Full Disc Rear Wheel vs Deep Section for Triathlon and TT

Hi,

I have a 2018 Cervelo P5 and use Enve 7.8 wheels to do some local TTs as well as Oly, HIM, and IM triathlons. I’ve been exploring full disc rear wheels and contacted ENVE, Zipp, and Specialized about their offerings and wanted to get some group wisdom.

Per ENVE, they say riders are better off on their deeper 7.8 wheelset vs. their newly released disc wheel if they cannot sustain 27+mph. I cannot sustain that over the course of a race.

Per Specialized, their new Roval 321 disc is only 4 seconds faster over a 40K TT (across a variety of yaw angles and speeds). I was shocked they claimed only 4 seconds faster.

Per Zipp, they wouldn’t give me a watt or time saving for their Super 9 disc wheel, but sent me a CFD picture showing me the drag coming off a 808 rear wheel vs. Super 9.

My A race next year is Ironman Arizona which is characterized by a 10-12 mile 1-3% grade going out of town, which riders get the benefit of going back into town (I assume 27+ mph possible for this part, depending on wind).

All of the data from the companies is pointing me towards NOT upgrading to a full rear wheel, but I wanted to hear from those of you who may run a full disc. I know the TR crew used the prototype ENVE disc wheels in their time trial effort this summer, but perhaps they can maintain a very high speed. I’ve got no interest in a disc cover given I’ve got some pretty good wheels already in the 7.8s.

Any thoughts and expertise will be appreciated!

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I can only offer anecdotal evidence. I too run a set of Enve 7.8’s. I also have a HED Jet+ disc. In even the slightest crosswind to more severe crosswinds the disc has been faster. Sorry no data to back that up. When wind is very still I can not see/feel/observe/record any difference. FWIW I used the same tires and same brand and type tubes inflated to the same pressure.

Living here in PHX the AZ Ironman course will generally see a crosswind and if it were me my disc would be the way to go. Anecdote #2…my buddy who competed in this years AZIM used my disc and PR’d the course. He said he attributed the disc as one of a few reasons. I understand that’s like saying shoveling the drive way is the reason I won, but that’s all Ive got.:grinning:

With all that said, the 7.8 is the fastest darn wheel set I’ve even used. I would not run a disc just for the sake of running a disc. For example a super narrow old school disc (IMO) would be slower than the 7.8 SE rear. Also Conti TT or GP5000 with latex FTW!

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It may be worth looking at Hambini’s data from testing a range of aero wheelsets in a wind tunnel.

(The relevant graphs can be found about 2/3 of the way down, with testing at 30 kmh and 50 kmh.)

His general conclusion is that power required to maintain speed decreases with increasing rim depth (with only slight differences between brands) but his control test of a full disc wheel does show an improvement over even 80mm wheels - especially at higher speeds.

Note that Hambini’s inclusion of shorter transients at different yaw angles in his test protocol has been somewhat controversial from the point of view of existing test data.

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I read this article several times before pulling the trigger. Decided to go for a disc and I will use it under any condition. There’s a lot of talk about it online with different gains but I think it is a consensus that discs are faster, the discussion lies more on by how much.

Here’s my anecdotal point of view. I race TTs using 80mm wheels. I compare well to riders who use disc wheels when the wind speed is low. However, when there’s a nice cross wind the same disc wheel guys seem to do better. It’s like the disc acts as a giant sail. Sometimes I get that benefit even with my 80mm wheels but I’d say it’s more pronounced with a disc wheel.

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Most, if not all of the pro’s seem to run a disc wheel for any major time trial. That said on a recent semi hilly circuit I saw Luke Durbridge running an 808 size wheel front and rear.

I always look to what the pro’s are running however, it’s interesting what ENVE say about the benefits of the disc only being reaslised above a certain speed. Almost had me thinking I needed some 7.8’s :grinning:

Same with Track cycling. You see almost all guns on the 5 spoke front and disc rear as the fastest combination. Not claiming to be a pro (so far from it), just my observations.

Sorry to bring this back up, but I’d like to further this discussion.

I’ve been running a Flo90 with a disc cover but I am re-assessing this setup.

I did aero testing between an ENVE 7.8 front and a Flo90 front and found the ENVE is only slightly faster (275 watts vs 276 watts for 41kph). But I am upgrading to the new Flo range which has almost identical widths so might remove that difference (or see the new Flo77 faster).

Flo isn’t making a rear disc in their new design.

What I have heard about rear discs is:

  • Generally a disc is faster
  • A rear cover looks to be the same as a disc, but like everything, there is variance (such as interaction with your frame etc)
  • Swiss Side said putting a cover on their fastest rear wheel made it slower
  • As noted earlier, ENVE says a rear disc is only relevant over 43kph. Which doesn’t work in my mind. Disc helps more the higher the YAW. The faster you go, the lower the YAW. So I would think a disc is better at slower speeds.
  • Aerocoach states moving from a Zephyr pair to a Zephyr+disc saves you 7 watts at 45kph (https://www.aero-coach.co.uk/store/AeroCoach-AEOX®-ZEPHYR-aero-wheels-p201820888)
  • Flo states their fastest disc vs fastest wheel, saves you 10 seconds over 40km at 48kph over “common” wind angles https://www.dward.us/files/images/flo/TimeSaved.png
  • Flo’s numbers state the higher the YAW, the more you get out of a wheel, even a disc https://www.dward.us/files/images/flo/TimeSaved2.png backing up my thinking from earlier.

It does seem like a rear disc (cover or built disc) is faster than a deep wheel. But not all agree. I think a disc is faster, but making more of a difference the slower (and/or windier) it is.
To add more evidence to that, Flo found their Flo60 carbon was faster than their Flo90 at 0 and very low YAW but then the Flo90 becoming faster at higher YAW (about 7 degrees and higher). Looking at the specs, the most obvious reason is the Flo60 is a little wider, so matting better with the tyre at 0 and low YAW, but the depth of the Flo90 gives it an advantages once the YAW angle increases. Once again showing a deep wheel helps more the higher the YAW which you see when you ride slower and/or a windy day.

Anyway, interesting discussion, keen to discuss further.

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Everything you need to know

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I tend to go with Hambinis line of thought, a static linear airflow is not realistic in the real world on the road. Id tend to go with his findings over manufacturer claimed results. Looking at his results a disc is clearly faster, by how much will depend :slight_smile:

Hambini is an idiot.

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Always use a disc if you have the option…unless the course ends on a climb. And even then, you should probably use it.

Now, it is only marginally faster than some of the fastest deep rim rear wheels…but iit is faster. Does the small time gain justify the cost? Only you can answer that question.

Just make sure you get a full car in construction…gotta get the “whomp whomp whomp” sound. :sunglasses::sunglasses:

id agree in a lot of ways, but doesnt mean he is wrong

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Hambini’s posts and videos are becoming increasingly offensive and attention seeking. That doesn’t mean his wind tunnel data is wrong.

Of course, it is probably easier to just “cancel” the entire output of anyone who has expressed any offensive views, rather than try to understand what they might be saying about a complex field like aerodynamics.

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Yep. This is the real benefit of a disc wheel.

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I don’t have an answer yet, but new 90/90s will arrive this week and I’ll then be Chung-testing the 90 rear vs. disc cover on my tri bike. If others do the same we might be able to generate a meaningful data set?

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Discs are always faster - Froome even used it in a mountain TT in the Tour which he one. That said I used to do tri but now just TT so I would say that…wind is not an issue as you are sitting on it and a deep front will cause more problems. Plus modern discs are pretty light…if you have a decent modern disc - ride it! :grinning:

They guys at Flo say always a disk, unless a pure hill climb.
I went with 60/disk at Ironman Wales and that has 7000ft of short sharp hills but still plenty of flat/rolling. And my Flo 60/disk are actually the same weight at my TT bike stock wheels

Disc wheel every time apart from Ironman Lanzarote where they are banned.

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As the saying goes, extraordinary claims require extraordinary evidence, and Hambini has repeatedly failed to present any. When questioned, he goes into attack-dog mode against those who dare to doubt his self-perceived brilliance. I don’t understand why anyone would buy into his schtick.

And Kona.