How much difference does an aero frameset make independent of everything else

While I’ve seen endless comparisons between aero bikes and “climbing” bikes, I haven’t come across a comparison where two bikes are tested with everything identical except for the frameset. I have 2 bikes on completely opposite ends of the spectrum - a steel bike with external cables, non-aero fork, etc (Ritchey Road Logic), and a top-end aero road bike that I’d prefer to NOT mention because I don’t want to cast a negative light on it. The build between them is very similar (mechanical D/A on the Road Logic and Ultegra Di2 on the aero bike) and the fit, at least saddle-handlebar drop/reach, is with 2mm. They are both rim brake and both have the same handlebars. I have 165mm cranks on the aero bike and 172.5 on the Road Logic. If I take the Hed Jet 6s that I have on the aero bike and put them on the Road Logic, I’m finding that I’m usually somewhere around .3 mph / .5 kph faster (edited to .2 mph / .3 kph after taking into account the differences in power meter values between the 2 bikes) on the aero bike than the Road Logic at the same wattage. I’d love to see a comparison between something like a Canyon Ultimate vs Canyon Aeroad (no, my aero bike is NOT an Aeroad!) with 100% identical components (ESPECIALLY wheels / tires / handlebar) / riding position, or maybe Scott Addict RC vs Scott Foil, etc. The main point of the comparison - how much of a benefit is an aero frameset which beats the snot out of you every time it even comes near a bump in the road vs a non-aero frameset that actually absorbs bumps and is lighter. And no - the Road Logic is NOT lighter than my aero bike, but the difference in comfort between my Road Logic and my aero bike is crazy! That being said, the difference in lateral frame stiffness between the 2 is also night and day, but the whole “is a laterally stiff frame any faster” is a topic for another day. I don’t want to rely on the manufacturer’s wind tunnel / marketing B.S., but rather a real-world test, preferably on flat roads since we already know the difference that weight makes on a climb. I wonder if my experience is the same that others have seen - a roughly .5 kph difference.

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Sounds about right.

The 45 seconds over a 40km TT which is what many advertise to be the benefit of an aero frame by itself is just about 0.5 km/hr. For me aero bike is comfortable so there is absolutely no downside there.

I don’t think we can generalize as it can vary between brands, and a lots of now “climbers” bike have introduced kamm tail shaped tubes and other features of bikes dubbed aero years earlier.

The only way to tell is to have 2 identical bikes built at your disposal with exact same contact point setup. Then ride them back to back with the same set of pedal base power meter on the very same stretch of empty road in the very same weather conditions back to back while keeping a sustained power and position and see if you have been significantly faster on that section. Then repeat that test day after day until you have enough data to iron out differences to draw a chart and see if there is a pattern. If one of those bike is always faster maybe you have a clue.

I doubt there is a huge difference. Dialing your position and training your body to be flexible, especially in the neck area to have a fast position make a much bigger impact. Aero extensions do too as well.

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I prefer to just google it.

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I’m guessing that Specialized came to a similar conclusion to yourself and that’s why they decided to kill the Venge and position the Tarmac as an aero enough all rounder that’s also lightweight.

For any significant aero gains you need a non UCI compliant frame such as the ones used in triathlons.

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I’d also add that I ride with someone who sometimes rides a Systemsix and it makes a cool whooshing sound. That should be an important consideration when deciding whether to buy an aero bike.

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Surely that noise is the primary reason!

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I did Google / Youtube it, but the tests I saw always seemed to have something skewing the results other than strictly the frameset - ex., different tires, a noticeably different position, etc. After I initially posted this, it dawned on me that the two bikes in question have a different power meter, and that when I compare both bikes against my smart trainer (man do I spend way too much money!), the one on the aero bike is consistently reading 2-3% lower than both my smart trainer & Road Logic when all 3 units are calibrated. A better estimate is probably .3 kph instead of .5 kph. I should also point that the rides I’m referring to are solo rides on rolling terrain at between 20 and 22 mph (32 - 35 kph) average, so not racing speeds, but what I’d call “brisk”, where I should see at least some aero benefit.

I prefer to google it

I was being snarky regarding the comment that the only way to tell is to have two identical bikes other than frame profile and then test them many times.

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Sounds about right.

Riding at 25mph/40kph, with a very clean drivetrain, in a reasonably aero position, on a perfectly flat road, on a calm day, requires 325w according to An interactive model-based calculator of cycling power vs. speed. This is obviously a VERY ballpark figure but lets roll with it.

The advantage of an aero frameset is typically cited as anything between 10 and 30w at 40kph. So again, making very ballpark calculations, at the same power you’d (very roughly) travel 0.5kph faster.

Assuming you’re not travelling at 40kph for the whole ride, 0.3kph on average sounds perfectly reasonable.

(IMO that difference is a total irrevelance if you’re not at the very pointy end of racing, but YMMV.)

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It doesn’t hurt to go 0.3-0.5 km/hr faster for absolutely no extra effort, though, either. Let’s call it 1% - why not take it? I just don’t see the downside. Well, I do read that some aero bikes, especially the early ones, are uncomfortable but, well, mine isn’t.

What really seals the deal for me is that I find the straight-ish top tubes and aero profiles of many aero bikes to be more aesthetically pleasing than the slightly lighter “climbing” bikes, though.

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Oh I’m not saying there’s a downside as such, just more along the lines of ‘don’t specifically buy one just for the promise of free speed’ - it doesn’t make a big difference. So yes, if it’s comfortable, fits, is in budget, and the integration isn’t an issue, great. IMO there are often trade-offs on at least one of those fronts, but per se, I have no issue with aero bikes.

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I am wrenching my own bikes and stopped racing 3 years ago. I happily trade half a kph for external cable routing.

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I am waaaay faster on my TT bike than my roadie (except on climbs). The difference is clear. An aero bike isn’t a TT bike but the wind doesn’t understand that - aero equipment makes you faster.

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But that is mostly your position, not the bike itself.

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Sure, but the aero bike puts you in that position. I don’t believe you can separate the two qualities. I get what you’re implying - which is whether the slipperiness of the frame itself contributes. But that’s only half of it - position is the other half.

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But the OP is talking about an aero road bike vs a standard road bike, so the position is essentially the same between the two….

I’m as big an aero geek as the next guy, but overall, the design of a frame is not a massive game changer. But I’ll take every advantage I can find.

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Indeed, the OP evidently tried to mimic his position as closely as possible

The vast majority of the difference a TT bike makes is the lower and narrower position as facilitated by the base bars, extensions and forward seat position.

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Current crop of bikes I maintain, which includes mine and my wife’s (and kids’ too, but those are all externally routed), I simply installed cable liners through the frame upon first cable replacement, so cable replacements are now basically “get old cable out, feed new cable in, job done”. The difference between recabling an internally and externally routed bike amount to less than the time you save on a 40km ride once you installed cable liners in it (which took some minutes of faff initially, though, but well worth it).

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0.5kph sounds reasonable - but it might not be down solely to aerodynamics though. Your aero frame sounds like it’s significantly stiffer than the Ritchey, which may result in more efficient power transfer, different carbon lay-ups can also influence this as well though. FWIW my previous bike was an Argon Gallium Pro and it felt like had gained 15w just by riding that - particularly when climbing. My current BMC is great but nowhere near how efficient the Argon felt, both with similar weights and equipment.

In the TT world it’s generally accepted that the frame is the last thing you upgrade as it makes pretty minimal difference. You can make older Cervelo P3C frames nearly as fast as Cervelo P5s with the right kit (and a good position).

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