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!

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.

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.