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Air resistance increases with the square of speed so if you are saving 4W at 50kph then you are most likely saving 0.5W at 25kph.
I did say it was counter intuitive.
If you're a pro then you're always riding into a headwind at 50kmh, there's much less of a yaw angle.
All these U-sectioned rims and Kamm tail frames are of maximum benefit when there is a significant yaw angle.
Your average sportive plodder (or even a fast club rider) doing <20mph on a breezy day spends far more time in a far more angled apparent crosswind than a pro doing pro speeds.
"Faster riders generate more drag", Jean-Paul adds, "because drag is proportional to the square of velocity. But faster riders are also on the course for less time, and experience a narrower range of yaw angles. Through our simulations, we see that slower riders actually save more absolute time. They're out on the road for longer and can therefore benefit from the bigger aero gains for longer."
www.road.cc/content/feature/why-riders-you-need-get-more-aero-213876
@Mark, pasting links seems to be broken? it I paste that as https://road.cc....... it pastes it as the title of the website but without a hyperlink? e.g :
h t t p s : / / road.cc/content/feature/why-riders-you-need-get-more-aero-213876
without the spaces becomes:
Why riders like you need to get more aero and wheel weight doesn't matter | road.cc
I agree and disagree with what he's saying. Some changes in MTB tech are/have been ground-braking and will have made us all faster (if you've been doing it for long enough). I agree in so much that this years Zeb isn't going to make any difference to your riding from last years Zeb, but the change from a bike with around 1200mm of wheel base will feel a whole lot more stable and ultimately faster than a bike with say under a metre of wheel base. Or this years Zeb is going to revolutionary if you're swapping from a 2005 Fox Talas. Bike tech, like lots of other areas I think goes through monumental changes every decade or so, and in between is a bunch of tidying up.
I also agree that many bike brands are very keen to sell you on how much better you'll be on their bike, but I reckon that most folks who're throwing several thousand on a bike probably already know that's not true, in the same way that Lynx doesn't make girls knickers magically fall down either.
in the same way that Lynx doesn’t make girls knickers magically fall down either.
Wait, WHAT?!
Your average sportive plodder (or even a fast club rider) doing <20mph on a breezy day spends far more time in a far more angled apparent crosswind than a pro doing pro speeds.
I think there are multiple things getting mixed up and conflated here.
Firstly, if you are riding in a group then the apparent wind is going to be very different compared to riding solo. Secondly, the article you linked seems to only be looking at deep rims vs regular box rims. It could well be the case but I'd be surprised if any other aero improvements made anything like the same gains, crosswinds or not.
From the graph in the article it looks like they are saying that just by switching to 80mm rims you will save 20W over regular box rims (at the right yaw angle although they don't say what the effective wind speed is which is kind of important). It seems a bit much but it's probably worth a try. Next time you wear out your rims it seems like it might be worth an experiment (oh, you also switched to discs last time you changed bike and don't wear out your rims anymore? That's a shame). 😉
I'm not sure I buy the argument about percentage time saved vs absolute time saved. No matter how slow I go (and believe me, I can go slow) I am absolutely certain the pros are spending far far more time than me in the saddle.
Anyway, he's not my favourite person but Hambini has some interesting thoughts regarding aerodynamics and yaw angles, as you might expect:
https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/
Interestingly, the difference between the best and worst rims at 30km/h was around 20W.
Is that the article in which he roundly criticises a particular wheel manufacturer, and then subsequently refused to share his testing protocol with anyone so that his results could be verified, then accused them (falsely) of setting their lawyers on him?
Here's their response to that article
Anyway, he’s not my favourite person
Hambini is a ****ing idiot, who's managed to demonstrate his idiocy repeatedly. Nothing he says should be taken with anything other than a massive pinch of salt.
Yeah, I'd agree about taking anything he says with a massive pinch of salt.
However, I'm also taking road.cc articles where they tell me I can save 20W if I spend a few thousand on a set of wheels with a massive pinch of salt, as well.
But the fact both articles seem to come to roughly the same final number is interesting.
Still not spending 3K on my next wheelset though.
I’m not sure I buy the argument about percentage time saved vs absolute time saved. No matter how slow I go (and believe me, I can go slow) I am absolutely certain the pros are spending far far more time than me in the saddle.
Back in the McLaren era of the Specialized Venge they (or one of the mags) ran a similar article where the author rode a Tarmac and a Venge around a race circuit. Based on the wind data and their power meter McLaren could (obviously without an actual proof beyond an assurance that the models were well validated) say that he was so many seconds quicker on the Venge even though he admitted he was deliberately sandbagging to try and upset the data (i.e. his Venge time was slower, but they could still quantify how much quicker it was than if he'd done the same lap on the tarmac, and the reverse was true, his fast lap on the tarmac would have been faster on the venge, but not by as much.
So it's an idea the industry seems to have been settled on for quite a while.
20W's not to be sniffed at even if it is optimistic. 20W on your FTP is a solid 10 week training block for most people. Probably more than they manage to improve over a summers un-structured riding.
From the graph in the article it looks like they are saying that just by switching to 80mm rims you will save 20W over regular box rims (at the right yaw angle although they don’t say what the effective wind speed is which is kind of important).
It is road.cc, not a scientific journal like the International Sports Engineering Association (fun fact, I did once have my research published in their journal which is how I know it exists!) so I can forgive them not publishing a follow-up paper studying the effect at different velocities as well as angles.
I remember reading an interview about 1p years ago with one of the TDF riders on a Specialized sponsored teams who said he was as fast on his carbon as he was on his Roubaix as he was on his Race bike (and it was more comfy) but Specialized said they had to use their race bikes as that’s how they sell them.
20W’s not to be sniffed at even if it is optimistic. 20W on your FTP is a solid 10 week training block for most people. Probably more than they manage to improve over a summers un-structured riding.
Absolutely.
I just can't shake the suspicion that there is a way of getting the same effect with a Mavic 119 rim, a carving knife, and a big lump of high density polyurethane foam 🙂