It seems that the trend these days if to have wider rims, and HED and Zipp claim to much aero advantage.
How much truth is there to that?
Common sense tells me that thinner and more streamline shapes are more aero..like the cervelo s3
Wider rims= more aero?
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shape is important...like aero profil which is wider against thin flat profile
aero is more aerodinamic
aero is more aerodinamic
If you take a typical symetrical NACA profile the thinner the better at whatever speed under the speed of sound. But thinner is not stronger so the challenge now becomes... How to make something strong but also aero? A comprimise of both.
But credit for Zipp and Hed, their wheels seem to be the most aero. You see, in rims its not so straight forward as a NACA profile as you have to take into account all other structural elements like spokes, fork, and most importantly tire. In wheels the rim toirdal shape is aerodynamically more efficient in combination with having a round frontal area (tire). Being thicker it also helps to decrease turbulance between spokes and frame (fork or chain stays). The same philosophy is used with rear disc wheels. The P4 has its chain stays set closer to the rim decreasing turbulance between it and the rim (flat disc). The same in reverse order, a toriodal rim disc will have the same effect with a bike with wider chain stays.
If you have a V-Shape rim then it might be more aerodynamic to use a thinner tire, and in reverse if you have a wider rim it will be more aero to go for a wider tire.
Trek on the other hand claim that their new tube profiling (with cut trailing edge) is more aerodymically efficient then a complete 3 to 1 profile. At low speeds (if anything) that maybe be true, but personally Im not going for it. I think its just an excuse to using a more sensible structural element (lighter=not oversized aka cervelo) tubing and still call it aero.
But credit for Zipp and Hed, their wheels seem to be the most aero. You see, in rims its not so straight forward as a NACA profile as you have to take into account all other structural elements like spokes, fork, and most importantly tire. In wheels the rim toirdal shape is aerodynamically more efficient in combination with having a round frontal area (tire). Being thicker it also helps to decrease turbulance between spokes and frame (fork or chain stays). The same philosophy is used with rear disc wheels. The P4 has its chain stays set closer to the rim decreasing turbulance between it and the rim (flat disc). The same in reverse order, a toriodal rim disc will have the same effect with a bike with wider chain stays.
If you have a V-Shape rim then it might be more aerodynamic to use a thinner tire, and in reverse if you have a wider rim it will be more aero to go for a wider tire.
Trek on the other hand claim that their new tube profiling (with cut trailing edge) is more aerodymically efficient then a complete 3 to 1 profile. At low speeds (if anything) that maybe be true, but personally Im not going for it. I think its just an excuse to using a more sensible structural element (lighter=not oversized aka cervelo) tubing and still call it aero.
Last edited by aerozy on Wed Oct 21, 2009 8:41 am, edited 1 time in total.
Factor O2 Rim / Winspace 1500 Disk / Yoeleo R6 Rim / Cervelo S2 Rim
I am running the HED Ardennes, and i have been very pleased with their perfromance.
My undeerstanding of the benfit of the wider rim is that it allows a smoother transition from the standard 23mm tyre leading edge to the rim trailing edge, thus allowing air to remain attached to the rim for a greater portion of th profile, decreasig turbulence and thus drag. (A Toroidal form perfoming this characteristic for a greater dgree of yaw angles and air speeds, at least those encountered by road bikes).
I also beleievee a similar condition can be acheived running a 21mm tyre on a standard 19-21mm wide rim of a similar profile. Only problem is for most road conditions 21mm tyres have a poor ride due to the higher pressures you have to run to prevent pinch flat. Conversely on avarage surfaces this increases rolling resistance, reduces traction etc.
Whatever the science says i can attest to the Ardennes rolling exceptionally well and performing very well in a variety of yaw angles and wind speeds. (basis for comparison is Kysirium which responds poorly to high yaw angle winds and doesn't role that well.) The added bonus of agreater air chamber and lower pressures simply adds to the ride characteristic and handling.
I can honestly say they are the best money i have ever spent on a bike (as an upgrade).
My undeerstanding of the benfit of the wider rim is that it allows a smoother transition from the standard 23mm tyre leading edge to the rim trailing edge, thus allowing air to remain attached to the rim for a greater portion of th profile, decreasig turbulence and thus drag. (A Toroidal form perfoming this characteristic for a greater dgree of yaw angles and air speeds, at least those encountered by road bikes).
I also beleievee a similar condition can be acheived running a 21mm tyre on a standard 19-21mm wide rim of a similar profile. Only problem is for most road conditions 21mm tyres have a poor ride due to the higher pressures you have to run to prevent pinch flat. Conversely on avarage surfaces this increases rolling resistance, reduces traction etc.
Whatever the science says i can attest to the Ardennes rolling exceptionally well and performing very well in a variety of yaw angles and wind speeds. (basis for comparison is Kysirium which responds poorly to high yaw angle winds and doesn't role that well.) The added bonus of agreater air chamber and lower pressures simply adds to the ride characteristic and handling.
I can honestly say they are the best money i have ever spent on a bike (as an upgrade).
A couple other people are getting at it.
If you take the shape that Hed is now using and shrunk it by say 10% to match a 20mm tire, yeah the 20mm version would probably be more aero than the 23mm.
However, Hed and Zipp are designing for a wide audience. Even when they designed wheels for 19-21mm tires, you know what everyone did? Put 23mm tires on them for comfort and cornering and yada yada yada. So instead of telling their customers to quite being stupid, they made them a wheel that fit what they were doing anyways.
If you take the shape that Hed is now using and shrunk it by say 10% to match a 20mm tire, yeah the 20mm version would probably be more aero than the 23mm.
However, Hed and Zipp are designing for a wide audience. Even when they designed wheels for 19-21mm tires, you know what everyone did? Put 23mm tires on them for comfort and cornering and yada yada yada. So instead of telling their customers to quite being stupid, they made them a wheel that fit what they were doing anyways.
athletic91 wrote:It seems that the trend these days if to have wider rims, and HED and Zipp claim to much aero advantage.
How much truth is there to that?
Common sense tells me that thinner and more streamline shapes are more aero..like the cervelo s3
You do understand that 0º yaw almost never happens. Plus, at 0º even a brick is fast (ask an R3
). Someone said it earlier; shape is more important. Aerodynamics is a game or frontal area and shape. If you decrease the frontal area but have a bad shape you could be doing more harm than good. The wider rim allows them to make a smooth(er) transition between the tire and rim making the whole thing faster at even higher yaw angles while marginally increasing frontal area. 2nd, the increase width allow for a fatter tire and (theoretically, given an equal pressure) lower Crr. That last one is a big assumption but all things being equal (including tire pressure) it should equal less Crr.Starnut
Yes, it's not as simple as "narrower is better".
Check this out:
http://www.zipp.com/_media/pdfs/technology/rimshape.pdf
This article is obviously on the Zipp site, so I dunno if there's any propaganda in there
Other than that, Google "toroidal" and "aerodynamics", and you should get lots of search results
Check this out:
http://www.zipp.com/_media/pdfs/technology/rimshape.pdf
This article is obviously on the Zipp site, so I dunno if there's any propaganda in there
Other than that, Google "toroidal" and "aerodynamics", and you should get lots of search results
athletic91 wrote:It seems that the trend these days if to have wider rims, and HED and Zipp claim to much aero advantage.
How much truth is there to that?
A rim that is designed to work well with a 20mm tire will be more aero than a rim designed to work well with a 23mm tire. The issue is that very few people want to run 20mm tires, and besides that a 20mm tire will have greater rolling resistance all else being equal. So now they are working on rims that are optimized for 23mm tires in the hopes of squeezing out an extra bit of overall performance.
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athletic91
- Posts: 311
- Joined: Sun Sep 27, 2009 10:03 am
so can we say the new zipp 101 is as aero is 40-50mm rims out there?
thanks to its wide rim and toridal shape
thanks to its wide rim and toridal shape
Actually, it would appear from the data supplied with the launch of the 101 wheels (insert grain of salt here as needed) that they are significantly more aero then the Reynolds DV46 rims - when both are mounted with 23mm tires. While I haven't seen any data, my understanding as mentioned above, is that the DV46C would perform much better with a 20-21mm tire.
I have a pair of Reynolds DV46C's and always thought the tire sat reasonably flush with the braking surface, but maybe it's because the walls on the Clincher are thicker then the Tubular... not sure which one Zipp tested in the tunnel (though I think they tested everything with Evo clinchers, which suggests "C"). Either way, if the DV46C's aren't registering that well for aero because of their tire/rim interface, I'd hate to see what my Solitudes would do in a tunnel.
I believe the Solitudes are made with the Kinlin rims that everyone here seems to rave about. While they might be lightweight, they have a significant 'lightbulb' effect on the tires, indicating that despite their 30-31mm depth, they'd be piss poor in a tunnel.
The difference in rim width between these two wheelsets is such that when switching from the Solitudes to the DV46C's, I can fully open the QR on my SRAM brakes and have the same amount of throw on my brake levers - and this is with well worn Swiss Stops for my DV46C's versus new DA pads for my Solitudes.
Interestingly enough, the Shimano wheels that always seem to punch well above their weight in the aero-testing (including independent ones) have been noted as having one of the widest rims of the 'normal' styles - ~21mm versus 19-20mm from most others.
I have a pair of Reynolds DV46C's and always thought the tire sat reasonably flush with the braking surface, but maybe it's because the walls on the Clincher are thicker then the Tubular... not sure which one Zipp tested in the tunnel (though I think they tested everything with Evo clinchers, which suggests "C"). Either way, if the DV46C's aren't registering that well for aero because of their tire/rim interface, I'd hate to see what my Solitudes would do in a tunnel.
I believe the Solitudes are made with the Kinlin rims that everyone here seems to rave about. While they might be lightweight, they have a significant 'lightbulb' effect on the tires, indicating that despite their 30-31mm depth, they'd be piss poor in a tunnel.
The difference in rim width between these two wheelsets is such that when switching from the Solitudes to the DV46C's, I can fully open the QR on my SRAM brakes and have the same amount of throw on my brake levers - and this is with well worn Swiss Stops for my DV46C's versus new DA pads for my Solitudes.
Interestingly enough, the Shimano wheels that always seem to punch well above their weight in the aero-testing (including independent ones) have been noted as having one of the widest rims of the 'normal' styles - ~21mm versus 19-20mm from most others.
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athletic91
- Posts: 311
- Joined: Sun Sep 27, 2009 10:03 am
i own a set of reynolds solitute too.
yes the 23mm tires really budge out. i guess the more unaero feature of the wheel are its spokes.
The round dt spokes create alot of turbulance
yes the 23mm tires really budge out. i guess the more unaero feature of the wheel are its spokes.
The round dt spokes create alot of turbulance
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zebragonzo
- Posts: 971
- Joined: Thu Oct 18, 2007 7:35 am
rruff wrote:A rim that is designed to work well with a 20mm tire will be more aero than a rim designed to work well with a 23mm tire.
Assuming it's the same cross sectional shape.
Zebra, double post deleted as per your request. Powerful Pete
edit - thanks pete!
Last edited by zebragonzo on Fri Oct 23, 2009 10:50 am, edited 2 times in total.
Dimples: Laminar flow separates more easily from a surface than turbulent air. Delayed separation reduces drag. A groove perpendicular to the flow triggers laminar to turbulent conversion. A spinning object uses dimples so an edge always faces the flow.
Yes, I suppose I should have added that it is assuming the same rim depth and design.
I recall seeing the results of a test from awhile back where 20mm and 23mm tires where tested on a deep (HED I think) rim in the tunnel. The results combined with rolling resistance data indicated that 20mm tire was likely the fastest choice above ~22mph or so. So if they can redesign the rim for a 23mm tire there might be a little bit to gain.
I like the idea of aluminum clinchers having a 21mm brake track since there is even less reason to use 20mm tires with these. IMO the HEDs at 23-24mm are too wide though and combined with a mere 24mm depth I don't see much aero advantage. Surely a 21mm x 26mm rim would be better.
I recall seeing the results of a test from awhile back where 20mm and 23mm tires where tested on a deep (HED I think) rim in the tunnel. The results combined with rolling resistance data indicated that 20mm tire was likely the fastest choice above ~22mph or so. So if they can redesign the rim for a 23mm tire there might be a little bit to gain.
I like the idea of aluminum clinchers having a 21mm brake track since there is even less reason to use 20mm tires with these. IMO the HEDs at 23-24mm are too wide though and combined with a mere 24mm depth I don't see much aero advantage. Surely a 21mm x 26mm rim would be better.
easton's workaround to zipp/hed's patent on toroidal rim shape. go narrower. we need to see a new 2010 tour aero wheel test soon.
easton new tt wheelset. they have the cahones to take on the zipp's dimple marketing machine.
NARROW IS FASTER
Easton’s proprietary narrow-flange R4TT front hub reduces frontal spoke area by 50% for improved aerodynamics. Combined with a new wind tunnel-tuned 90mm rim, and the new EC90TT displays lower drag than the Zipp 808 at 0, 5, 10, 15 and 20 degree yaw angles. It even rivals the much deeper (and heavier) Zipp 1080 at 5 and 15 degrees.
FASTER AND LIGHTER
At 1424 a set, the EC90 TT is a full 30 grams lighter than the Zipp 808, and still 9mm deeper in rim profile, thanks to Easton’s Variable Nipple Bed (VNB™) Technology. This process of internally tapering the rim bed eliminates excess carbon between spoke holes and allows for a sharper inner edge. Less weight, improved aerodynamics with no loss in strength.
AERODYNAMICS 101: LEADING EDGE VS. TRAILING EDGE
There are two ways to make a wheel fast in the wind. One is to design the leading (forward) edge to help smooth the path of the air around the tire. Zipp’s bulged rim profile attempts to do this. The other way to design a fast wheel is to focus on sharpening the rim profile on the trailing edge to manage the air as it exits the rear edge of the wheel. You can’t have it both ways. At Easton we feel you can design a faster wheel with a sharper, narrower profile like the EC90. And our wind tunnel data confirms this.
DIMPLES ARE FOR GOLF
Dimples work on blunt objects like golf balls, but they’re irrelevant on bicycle wheels. On a golf ball, they reduce drag because they create turbulent flow. They diminish what's called pressure drag, caused by a relative "void" behind the ball. However on sharper, wing-shaped objects like deep section wheels (or F1 cars) dimples don’t work because the air is already flowing over a narrow, optimized shape that by design reduces pressure drag.
http://www.eastonbike.com/PRODUCTS/WHEE ... T_'10.html
easton new tt wheelset. they have the cahones to take on the zipp's dimple marketing machine.
NARROW IS FASTER
Easton’s proprietary narrow-flange R4TT front hub reduces frontal spoke area by 50% for improved aerodynamics. Combined with a new wind tunnel-tuned 90mm rim, and the new EC90TT displays lower drag than the Zipp 808 at 0, 5, 10, 15 and 20 degree yaw angles. It even rivals the much deeper (and heavier) Zipp 1080 at 5 and 15 degrees.
FASTER AND LIGHTER
At 1424 a set, the EC90 TT is a full 30 grams lighter than the Zipp 808, and still 9mm deeper in rim profile, thanks to Easton’s Variable Nipple Bed (VNB™) Technology. This process of internally tapering the rim bed eliminates excess carbon between spoke holes and allows for a sharper inner edge. Less weight, improved aerodynamics with no loss in strength.
AERODYNAMICS 101: LEADING EDGE VS. TRAILING EDGE
There are two ways to make a wheel fast in the wind. One is to design the leading (forward) edge to help smooth the path of the air around the tire. Zipp’s bulged rim profile attempts to do this. The other way to design a fast wheel is to focus on sharpening the rim profile on the trailing edge to manage the air as it exits the rear edge of the wheel. You can’t have it both ways. At Easton we feel you can design a faster wheel with a sharper, narrower profile like the EC90. And our wind tunnel data confirms this.
DIMPLES ARE FOR GOLF
Dimples work on blunt objects like golf balls, but they’re irrelevant on bicycle wheels. On a golf ball, they reduce drag because they create turbulent flow. They diminish what's called pressure drag, caused by a relative "void" behind the ball. However on sharper, wing-shaped objects like deep section wheels (or F1 cars) dimples don’t work because the air is already flowing over a narrow, optimized shape that by design reduces pressure drag.
http://www.eastonbike.com/PRODUCTS/WHEE ... T_'10.html
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rruff wrote:...Surely a 21mm x 26mm rim would be better.
Not according to Waldo (Zipp) in thisthread. His argument, as I understand is that frictional elements and deep sections give better high yaw performance than shallower narrower rims with thinner tires. And that makes sense.
That said, I really wonder if a narrower hybrid toroidal rim shape (new SRAM wheels), with narrow 19mm winged Bontrager TT tires would not be getting close to the wider zipp rim with a CX tire. Might be a poor mans solution to aero "everyday" wheels since the SRAM wheels are 1/2 the price of the 101s.
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