Choosing your tire width
Written by: Greg Kopecky
Added: Mon Nov 11 2013
On a ‘700c’ wheel, you can have a range of different widths. 23mm wide tires have been the standard for most road cycling over the past couple decades. You might see a 700x20c, or a 700x25c. On a cyclocross bike or 29-inch mountain bike, you could see tires as wide as 700x35c or 700x58c.
Nuances of Width
Let’s pretend that you have a triathlon bike with 700c wheels and 23mm wide tires (e.g. 700x23c). That’s the ‘standard’ today, so chances are your bike has this exact setup. Why might you pick a different width of tire?
The general tradeoff to consider is this: Narrower tires tend to be lighter weight and more aerodynamic. Wider tires tend to be more comfortable and have lower rolling resistance (e.g. they roll slightly faster over the pavement). Tire width generally does not have any blanket effect on its puncture resistance.
Let’s hit each of these key considerations one-by-one.
Weight is pretty easy to understand. If your bike weighs less, there is less weight to carry around… so it’s easier to pedal up hills. With tires, I tend not to worry about buying the absolute lightest tire – the attributes of aerodynamics, puncture resistance, and rolling resistance are all more important to me (and there are so many other places to save weight on a bike). For racing, I would not buy a super heavy tire, but not because it is heavy. Most of those very thick tires also have a stiff casing, which tends to be higher in rolling resistance and have a harsher ride quality. It is those other consequences of the weight that are deal-breakers.
As we can all expect, narrower tires tend to be more aerodynamic. There is less tire for the wind to ‘see’. There is something else to consider aside from just your tire width, however – the width of the rim on which it is mounted.
Put simply, the width of the tire and rim should roughly correlate. There is less aerodynamic penalty with a wide tire when you use it with a rim that is also wide. The two pieces put together make a relatively smooth shape, compared to a very wide tire on a narrow rim (which tends to look like a lightbulb).
Ride comfort is straightforward. If you have more tire underneath you, you’re effectively riding on a larger pillow of air. This tends to mean that the ride is smoother. Less tire = less pillow.
What we need to understand, however, is that pressure is necessarily related to this ride comfort. Lower pressure lowers the spring rate of the tire, making it more comfortable. If you go too low, however, you can bottom out the rim on bumpy roads, causing a ‘pinch flat’ to your inner tube.
Wider tires allow you to use a lower pressure with less risk of pinch flatting compared to narrower tires. If you use the same pressure on a 23 and 25mm tire, the 25mm tire has 2mm more distance that must be compressed before the tube will pinch. Narrower tires must be ridden at higher pressure.
In simple terms, rolling resistance is the amount of power loss caused by your tire as it rolls down the road. This does not mean that it’s the coefficient of friction between the tread and the asphalt. It is the amount of energy that the tire ‘uses up’ as the casing contacts the pavement and deforms, and then returns to its normal shape as it leaves the pavement. Not all tires are created equal in this regard. Most of the latest research shows that – for a given type of tire – the wider tire has slightly better (lower) rolling resistance.
Training vs. Racing tires
You might hear people call a tire a ‘training tire’ or ‘racing tire’. What are the key differences between the two?
The big secret is this: There is no such thing as a training tire or a racing tire. There are no actual minimum standards to call a tire either name. There is no governing body that regulates it.
What people are really telling you is that a ‘racing’ tire is similar to a racing car – you give up durability for performance. You make a risk, hoping for a reward. In other words – they weigh less, roll faster, are more prone to punctures, and cost more. A training tire tends to be the opposite – they weigh more, roll slower, are more resistant to punctures, and cost less. Unfortunately there is no free lunch and you can’t have it all.
It is worth noting that the width of the tire printed on the label isn’t always accurate. I’ve had ‘25mm’ tires that actually measure 23mm… and ‘25mm’ tires that actually measure 28mm (on the exact same width of rim). That’s a huge range of error, and a real problem for our industry.
What we pose to the industry is this – printed tire sizes ought to be taken from actual tire measurements. In addition, the rim width that they use ought to correlate with the tire width. Perhaps that means that 20mm tires are measured on 20mm rims and 23mm tires are measured on 23mm rims. This can’t remain a 1:1 ratio as tire sizes really grow, but it should be in the ballpark. Maybe I’ll start my own protest in the streets of America to begin the movement. Join me?
How do you decide?
In general, the tire that came on your bike is a good place to start. If you have 23mm tires, your bike will probably continue to do fine with 23’s.
My general advice to most people is this:
1. For training, err to larger and more durable tires. I personally pick the largest tire that will fit inside my brake and frame. On many road or triathlon bikes, this is a 25mm tire (some may go up to 28mm).
3. I always trend my tire width with how rough the pavement is – regardless of whether I’m training or racing. If I know a course is very rough, I’ll race on 25mm tires. If I’m training on rough roads, I’ll saddle up with fat 28mm tires. Especially for riding on aerobars, tire comfort makes a huge difference. Road bikes allow you to bend your elbows to absorb shock, making tire comfort less important. On a triathlon bike with aerobars, you ride right on your elbows, so every bit of ‘tire suspension’ counts. Of course, if I know the pavement is smooth, I pick a narrower and more aerodynamic tire.
What do you think? If you’re a beginner, did you know much about tire sizing? Are you interested in the fastest tire, the most durable tire, or something else entirely?
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