Working a bit off the Ventum thread, but not wanting this to be about Ventum specifically, I wanted to address just how difficult it is to compare one frame vs another, and how you should be highly suspicious of any numbers put out by manufacturers and/or publications. Not because they're lying to you; to the contrary, I think most manufacturers do the best they can and attempt to put out accurate data, though obviously skewed in favor of their particular product. It's just there are so many variables that need to be controlled which can all have a significant impact on results, and it's virtually impossible, both physically and fiscally, to cover them all. Let me explain (this is going to be a little long...hang in there and follow if you can):
First , if all you want to do is test frame vs frame, with nothing else attached, fine. Have at it, test away. The numbers don't mean much to me, but post them anyway for the world to see. But let's make it more realistic, shall we?
Let's add aero bars into the equation. This will be your first big problem because you've just introduced a boat-load of variables:
Now then, let's just for the hell of it say we can do everything listed above, and all the other things we can all think of I don't have the patience to list. Let's just live in our little happy world for a moment and say we can do it to everyone's satisfaction. Ah, yes, life is good! And then we put a rider aboard. Well, shit.
This is where it all falls apart boys and girls. Placing an athlete on a bike for aero testing just added a virtually uncontrollable variable. But wait, you say, everything is the same, so the athlete is in the same position, right? Negative, Ghostrider...it ain't gonna happen. Trust me when I tell you this because I'm pretty sure there aren't many people who've aero tested athletes on bikes more than me...there is no frickin' way you're going to make sure that athlete is in the same position from test-to-test. No way you can insure the clothing on that athlete is set exactly the same - every wrinkle in the same place, every seam rotated on the body exactly as every other test. There's no way you can insure the helmet the athlete is wearing doesn't move even one degree from test to test, that the athlete's head angle is exactly the same test to test. No Way.
Let me give you an example. I've been conducting a lot of independent aero testing of late for a new web site we're about to launch. I, myself, was a test rider working on arm angles, and in the middle of multiple tests purposely scooted approx 1cm forward on the arm pads creating a bit more reach. Nothing on the bike changed...this was mid-test. Most people wouldn't even be able to tell I moved. Still, the difference in drag was substantial every time - about 5.5 to 8 watts. A small movement made a big difference EVERY TIME I tested. Want to really skew a test? Try shrugging in one test just a bit more than the others. You just changed the results substantially. Look up just that little bit more. Create a little wrinkle on the shoulders of your skin suit. Bam...different results.
Oh, but you point out, we have a solution for this! Cervelo's famous "Dave" mannequin will save the day for us! Will it? Not likely. From the tests I saw with Dave, it appeared to me pretty much impossible to put him on each bike identically from test to test. Specifically, arm and hand position one bike to another. Now a lot of this was because all of the above could not be controlled. That's fair, but then why test? But, just for the sake of argument, let's say we can absolutely, without doubt, ensure Dave is in the same position and we can, therefore, test to our satisfaction. Will that do it? Maybe.
Here's the part that might fry you. If you're going to test and show me the results, I want a few things from you.
Aero testing isn't easy. The more variables you introduce, the more you open yourself up for inaccurate results. What I'm trying to point out is, especially when comparing bike-to-bike, while the numbers are important, they can be unintentionally deceiving when the most important thing is whether or not a particular bike will allow you to attain your optimal position. Do you know your optimal position? I bet most don't. I'm lucky enough to work with some of the best age group and pro athletes in this sport and I can tell you the majority are no where near optimal when they come here. Position is, BY FAR, the most important piece of the aero puzzle. After position, do you know if your wheels, helmet, and clothing are all optimal? We see larger gains from all of these then the differences between most of these "super bikes." Even your hydration/nutrition setup will often trump the differences between all these frames. Keep it in perspective, think of your aerodynamics as the whole of your set up, not just several individual pieces.
Lastly, as a consumer, if you're going to put weight on the numbers manufacturers put out there, demand to see the data. All the data! Long, long post. I apologize for the inevitable grammar and spelling mistakes. I'll try to answer as many questions as possible, but I can't always track this forum as I actually work for a living! :-)
Jim Manton / ERO Sports
First , if all you want to do is test frame vs frame, with nothing else attached, fine. Have at it, test away. The numbers don't mean much to me, but post them anyway for the world to see. But let's make it more realistic, shall we?
Let's add aero bars into the equation. This will be your first big problem because you've just introduced a boat-load of variables:
- What aero bar are you adding? Proprietary to your bike? That's okay, what do you put on the other frames? If they have proprietary bars as well, that solved one problem but adds others. If they don't have proprietary bars, who chooses which set of bars you put on the other frames? Let's just stipulate to OEM because it's easiest. It's just that, let's make sure it's an OEM bar at an equivalent price point for every bike tested so we're being fair. After all, the aero bars that come on the P2 vs the P3 are different; same frame dimensions, different aero bars with likely different drag numbers.
- How will you insure the aero bars are in the exact same position on all bikes? Good luck with this one because in order for the results to be meaningful, these numbers need to be replicated. Is the pad stack and reach exactly the same? To the millimeter? What about the extensions? Will you replicate those, or are we going OEM? I guess we can go OEM, but I'd prefer the same extensions, and we have to have both the pads, extensions, and the base bar all at the same angle to be fair (you could argue base bar angle here...I wouldn't give you a lot of push back on that). Good luck to anyone taking on that challenge.
- Let's say you can match the above. How are you going to do it? For pad stack, will you put spacers under the stem, or do the aero bars allow your to stack spacers under the extensions/pads. Most agree that the latter is better than the former. For pad reach, how do you achieve this? Are you simply moving the pads fore/aft? Are you using a longer or shorter stem? A combination of both perhaps? Are you using a similarly angled stem to your bike? This makes a difference.
- I think it's fair to stipulate to OEM saddles. Unless, of course, your bike doesn't come with an OEM saddle, in which case you're free to choose whatever you want and, trust me, without a rider aboard, some saddles will test faster than others.
- Who chooses saddle height? Better make sure it's exact to the millimeter.
- Who chooses saddle angle? It absolutely needs to be exact across the board, but can be highly deceptive based on the make/model.
- Fore/aft position of the saddle? Another variable which must be matched.
- Are we matching drivetrains? Again, let's just stipulate to OEM spec at matching price points to make it easier.
- Who does the cabling? This is where it gets sticky. The simplest solution is to go with no cabling; however, many bikes are fast partly because they handle cabling so well, so this should be part of the equation. We need this to be fair, though, and trying to be fair when it comes to cable/housing length and routing is something easily overlooked/manipulated. Again, when it matters, everything must be exact bike to bike.
- When you test, are all bikes set in the same gear? Are the cranks set at the exact same angle? To the degree? Let's not even deal with pedals.
Now then, let's just for the hell of it say we can do everything listed above, and all the other things we can all think of I don't have the patience to list. Let's just live in our little happy world for a moment and say we can do it to everyone's satisfaction. Ah, yes, life is good! And then we put a rider aboard. Well, shit.
This is where it all falls apart boys and girls. Placing an athlete on a bike for aero testing just added a virtually uncontrollable variable. But wait, you say, everything is the same, so the athlete is in the same position, right? Negative, Ghostrider...it ain't gonna happen. Trust me when I tell you this because I'm pretty sure there aren't many people who've aero tested athletes on bikes more than me...there is no frickin' way you're going to make sure that athlete is in the same position from test-to-test. No way you can insure the clothing on that athlete is set exactly the same - every wrinkle in the same place, every seam rotated on the body exactly as every other test. There's no way you can insure the helmet the athlete is wearing doesn't move even one degree from test to test, that the athlete's head angle is exactly the same test to test. No Way.
Let me give you an example. I've been conducting a lot of independent aero testing of late for a new web site we're about to launch. I, myself, was a test rider working on arm angles, and in the middle of multiple tests purposely scooted approx 1cm forward on the arm pads creating a bit more reach. Nothing on the bike changed...this was mid-test. Most people wouldn't even be able to tell I moved. Still, the difference in drag was substantial every time - about 5.5 to 8 watts. A small movement made a big difference EVERY TIME I tested. Want to really skew a test? Try shrugging in one test just a bit more than the others. You just changed the results substantially. Look up just that little bit more. Create a little wrinkle on the shoulders of your skin suit. Bam...different results.
Oh, but you point out, we have a solution for this! Cervelo's famous "Dave" mannequin will save the day for us! Will it? Not likely. From the tests I saw with Dave, it appeared to me pretty much impossible to put him on each bike identically from test to test. Specifically, arm and hand position one bike to another. Now a lot of this was because all of the above could not be controlled. That's fair, but then why test? But, just for the sake of argument, let's say we can absolutely, without doubt, ensure Dave is in the same position and we can, therefore, test to our satisfaction. Will that do it? Maybe.
Here's the part that might fry you. If you're going to test and show me the results, I want a few things from you.
- Multiple tests/sweeps. The more I test, the more I'm convinced that one test on the velodrome or one sweep in the tunnel just doesn't do it for me. I want multiple tests; 3 does it as long as the results are consistent, but what the lay person might not understand about aero testing is the results aren't always consistent from test to test or sweep to sweep. You need to test multiple times to really get your answer. The differences aren't necessarily significant (though they certainly can be), but they rarely match. In fact, you want to see us geek out at ERO? Watch us when a rider completes two laps matching to the 4th integer! That's exciting stuff for us.
- Show me the results! Not just the ones you want me to see. As a consumer, do you know what results you're seeing? How do you know that a particular manufacturer doesn't take their lowest result and compare it with everyone else's highest results? Every test will yield a slightly different number, so how do you know which one you're being provided? If a manufacturer chooses to give you an average of all runs, I'm okay with that. In fact, I applaud it, but I still want all the data to see how those averages came to be.
Aero testing isn't easy. The more variables you introduce, the more you open yourself up for inaccurate results. What I'm trying to point out is, especially when comparing bike-to-bike, while the numbers are important, they can be unintentionally deceiving when the most important thing is whether or not a particular bike will allow you to attain your optimal position. Do you know your optimal position? I bet most don't. I'm lucky enough to work with some of the best age group and pro athletes in this sport and I can tell you the majority are no where near optimal when they come here. Position is, BY FAR, the most important piece of the aero puzzle. After position, do you know if your wheels, helmet, and clothing are all optimal? We see larger gains from all of these then the differences between most of these "super bikes." Even your hydration/nutrition setup will often trump the differences between all these frames. Keep it in perspective, think of your aerodynamics as the whole of your set up, not just several individual pieces.
Lastly, as a consumer, if you're going to put weight on the numbers manufacturers put out there, demand to see the data. All the data! Long, long post. I apologize for the inevitable grammar and spelling mistakes. I'll try to answer as many questions as possible, but I can't always track this forum as I actually work for a living! :-)
Jim Manton / ERO Sports