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Aerodynamic wheels - compared to what exactly?

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Aerodynamic wheels - compared to what exactly?

Old 02-16-19, 11:19 AM
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canuckjgc
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Aerodynamic wheels - compared to what exactly?

I haven't shopped for new wheels in few years. Looking for a new set of hoops for a new Cervelo R2. Training and group rides and the odd event. Rolling terrain in a generally windy area. It's information overload out there on wheels. One thing that is not clear - aerodynamic wheels tested to save X watts at speed compared to what? A traditional box rim with 36 spokes? Not usually even a consideration for a performance bike. When you compare to rounded but shallow rims with aero spokes, don't the benefits diminish fairly quickly? I like these DT Swiss wheels because the 240 hub is quick to engage with 36 ratchet, low drag and you can't overtighten the RWS skewer, and they are just generally good wheels:
https://www.dtswiss.com/en/products/wheels-road/performance/pr-1400-dicut-21/pr-1400-dicut-21/
Would I really be losing that many watts compared to 32mm or 45mm wheels? Given the endless variations in wind angle, rim shapes, spokes, can it really be said that those wheels with a rounded rim, few and aero spokes are much slower than a deeper alloy rim? I want alloy for braking and cost - not cheaper carbon.
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Old 02-16-19, 01:27 PM
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Tires and tubes make a bigger difference than wheels. If you're looking for performance, that'd be the first place I'd start. If you're losing placings by inches, or you think carbon wheels look awesome and your bike does not, then I'd go with the deeper carbon wheels.
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Old 02-16-19, 05:58 PM
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Windy? Sounds like a job for a 404 FC Zipp. Not too much profile but about as good or better than the old 808. Or something agreeable at a good yaw angle. Or a FLO.

Also, if you don’t care people looking funny on a ride then nicer aero wearable kit is worth more also. Helmet, jersey or suit, etc.

I could learn the tube lesson myself and use latex. Could mean the difference between pulls at SS or closer to threshold.

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Old 02-16-19, 06:27 PM
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Originally Posted by canuckjgc View Post
I haven't shopped for new wheels in few years. Looking for a new set of hoops for a new Cervelo R2. Training and group rides and the odd event. Rolling terrain in a generally windy area. It's information overload out there on wheels. One thing that is not clear - aerodynamic wheels tested to save X watts at speed compared to what? A traditional box rim with 36 spokes? Not usually even a consideration for a performance bike. When you compare to rounded but shallow rims with aero spokes, don't the benefits diminish fairly quickly? I like these DT Swiss wheels because the 240 hub is quick to engage with 36 ratchet, low drag and you can't overtighten the RWS skewer, and they are just generally good wheels:
https://www.dtswiss.com/en/products/...1400-dicut-21/
Would I really be losing that many watts compared to 32mm or 45mm wheels? Given the endless variations in wind angle, rim shapes, spokes, can it really be said that those wheels with a rounded rim, few and aero spokes are much slower than a deeper alloy rim? I want alloy for braking and cost - not cheaper carbon.
Generally compared to a 32-spoke low-section rim....any good study worth reading will specify.

If you're shopping the $1,000USD wheelset level--you have the choice of all the best hubsets and rims available. 240s are nice, so are Whites, and Onyx, and on and on. Rims--AL33, R90SL, Belgiums to name a few very nice ones.
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Old 02-16-19, 07:01 PM
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I don't have a useful wheel suggestion, but I've had two Cervelo R series bikes. Your R2 is a fantastic ride, hope you love it. I have a wheelset with DT 240s as well and they're as great as anything.

Come back with pictures when you have the wheels set up.
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Old 02-16-19, 09:08 PM
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Not a specific answer to you question, but this gives a good sense of the principles involved.



In my personal experience, I would be consistently passed on descents by a riding buddy who outweighs me by ~40 lbs.

when I got some 60mm deep wheels, this stopped, until several years later when he got a new bike w/ deeper wheels.
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Old 02-17-19, 08:10 AM
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Originally Posted by canuckjgc View Post
I like these DT Swiss wheels because the 240 hub is quick to engage with 36 ratchet, low drag and you can't overtighten the RWS skewer, and they are just generally good wheels:
https://www.dtswiss.com/en/products/...1400-dicut-21/
Would I really be losing that many watts compared to 32mm or 45mm wheels? Given the endless variations in wind angle, rim shapes, spokes, can it really be said that those wheels with a rounded rim, few and aero spokes are much slower than a deeper alloy rim? I want alloy for braking and cost - not cheaper carbon.
If you like the DT wheels, then get them. For the same approx weight though, deeper rims will be faster.. how much so obviously depending a lot of things.
Personally, I'm tempted by these, which you could consider if you're wanting to stick to alloy.

https://www.bike24.com/p2306399.html?q=tsr

Last edited by Sy Reene; 02-17-19 at 08:15 AM.
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Old 02-17-19, 08:21 AM
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Compared to what ever will make the saved watts claim as big as possible. IE a square box section rim. Im betting, if you compared to a half decent, semi aero shaped rim, like a Fulcrum quattro wheel, the difference is nil or bordering on not detectable anywhere but in the lab.
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Old 02-17-19, 09:38 AM
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few things:
1. Find out what can fit your R2. A modern, wide rim w/ 28mm tires might not clear the frame. Figure your max clearance and go from there.

2. Most publish data at 40 or 50kph, not compared to box rims, but raw data on how many watts. You can compare to box or shallow alloys, if you can find data on your setup.
The savings are pretty big compared to box or shallow alloy wheels.
Less so between various shapes of carbon wheels at the same depth.

3. low count, bladed or rounded spokes on shallow rims are ok but the spokes are longer than on a deep carbon hoop.
That's a bigger aero factor.

4.The aero gains may or may not overweigh the downsides to deep carbon hoops, so think about the practical side too.
If you race, yes, the carbon hoops are great.

5. those dt swiss you linked look like nice, cheap alloy wheels. But, they are as aero as an ice cream truck.

Originally Posted by canuckjgc View Post
I haven't shopped for new wheels in few years. Looking for a new set of hoops for a new Cervelo R2. Training and group rides and the odd event. Rolling terrain in a generally windy area. It's information overload out there on wheels. One thing that is not clear - aerodynamic wheels tested to save X watts at speed compared to what? A traditional box rim with 36 spokes? Not usually even a consideration for a performance bike. When you compare to rounded but shallow rims with aero spokes, don't the benefits diminish fairly quickly? I like these DT Swiss wheels because the 240 hub is quick to engage with 36 ratchet, low drag and you can't overtighten the RWS skewer, and they are just generally good wheels:
https://www.dtswiss.com/en/products/...1400-dicut-21/
Would I really be losing that many watts compared to 32mm or 45mm wheels? Given the endless variations in wind angle, rim shapes, spokes, can it really be said that those wheels with a rounded rim, few and aero spokes are much slower than a deeper alloy rim? I want alloy for braking and cost - not cheaper carbon.

Last edited by cruiserhead; 02-17-19 at 09:47 AM.
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Old 02-17-19, 09:56 AM
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Specialized built a wind tunnel in NorCal to test their cycling equipment. The guys that run the tunnel run tests based upon rider questions.

The video below compares wheels, clothes and helmet. Note that they do not test at different wind yaw angles but more than likely, that will add to the benefit of aero wheels. I use Fast Forward 45 mm carbon clincher on my Cervelo R5.

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Old 02-17-19, 10:22 AM
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"The savings are pretty big compared to box or shallow alloy wheels.
Less so between various shapes of carbon wheels at the same depth."

Just a reminder. Alloy vs carbon is irrelevant in the scope of aero. Shape is important ;-)
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Old 02-17-19, 10:25 AM
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Originally Posted by rubiksoval View Post
Tires and tubes make a bigger difference than wheels. If you're looking for performance, that'd be the first place I'd start. If you're losing placings by inches, or you think carbon wheels look awesome and your bike does not, then I'd go with the deeper carbon wheels.
Actually that's determined by speed. Below a certain threshold, tires matter most. Beyond that and the wheels become the greater determining factor. I'm pretty sure we've had this discussion before?
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Old 02-17-19, 10:37 AM
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Originally Posted by KraneXL View Post
Actually that's determined by speed. Below a certain threshold, tires matter most. Beyond that and the wheels become the greater determining factor. I'm pretty sure we've had this discussion before?
Yeah, at lower speeds tube and tyres are your best bet if you cant have both. Aero gains are always measured at ludicrous speeds, because power to overcome "wind resistance" goes up by the cube of the speed. For instance power to overcome wind resistance at 50 km/h is almost double that of 40 km/h and 4.6 times that of 30 km/h.

Last edited by Racing Dan; 02-17-19 at 10:44 AM.
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Old 02-17-19, 10:49 AM
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Originally Posted by KraneXL View Post
Actually that's determined by speed. Below a certain threshold, tires matter most. Beyond that and the wheels become the greater determining factor.
What's that threshold? 50 mph?

I seriously question that assertion.

Originally Posted by KraneXL View Post
I'm pretty sure we've had this discussion before?
I don't recall.
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Old 02-17-19, 10:52 AM
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Originally Posted by Racing Dan View Post
Yeah, at lower speeds tube and tyres are your best bet if you cant have both. Aero gains are always measured at ludicrous speeds, because power to overcome "wind resistance" goes up by the cube of the speed. For instance power to overcome wind resistance at 50 km/h is almost double that of 40 km/h and 4.6 times that of 30 km/h.
Gatorksins on disc wheels versus Conti 5000 TLs on Hed Ardennes.

I'd bet on the latter at 10 mph, 30 mph, 50 mph, etc.
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Old 02-17-19, 11:13 AM
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Originally Posted by Racing Dan View Post
Yeah, at lower speeds tube and tyres are your best bet if you cant have both. Aero gains are always measured at ludicrous speeds, because power to overcome "wind resistance" goes up by the cube of the speed. For instance power to overcome wind resistance at 50 km/h is almost double that of 40 km/h and 4.6 times that of 30 km/h.
I assume that it's actually relative wind speed that's important. It's not at all unusual to find days with eg. 15km/h tailwinds for portions of a ride's course.
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Old 02-17-19, 11:13 AM
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Originally Posted by rubiksoval View Post
What's that threshold? 50 mph?

I seriously question that assertion.



I don't recall.
It varies from rider to rider. But generally, the more aero you are the lower your resistance. I'd say the effects begin to gain prominence somewhere in the upper teen mph (30kph). Below that and the advantage go to being a light as possible. Then the tube/tires.
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Old 02-17-19, 11:19 AM
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Originally Posted by KraneXL View Post
It varies from rider to rider. But generally, the more aero you are the lower your resistance. I'd say the effects begin to gain prominence somewhere in the upper teen mph (30kph). Below that and the advantage go to being a light as possible. Then the tube/tires.
I'm not talking about being light. Tires/tube selection has to do with rolling resistance, which is far more significant than either of the things you're asserting.
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Old 02-17-19, 11:20 AM
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Originally Posted by Sy Reene View Post
I assume that it's actually relative wind speed that's important. It's not at all unusual to find days with eg. 15km/h tailwinds for portions of a ride's course.
It's not. Rolling resistance is constant. Uphill, downhill, headwind, tailwind, solo, in the group.

More significant than aero wheels.
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Old 02-17-19, 11:23 AM
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Tire size impact to aero

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Old 02-17-19, 11:24 AM
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Originally Posted by rubiksoval View Post
It's not. Rolling resistance is constant. Uphill, downhill, headwind, tailwind, solo, in the group.

More significant than aero wheels.
I was suggesting that aero wheel benefits can come more into play, even for us mere mortals who don't cruise at 30mph in calm conditions, but may be finding ourselves riding into a 10mph headwind from time to time.
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Old 02-17-19, 11:26 AM
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Aero at slower speeds

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Old 02-17-19, 11:27 AM
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Originally Posted by Sy Reene View Post
I was suggesting that aero wheel benefits can come more into play, even for us mere mortals who don't cruise at 30mph in calm conditions, but may be finding ourselves riding into a 10mph headwind from time to time.
But that's what I'm saying. The tires/tube comes MORE into play, regardless of speed.

That's why I said go with tires/tubes first over wheels for performance if you have to choose. If you don't, then pairing the both is best.

But aero wheels with crap tires/tubes will be slower than nonaero wheels with fast tubes/tires.
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Old 02-17-19, 11:34 AM
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Originally Posted by rubiksoval View Post
I'm not talking about being light. Tires/tube selection has to do with rolling resistance, which is far more significant than either of the things you're asserting.
No, they are not. I was being polite.
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Old 02-17-19, 11:37 AM
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Like anything else the engineering is all about nominals. Huge, deep section, carbon rims are going to be heavy & the aero benefits diminish the deeper you go.

A lighter less deep section rim might be better at a moderate real world cycling speeds because the forces required to spin up the disc in relation to the aerodynamic losses are less.

For mountain climbing or training rides around town, Aero just doesn't matter. Weight is king.

I seem to remember reading that Enve 3.4's were the best all-round wheels because with deeper rims 60, 70, 80, 90, whatever, the additional aero gains to be had at a speed you actually ride are thwarted the minute you come out of an aero tuck to scratch your nose or sit up to sneeze. For a TT that means that fraction of a second of gain of super deep section rims could easily be tossed & you could actually be slower because of all that weight you had to carry around & keep up to speed. But the Enve 3.4's were light enough to spin up easily & as fast as the lightest box section rims & were aerodynamic enough to be within the "sneeze margin" of the super deep rims.

The question is: "For what purpose will you actually be using your wheels?" Are you disciplined enough to get the full benefit of those super deep rims & strong enough to keep them up to a speed where they will work as advertised?

We live in a hilly area. I run 35's Maybe someday, maybe I'll pick up 35/50's, but in the end, since I'm not racing, it's just not worth the cost. Watt for watt, my fully loaded 70 pound commuter with panniers, 32 spoke Velocity A23's & 32mm tires is 1 mph slower than my 16 pound R5 with bladed 20/24 spoke count "aero" carbon rims & 25mm tires. Both have power meters. So I have the data. Between these seeming opposites there is hardly enough difference for general cycling & training.

The R5 is more fun to ride though and the obvious choice for an event. 1mph for a 5-6 hour century would be about 20 minutes of moving time between the two.

I hope I helped.

Last edited by base2; 02-17-19 at 12:01 PM.
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