## Aero vs light wheels

Everything about building wheels, glueing tubs, etc.
airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
Journalists placebo? Heaven forbid!

More like long term loans and hospitality.

We all suffer from placebo everyday. It's nothing new. We just hate to admit it.

I've given you some data from wind tunnel tests that suggest the gain would be marginal at best. Can you give me something to suggest that those findings are in anyway wrong?

We're also putting out less power. Aero is still the main contributor to power as a fraction of the total. The threshold for aero being dominant is closer to 10 mph than 25 mph.

Looking at a Tour review of wheelsets(as I'm bored ), the difference between the best and worst ( Ksyrium/ Zipp 404) at 50kph is 12w. At 40kph it's 6w and at 30kph it's 2.5w. Just 2.5w! At just 16kph what will that difference have reduced to?

djconnel
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Location: San Francisco, CA
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Now compute the difference of 1 kg extra on your frame. I'll ride up a hill which would have taken me maybe 4:30 in maybe 4:33. This forum is all about small differences.

DMF
Posts: 1062
Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden
Are you trying to make your point based on that 12w isn't significant? We're talking about high speed flats here... I'd say 45-50km/h is fairly normal for most of us on 500-1.500m long flats? And at what wind angle (yaw) was this test... The difference between low/high profile wheels is no where ner linear between head on wind and side wind.

airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
djconnel wrote:Now compute the difference of 1 kg extra on your frame. I'll ride up a hill which would have taken me maybe 4:30 in maybe 4:33. This forum is all about small differences.

Very small differences! An S2 is worth 30 seconds at 40kph over an hour but weighs 340g more than an R5 which will cost you roughly 1.4secs per km on an average gradient. Remarkably little gain (if any) considering certain advocates swear that it's night and day.

DMF. Ignore the 12w headline - think 0.2 kph. That's the reality. If you are going to be riding 40km TT's every week I've got nowt against the benefits of aerodynamics. Is that what you are doing? Or what happens at the end of the 1 to 1.5km flat that you ride? The benefits for TT are clear and evident. It's road bikes that I have an issue with - where there is no clear benefit demonstrated under realistic test conditions.

DMF
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Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden
Let's say your pushing some 250w on a straight road, and then you try and push an additional 12w - or for that matter ease off 12w - would you not notice that difference, ignore speed wise, but on how it feels to your body?

Most of my riding is 500-1.500m relatively flat straights, followed by a series of curves, inclines/declines, intersections or something else that brakes my ongoing speed, followed by another 500-1.500m of flat straights. And so forth... I don't ride on a trainer in a windtunnel, nor in the mountains, nor on a velodrome. I think the landscape I ride in is pretty common though...

slyboots
Posts: 445
Joined: Sun May 10, 2009 3:31 pm
Location: Russia, Moscow
airwise wrote:Very small differences! An S2 is worth 30 seconds at 40kph over an hour but weighs 340g more than an R5 which will cost you roughly 1.4secs per km on an average gradient.

Yeah, a pretty "average" gradient of 10%, which means that over a course of 40 km you have to gain (and drop) 2000 vertical meters to achieve savings of 1.4*20=28 secs due to weight. Looks exactly like an everyday ride for the most of us.

kgt
Posts: 6723
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece
@ DMF
I have medium profile Corima aero +. The first time I rode em they really felt 'night and day' in comparison to my Fulcrum zero. And yes, I still love my Corimas and would never buy any low profile wheelset for my Cento Uno again. Why? Because I love the way they feel.

But, that does not mean that in reality the aero benefits are analogous to the feeling. Many times something feels like a*10 but in reality it is like a*1.1.

airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
slyboots wrote:
airwise wrote:Very small differences! An S2 is worth 30 seconds at 40kph over an hour but weighs 340g more than an R5 which will cost you roughly 1.4secs per km on an average gradient.

Yeah, a pretty "average" gradient of 10%, which means that over a course of 40 km you have to gain (and drop) 2000 vertical meters to achieve savings of 1.4*20=28 secs due to weight. Looks exactly like an everyday ride for the most of us.

7/8% gradient actually but that's besides the point. It's also worth noting that the effect of weight increases the slower you go uphill according to tests - the suggestion being the slow speeds increased the effect of the dead spot.

But if someone is doing 40kph over 40km, obviously the ride will be longer if it includes climbs. I'm just trying to understand how many people on Weight Weenies just do 40km time trials by them selves on totally flat courses? I don't know any of my friends who ride like that. A typical ride in SE England will probably see 10m elevation gain for every 1km of the ride ( so 100km results in around 1000m ascent). Same goes for most rides I've done across continental Europe.

It would be interesting to know what percentage of enthusiasts on here just ride flat TT's.

DMF
Posts: 1062
Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden
kgt, I totally agree - and honestly I don't give a smack about if something is 1% or 50% better when it actually feels a 100% better to my body, and I'm not talking about placebo feel but actual feel...

As you say, the difference in feeling is huge - and to me, riding for the pleasure of riding - that counts for more than anything else... I mean, the differences in watts and seconds between tubulars and clinchers are nowhere near as big as the difference in feeling. Numbers simply doesn't present the whole truth...

djconnel
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Pick one of the 4:

1. aero and weight are both important
2. aero is important but not weight so much
3. weight is important but not aero so much
4. neither aero nor weight is important.

If you picked 4, fine, but then why are you here? If you pick 3 and all you care about is climbing times, which is fine, but this is the correct answer for only a small fraction of cases. You can't pick 3 on the basis the effect of aero is too small to feel, because so is the effect of a kg of bike mass.
Last edited by djconnel on Tue Aug 09, 2011 7:43 pm, edited 1 time in total.

airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
I'd probably pick 4 to be honest but I like pretty things and the forum has lots of pretty things. If I want to go quicker I fit a Powermeter and hire a coach.

djconnel
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Joined: Wed Sep 26, 2007 1:57 pm
Location: San Francisco, CA
Contact:
P.S. Typical dream bike:
1. Scott Foil with Red.
2. Cervelo S5 with Di2
3. Naked Cannondale Evo with AX-Lightness and tuned shifters
4. Painted Pinarello Dogma with Di2

airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
djconnel wrote:P.S. Typical dream bike:
1. Scott Foil with Red.
2. Cervelo S5 with Di2
3. Naked Cannondale Evo with AX-Lightness and tuned shifters
4. Painted Pinarello Dogma with Di2

My dream bike looks great, handles superbly and fits me like a glove.

slyboots
Posts: 445
Joined: Sun May 10, 2009 3:31 pm
Location: Russia, Moscow
airwise wrote:7/8% gradient actually but that's besides the point

No, it is not. You seem to be using a model that somehow makes weight look more important then it is. For example, to enjoy those kind of savings (1.4 sec over 1 km) on a 8% climb you need to be climbing at around 200 watts, which is kind of small.
Moreover you then say that your normal rides translate to more like 2% steady climbing/descending. So your "average" savings due to weight of 1.4 sec over 1 km suddenly turn into 0.25 sec.
Light is good and I enjoy riding my light bike, but in general aero is much more important in road cycling.

airwise
Posts: 1049
Joined: Tue Jul 27, 2010 8:31 pm
Firstly the model I'm using is the one applied by Grappe, Ferrari and others so we seem to be getting our wires crossed. And around 200w is not small if you weigh around 55kg as friends of mine do. FWIW 1kg is worth 4 seconds a km at 280w.

As for my typical rides, I've climbed around 175,000 vertical meters in the past four months so I'm both not typical and don't really represent an ideal subject for this. Having said that I only need a lighter bike if I want to set a time or have an easier ride. I don't enjoy myself more.

It's one of those circular arguments no one is going to win so I'll drop out. No one has yet shown me that an aero bike or wheels will make me any faster in the real world on real rides. Until I take up time trialling I'll stick with choosing something that looks nice like a Pegoretti or C59 with some nice Chris King handbuilts.

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