 Selecting the right tire and tire pressure can make a huge difference to your speed. A few quick changes could save you 10 to 20 watts or more, but navigating which tires and pressures are slower and faster is not always intuitive. In fact, if history is anything to go by, then most people's intuition can often be wrong when it comes to determining what's fast. Today's video is going to be a little bit different than my usual style of video. I got a chance to sit down with Josh Portner and talk all about marginal gains, and this is the first part of our conversation on tire rolling resistance. For those of you who don't know who Josh is, he's a marginal gains pioneer. He's currently the owner of Soka, but before that he was the technical director at Zip and helped to bring aerodynamic carbon wheels and power meters to the Pro Peloton, which we all take for granted today. He's also the co-producer of the marginal gains podcast, which is one of my favorite podcasts to listen to because Josh will go super in depth on all these little things that you can do to go faster from making your drivetrain as efficient as possible to every aerodynamic hack that you can think of to things that you might not think of like the placebo effect. Anyway, Josh has such a depth of knowledge in all of these topics, and I was super excited to have him on for this video. So let's go ahead and jump into our conversation on rolling resistance. Yeah, I think, you know, those are all things that we can calculate and, you know, we've got, if you've used it, a tire pressure calculator. I think I used that before every single race that I do because it's not like, oh, my tire pressure is 30 psi and that's what I run. It's dependent on the course, it's dependent on the tire width, it's dependent on your weight. I'm probably missing a few factors off the top of my head here, but yeah, for one person, the correct tire pressure could be completely different depending on all these variables. Glad you like it. And, you know, we built that tool because I, you know, we spent years doing these optimizations in notebooks and trying to look back at, you know, oh, okay, last year, we, you know, this rider at this weight on that tire at that width on this, you know, and it's pretty easy with these European road races in particular because they're typically the same every year. I mean, Roubaix changes a little bit here and there, but we, you know, we know those Pave sections, we know the courses. And then eventually just had to create this tool to help myself because people would ask questions and, you know, you just start to confuse yourself with, oh, God, well, it could be, you know, I'm trying to do the mental math. But a tool like that, you know, it will get you very close to the right number and I think it will allow you to then, I think what I like about it is it allows you to pick the tire that you think for that event and then get straight to the pressure quickly in a way that, you know, you go to unbound a few days early, you know, you can ride some sections and it really becomes more about the tire choice than, than having to refigure the whole algorithm every time. You know, I go, it's going to be really dry and hard this year. So maybe I'll go with a little bit smaller tire and then you can test ride that section and look at your data and think, is this a good decision or do I want to go back to something a little bit wider? Yeah. And one point that I want to drive home here is that when we're talking about tire pressure, lower pressure is not only making your bike more comfortable, it is doing that, but it's actually reducing the amount of watts that you need to produce at a given speed. Of course, there's too low. You can go too low. But I've actually done this test. I've got a section of gravel road where I'll ride it at the exact same power output and maybe I've got two sets of wheels with different tires on them and I'll do them back to back, try to see which tires faster and then I'll lower the pressure to try to see if that's faster. I'll raise the pressure, try to see if that's faster. It's not perfect, but I have found that I've found the point at which it's too low and I've found the point at which it's too high and I've kind of found the optimal pressure. And my biggest takeaway when I do that and when I use your tire pressure calculator is a lot of times the right pressure is lower than people think it is. Most people are running too high. Yeah. I mean, that's been a drum that we've been banging on for 12 or 13 years now since we really discovered that effect. It was a guy, Tom Anhalt, in California who's just a super genius of a guy and a close friend of mine was the first to really kind of notice this. Wait a minute. Roller data, the roller says that the rolling resistance goes down as pressure goes up. But in the real world, if we're using a virtual elevation or the Chung method, and we've got power meters and all these things, you know, those tools became more prevalent. And he was the first to really point out, wait a minute, it actually goes up again. And then we really pwned in on what is that and why is that happening? And I was around 0708, I think that we first quantified it with some pro athletes actually during the 303 development with the Saxo Bank at the time. And yeah, I think the big takeaway for people to think about there is that the rolling resistance improvement as pressure goes up is quite shallow. But what we call impedance, the losses due to the vibration of having to like bounce over all those bumps, the impedance is typically steeper than the casing loss. And so you're always better to be lower than higher. Five PSI too low might be half a watt, five PSI too high might be five watts. Yeah, which I think a lot of people would find surprising because I think at least most road riders, maybe mountain bike and cyclocross, they know the value of low tire pressure, but at least most road riders probably assume, well, it's better to be on the high end than on the low end. But what you're saying is that it's the opposite. Yeah, absolutely. Absolutely. And I think that's how we grew up. I mean, I certainly grew up in an era of the more you can get in there, the better. And you need a silica pump because it goes to 210 and you might need it. And we look at that now and it's, I mean, even on really high quality track surfaces, we can see these breakpoints. You have to get to like a polished, varnished wood track before you can even dream of seeing like a 200 PSI pressure. But I'm even a lot of like the concrete velodromes in the country here. I mean, they might have optimal pressures on a 23 millimeter tire of 110, right? I mean, which is way below what you go talk to people at events. I mean, we joke, we have a van, we call the, in a setup, we call the inflation station, we take it to events and it's, you know, free pumps for people to use and talk, have a talk with us and lube your chain. And the joke is that, you know, we carry these pumps all over the country for these events. And almost all that we do is let air out of people's tires. It is very rare that we're actually inflating a tire. Need a rename deflation. The deflation station. To me, it's not necessarily intuitive which tire is faster than another tire. I think a lot of people just immediately, they're, they're looking at the tread pattern. Maybe less so for road because, you know, road tires are generally slick, but at least for gravel and mountain bike, first thing they're looking at it is the tread pattern. And if the tread pattern looks pretty smooth, they assume that's going to be faster. And if it's very knobby, they assume that's going to be slower, that obviously plays a role. But what other factors are there in making a tire fast versus slow? Yeah, this one's hard. And you really just need to test them as kind of the first thing I'll say. I mean, the, I would say if there is, if there is a rule of thumb for tire rolling resistance, it's probably going to be that lighter tires are generally going to be faster. And of course, that starts to fall apart when you get to like the two foe road tires, which can be very light and very slow. Although they've, they're updating and changing their technology. And I know they've made some huge improvements there. But yeah, you know, you think of the, the loss in the tire is what we would call hysteresis, right? So it's essentially when deflection within the tire is leading to some conversion to heat, right? There's some sort of like rubbing or losses that convert to heat. And so the rubber compound, the rubber material is a big deal. Some are just higher loss than others. And, you know, the way to think of that is like these running shoe foams, you know, like Nike's got this Peabox running shoe foam that is like one of the most efficient foams known to man. It's actually what we make the silk bar tape is made from the same stuff. And it's just a super efficient foam. It's got something like a 15% hysteresis loss where like EVA foam in a traditional classic running shoe, you know, that might have a 40% loss. And you think of something like Sorbithane, right, is a pretty well known trade brand name for, for foam. And, you know, Sorbithane is like a 60% loss. And so, you know, which would you rather make your attire out of, right? You want the lowest loss possible. And so that's where you see people trying to add a lot of fancy names or chemicals to the rubber to make it lower loss. But of course, if you don't have a test machine, you know, how do I know what black chili means from continental or, you know, what graphene is actually doing in Victoria, you know, typically, the higher TPI casings are going to be lower loss because they're thinner. But as we've seen testing, that's not always true. You know, some brands use latex, like, you know, Vittoria does a great job of using very pure latex in their sidewalls. And latex is extremely low hysteresis. But then there's other brands with 320 TPI casings that are using less efficient rubbers and those tires don't test as well. So, you know, there's sites out there, I think bicycle rolling resistance.com is a good one to use those numbers. I subscribe to bicycle rolling. You do? Yeah, his numbers aren't quite real because he's not converting from round drum to flat. So, you know, he says, oh, this is a 12 lots and that one's a 15. Those aren't exactly real world numbers. But I mean, they're the trend holds. If tire A is faster than tire B on the drum, it's going to be faster in the real world. You know, and I think that for me, the most exciting thing really happening in tires is tubeless sealants getting better. And what that allows for is thinner tires with less with fewer plies or fewer layers. And you think every, every time we want to put a layer of protection or something in a tire, that's just another opportunity for this hysteretic loss. And so, you know, if I can take the puncture belt out of a tire, the tire gets faster. If I can make the tread thinner, the tire gets faster. If I can make the casing thinner, the tire, you know. And of course, that only becomes possible with really high quality sealants because of what you're doing otherwise is effectively making really fragile tires. An example that you've used that I think really helps people to visualize hysteresis loss in tires is the memory foam, like a memory foam mattress versus, you know, I don't know, like a bouncy ball. Yeah. And I think that's a great way too, to visualize this static versus dynamic stiffness thing that happens. So yeah, you think of the memory foam commercial, right? When they push the hand in and you pull the hand away and the handprint stays, that's a very high hysteresis material. And the, there's this thing called dynamic stiffness that happens where, you know, as an engineer, I like to talk in graphs. And so, you know, you put something in the test machine and you push it and you say, oh, it's so many Newtons per millimeter of stiffness. Well, if you think, you know, if you put a metal coil spring in there and you push it down and then you lift, it goes with you, right? That's a very low hysteresis thing. A high hysteresis thing, you know, you push it, push the hand in, move it up, and then it takes time for that to come back up. Well, you think of that in like hitting cobbles or hitting bumps, you know, you hit that first bump and it compacts, and then you're hitting the second bump before it's had time to rebound. And so now you're effectively, you think of like, if you're punching the memory foam mattress, eventually you just collapse that foam down until it's, you know, nearly rigid. And then you're just hitting the rigid thing. And so, you actually have this very high stiffness. And that's one of the reasons why, you know, you can run, you know, a really beautiful tire at one pressure and then put like a crappy training tire on and run it at the same pressure and it feels awful, right? And you think, well, if they're the same pressure, they should have the same stiffness. And if I push on them one way with my test machine, they do have pretty much the same stiffness, but this dynamic stiffness characteristic or component, it's much harder to measure for, but that's really what you're feeling. And, you know, the mountain bike guys will talk about this as packing, right? You'll hear someone talk about like washboard, you know, the suspension forks will pack down over washboard. And that's effectively telling you that you're, you're over damped for that surface. And so that's one of the reasons that, you know, these high hysteresis tires are not only slower, but they're actually quite a bit less comfortable. And they also don't hold the road as well on rougher surfaces because the tire isn't able to respond to the road surface in a way that's giving you the optimal contact patch at all times. One more thing on tires. Tire inserts have become more and more popular for mountain bike gravel. And now we're seeing it in road as well. How does a tire insert affect the rolling resistance? So it really depends what type. We've done a lot of work with these and I have to say we've really successfully implemented them with EF, in particular, the Education First team. There's two types. You have the sort of mountain bike, you know, I'll call it like the Huck Norris or the Apheto Mariposa, where you're essentially, you know, you're taking like the volume of the tire and you're putting something in the volume of the tire that's really giving you protection from a bottom out. And those don't affect resistance unless they are loading the sidewall of the tire in a way that, you know, if you think if it's wide enough that it's touching the sidewall of the tire, it's now involved. Every time the tire rolls, you know, gets to the bottom, it's compressing this way, which means that it's bulging out a little bit wider. And then as soon as it comes up from being at the contact patch area, it's squeezing back in. And if that foam is touching it, that's just a new hysteretic loss, right? That's just a new inefficient thing in your system. And so the size of those is really critical. But I would say typically, you know, you're using them in applications where like, do you really care about that last lot of rolling resistance? You know, I probably not. For road, we've seen some similar things where, you know, you've got these higher volume inserts that are touching, that's bad for rolling. But Vittoria in particular has an insert that is really more meant to squish down in between the bead. And what's cool about that particular insert being a closed cell foam is that when you inflate the tire, the higher pressure around the foam actually causes the foam to shrink down. And so when the tire is at pressure, the insert is sort of collapsed down in between the beads at a place where it's really not affecting the rolling resistance because it's not engaging in any of the compression or the movement of the casing. And then of course, as soon as you flat, it pops, you know, it poofs open. And now you're running on that. But, you know, we had two punctures at Roubaix last year with EF and both riders were able to finish on the foam insert without issue. And that's, you know, that that's magic, right? And it's for for the time that you're on the insert, it's a couple, you know, it's whatever, five or eight or 10 additional watts of rolling resistance, because the foam is not that efficient. But that's a whole lot better than, you know, stopping at the side of the road and waiting for two minutes for the team car to come and give you, right? I mean, so so that technology is pretty exciting to me. And it's been really fun to be a part of watching that grow. Thanks for watching. Let me know down in the comments if you enjoyed this different style of video. I have a lot more of this conversation that I plan on releasing. If you enjoyed the video, be sure to give it a like, subscribe, and share this video with your cycling friends. I'll see you in the next one.