The Fastest Tyre Width is NOT What You Think

We’ve always been told that narrower is more aero, but is it faster overall? In one of our biggest tech deep dives yet, we put 28mm, 30mm, 35mm, and 40mm tyres head-to-head to finally find out which size is truly the fastest.
We tested every tyre for both aerodynamic drag AND rolling resistance to get the complete picture. The results will definitely surprise you and might just change what tyres you choose for your bike!
What tyre width are you currently riding? Let us know in the comments below! 👇

Chapters ⏱️

00:00 Introduction
00:51 Why The Fastest Tyre Is Not The One You Think It Is
01:37 What Is Being Compared & How
04:18 Aerodynamic Drag Results
06:11 Rolling Resistance Results
07:48 Conclusion

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What tyre width are you currently riding? Let us know in the comments below! 👇

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Big fat road bike tires. Are they really the future? Some people say yes, some people say no. But I think the fastest tire with is probably not the one you think it is. Well, I’ve traveled here to the Silverstone Sports Engineering Hub to put these big chunky 40 mm bad boys to the test in the wind tunnel against a 28, a 30, and a 35 mm tire to see how they compare in terms of aerodynamic drag. Not only that though, I’m also going to later on in this video explain about the other factors affecting overall tire performance such as weight and rolling resistance so that you can decide if big chunky road bike tires are actually the future for you. Right, let’s do it. Now, before we get into all the details and talk about the ifs, the buts, and the mayers, I want to say the results that I came away with surprised me. And I also want to know if the results surprise you once you know the outcome of the tests. So why is it that I think the fastest tire width is probably not the one that you think it is? Well, the reason for that is because many people, myself included, seem to attribute the feeling of speed with the vibrations that we can feel through our bike coming up from the road surface, which really isn’t the case. Otherwise, we would all be riding around with 120 PSI in our tires, which hopefully by now we all know is actually a really bad idea. Okay, let’s talk about what it is I actually tested and the results. Now, first I visited the wind tunnel alongside some testing that was being conducted by Elite Wheels. And then later on down the line, Ollie and I visited the pedaling efficiency rig. You know, the one where we did that shoes testing video. Yeah. Um, anyway, in the wind tunnel, I tested a front wheel in isolation. Now, a number of different reasons for that. Firstly, because it removes the inaccuracies of having a moving rider in there. Two, because some bikes perform better or worse with wider or narrower tires. And then three, the reason is because I’m doing a front wheel in isolation rather than the back wheel is cuz the front wheel plays the largest contributing factor to aerodynamic drag. So, it’s important to bear that in mind because you can’t simply take the aerodyrag from a front wheel only and double it to have two wheels cuz it just doesn’t work that way. And then on the pedaling efficiency rig, well, the surface we used is what’s described as your typical average quality road, if there is such a thing. Now, both tests we conducted at 30 and 40 km an hour in the hopes to cover realworld speeds that are relatable to everyday riders. In the wind tunnel, it’s worth noting that those speeds are for both the wheels rotational speed and the wind speed as well. In terms of the actual tires that I’ve tested, well, we’ve got four different sizes here, a 28, a 30, a 35, and a 40. all in the same tire type, which is a PO race TLR, but with TPU inner tubes fitted to them for an easy life because I had to do lots of different tire changes on lots of different wheels. And then all of the tires were inflated to a pressure relevant to the tire width as recommended from the Silka tire pressure calculator, which optimizes for speed. But I do want to point out I did use two different wheels in the winter. Now, you might be going, “Oh, that’s completely rubbish. Why did you do that?” But no, it’s not rubbish. You see, the wider your tires, the wider the wheels internal rim width that the tire is designed and optimized for. So, on the 28 mm tire, I used the D50 wheel with its 21 mm internal rim width. And then on the wider tires, so the 30, 35, and the 40, I used the Elite Wheels G45 with a wider rim width, but 5 mil shallower rim depth. And in the interest of science and trying to conduct a fair test, well, I run the 30 mil tire on the narrower wheel and also run the 28 mil tire on the wider rim. Yeah, there was a lot of tire changes happening in a very short space of time. Anyway, enough chat about that. Let’s actually talk about the results. So, at 30 km an hour in terms of aerodynamic drag expressed in watts, well, the lowest was the 28 mm tire on the narrower wheel. We’ve got a drag of 7.857. 857 watt. And then if we follow up through to the highest where it goes, the 28 mil tire on the wider rim, the 30 mil tire on the narrow rim, the 30 mil tire on the wide rim, then the 35, and then the 40. So those were kind of as I would expected. And then the difference here was much smaller than I expected. So between the 28, the 30, and the 35 mm tire, there was just less than one watt difference between them all, which in my eyes is a good to no difference at all. And then if we go from the lowest to highest drag setup, it’s just 2.4 W extra going from the 28 all the way up to the massive 40 mm tire. So aerodynamically, at those speeds, your tires are not having a significant impact on your performance. Now if we go up to higher speed 40 km an hour the results followed the same order and trend. However there was a larger difference here between them. The 28 and 30 mil tire all within one watt of each other but then having the 35 gave you a 2 watt aerodynamic penalty and then the 40 goes up to a 5.1 watt penalty which if you’re racing is perhaps enough to start to care about but for your weekend rides well I wouldn’t even let it cross my mind. So, broadly speaking, if I take an average from both of the speeds, going an extra 2 mm wider from a 28 up to a 30 has a 0.7 watt aerial penalty. Going 5 mil from a 30 to a 35 adds a 0.6 watt penalty. And then going extra 5 mil from a 35 to a 40 has a 2.3 W penalty. But that is just aerodynamic drag, which is just one piece of the puzzle. The far more significant factor to affecting performance is rolling resistance. And to measure that, well, we need to head to the pedaling efficiency rig where we can monitor the power in from me, the rider, and then monitor the power out at the back wheel. Now, some of the losses that we’re able to measure will come from the bike, so the chain and the things like bearings. But by then swapping out the tires, we can see what a difference that makes. Now, this is where I was surprised, but also kind of pleased. So, instead of the power losses tracking up with the increased tire width, it would appear that the 30 mm tire had the lowest power loss out of all the tires that I tested. And it was actually lower than the power loss from the 28 mm tire. At 30k an hour, it’s 0.56 W lower. And then at 40 km an hour, 2.06 watt lower for the 30 mil tire over the 28. Now, it’s not much at all, but to be able to have a wider tire that has the potential to offer increased grip and greater comfort without any losses in performance in my eyes is a good thing. Second lowest in terms of rolling resistance power losses was the 28. Then you have the 35 and then the 40. Now these differences are far more significant and unlike aerodynamic drag, these numbers can simply be doubled to get the figures for a bike which as we all know uses two wheels. Last standing start of the day. So what does all this actually mean? Well, in terms of aerodynamic drag, let’s not really worry about tire width too much. Yes, there is a difference, but I certainly won’t be losing any sleep over it, and I don’t think you should either. But in terms of rolling resistance, well, there is a significant difference here. And yes, I already know this, and I’m sure lots of people at home knew this, but what I didn’t know or expect was for the 30 mm tire to outperform the 28 mm tire. Now, at 30 km an hour, using a pair of 30 mm tires over a pair of 40 mm tires requires 19.5 W less power. And then at 40 km an hour, it requires 24.3 W less power. Plus, on top of that, you need to factor in the difference of aerodynamic drag. So, at 30k an hour, that’s 1.8 W. And then at 40 km an hour is an extra four watt. Now, at this point, there’s a lot of numbers that I’ve gone through here, and I should stress that these results, whilst I think are good, and I’m pleased with what I found out from my testing today, they are going to vary depending on what wheels and what tires you use, but I would imagine and hope they would follow a similar trend. So, what have I actually learned from these tests, and what does it mean for you guys at home? Well, my fairly simple testing has shown that from a power perspective on typical smooth roads at slower riding speeds, a 30 mm tire seems to strike the perfect balance between aerodynamic drag and rolling resistance. And it’s even trumped the 28 mm tire, which I would say is like the go-to or standard tire for modern bikes. And what this means for me is I’m probably going to see the 30 mm tire as my go-to option. Plus, it has the added benefit of providing me with more grip and more comfort. Happy days. So, what this means for you is that when you’re trying to decide on some new tires to buy, providing they fit into your bike, I would say go for it and give some 30 mm tires a try. But what about if you’re riding on rougher surfaces? Well, in this case, there’s likely to be an advantage to going for an even wider tire and running it at a lower tire pressure. This is going to help the tire to absorb the vibrations from the road rather than rattling your entire bike down the road. Now, this advantage is also likely to outweigh or at least offset some of the disadvantages in terms of rolling resistance and aerodynamics. Now, I haven’t actually been able to test this today, but it is something I’d like to test in the future, and current data and research out there suggests that this would be the case. So, I am intrigued to explore this a little bit further later on down the line. And then finally, like all bike tech, the fastest setup will depend on a number of different factors like your system weight, the speeds you ride at, the surfaces you ride on, the conditions you ride in, the wheels you use, and of course, the tire pressure that you have your bike set up to run, which in many cases will outweigh the difference in performance from tire types and tire width. So, make sure you get those pressures dialed in. And then just to caveat all of that, the fastest setup also needs to account for the grip and puncture protection from a certain tire because you’re not going to be going anywhere fast if you’re at the roadside with a puncture or haven’t sat there having crashed. There are so many different variables at play here. It’s nearly impossible to say there’s one tire setup that is going to be fastest in all conditions. It’s always going to be a case of having to compromise in some areas or tweak your setup depending on the conditions that you’re riding in. But having finally tested this for myself, it’s nice to actually have the answer. And then if you cast your minds back to when Connor and Ollie tested 28 mil tires against 40 millimeters tires out on the roads in the real world, well, you’ll remember that they found the difference in terms of speed riding at the same power over a 7 km loop meant that the 28 mm tire was 18 seconds faster than the 40. So there you go. Keep that in mind as well. But the most important thing out of all of this is to remember that if you’re just out there riding your bike and you’ve got a smile on your face, well, I’ll be happy with that. So, there you go. That is more than enough chat about tire widths, tires, pressures, and anything else like that. But I do hope you’ve enjoyed this video. And if you have, please do give it a big thumbs up. And as I said at the start, let me know in the comments section down below if the results surprised you as well. And um if you have ridden some crazy wide tires like these bad boys, let me know how you got on with them. Right, I’m out of here. And if you want to help support our channel, subscribe to GCN Techch. Turn on notifications. See you.