Yes, the majority of the gains are from position, but to be a bit pedantic, it is the bike that allows you to get in that position. The stack / reach and seat tube angle of a TT bike are the keys to getting into a fast position. It is really difficult to achieve the same position on a road bike (but it can be done).
But to your point, the aerodynamics of the frame are not going to be that much superior to an aero road frame.
Yes, but from what I’m seeing, with aero bars and proper fitting you can achieve almost the same performance - at least on the bike. The tests I’ve found, show ~5W difference. Is that the right figure ? If yes, then I’m tempted to say that for the bike leg only, there is no real advantage - at least for me, 5W would not be worth it (I think my psychological threshold would be somewhere around a 15-20W improvement).
However, I’m reading that Tri bikes also put you in a better position for running, as they are less taxing on some muscles that are also used in running - and I don’t see any data about it (I can imagine the testing protocol would be pretty complicated for that one…). Any opinions / experience on that ?
I wouldn’t put much stock over this aero foil saving x watts compared to the competition or last year’s model. Like people have written in this thread, the biggest gain is the body position a tri bike puts you in. Overall, you can’t come close to that on a road bike, even if you put the same wheels and aerobars on it. The next huge gain is clothing: a tight-fitting skin suit really saves you a lot of watts, way more than wheels or some such.
Compared to a TT bike you also have other options for nutrition and hydration, so that’s also a big gain — the fourth discipline in a tri is nutrition after all. So that’s a big gain, although not one in terms of watts, but in utility.
Overall, it depends on your budget and how serious you are. If you want to be competitive at the pointy end, you will definitely need a tri bike. However, there are some events (especially shorter distance events) that have athletes compete on road bikes.
I would be extremely skeptical about tests that claim to isolate differences in the single watt range. Basically, you should be very cautious about anything done in a wind tunnel, because wind tunnels are designed to give you a laminar flow of air. Outdoors, you never have a laminar flow.
The second very crucial point is whether you are able to replicate a TT or tri bike body position on a road bike.
Lastly, you have to come back to your expectations of gains: let’s say a TT or tri bike gives you an advantage of 30 seconds per hour. How much is that worth to you? If you are competing for national champs, it is likely a huge deal. If you are just doing your first tri and your goal is finishing, I’d say “Who cares?”
One other important caveat: even if you can manage to replicate a TT/tri position, you wouldn’t want to use the bike in that position in “road bike mode”. Another issue is shifting, at least if you have mechanical shifters: you would have to reach down to your regular shifters. With electronic shifters, you can buy blips, of course.
If you are targeting a sub-10 time, then a Tri bike would, IMO, absolutely be worth it. There are a number of different ways to calculate the time savings, but Best Bike Split is usually very reliable.
I’d look at the advice from people with experience and go from there. @jezza323 wrote he is about 3–4 km/h faster at 300 W. @Majoeric reported a 4 % difference at 340 W, i. e. 1.2 mph = 2 km/h. @Cassopher wrote he is 1–2 mph = 1.6–3.2 km/h faster when riding tempo. @Amnesty reported a much larger differential of 7 km/h during Iron Men on his tri bike vs. road riding on his road bike.
The difference in most cases seems to be 2–3 km/h for most who posted here. I haven’t done a triathlon, but I have done road races. If you told me that switching bikes will give me a net gain of 2 km/h during races, this would be a no brainer.
According to this page, bike speeds for average athletes range between 27 km/h and 40 km/h. For simplicity, let’s assume your average is 30–35 km/h. A speed differential of 2–3 km/h then amounts to approximately 6–10 %, which I think is quite sizable. Keep in mind that at faster speeds, your competition gets tougher, too, so the smallest gain (35 km/h —> 37 km/h) might be crucial for you placing well.
Converted to time, a 30–35 km/h average converts to about 5–6 hours. A gain of 10 % (30 km/h —> 33 km/h) corresponds to arriving 36 minutes earlier, which I think is massive. On the low end you will still be 18 minutes faster.
Overall, doing a sub-10 tri seems very ambitious. And not having a tri bike will probably make that much, much more difficult.
I’m not speaking from personal experience, but I think just having an integrated, aero hydration solution and a built-in bento box is a huge gain. You are more likely to take in enough carbs and liquids, it is safer and more comfortable to do so.
It is one reason why I love a backpack with a hydration pack on long mountain bike rides: I tend to drink more often and can safely drink in many more circumstances.
I started riding and doing tris in 1985. Everyone was on steel framed bikes w/ column shifters and toe clips. TT bikes didn’t exist. Aero bars didn’t exist. Power Bars didn’t exist. We just rode hard. When tri bikes started coming out, I thought they were hideous (ie, the Soft Ride). They’ve evolved into even-more-hideous (ie Ventum). They look like a nice road bike was run over by a steam roller. I use a road bike for tris and “aqua bikes” (knee isn’t having the run anymore. But when I did run, I had PR’s of 1:25 for 1/2 IM and 3:35 for IM splits, so I’m not buying the "legs feel fresher w/ a TT bike). I’m 55 and beating my times from 20+ years ago. In many ways I feel the road bike is faster (especially on hilly, technical courses here in central Texas). I averaged 21.7 mph for a hilly 56 mile (after a very cold 1.2 mile swim). Dropped a lot of TT rigs in the process. And yes, I blatantly abuse “puppy paws”
Hi Pawel, I have to ask - what are you reading? Can you give us a few links and quotes?
I’m always happy to challenge ideas but I think it’s accepted that tri bikes will be faster on any course. How much faster maybe be the subject of discussion, but if you’re looking at sub10 this is a quick win and move on.
The question is not whether you ran (or could run) fast times off a road bike split, the question is whether you could have run faster if you used a Tri bike.
Let’s say your bike split was 5 hours, flat. If you rode a Tri bike to that same time split, your NP would be substantially lower, meaning you expended less energy on the bike, leaving you fresher for the run.
Sure…no one is saying that riding a road bike means that every person on a Tri bike is gonna be faster. How you ride relative to others in this context is almost irrelevant. Again, the question is whether you would be faster ( or more efficient for the same time) on a TT bike. The answer is an unequivocal “yes”. The next question is whether it is “worth it”, which is a personal decision that each athlete needs to make.
(I’d also note that a lot of those people you were passing on Tri bikes probably all had a run leg in front of them still, where you were charging towards your finish line. Not exactly a direct comparison)
For the sake of science and curiosity, I went ahead and did a nonstop century on my road bike using the same route I use when I do my sub four hour centuries on my TT bike. These are unsupported and solo on roads with little to no traffic. The chart below displays my best TT bike data and my Road bike data. I also used the same pedal PM for both efforts and would say the weather was similar with only minor winds.
My TT bike is a last gen speed concept and my Road bike is a Canyon Aeroad.
Look my up on Strava if you want to review more data (Eric O)
If you are in the sub 10 part of a decent sized Ironman race then I should imagine you will be the only athlete who is not on a TT/tri bike. It will be quicker on 99% of courses. Chris Froome even used a TT bike and disc while winning the mountain TT in the 2016 tour
Interesting, but without info about your actual position on both bikes, it’s lacking in details that are large factors in the results. It would be helpful to see pics of you on each bike, in the position used for most of each ride.
As I said in my post, IF you can achieve your optimal triathlon position on a road bike with aero bars, then you’ll be nearly as fast as riding that same position on a tri bike. But it’s a big “if” - tri bike geometry is designed to put you in a good tri position, road bikes are designed to put you in a good road position, which is different. Even if it can be achieved there will be compromises in other areas.
So yes, if you don’t have budget or space for a tri bike, and/or just want to finish your IM and aren’t too fussed by time, then you can certainly go fast on a road bike. But if you’re targeting a sub 10 finish and can afford another bike, then on a pretty flat course like Taupo a triathlon bike is 100% the best choice.
Yeah perhaps if you break it down like that maybe it’s an investment worth considering.
I like to do 4ish hour tempo/z2 blocks on Sunday and it just so works out that my pace is usually good for 25+ mph. From experience I knew the road bike wasn’t far off at those speeds but I’ve never tried staying in an aero position until yesterday.
As mentioned on paper the tri bike will be faster on a long bike leg. I just want to add that you have to deliver the same power to reap that benefit. Going full aero on the extensions brings you in a very different position compared to a road bike and most riders will - at least initially- see a drop in sustained power. So if you decide to get a tri bike than it’s best to plan some time to bringing up your power in the aero position and getting used to riding in the extensions - a thing that’s far from amusing in gusty wind, high traffic or technical environment.
Just putting on the aero bars wouldn’t be enough though right? As putting them on top would add stack so your aero bar position would be quite a bit higher and therefore likely slower than your aero hoods/drops position. So to get the same or better aero than your hoods position you’d need to drop your bars. Either by removing spacers, or if you don’t have any spacers to remove (guessing there’s a high chance of this given how aero your road bike position is!) by using a negative angle stem. Plus having your arms closer together and more central effectively reduces reach so you’d probably also want a longer stem. All of which may be doable (or may not if it’s an aero road bike with a highly integrated cockpit), but is a bit of a compromise. Also means your road bike no longer works particularly well as a road bike since the hoods and drops are in the wrong place for optimal road position. For me this is the main reason to buy a tri bike - it’s possible to set a road bike up like a tri bike, but then it’s not really a road bike any more. So you might as well just buy a tri bike which is designed to be set up and ridden that way, including not just the geometry but all the other good stuff like integrated hydration and storage, bar end shifters, etc (assuming assuming budget and space of course).
You must have a great road position by the way, that speed on those watts is outstanding!