 I'm going to be honest, I thought I knew a lot about aerodynamics going into this. I thought that a trip to the wind tunnel would certainly be a cool experience, but I wasn't necessarily expecting to learn something that I didn't already know. I was wrong. Some of the results that we got here were genuinely shocking and changed the equipment that I use. I've been working with Silca on their Road to Emporia project, and as part of that project they invited me to the ARC wind tunnel in Indianapolis to do some testing. We had Josh Portner from Silca and Graham Shrive from Factor facilitating the testing, both of whom have hours of wind tunnel experience, so we were in good hands. Before we jump into the results, I want to address a couple things right off the bat. First of all, this was a gravel focused wind tunnel test. That's right, I had my Factor Ostro Gravel aerodynamic gravel bike in the wind tunnel, and we were testing many of the aero questions that gravel racers have, such as tire size, hydration packs, on-bike storage, number plate position, aero bars, and more. Wow, this is probably the most anti-spirited gravel thing I've ever heard of. I mean, you're definitely asking for a flat and unbound this year because of this. That's all I'm saying. Part of the reason for this is that I personally am a gravel racer, but also as I said, this is part of the Road to Emporia project, which is all about optimizing for the unbound 200. And I'm going to be referencing time savings from that race as a benchmark in this video. That being said, before all you roadies who are watching tune out or click on one of those GCN videos that are recommended to you on the sidebar, know that a lot of what we tested here pertains to road riders as well. I actually think there are a lot of results in this video that all cyclists can learn from. Everyone from roadies to mountain bikers. Yes, I said mountain bikers in a video about aerodynamics, which brings me to my next point. I want to address this myth that at slow speeds, aerodynamics doesn't matter. I've done this before on this channel, but it's worth a refresher because so many cyclists believe this to be true. Now, it is true that at a slower speed, you are saving less watts for a given aerosavings. For example, let's take a straightforward aerosavings like moving from a upright hoods position to the drops. We actually tested this, so these are real numbers here. At 35 kilometers per hour, that was about a 13 watt savings. Over the 200 mile unbound distance, we're talking about a time savings of around 9 minutes and 15 seconds. Now, 35 kilometers per hour may be reasonable for the pros at unbound, but let's be honest, most people are not doing that. A much more reasonable speed would probably be 25 kilometers per hour. At that speed, all of a sudden that 13 watt savings turns into a savings of only about 5 watts. As you may have noticed, the relationship between speed and aero drag is not linear. In fact, as a rule of thumb, when you 2x your speed, you 4x the drag and you 8x the power required to ride at that speed. So with that said, surely that 5 watt savings at 25 kilometers per hour is so insignificant that it's not even worth worrying about, right? Well, you may be surprised to learn that over a 200 mile distance, that 5 watt savings would save you roughly 12 minutes and 10 seconds, which is actually more time saved than when riding at 35 kilometers per hour. That doesn't seem to make sense though. How is an aero savings saving you more time at a slower speed? Well, the slower you go, the longer you're out on the course. Taken as a percentage of the total time, it might be less, but the point that I'm getting at is that the time savings I'm going to be giving you in this video not only apply to you if you ride slower, but will actually be greater if you ride slower. This is also before you've taken into account wind speed. For example, at a race like Unbound or really just when you're riding your bike in general, you're going to hit a headwind. It's easy to look at the results from a 50 kilometer per hour test and think, well, I don't ride that fast, so those results don't apply to me. But if you're riding at 25 kilometers per hour and you hit a 25 kilometer per hour headwind, then all of a sudden you are experiencing 50 kilometers per hour of wind speed and the aero savings here can be massive. For example, that 13 watt savings at 35 kilometers per hour, all of a sudden bumps up to around 38 watts. All of this leads me to say that yes, aero still matters at low speeds. And just because you ride gravel or even mountain bike for that matter, where the speeds are lower does not mean that you should just ignore aerodynamics. With that ran out of the way, just one more thing and then we'll get into the results. I've seen the comments under wind tunnel videos before and inevitably there are always people saying, oh, you should have tested this or you should have tried that. We only had so much time in the wind tunnel as wind tunnel time is pretty expensive. And while we would have loved to have tested every piece of equipment at every yaw angle, we did the best we could with the time we had and tested as much as we could. That being said, if you do have suggestions for our next wind tunnel trip, we'd still love to hear them. I also want to give the caveat that these results are for me and my bike setup and for you and your bike setup, you very well may see different results. Just as an example, helmets tend to be like this. One helmet may be faster on one person and slower on another. So it's very hard to say that one helmet is the fastest. Some of the results we got here are a bit surprising, but I do have some theories from Josh and Graham as to why we got them. They're more so just educated guesses though. If there's anything I've learned from doing aero testing, it's that aerodynamics isn't always intuitive. All right, without further ado, and I know it's been a lot of ado up to this point, let's get into the good stuff. What are the results? Instead of giving you the raw CDA numbers, which most people don't have any context for, I'm going to be giving you the watt savings or penalty at 35 kilometers per hour, and I'm going to be giving you the time savings or penalty over a 200 mile distance at 35 kilometers per hour. Again, we're using unbound as the standard here, but you can take these time savings and adjust them to fit any distance. First up, let's talk about the most common question that you hear at a gravel race. No, I'm not talking about what mustache wax do you use. Talking about what tires are you running. I'm going to suggest a new drinking game. Every time this dude mentions tires, you got to take a drink. I'm going to be impressed if you make it through half a video, honestly. What we tested specifically here was how much of an impact does tire width have on aerodynamics. For this test, we used the Pirelli Centurado gravel H and looked at three common gravel tire sizes, 35 millimeters, 40 millimeters and 45 millimeters. And here's what we found. Using 35 as the baseline, switching to the 40 millimeter tire was 2.3 watts slower, which would cost you one minute and 42 seconds over 200 miles. Moving up to the 45 millimeter tire and we see a 5.8 watt penalty over the 35s, which would cost you four minutes and 19 seconds. A quick note on tires before we move on. Obviously a narrower tire is going to be more aerodynamic, but as the surface that you're riding on gets rougher, the rolling resistance penalty for a narrow tire over a wider tire also increases. If you're trying to find the optimal tire size for a given course, the question then becomes, at what point does the improved rolling resistance negate the aero penalty? If we take Unbound for example, which has relatively rough gravel, it could be the case that a 40 millimeter tire might be costing you two watts from an aerodynamic standpoint, but maybe it's saving you four watts in rolling resistance, making it more advantageous to use the 40 over the 35. This is also of course setting aside the colossal risk of getting a flat tire with 35s at Unbound. These are obviously just made up numbers for now. Soka and I are working on this question. We already have the aero data, now we just need the rolling resistance data, and we plan to get to the bottom of this optimal gravel tire size question, so you don't have to talk about it anymore on the starting line of a gravel race. So look forward to that. Moving on, we have the infamous aero sock. All right, let's get the eye rolling and the retro grouch comments out of the way. Okay, let's see if these things can actually save you anything. The baseline sock here is rule 28 pro sock, which is just an everyday sock, not an aero sock, and we compared that to their aero sock, as well as Soka's aero sock. For context, the Soka sock is just a standard knit sock with aero patterns on the side, while the rule 28 sock is more of an aero race sock, with a sort of ribbed lycra pattern. The Soka aero sock saved 1.6 watts, which would save you one minute and 11 seconds, and then the rule 28 socks saved 4.8 watts, or three minutes and 34 seconds. For as much hate as I see aero socks get, I have to say that these results were seriously impressive. In fact, out of all the equipment changes that we tested, aero socks had the biggest savings, and aero socks only cost 30 to 40 bucks. Now, that may seem expensive for a pair of socks, but if you put it in terms of dollar per watt saved, it's one of the most cost effective aero savings that you can find. To put this in perspective, upgrading to an aero helmet, like going from the vented cask pertone to the aero cask utopia, which is an extremely common aero upgrade, only saved me 2.9 watts, or two minutes and seven seconds. And oh yeah, aero helmets cost 200 to 300 dollars. If you're scratching your head as to how the hell a pair of socks can save you so much time, then I recommend you watch my interview with Josh Portner on Aero Dynamics, which I have linked below. And if you want to try the Rule 28 aero socks or the silica aero socks for yourself, then I've left links to those below as well. Next up, let's talk hydration and storage. This is a big topic of discussion at Unbound because it is a very long, often very hot race with minimal spots to refill. So you're going to have to carry a lot of fluid with you, a lot of fuel and spare tubes and tools as well. But it also applies to cyclists in general, because generally it is a good idea to carry water and tools with you when you ride your bike. So what is the most aerodynamic way to do that? Water bottles, hydration packs, frame bags? This section produced the most surprising results of the day. So let's get into it, starting with hydration packs. We tested two different packs here, the Osprey Katari 7 and the Yusui Outlander Pro. And this is where things start to get very interesting. The Osprey pack was 2.1 watts slower in an upright position, which would cost a minute and 33 seconds. Personally, I was expecting this. I haven't been a huge fan of using a pack while racing because they're heavy, they put more strain on your upper body, they trap heat on your back, and I assumed that they were less aerodynamic. But as I've said many times on this channel, you can't always trust your assumptions. As it turns out, the Yusui pack was actually faster, saving 1.3 watts or 57 seconds. That's right, wearing the Yusui pack was faster than not wearing it. That being said, this is in an upright position. What about a more aerodynamic position with a flat back? When comparing that position with and without the pack, would it still be faster? And it turns out the answer is yes by an even greater amount. Now we're talking about a 3 watt savings or 2 minutes and 11 seconds. The savings for putting things on your back doesn't stop there either. A Yusui Zulu II hit pack or fanny pack saved 1.8 watts or 1 minute and 19 seconds, and putting a bottle in my back jersey pocket saw a whopping 3.6 watt or 2 minute and 36 second improvement. I don't know about you, but my mind was absolutely blown by this. Graham from Factor on the other hand wasn't too surprised and said that it was likely due to the fact that having something on your back allows the air to stay attached for a little bit longer, thereby reducing the drag. When you're in an aero position with the pack on, likely the same thing is happening, but with the air coming off of your helmet. That being said, this is absolutely an area where something that worked for my body shape might not work for everybody's shape. And as we already saw, not every pack is more aerodynamic. The Yusui pack is very bare bones and quite smooth. Probably making it one of the best options from an aero perspective, and it's super lightweight to boot. But as soon as you start adding in extra pockets and straps, that pack is probably no longer helping you. Great, now everybody on the group ride is gonna start wearing a freaking backpack like it's the first day of third grade or something because they watch this dork on YouTube. I'll take three. I've left links for both the Yusui packs down in the description below so you can find them there. Of course, on your body is not the only place to store your hydration. Most cyclists store their hydration in bottles on their frame. What is the most aero configuration there? Using two 750 milliliter bottles as a benchmark, we then tested adding a bottle on the bottom of the down tube, which many gravel riders do, although try that at your own risk if you ride through cow pastures. We tested 1000 milliliter bottles, also very common in long distance gravel racing, and we tested no bottles or cages at all, which is not common, but hey, why not test it and find out if it's faster? What we found was that a bottle under the down tube was 0.4 watts slower or 17 seconds. One liter bottles were actually faster by 1.4 watts or 1 minute and 2 seconds, and perhaps most surprising of all, taking all the bottles and cages off was actually slower by 1.3 watts or 58 seconds. These results definitely take some explaining, because they don't line up with results that have been found on road and time trial bikes. Usually the larger the bottle, the more drag you see, and taking the bottles and cages off the bike, if we're talking about these round bottles, and we're not talking about a frame that's specifically designed for them, will make the bike faster as well. We do have to remember though that this test was done on a gravel bike, and it's certainly possible that the size of the tires and the knobs on the tires was making the air turbulent as it moved around the frame, more so than on a road or time trial bike. It could be that anything in there to keep the air attached even a little bit was helping. This could have been affected by the bike design as well. I guess the takeaway from this section is a bit of good news for gravel racers. All that extra hydration on your bike is probably not slowing you down and may even be helping, at least aerodynamically. However, carrying all that extra liquid is quite heavy, so I wouldn't go overboard here if you don't need it. Yeah, what I heard is that water is heavy, and therefore it's slow, and the less of it the better. Cool, I'm glad I got something out of this video. Similar results were also seen for on-bike storage systems. In this category, we tested the OroCase top tube bag, the Outershell half frame bag, a prototype Silca bike packing saddle bag, Silca's Matone saddle bag, and a prototype handlebar mounted burrito bag. What we found was that the top tube bag was 1.3 watts faster or 57 seconds. The frame bag was 1.7 watts or 1 minute and 14 seconds faster. The bike packing saddle bag was shockingly 2.1 watts or 1 minute and 32 seconds faster, yet the normal sized saddle bag was actually slower by 0.3 watts or 13 seconds and the burrito bag despite being the trendiest way to hold your snacks was by far the worst costing an insane 9.8 watts or 7 minutes and 22 seconds. The top tube bag and frame bag improving aerodynamics a small amount wasn't too surprising to me. What was surprising to me was the fact that the bike packing saddle bag was faster, especially considering that the normal saddle bag was slower. Again, though, this may be because the long tail of the bag is keeping the air attached for longer as it comes off of my body. And then no surprises, the burrito bag really is an arrow killer. I think they're cool if you're just doing an endurance ride or exploring, but if you're trying to actually go fast, best to leave that one off of your bike. I also do think that while adding all this storage to your bike could potentially make your bike marginally more aerodynamic, we are also starting to really weigh down the bike at this point and it's top heavy weight which will negatively affect the handling. I do race with a top tube bag and I may try another storage option for unbound, but I won't go overboard in this category. Alright, let's talk about number placement. I already know that race promoters are going to hate me for this one. Bending your number in weird ways to make it more aerodynamic often screws up the chip timing and readability of the plate and causes a huge headache for race promoters, but as you'll soon see, there is a good reason why racers do this. As it turns out, putting a number plate on my bike was the biggest equipment-related aero penalty we found, costing a massive 12.3 watts or 9 minutes and 19 seconds. A common solution to this is wrapping the number plate around the head tube, and this reduced the penalty down to 2.9 watts or 2 minutes and 8 seconds. Now a solution that I've been using is to tape the number plate to the frame so that it's parallel with the wind. I personally think that this is a good solution for two reasons. One is it cuts down on aero drag even further and also you don't have to bend your plate which could cause your chip timer not to work. Again, race promoters are going to hate that I just said that and you should check with the rules before you do this because you don't want to get de-queued because you had your number in the wrong spot. That being said, this was the fastest number pinning solution by far, only costing 0.7 of a watt or 30 seconds. Now at Unbound, they have very explicit rules about number placement, so I wouldn't try anything funny there, but it is just interesting to think about how they are essentially giving every rider a 10 minute penalty by giving you this number that you have to put on your bike. Just something to think about. Alright, I've saved the biggest aero gains for last because now we're talking about positional changes. Equipment changes are great, but for the most part the biggest savings that you're going to see are free and require you to just change your body position. In this section we test an upright hoods position, an aero hoods position, drops the now UCI illegal elbows on the bar position, and the now Unbound illegal, well for the pros that is, aero bar position. And we even test the aero penalty of having aero bars on your bike but not using them because in a gravel race you will certainly not be in your aero bars for the whole race, not even close. So here are the results. Going from the hoods to the drops as I said at the top of the video saved 13.2 watts or nine minutes and 23 seconds. Going to the aero hoods position saved 31.1 watts or 21 minutes and 12 seconds. Elbows on the bar saved 34.4 watts or 23 minutes and 17 seconds. And the aero bars saved 41.4 watts or 27 minutes and 35 seconds. Using aero bars to gain an advantage at a gravel race may piss off the spirit of gravel but those numbers don't lie. 40 plus watts at 35 kilometers per hour is absolutely massive. Now a note on the time savings at a race like Unbound or really any gravel race for that matter. As I said you won't be able to be in the aero bars for the entire time because there will be sections where you're climbing or descending or it's too rough or you're in a pack etc. So the question then becomes what percentage of the race do you need to ride in the aero bars in order to make them worth it? Well having the black ink aero extensions on my bike and not using them costed me 4.5 watts or three minutes and 20 seconds. If you do the math you'd have to use the aero bars for roughly 1 eighth of the race or 25 miles at Unbound. I've done Unbound three times now and I'd say that a rider who's used to using aero bars could probably do a fourth to a third of the race in aero bars. So yes they're absolutely worth it if you don't mind riling up certain riders. This is also of course assuming that there's no wind. Josh highlights this over on the silca blog stating that 15 watts at 15 miles per hour may not seem like a lot but add in 15 miles per hour of headwind and all of a sudden we're talking about 30 miles per hour or 50 kilometers per hour of wind and 120 watts of savings. Over a 10 mile headwind section that right there is 14 minutes and 12 seconds saved at the supposed aero doesn't matter speed of 15 miles per hour or 25 kilometers per hour. And I'll just tell you right now if you do Unbound you're going to experience a lot more than just 10 miles of headwind. Dude can you and your aero bars just get a room already? This is getting really awkward for all of us. Dave said our April Fool's thing should be how silca ruins gravel because we made it so technical and yes that would be a great April Fool's. Anything about ruining gravel. That's it for this video be sure to check out Silca's video on the wind tunnel trip as well as the rest of the Road to Emporia series. If you enjoyed this 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.