Aero tests

cycleclinic

Most aero tests have issues. A wheel or a wheel in a bike is tested with or without a dummy or rider. Sometimes with half a dummy. All these differences affect the significance of the overall result as it is impossible to tell the overall effect of the wheel in the system as a whole. Not to mention the air flow around the wheel is affected by the presence of a fork or the absences of it.

Sometimes the wheels are static and a spinning wheel behaves differently to a static one.

The final problem and this is a big one all aero tests you see are done by running the air flow at 50kph for a time at a static angle. Stop recalibrate and reset at the next increment. This does not predict real world conditions

As you ride the bike rocks, the front wheel and changes direction constantly. The changes in direction are small but if the front wheel did not do this you would fall over. Also when you pass gaps in hedge rows or buildings, even when cars pass on busy roads the airflow will osscilate sometimes widely.

Most wind tunnels don't simulate osscilating airflow. All this, means the results from most wheel aero tests are not that informative because the wheel behaves quite differently when the airflow oscillates and therefore behave differently in the real world. For starters you can spot the wheels that are at risk of speed wobble this way.

What Hambini is onto is important. at 30 kph many wheels behave as well as each other. At 50 kph (not drafting) some bigger difference emerge due to the way the air seperates and reattches at those speeds. However Since I like many cant hold 600W (thats what it takes for me to move at this speed) then the choice of wheel should not be affected too much by aero perforamce at this speed. The gain over shallow rims at 30 kph is real though and probably worth an extra 1 kph. not life changing for sure but real never the less.

The import result is though for rim of a particular depth they are mostly as good as each other at 30 kph. Tyre size is important as well and needs to match the rim. narrow rims need narrower tyres and what is not modelled here is how rolling resisantce and road surface changes affect over all speed. Some rims do worse simply because of there profile (too blunt). Rims that are more V shaped or better matched to the 23mm Conti GP4000sII tyre do better. Deeper rims do better on average. Depth is king. The "sweat spot" seems to be around 50mm as we already knew for a good balance.

The best anology as to what the results of this test mean is car MPG. The results will not tell you which wheel is best for the club 10 mile TT on a particular still day. They will tell you overall how well they perform in a variety of conditions exerienced over the course of a year. This is a very different kind of test. It does need some explanation though.

https://www.hambini.com/blog/post/bicyc ... s-fastest/

svetty

Rather like expensive Hi-Fi it isn't the hard real world differences that really count or drive this - it's the debate, the tinkering, the agonising over purchases, the placebo benefits and the tantalising prospect of 'just a little bit faster'.

The industry will use all this to generate profit and we can continue in our whimsies

w00dster

What it shows to me is that for all of the R&D some companies have done, Yoeleo have managed to produce a fast set of wheels! Other more on trend wheels appear to be not as quick in the tests.
Does look like the move to wider tyres is about to end and we will all be heading back to 23's!.....Just took my 23mm Conti's off and gone tubeless with 25's on a wheel that isn't really that wide, no chance am I going back as they are a pig to get on and off the rim... at least not until the end of next spring. (Ps - that's tongue in cheek, I know we will all just get wider internal rims)
As you mention the modelling of the different tyres on road surface hasn't been done, I'd love to see some sort of test showing the benefits of using aero wheels, fast 23mm tyres vs the same rims with fast (low rolling resistance) 25mm tyres. On a rolling course with mix of good and broken road surface. Be interesting to see what is actually real world faster, full on aero, or a slightly wider tyre.

cycleclinic

Not all 25mm or 23mm tyres are the same bead to bead distance though. So it make little sense to say I have put a 25mmm tyre on.

modeeling road surfaces is even more difficult. It cant be done in a wind tunnel. Riding on the road means the variables are too large and will mask any result that emerges.

graeme_s-2

Interesting stuff.

I remember reading an article a while bike about wheel aerodynamics that also touched on the impact the tread pattern of a tyre can have:

You'll often see trips on aerodynamic profiles; small raised or rough sections. Some bike wheels even have them. These trips cause turbulence, and the turbulent layer of air helps the flow to stay attached to the surface. The tread pattern of a tyre can act as a trip and help the wheel to remain aerodynamically efficient at higher yaw angles. It can do that. It doesn't always do that.

"The best tyre we've found is the Continental GP4000S", Jean-Paul told me, and that's what our test bikes were shod with. Is the tread pattern designed for that job? Probably not, he conceded, it's more than likely just a coincidence. But there are other tyre manufacturers that are definitely designing their sidewall profiles with aerodynamics in mind, whether they're talking about it or not.

And how much difference does it make?

"If you fit a GP4000S to one of our Hadron wheels the flow will stay attached to 18 or 20° of yaw," Jean-Paul said. "With another tyre, one with a completely smooth profile, the figure drops to 8-10°".

One look at our yaw graph above shows that you're losing almost all of the aero advantage of a deep section if that's the case. That's a major issue, and one that most people won't have considered at all in the whole aero equation.

https://road.cc/content/feature/213876-why-riders-you-need-go-aero-wheel-weight-doesnt-matter-—-and-how-wind-tunnel

cycleclinic

What has a bigger effect is the width of the rim and how that matches the tyres real width. Tyres and rims go together.

Flow cant stay attached till 18 degrees yaw. That is impossible fromt the quoted text. 12 degrees is the limit. Some very blunt prfile maange a bit more but they pay for it with increased drag at lower angles and instability when the flow oscilates. In fact very bluint rims see the air flow seperate when the flow oscilates more easily and then not reattached. That is the mechanism for increased drag. MFCK rim are that kind of very blunt profile and there a number of others.

pippi_langsamer-2

Great to see the Hunts performing so well.

The epitomey of marketing BS...

cycleclinic

I think the hunt 50 maybe a bit too blunt in there profile. Still at 30kph having the hunt wheels is not a massive disadvantage

MiddleRinger

Interesting reading.

Luckily I just ride my 60's because they look awesome, rather than for the aero benefits... 8)

timothyw

That should certainly help Planet X sell some TT wheelsets. Ironic as I'd have thought they're the people least likely to have bothered doing any wind tunnel testing - more likely just buying whatever they can get at a good price from the far east.

Non-zero graph plots are always a little tricky but for context, even the biggest disparity, from the Planet X disc wheelset to the Ksyriums is only 13% at 50kph, more like 11% at 30kph. Still, not the sort of gain anyone with any ambition of succeeding at TTs can give up.

cycleclinic

A zero plot on this graph would hide any difference. It done by an engineer who thinks number like I do. You have to look at it like one though.

A 32 spoke box section wheel should be be around 200w

graeme_s-2

TimothyW wrote:

That should certainly help Planet X sell some TT wheelsets. Ironic as I'd have thought they're the people least likely to have bothered doing any wind tunnel testing - more likely just buying whatever they can get at a good price from the far east.

Non-zero graph plots are always a little tricky but for context, even the biggest disparity, from the Planet X disc wheelset to the Ksyriums is only 13% at 50kph, more like 11% at 30kph. Still, not the sort of gain anyone with any ambition of succeeding at TTs can give up.

The planet x wheel set is the only one that includes a rear disc isn't it? The others are all various depths of rim. So presumably it's demonstrating the aero advantage of a rear disc over deep sections rather than showing that Planet-X wheels are particularly aero (maybe they are, maybe they aren't, but you'd need to compare them to other wheel sets with a rear disc wheel to find out).

cycleclinic

exactly. Some disc wheels will be quicker than others. the width of the rim relative to the width of the tyre will be important.

barongreenback

This is excellent news. I can buy cheap carbon rims to make my bike look awesome without having to worry about which one will gain me 0.5w on my usual slightly sub 20mph bimble around the country lanes. Marvellous. Although if anyone wants to give me some Zipp NSW wheels to complement my completely non-slammed Domane, I'd be very grateful.

timothyw

Graeme_S wrote:

TimothyW wrote:

That should certainly help Planet X sell some TT wheelsets. Ironic as I'd have thought they're the people least likely to have bothered doing any wind tunnel testing - more likely just buying whatever they can get at a good price from the far east.

Non-zero graph plots are always a little tricky but for context, even the biggest disparity, from the Planet X disc wheelset to the Ksyriums is only 13% at 50kph, more like 11% at 30kph. Still, not the sort of gain anyone with any ambition of succeeding at TTs can give up.

The planet x wheel set is the only one that includes a rear disc isn't it? The others are all various depths of rim. So presumably it's demonstrating the aero advantage of a rear disc over deep sections rather than showing that Planet-X wheels are particularly aero (maybe they are, maybe they aren't, but you'd need to compare them to other wheel sets with a rear disc wheel to find out).

Right, but suppose I'm taking up TT/triathlon, and want to buy some wheels to help out.

Why would I buy anything than the Planet X disc rear and trispoke front? It's £800 for the set and considerably quicker than anything else (eg the Borg 50mm which are somewhere mid table and also £800...)

The real question I want answered is how quick those bottom of the pile Ksyriums go with a £30 disk cover on the back.

Interesting how poor the Flo wheels tested given their aero hype. Hunt, as mentioned seem to be the other major losers in the test.

cycleclinic

Zipp NSW's though for the hype dont do so well. They have tried to improve cross wind stability but physics got in the way and increased overall drag.

Until more disc wheels are tested it is impossible to know if they are much of a muchness. Hambini is doing us all a proper service.

Yes it does show that most aero wheels are much of a muchness aero wise. It also shows to be "quick" it does not have to be a popular brand name or expensive. Maybe this will lead people to focus on other thing like ease of repair and how serviceable the hubs are.

There is quite big difference in other important factors between the wheels though. I would like magazines for example when they review to look at what the bearing size, what bearings are they, how easy are the hubs to take apart and replace the bearings, can you buy replacement rims and spokes easily.... That is really important stuff and often overlooked. Even things like axle diameter and bearing placement have a impact of how much the wheels flex.

barongreenback

In all seriousness I would want deep enough rims to look aero, a little bit of aero benefit and most of all good quality wheels that can be serviced as last a long time. I run disc brakes so rim wear is not a concern. Might give you a call when it’s bonus time next year

philbar72

at 55-65 mm there is virtually nothing in it. I note the sweet spot in terms of width seems to be around 26mm for higher speeds...

I also note that NSW's are widely regarded as more comfortable to ride on compared to firecrests, but aren't as fast at the top end. I think it was Xavier Disley that found Firecrests were quicker compared to NSW's... and he knows what he's going on about.

Killerclown

‘Tests performed in a lab don’t reflect real world performance adequately’ shocker. In other news, bears do crap in the woods, and the pope is Catholic!!!!

imposter2.0

Killerclown wrote:

‘Tests performed in a lab don’t reflect real world performance adequately’ shocker. In other news, bears do crap in the woods, and the pope is Catholic!!!!

Once again, it doesn't look like you've bothered to read either the contents of the link, or the contents of this thread, before posting... :roll:

cycleclinic

That has not happened before has it imposter.

imposter2.0

thecycleclinic wrote:

That has not happened before has it imposter.

definitely the first time

timothyw

Anyone been following the complete shitshow that has followed on from these tests on the slow twitch and weight weenie forums?

Hambini has now published a letter apparently from Flo cycling's lawyers to his HR dept (which if genuine is incredibly low on their part!) with Flo denying any involvement, Hambini on the other hand has failed to cover himself with any sort of glory in frequently resorting to personal insults against his detractors.

I'm starting to wonder if the whole test is a complete sham - it is undeniable that the protocol he claims to have carried out would take a very long time and immense discipline from the rider on the bike during the testing.

Interested to see what the truth of this one is (and whether it ever comes out!)

akh

I've no idea if the results are accurate, but all the people rubbishing them have got me thinking. If it really is so important to get the pressure right to a fraction of a PSI, use exactly the right tyre, etc, etc, aren't they basically saying that outside a controlled lab it's basically impossible to know how aerodynamic a given set up is?

Corkea

thanks for this thread, guys!
Cheers.

First.Aspect

I might be missing something, but is there any actual data in that blog post?

There's lots of words, some of which aren't obviously nonsensical, and some Excel bar charts, which I'm not completely convinced by - if you give me half an hour I'll put something together on Excel that shows the lift generated by a 1970 Volvo estate is better than Concorde. I could even give you error bars.

Hambini's, um, "graphs" purport to show aero tests on about £50,000's worth of wheels conducted in a wind tunnel in someone's spare time. He repeatedly mixes up a description of observations on the road with those of his testing "protocol", which he doesn't quite actually describe. He says the problem with wind tunnels is that they can't mimic the conditions on the road, as regards transient changes in airflow, but doesn't actually explain how he has miraculously addressed these drawbacks with his "protocol". His conclusions section is about as shocking as the Pope's religious persuasion.

Now I would have thought that wind tunnels were both expensive to run and in high demand. He must have a very accommodating employer, or have one in his garden shed. Only, there's not an actual photo of a wheel, nor of anything in a wind tunnel. And the bloke who posted this appears to sell ball bearings. And he owns a Ford Focus.... well I guess he did spend £50k on wheels....

The name he gives doesn't seem to relate to any aerospace engineer with an online presence. The company "Hambini Engineering" isn't registered. Whoever he is, he doesn't seem to want his professional life to be linked to that website.

I am a natural sceptic, and I may be wrong, but could this possibly be a hoax?

timothyw

First Aspect wrote:

I am a natural sceptic, and I may be wrong, but could this possibly be a hoax?

Well, yes.

Funny enough GCN have had him on this week to talk about bearings - https://www.youtube.com/watch?time_cont ... RLbamNQa_0

Anyway, word on the street (and the most charitable interpretation) is that he works at airbus, and has access to the advanced wind tunnel facility there - someone there, presumably in a position of quite some importance, was planning on doing an Iron Man and wanted to find out which wheelset would help him do it quickest.

Presumably they then got in contact with all the cyclists they knew, asked, can we borrow your wheels, and got cracking in the wind tunnel (hence the somewhat random selection of wheels on test).

It's either that or he decided to have a bit of fun with excel.

graeme_s-2

Back when I was an F1 fan and used to read about this sort of thing, there was a bit of am arms race between the big teams in building their own wind tunnels. I once read an article that mentioned there are a fair number of aerospace wind tunnels around that they could have used in theory, except they’re “too fast” as they’re built to test aerodynamics at speeds far faster than an F1 car would ever go. Seems weird that airbus would have a wind tunnel that would be suitable for testing bicycle aerodynamics.

Or the article I read was total bollocks, or wind tunnels have moved on since the early 00s and can now be used across a huge range of speeds?

timothyw

Well, this article (from 2007) mentions the wind tunnel is specifically used for low speed (by aircraft standards) testing and was used by Ferrari in the 90s.

https://www.airbus.com/newsroom/news/en ... rsary.html

Over the years the wind tunnel has contributed to many other feats of engineering design where aerodynamic properties are important. It has been used to test models of bridges, oil platforms, hotels, sails for ships, ski bikes for the Army, traffic lights, windmills, golf clubs and weather-proof clothing. One especially memorable client for several years in the mid 1990s was the Ferrari Formula One team who used the wind tunnel to test their racing car design.

Certainly doesn't seem beyond the realms of possibility it could be used for bike testing, if you had access.

bristolpete

He is kosher. Well known at Aerospace; Bristol and my brother who has worked there for 30 years in it's various guises ( now GKN ) knows him and of him.

Decent guy, basically a genius and likely on the spectrum, but he knows his lemons and is being discredited by the industry as he talks a lot of sense and is blowing gaping holes in the marketing bollox we all read over and over and over again.

His bottom brackets are unbelievable quality in every sense of the word.

His twitter is a tad bombastic, and clearly not a Teresa May fan, but I think he deserves some respect.

Pete.

First.Aspect

bristolpete wrote:

He is kosher. Well known at Aerospace; Bristol and my brother who has worked there for 30 years in it's various guises ( now GKN ) knows him and of him.

Decent guy, basically a genius and likely on the spectrum, but he knows his lemons and is being discredited by the industry as he talks a lot of sense and is blowing gaping holes in the marketing bollox we all read over and over and over again.

His bottom brackets are unbelievable quality in every sense of the word.

His twitter is a tad bombastic, and clearly not a Teresa May fan, but I think he deserves some respect.

Pete.

Hmmmm. I'm probably with you on the marketing bollocks.

So his employers let him play with the wind tunnel at weekends do they?

I'm struggling a bit to be honest. Its not that he can't write a self consistent technical report, because I'm used to that from industrial researchers, it's just that the technical report doesn't contain anything substantive and that he claims to have had access to a multi million pound facility to run tests on his annual salary's worth of kit.