Carbon Wheels Tradeoff

Everything about building wheels, glueing tubs, etc.
CAAD8FRED
Posts: 70
Joined: Mon Jun 18, 2018 10:52 pm

by CAAD8FRED

zefs wrote:
Sat Aug 04, 2018 7:32 am
I did the same route (same weather conditions) with 50mm carbon wheels (1750g) vs 23mm alu wheels (1500g) and the average speed/heart rate/watts came out the same. At those speeds and elevation they weren't faster for me and I sold them since all my rides have that kind of elevation. Not sure how their results are a few seconds only on a 10km 6% climb with 1kg difference on setups.


carbon.jpg
alu.jpg
Have you tried the experiment with deeper carbon if you have them or a 50 mm that’s a different shape?

zefs
Posts: 129
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

Have only tried a U shaped 50mm (Yoeleo SAT C50 disc).
Last edited by zefs on Sun Aug 05, 2018 8:39 am, edited 1 time in total.

by Weenie


alcatraz
Posts: 1298
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

CAAD8FRED wrote:
Sat Aug 04, 2018 3:05 pm
Hey Beaver,

What is the lowest crosswind wheel you’ve seen in your research?

Rob
Thing is Caad8fred, that you need to compare similar performing rims to see which shape is more crosswind stable.

If you compare a rim that is slower in a straight line with a fast rim, and find out that the slower one is more stable, would you rush to buy it? What if I tell you they are the same depth? Simply different shapes.

My personal opinion is that in a straight line the best shape is a deep naca profile but they arent practical. The compromise is toroidal rims that maximize use of a truncated depth (low drag = speed) while still offering decent crosswind stability by being oval in their crossection.

TobinHatesYou
Posts: 1876
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Beaver wrote:
Sat Aug 04, 2018 2:11 pm

The 32mm wide Knøt 64 and Hunt's new 23C 35.5mm wide rim (for 28mm tires) will be great in the wind tunnel but prone to crosswinds. They cause less drag, but the airflow seems to get compressed at the the wind faced side.
Once again, this is not the key in crosswind instability. The difference in sideforces on the leading side of the wheel and trailing side of the wheel is what causes your wheel to suddenly steer. If the side forces are identical, the wheel stays straight. This is why rear wheels can be deeper without much penalty...because they don’t pivot/steer.

Imaking20
Posts: 1621
Joined: Fri Nov 18, 2011 5:19 am

by Imaking20

Beaver wrote:
Sat Aug 04, 2018 2:11 pm
And that's the hitch, that shape is heavier than the others.
Clincher maybe. My Aero 46 tubular is 1235g actual. As far as I'm aware, that's the lightest of any major brand with the exception of may Bontrager. But the braking is also better. And they handle crosswind better than even my FSE 35
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Beaver
Posts: 501
Joined: Wed Aug 18, 2004 6:06 pm
Location: Lower Saxony - Germany

by Beaver

TobinHatesYou wrote:
Sun Aug 05, 2018 10:02 am
Beaver wrote:
Sat Aug 04, 2018 2:11 pm

The 32mm wide Knøt 64 and Hunt's new 23C 35.5mm wide rim (for 28mm tires) will be great in the wind tunnel but prone to crosswinds. They cause less drag, but the airflow seems to get compressed at the the wind faced side.
Once again, this is not the key in crosswind instability. The difference in sideforces on the leading side of the wheel and trailing side of the wheel is what causes your wheel to suddenly steer. If the side forces are identical, the wheel stays straight. This is why rear wheels can be deeper without much penalty...because they don’t pivot/steer.
Is it really opposed? You explained the general physical effect, I tried to explain why shapes behave differently. How would you explain, why the teardrop shape is better?

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Beaver
Posts: 501
Joined: Wed Aug 18, 2004 6:06 pm
Location: Lower Saxony - Germany

by Beaver

CAAD8FRED wrote:
Sat Aug 04, 2018 3:05 pm
Hey Beaver,

What is the lowest crosswind wheel you’ve seen in your research?

Rob
According to users and reviews the Reynolds teardrop (NACA) rims are best here, then round V-shapes, then round torodial, Kamm tail is worst.

In last years Tour Mag. test the Reynolds 46 Aero Disc had 1Nm side force (same as low 25mm rims), Zipp's 303 Disc 7Nm, watt difference was 1.3 watts at 45km/h, so nothing noticable.

https://www.tour-magazin.de/komponenten ... 45092.html

TobinHatesYou
Posts: 1876
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

The aim of a toroidal rim and appropriately sized tire is to create symmetry This way at whatever yaw angle, the flow separation and side force at the front plane is equal to that of the back plane. The total side force is not as important as the difference between front and back. A gust of wind isn’t making a wheel tire lose grip and slide sideways, but it is effectively a force that cocks the wheel.

When you use Vs or hybrid Vs, the wheel front plane is a mirror image of the rear plane o>———<o

The flow separation and side force on the front of the wheel will be different than that of the back of the wheel. With unbalanced side forces, the wheel will steer.

Again, visualize this using the metaphor of a traditional balance scale. If you put equal force/weight on both sides of a balance scale it stays neutral. If you put more force on one side, then the scale will tip.

Now some people will anecdotally say modern toroidal wheels feel wobbly in strong crosswinds. That’s most likely because such wheels require less rider input to keep straight. With V shaped rims they subconsciously would have already applied a constant counter steer in a similar scenario.

e: Included an image. Note the completely different angle and flow separation on the V shaped rims depending on front or back. Based on the fact that the front of the V shaped wheel wants to do something completely different than the back and the U-shaped ones are more balanced, which one do you think will be more unstable? :)

Image

In addition no wheel with tire mounted has a truncated NACA profile like you keep linking.

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Beaver
Posts: 501
Joined: Wed Aug 18, 2004 6:06 pm
Location: Lower Saxony - Germany

by Beaver

TobinHatesYou wrote:
Sun Aug 05, 2018 8:33 pm
The aim of a toroidal rim and appropriately sized tire is to create symmetry This way at whatever yaw angle, the flow separation and side force at the front plane is equal to that of the back plane. The total side force is not as important as the difference between front and back. A gust of wind isn’t making a wheel tire lose grip and slide sideways, but it is effectively a force that cocks the wheel.

When you use Vs or hybrid Vs, the wheel front plane is a mirror image of the rear plane o>———<o

The flow separation and side force on the front of the wheel will be different than that of the back of the wheel. With unbalanced side forces, the wheel will steer.

Again, visualize this using the metaphor of a traditional balance scale. If you put equal force/weight on both sides of a balance scale it stays neutral. If you put more force on one side, then the scale will tip.

Now some people will anecdotally say modern toroidal wheels feel wobbly in strong crosswinds. That’s most likely because such wheels require less rider input to keep straight. With V shaped rims they subconsciously would have already applied a constant counter steer in a similar scenario.

e: Included an image. Note the completely different angle and flow separation on the V shaped rims depending on front or back. Based on the fact that the front of the V shaped wheel wants to do something completely different than the back and the U-shaped ones are more balanced, which one do you think will be more unstable? :)

Image

In addition no wheel with tire mounted has a truncated NACA profile like you keep linking.
This image was meant to show the effect of the 105% rule. The Easton and Zipp rims are narrower than the tire and yes, this would decrease crosswind stability, but nowadays these are also wider and the flow separation will be much "later" as seen on the Bontrager rim. And Bontrager's XXX rims are now more of a V-shape - just to improve crosswind stability.

And yes, a Reynolds rim with tire mounted is no perfect teardrop shape, but nothing comes closer.

Users here and in other forums confirm these to be very stable, so does the Tour Mag. test and I also tried a Aero 46 front wheel myself on a windy day. There really is a difference. ;)

TobinHatesYou
Posts: 1876
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

You still don’t understand what causes crosswind instability. Even ignoring the size of the tire, the V shape is fundamentally flawed as a wheel cross-section. I challenge you to find a image of a V shaped rim creating the same airflow pattern forward and back.

If you want to argue a very narrow tire mated to a rim profile that gets wider to the center and then tapers to a blunt V is better than a U, then sure. Perhaps we will see rims designed for 23mm tires that widen to 35mm at the widest part. These would be great in crosswinds, but less aero than narrower rims at shallow yaw angles.

alcatraz
Posts: 1298
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

V-shape is clearly very bad in crosswinds. Leading edge performs drastically different than trailing edge = lots of steering influence.

By truncated naca I don't mean ugly trek/scott kammtail shapes I mean truncated further down in the naca shape. It almost results in an oval toroidal shape if you round the corners.

/a

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Beaver
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Joined: Wed Aug 18, 2004 6:06 pm
Location: Lower Saxony - Germany

by Beaver

Bontrager has tested several rim shapes...

Image

...and ended up with a sharper shape for the higher rims as a compromise of drag and crosswind stability:

Image

https://www.bikerumor.com/wp-content/up ... aper_3.pdf

These are not flat V-shapes (to keep the airflow attached to the rim) and neither is the Reynolds shape.

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