If you are shopping for a new pair of tires for your road bike or gravel bike, the vast number of size options can be overwhelming. Should you go narrow or wide? And what do all those numbers and letters mean?
In this article, we will take a deeper dive into how road/gravel tires are measured, the importance of tire width, how it affects speed and ride quality, and what other qualities influence the ride quality of a tire.
June 2023: Updated to include more info on gravel tires as well as adding a new graphic.
How Gravel & Road Bike Tires Are Measured
If you are new to the world of bicycles, road and gravel bike tire sizes can be confusing. But don’t despair! It’s actually very simple….
Road/gravel bike tire sizes have two numbers to pay attention to. The first refers to the wheel diameter and the second to the tire width. So, for example, a 700c x 26mm tire has a diameter of approximately 622mm and a width of 26mm.
Most road and gravel bikes have 700c (622mm diameter) wheels, although some triathlon bikes and extra-small women’s road bikes may have 650c (571mm diameter) wheels. Check your existing tire to find the correct diameter. It should be printed on the sidewall.
The second number–the width- is more variable and can be chosen based on road conditions, weather conditions, and personal preference. We go into this in much more detail below.
Thin To Win?
Road tires and rims have both gotten wider, but this is a relatively recent trend in the cycling industry. Just ten years ago, a road tire would commonly range between 18-23mm, but today, 26-28mm seem to be the most popular choice.
While in text, these look like very small changes, the differences are quite noticeable on the road. Air pressure is a large factor contributing to ride quality – the lower the pressure, the smoother the ride.
Cyclists once believed that running a narrow tire at high pressure would be the fastest option. Even though this set-up would have a very small patch of contact with the ground, the high pressure makes the tire so hard that it bounces off the road debris.
When running lower pressure in wider tires, the tires provide a small amount of suspension – just enough to glide smoothly over debris without adding noticeable drag.
A wider tire is even more important when riding gravel. Lower pressure means more traction.
VeloNews tested popular tires, and an interesting result to note is that when they tested the same tire (Specialized S-Works Road Tubeless) in both the 24mm and 26mm width, the 26mm tires came out ahead. This is a good test to see the impact of width on the speed of a tire. Since the rubber compound is another important factor, testing the same tire removes the influence of compound from the equation.
Is Bigger Always Better?
Road bike frames do a pretty good job of steering riders to the most efficient choice. Many current road frames have a recommended max tire size of 700 x 28mm.
As a recent convert to 700 x 28mm road tires, I immediately noticed the smooth ride. My common routes have some pretty rough, torn up roads, so I appreciate the additional give.
Wider tires are also beneficial in adverse conditions. When the roads get wet, riders will benefit from the low pressure and increased contact with the road.
With the recent popularity of gravel bikes, the line between road bikes and gravel bikes continues to blur. Some gravel frames boast a tire clearance of 700 x 42mm or more!
When tires start to get this wide, it is easy to feel the suspension that accompanies the low pressure. In these tires, 50 psi is not an uncommon pressure to run, especially if the tires are set up tubeless. This low pressure helps the tires grip on loose gravel and dirt, but have a noticeable pedal bob when hammering away on pavement.
The Sweet Spot
The final decision on the best tire width is going to come down to road and weather conditions, and a bit of personal preference.
For most applications, a 700 x 26mm tire is going to be your best option on pavement. 26mm tires do not weigh much more than their thinner counter parts, so the additional rotational weight will be very difficult, if not impossible, to notice. These tires can be run at a low enough pressure to smoothly roll over debris, but not low enough to experience pedal bob.
On gravel, a 40 or 42mm tire will be best for most applications. If you’re riding more pavement than gravel, you’ll want to go narrower. Or, if you’re bikepacking or riding singletrack trails, a 50mm tire will be best.
While width is important to consider, there are a few other characteristics to take into account when choosing the perfect tire for you.
Tread is very important for off-road road applications. Traditional road riders do not tend to delve into this as much as their gravel counterparts. However, if you have a few hours to spare, ask any gravel racer about their tires.
There are many different options out there to help these riders confidently tackle the many different types of terrain they encounter. As someone that merely dabbles in gravel riding, I find the Specialized Sawtooth tires in a 700 x 42 work well for most applications. These tires have a relatively slick tread, which makes them a good tire for those who need to ride some pavement to get to the gravel or dirt.
There is a lot of engineering that goes into a small amount of rubber. Developers need to consider durability, rolling resistance, and grip when designing the perfect tire. It is tough to develop a compound that can satisfy all these needs. Depending on the application, tires will excel in certain areas and fall short in others.
Rolling resistance and ride feel are often prioritized over durability when it comes to race tires. Race tires will tend to have a higher TPI, or threads per inch. The higher the TPI, the thinner and more flexible the tire is. High TPI tires are incredibly supple, but do not have the durability of a tire with thicker thread, and less threads per inch.
Many tire companies include additional flat protection on their tires, but on race tires, this protective layer is omitted at the sidewall. It makes sense to reinforce the center line of the tire, since this is where the majority of the contact happens. However, in order to achieve that buttery smooth ride feel, the sidewall of the tire needs to remain a bit thinner to allow for some flex.
The Best Road And Gravel Bike Tires?
It is hard to call out a clear “best choice” tire for every application. If you are a prolific road racer, it does make sense to have a set of dedicated race tires, as well as a set of training tires.
My race tire of choice is the Specialized Turbo Cotton in a 700×26. These are the smoothest rolling tires I have ever ridden. These tires have a very high TPI of 320, so not known for durability, but the ride quality is incredible.
For a training tire, I am a huge fan of the Specialized Turbo Pro tires in a 700×28. These tires have a much lower TPI (60), which increases durability. To make up for the thicker, less supple rubber, I went with a larger width to run a lower pressure. These tires set up at 90-95 PSI do provide a nice ride feel for how durable the tires are.
For gravel, the Specialized Sawtooth tires in a 700 x 42 is where it’s at!
More Reading For You
- 5 Simple Steps To Understanding Women’s Bike Sizing
- 5 Best Women’s Road Bikes Under $1,000
- 7 Best Women’s Road Bike Helmets
About The Author
Kira Maicke has been an avid cyclist since 2010. She started racing road bikes in college for the University of Georgia and switched over to mountain biking after graduating and moving out west. When she’s not on one of her bikes, she’s out playing in the mountains with her husky, Semenuk.