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There is a trend in the bike industry to push gravel tires bigger and bigger. That’s both in the smaller 650B diameter (eg. Open Wi.De with 60mm/2.4″ tires) and larger 700C diameter (eg. Giant Revolt Carbon with 53mm/2.1″ tires).
The reasoning is very simple: wider tires achieve more grip and comfort.
But is that true?
Comparing 43mm and 50mm Tires
To test this assumption, I needed to push the limits of my benchmark bike, a Jamis Renegade.
This gravel bike ‘officially’ takes only 40mm tires but having used Panaracer GravelKing SK 43mm tires on an everyday basis, I knew that my bike could take much bigger tires.
The key to success is that my Alex rims have a very narrow 17mm internal rim width, which doesn’t allow tires to achieve their true size. For example, my GravelKing SK 43mm tires measure just 41mm on my rim.
The front of the bike was an easy task. With the tire inflated to 40 psi, it was measuring just below 47mm. As you can see in the pictures, there is still some space between the tire and the fork.
The back of the bike was a different story…
The first attempt was not easy and I needed to let all the air from the tire just to put the wheel in place.
But when inflated the tire I discovered a new problem – the mounting point for the rear fender was blocking the tire from any movement – so I filed it off entirely (hey, it’s for science!).
After that not-so-easy task, I put the wheel back in and inflated it. Success.
Note: the space between the tire and the frame is very narrow so I sincerely do not recommend anyone trying this on their bike.
How Do The Different Tire Widths Ride?
Having now mounted these huge gravel tires to my bike, I went for a test ride and soon I discovered that my bike handled differently.
Riding on 43mm tires feels like you are on top of the front wheel, and riding on 50mm tires makes you feel like you are behind the front wheel. While the narrow tires feel more agile, the wide tires feel more stable.
I never expected that 2mm of trail change would make that noticeable difference to my steering.
To be honest, I prefer my bike more with the wide 50mm tires. It’s a little more engaging, and the ride is more rewarding because you have to work harder to change the bike’s direction.
Are Wider Tires More Comfortable?
To my surprise, riding the 50mm tires at 30 psi didn’t actually feel that comfortable. Even at 20 psi, I did not feel the ‘magic carpet ride’ that I was expecting. Let’s see what the vibration data says about this.
On a positive note, with the 50mm tires at 20 psi, you don’t need to worry (as much) about bottoming out the tire and damaging the rim. This is a possibility on a 43mm tire as the tire’s sidewall is shorter.
Vibration Test Results
You can see my vibration measurement procedure & outdoor test courses HERE.
Well, the wider tires were less comfortable in almost every situation!
On the bumpy forest trail, the wider tire offered a very slight improvement at the rear (2,4%) but similar vibration levels at the front. And on the fast gravel road, the wider tire was significantly less comfortable (-9,2%) at the rear of the bike.
The situation was even more interesting when riding at 20 psi…
Less air meant the wider tire could flex more, so it was no surprise that the front of the bike was now more comfortable with the wider tire.
But something really weird happened at the back.
At 20 psi, the 50mm tire created more vibration than the 43mm tire. This was both on the bumpy forest trail (2,3% more) and on the fast gravel road (16% more). I’m wondering if the combination of the big tire with the flex carbon seatpost made things simply too ‘springy’?
I then decided to do a re-run with tubeless setups. Below you will find the results for 30 psi and 20 psi.
In general, the trend remained the same when I set these tires up tubeless. However, the differences were a little less stark.
At 20 psi, the wider tire again worked out beneficial in terms of front comfort. But the rear was only more comfortable on the bumpy forest trail (5,2% fewer vibrations). On the fast gravel road, it was still a bit behind.
A Mistake In My Testing
After conducting these tests, I thought about the science behind why the wider tires might have been less comfortable.
It turns out a bigger tire requires a lower pressure to achieve the same tire casing tension (Laplace’s law states that the casing tension = internal pressure x tire’s radius). So when you use the same pressure between the 43mm and 50mm tires, the latter isn’t as eager to flex and absorb bumps.
If you didn’t already know this, you do now. It’s time for me to do some further comfort tests…
I always thought that the bigger tire would always be more comfortable, even at the same tire pressure.
But what I’ve learned from this is that I need to conduct new tests comparing different tire widths with the same casing tension. That means adjusting the tire pressure in accordance with Laplace’s law.
Perhaps by matching the casing tensions between tire widths, I will achieve the expected result of more comfort when using a wider tire.