Aero vs light wheels

[slyboots]

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.

You see, the only problem with your model is how you consider it "average". Constantly riding 7-8% grades is not average and neither is a 55 kg male cyclist. There are conditions when weight is more important, they are just not that common.
And 1 kg less weight on a 8% grade at 280 watts will net you 2.7 sec per 1 km savings per analyticcycling.com.

[rustychain]

Hard to imagine that 95% of us posting ride just for fun after reading all this isn't it

[airwise]

You see, the only problem with your model is how you consider it "average". Constantly riding 7-8% grades is not average and neither is a 55 kg male cyclist. There are conditions when weight is more important, they are just not that common.
And 1 kg less weight on a 8% grade at 280 watts will net you 2.7 sec per 1 km savings per analyticcycling.com.

It is average where I am living - and so it is for many many thousands of cyclists who inhabit this corner of the planet. It I were in the UK the gradients would be more severe.

Thanks for the link though. Having looked at the site I can't help but feel the middle "ytic" is somewhat superfluous

[clarkson]

Fascinating study at the USAPCC in the Vail time trial. Vandevelde used an R5ca with full TT gear, Levi used a Trek Speed Concept, and they finish on exactly the same time.

From cyclingnews:
"According to team sports scientist Robbie Ketchell, Vande Velde's position was actually nearly identical to that of his full-blown P4 time trial rig and given the nominal gains offered by even the best aero frames, the trick setup likely represented only a slight increase in drag in total.

More importantly, though, the ultralight chassis yielded a final package that was unusually light for a time trial bike – a key performance advantage for the second half of the course. According to team mechanic Geoff Brown, Vande Velde's aero-dressed R5ca was well under the 7kg (15.4lb)."

I'd like Levi to go back and ride it with a road frame to compare.

[trustbran]

Why is it that when I had road bars on my Cervelo P1 it felt way faster than my current bike now SL1 S-Works. My Sl1 feels like pedaling in sand when compared to the P1. The SL1 is light at around 14ish lbs and the P1 was heavy at about 17ish lbs. The SL1 is fast no doubt especially uphills but I'm just saying, the P1 felt way faster almost all around. Is it Aero? Obviously the P1 is very Aero but heavier where as the SL1 is Carbon and 3 lbs + lighter. So what else could it be? I still have my P1 frame and often wonder if I should move everything from the SL1 back to the P1 because it seemed so much faster!

[thisisatest]

You see, the only problem with your model is how you consider it "average". Constantly riding 7-8% grades is not average and neither is a 55 kg male cyclist. There are conditions when weight is more important, they are just not that common.
And 1 kg less weight on a 8% grade at 280 watts will net you 2.7 sec per 1 km savings per analyticcycling.com.

It is average where I am living - and so it is for many many thousands of cyclists who inhabit this corner of the planet. It I were in the UK the gradients would be more severe.

Thanks for the link though. Having looked at the site I can't help but feel the middle "ytic" is somewhat superfluous

slyboots should have said "constantly riding up 7-8% grades is not average." you always have to come down. and there's everything in between going up n down, too. especially in this forum, and expectedly given the name of the forum, weight is given more importance than aero, even though it isn't.

[nuttymango]

From this thread:http://weightweenies.starbike.com/forum/viewtopic.php?uid=9302&f=3&t=70829&start=45

Based on the calculator at http://bikecalculator.com/wattsMetric.html, it typically takes 551 watts (!) of power to maintain 50 km/h on a level road.

Now the difference in absorbed power between a standard wheel and a good aero wheel is only around 10 watts at 50 km/h, which gives: 10/551 = 1.8% difference.

If I understand correctly, that's a 1.8% difference between an aero front wheel and a non-aero front wheel. No rear wheel, drivetrain, frame, or rider.

Compared to the drag from the rest of the bike and the rider, the drag of front wheel alone must be relatively small. That 1.8% difference between unmounted front wheels must dwindle to below 1% when combined with the drag from bike and rider. Wish my math skills were up to the task of quantifying this.

And that tiny difference is at 50 km/h! Have I misunderstood something here?

[clarkson]

And that tiny difference is at 50 km/h! Have I misunderstood something here?

The power of the cervelo marketing machine, convincing the world that you may not survive your next group ride without more aero gear?
It's a buzzword, and if it can be used to move product it will be.

[thisisatest]

From this thread:http://weightweenies.starbike.com/forum/viewtopic.php?uid=9302&f=3&t=70829&start=45

Based on the calculator at http://bikecalculator.com/wattsMetric.html, it typically takes 551 watts (!) of power to maintain 50 km/h on a level road.

Now the difference in absorbed power between a standard wheel and a good aero wheel is only around 10 watts at 50 km/h, which gives: 10/551 = 1.8% difference.

If I understand correctly, that's a 1.8% difference between an aero front wheel and a non-aero front wheel. No rear wheel, drivetrain, frame, or rider.

Compared to the drag from the rest of the bike and the rider, the drag of front wheel alone must be relatively small. That 1.8% difference between unmounted front wheels must dwindle to below 1% when combined with the drag from bike and rider. Wish my math skills were up to the task of quantifying this.

And that tiny difference is at 50 km/h! Have I misunderstood something here?

i think you missed that the 551 watts initially stated is a complete bike with rider and two wheels. then changing the front wheel in the complete system saves 10watts, or 1.8%.

also other sources show a much larger savings than just 10 watts (vs a standard wheel). ex- zipp lists the 808 firecrest set as saving 32 watts. assuming the front makes the bigger difference, it would be closer to 20watts.

[fdegrove]

Hi,

And that tiny difference is at 50 km/h! Have I misunderstood something here?

The notion of that speed barrier should be taken in the proper context IMO.

We're not riding in windtunnels AFAIK so speed should not be entered into the equation as an absolute number.

Fact is that aero will trump weight most of the time so it does not hurt to have both in your favour.....
Add low rolling resistance and low friction bearings to it and you'd be fine.

Cheers,

[nuttymango]

i think you missed that the 551 watts initially stated is a complete bike with rider and two wheels. then changing the front wheel in the complete system saves 10watts, or 1.8%.

also other sources show a much larger savings than just 10 watts (vs a standard wheel). ex- zipp lists the 808 firecrest set as saving 32 watts. assuming the front makes the bigger difference, it would be closer to 20watts.

Yup. Thanks.

[User Name]

I'm not shooting any messengers on here, but one thing that annoys a bit about aero wheel tests is, what the hell is a 'standard' wheel these days? The tests usually compare an 'aero' wheel to a standard one, but as far as what most people are riding, there's no standard alu wheel any more. Maybe in the 'old days', when we all raced on 28 or 32-spoke Open CD4s, Omegas or MA2s, the comparison was much more relevant, but now it (the comparison) has lost a HEAP of meaning.

And, even worse, a lot of tests still use a 36-spoke box rim as the comparison! Who the hell races, or ever rides, on 36-hole box rims any more?!?!! They might as well use a 64-spoke dragster wheel off a kids' bike! Then, the people in the "my-deep-wheels-make-a-huge-difference" camp jump on the relatively large difference between their 404s and the 36-spoke wheel, and run with it, saying they're riding with a definite advantage. What, then, if 90% of people on here said they ride with Eurus or DAc24s (for eg), which are only a handful of watts slower than 404s? Does the argument for deep carbon rims go out the window?

Ha!

And another thing: people who SWEAR that they can notice a difference with deep wheels!! PARLEEEEZ!! With all the other things that can make a real difference to speed on the road, such as the teeeeniest change in wind or road gradient, people tell me that thet can feel that their aero wheels are rolling ~.5kp/h faster. Gimme a break! I tell ya right now, I can't tell any difference when I put my Flashpoint FP60s on; the only thing I notice is how much they flex and how crap they handle in crosswinds

The only thing I might concede if my arm was twisted, is that perhaps some of the heavier deep rims hold more momentum, and this could be what people notice. Some deep alu/carbon rims are heavy: my 2006 Flashpoints are about 595g each, which is hell of lot more than some of the light rims used by people on this forum. I'm not sure if it was my imagination, or that I was having some good rides, but I occasionally felt that the brick-like rims on my old Mavic Cosmic Pros (38mm-deep alu) held speed better than my shallower rims.

[User Name]

While I'm at it... this test done by German Tour Mag found that, at 45pk/h, the rider cut 22w of drag just by moving from the top of the bars to the hoods; a further 37w going to the drops; then another 37w switching to aero bars!! That's a total of 96w just with upper body postioning. I just like pointing that out.
http://www.dk-content.de/tour/pdf-archi ... l_0107.pdf

And that was using a pro rider (Uwe Peschel) who probably wasn't too horribly 'unaero' on the tops, compared to a lot of Joe Averages on here. Therefore, I'd argue that there are a lot of unflexible guys riding around up high who are creating 150w more drag that Uwe Peschel does in the drops, yet they insists on using their 404s for training rides. Say what ya like; it's funny.

[parajba]

For what it's worth I'll contribute to this thread in a few weeks.

Facts: Swapped from R3 to S2 recently. Standard set-up includes Zipp 404 tubs. I only race (crits and road races). Avg sped of an avg race is 40 km/h. We easily hit 50 km/h on flats. Race weight of rider: 66 kg. Height: 177cm.

The last race I won (Kenardington - UK) was 3 weeks ago, and it was on my beloved R3. 40km in the peloton, then 60km on a breakaway with 5 others. We won with a margin of 4 mins on the peloton. The 2nd came 1 second behind me.

I'll be racing on the S2 coming season and provide my honest opinion. Same geometry, same components. Honest.

[thisisatest]

... but I occasionally felt that the brick-like rims on my old Mavic Cosmic Pros (38mm-deep alu) held speed better than my shallower rims.

although a heavy wheel reduces speed at a slower rate than a light wheel, ignoring the very, very slight increase in rolling resistance from the entire rider/bike system being slightly heavier, it takes exactly the same amount of energy to maintain speed on flat ground. you are only working against rolling (mentioned earlier) and wind resistance (constant, and equal in both cases). the sensation, even the noise, can make the wheel seem faster, when it is merely different.

i agree with the "standard wheel comparison" argument, however. it would be nice to see a modern wheel used as the "standard wheel". i think some companies do (rolf prima?) use the Mavic Ksyrium SL, which aerodynamically is a very, very bad wheel. I cant remember if it might be WORSE than a 32hole box rim... I don't necessarily blame the wheel companies in trying to show themselves in the best light, as long as all the fine print is actually printed.