Our ideas of what is a performance bike have changed a lot in recent years! One of the most exciting bikes of the moment is 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 have to 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 the Bicycle Quarterly 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 Winter 2016 issue (BQ 58), have shown this once again: In a real-road scenario, even 54 mm tires don’t roll slower than 32 mm – or any size in between. Before this, we already tested tires between 20 and 32 mm tires and found that the 20 mm and 23 mm were slowest, and all the others offered the same performance.
By the way, we tested at 22 mph, so this factors in the greater air resistance of the wider tires. It appears that wider tires have slightly lower rolling resistance, which cancels out the small increase in wind resistance. This means that at lower speeds, wider tires probably are faster than narrower ones. We tested on very smooth asphalt. On rougher roads, wider tires also are faster.
Yes, I know it’s not what we used to believe – we were quite surprised when we saw the results of our testing, but 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 (at least up to 54 mm wide tires).
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’ models when you switch to wider tires, you’ll likely to 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 key, 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. And 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 traction 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 noticeable, and on rough surfaces or even gravel, it’s no contest.
Wheel size is another important consideration. The photo above shows three Bicycle Quarterly test bikes with identical geometries (head angle, trail, BB height, etc.), but different wheel sizes. What we found in that test: Wheel size greatly influence the handling of your bike. Larger wheels make the bike more stable, and so do heavier wheels – it’s the rotational inertia that matters, not the outer diameter.
Since wider tires are (slightly) heavier, you’ll 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 great racing bike even with wide tires.
Let’s a look at a few tire sizes that I enjoy riding, with their pluses and minuses:
38 mm wide
- To me, tires narrower than 38 mm don’t really make sense any longer. 38 mm tires still give you the “connected to the pavement” sensation that makes a racing bike feel so fast. Below 38 mm, all you gain is harshness. The bike doesn’t feel any better, just more jiggly.
- 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 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 the optimal wheel size.
- 42-44 mm tires are fine for most gravel riding. They have the advantage that good rim brakes (like our Compass centerpulls) fit over them – even with fenders. In fact, fender mounting becomes a compromise with tires wider than 44 mm (see below).
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 38 psi (2.6 bar), our Open U.P. test bike felt like a road bike. The tires made more noise as they rolled over the pavement, but otherwise, the feel wasn’t all that different from narrower tires.
- Letting out some air and reducing the pressure to 26 psi (1.8 bar) changed the bike completely. Now it was super-plush. The tires still had enough air so they wouldn’t collapse under hard cornering, but I could feel the ‘suspension’ when riding out of the saddle. At this pressure, the tires were ideal for rough gravel.
- For tires this wide, I definitely recommend 650B wheels. With 700C rims, your bike will just 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 a more agile handling. As a result, the bike feels remarkably similar to a good racing bike.
- Fender mounting is an issue with tires this wide and road cranks: Ideally, a fender should be about 20 mm wider than the tire, but the chain will hit a fender that is wider than 62 mm when riding in the smallest gear! The solution is using a 62 mm fender that doesn’t wrap around the wheel very much and mount it a bit higher above the tire. It works, and we now offer a 650B fender specifically for 47-48 mm wide tires.
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 650B x 38 mm tires. Compared to narrower tires, you get added comfort and speed on rough pavement, and more cornering traction, too.
I prefer a little extra rough-road performance and even better cornering traction, 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 traction you have in reserve, because the tires can really key into the pavement.
If my ride includes a lot of gravel, I’ll pick 650B x 48 mm or even 26″ x 54 mm. On pavement, the downside is that you get some tire roar – how much depends on the diameter of your bike’s frame tubes that provide the resonance chamber for the noise – and the tires’ feel is more sensitive to tire pressure. On the plus side, the traction in paved corners will blow your mind.
If you are using lightweight carbon rims and superlight tires, like our Compass 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 44+ mm tires, I’d use 650B. Otherwise, your bike gets that ‘small-wheeled’ feel: The bike doesn’t hold its line on its own, but requires active input 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.
- Bicycle Quarterly 58 reported on our latest performance tests of tires between 32 and 54 mm wide.
- Bicycle Quarterly 59 featured the test of the Open U.P.
- Our research on wheel size and bike handling was published in BQ 31 and BQ 64.
- More information about Compass tires.
Photo credits: Toru Kanazaki (Photo 8), Natsuko Hirose (Photos 1, 3), Nate King (10).