How Wide is Right for Me?

Our ideas of what is a performance bike have changed a lot in recent years! The most exciting bikes of the moment are bikes like the Open U.P. – a carbon race bike that accepts 50 mm-wide tires!

Not too long ago, every performance road bike had 700C x 23 mm tires. Now you can choose not just how wide you want your tires to be, but – thanks to disc brakes – even which wheel size you want to use! For Bicycle Quarterly’s test, we rode the Open with 650B x 48 mm tires, but our second tester, Nate King, raced his Open with 700C x 44 mm tires. Which is better? Or should you get several wheelsets for different courses? Is there a reason to switch tires and wheels on the same bike?

Let’s first talk about some fundamentals: Wider tires don’t roll slower than narrow ones. Bicycle Quarterly‘s latest tire tests, published in the Summer 2021 edition (BQ 76), have shown this once again: In a real-road scenario, even 44 mm tires don’t roll slower than 28 mm – or any size in between.

Other tests have shown that even 54 mm-wide tires aren’t significantly slower than narrower ones – provided they use the same supple casings. Conversely, tires narrower than 25 mm are slower – that’s why pro racers have moved from 20 and 23 mm tires to 25 mm in recent years.

By the way, we tested at 22 mph, so this factors in the air resistance of the wider tires. And we tested on very smooth asphalt – where wider tires are neither faster nor slower. On rougher roads, there is no doubt: Wider tires are faster because they glide over irregularities that make a bike on narrow tires bounce and vibrate.

Yes, I know it’s not what we used to believe – we were quite surprised when we first saw these results 15 years ago. Since then, we’ve confirmed this time and again. And so have others in recent years.

To summarize all this research: Narrow tires (<25 mm) are slow. Above 25 mm, the width of your tires are won’t change your speed on smooth pavement (at least up to 54 mm wide tires). On rough surfaces, wider tires are faster.

That doesn’t mean you can just slap any wide tires on your bike and expect it to go fast. What will change your speed is how supple your tires are: Tires with high-performance casings are faster, more comfortable and offer better traction, regardless of their width. If you choose heavy, reinforced ‘touring’ or ‘gravel’ models when you switch to wider tires, you’ll be disappointed – they’ll roll slower than racing tires because of their sturdy casings, not because of the extra width.

So we know that supple casings are important, and that width doesn’t matter. What size tires should we run then? Is wider always better? And what about wheel size?

Wider tires offer more cornering grip. This is true for racing cars and motorbikes as well as bicycles. On bicycles, there are two reasons for this:

• More rubber on the road gives you more traction.
• Wider tires are inflated to lower pressures, which means that they stay in contact with the road. If your tires don’t bounce over small irregularities in the pavement, they have even more grip than their width alone would suggest.

If you like to corner fast, you want the widest tires possible. Even on smooth pavement, the difference between 38 mm and 48 mm-wide tires is very noticeable. On rough surfaces and especially on gravel, it’s no contest.

Wheel size is another consideration. You often hear that larger wheels roll faster, but there is no evidence that this is true. All our tests show that among the popular wheel sizes, there’s no speed difference.

Wheel size doesn’t affect your speed, but it does affect how your bike handles. We once tested three bikes that had different wheels sizes – 700C/29″, 650B/27.5″ and 26″ – but otherwise were identical (same trail, wheelbase, BB height, etc.). We found that wheel size greatly influences the handling of your bike. Larger wheels make the bike more stable, and so do heavier wheels – because of the rotational inertia.

Since wider tires are (slightly) heavier, you’ll probably want to decrease the wheel size to keep the rotational inertia – and thus the handling – the same. That means that your wheel size should be chosen based on your tire width and tire weight. That way, you can enjoy the nimble handling of a racing bike even with wide tires.

Let’s a look at a few tire sizes that I enjoy riding, with their pluses and minuses:

32 mm wide

• Most modern race bikes can fit 32 mm tires, and that is a very good thing.
• You still get the ‘connected-to-the-road’ feel that makes a racing bike so much fun, but you take away most of the harshness.
• With 32 mm tires, road bikes are fast not only on smooth highways, but also on backroads that are much more scenic and interesting to ride (and have less traffic).
• In a pinch, you can take your bike on gravel, too – even if it’s just a detour around a construction site.

38 mm wide

• 38 mm tires are great for pavement and occasional gravel riding.
• To go with 38 mm tires, you have a choice of wheel sizes:
• If you’re running superlight carbon rims, go with 700C for 38 mm tires.
• With aluminum rims, if you like the nimble handling of a racing bike, then choose 650B wheels for 38 mm tires.
• If you prefer a bike that locks onto a cornering radius and won’t be deflected even if tense up in mid-corner, then use 700C wheels for 38 mm-wide tires.

42 – 44 mm wide

• Adding 4 mm to the width of your tires gives you some added plushness – compared to 38 mm, you’ve increased the air volume by 22%.
• In exchange for that added cush, you lose a little bit of connection to the road. To me, that isn’t a big loss, and I enjoy the greater traction and go-almost-anywhere capabilities of the wider tires.
• For tires this wide, 650B is a good wheel size, although 700C works fine, too (see below).
• 42-44 mm tires are perfect for riders who like to push the limits on pavement, as well as those who regularly explore gravel roads.

48 – 54 mm wide

• Now we are getting into some seriously wide tires for a road bike! A 54 mm tire holds twice as much air as a 38 mm tire.
• Tires this wide change their feel depending on the pressure you run:
  • With the tires inflated to ‘firm’ pressure (35 psi/2.4 bar; for a 155 lb/70 kg rider), your bike feels like a road bike. The wide tires make more noise as they roll over the pavement, but otherwise, they feel similar to narrower tires.
  • Letting out some air and reducing the pressure to ‘soft’ values (25 psi/1.7 bar for the rider above) changes the bike completely. Now it is super-plush. The tires still have enough air so they won’t collapse under hard cornering, but you can feel the ‘suspension’ when riding out of the saddle. At this pressure, the tires are ideal for rough gravel.
  • For actual air pressure recommendations for your weight, check the Rene Herse Tire Pressure Calculator.
• For tires this wide, I recommend 650B wheels. With 700C rims, your bike will tend to plow straight ahead like a 29er mountain bike, and you’ll need suspension to absorb the bumps that you cannot steer around. On my Firefly (above), I went with 26″ wheels for even more agile handling. That bike feels very similar to a good racing bike – but it can go almost anywhere.

How about tires wider than 54 mm? That might be interesting, but you can’t really fit them between road cranks with narrow Q factor. 54 mm tires already are quite wide: They have the same air volume as 2.3″ mountain bike tires – it’s just that they don’t have knobs on the shoulders, so they measure out a bit narrower. Below is a comparison of the air volume of my three favorite tire sizes (to scale).

To summarize, if you want your bike to feel connected to the pavement like a good road bike, I recommend 38 mm tires, either in the 700C or 650B wheel size. Compared to narrower tires, 38 mm give you added comfort and speed on rough pavement, and more cornering grip, too.

I prefer a little extra rough-road performance and even better cornering grip, so for paved rides, my choice is 650B x 42 mm. You lose a little of the connection to the road, but during hard cornering, you actually get more, not less, feedback of how much grip you have in reserve.

If my ride includes a lot of gravel, I’ll pick 650B x 48 mm or even 26″ x 2.3′ (54 mm). On pavement, the downside is that you get some tire roar and the bike’s feel is more sensitive to tire pressure. On the plus side, the grip in paved corners will blow your mind.

If you are using lightweight carbon rims and superlight tires, like our Rene Herse Extralights, then it makes sense to go up one wheel size to compensate for the lighter weight. So for 38 – 43 mm tires, I’d recommend 700C wheels, and for 44+ mm tires, I’d use 650B. Otherwise, your bike gets that ‘small-wheeled’ feel: The bike doesn’t hold a line on its own, but requires constant inputs from the rider to go straight. It’s not a big deal, but we are talking about optimizing your bike here.

It seems that more and more riders are converging on these tire sizes: BQ‘s second tester for the Open U.P. recently received the latest model from his sponsors (above), and he spec’d it with 650B x 48 mm tires – like our test bike. And he tells us that he loves it!

With these suggestions as a starting point, I recommend test-riding a few bikes with different wheels and choosing the ones you like best.

Further reading:

• The All-Road Bike Revolution, our book about the science that has revolutionized bicycles over the last 15 years.

Photo credits: Toru Kanazaki (Photo 8), Natsuko Hirose (Photos 1, 3), Nate King (10).