weight, and better traction on the snow. You also have narrow tires to thank for your improved braking performance. As for puncture risks, there are various ways to puncture-proof your skinny tires.
Ultimately, the terrain you travel most of the time should be the biggest factor in your choice. Merely living in a city doesn’t in and of itself mean a narrow tire is your best bet.
If your city streets are a glass-strewn nightmare of crumbling sidewalks, cracked asphalt, and potholes, a wider tire is the obvious choice. Just make sure to pick the size your bike has enough clearance for if you choose to outfit your road bike with wider tires. Happy urban trails!