I’m gonna say probably slightly slower with the new set up. The H3 is one of the fastest wheels ever made and hard to beat any type of disc. Of course the jet wheels will probably have slightly lower ruling resistance if you put 25 width tires on them and the tire to wheel transition will obviously be more aerodynamic . But I still say in the long run slower or smaller detectable difference than the margin of error.
Having said that you probably should still buy the jet wheels as a back up set they are great wheels and for the other reasons you described. Could always put a cover on the rear wheel. Then they’d be about as fast. Unless you’re considering disk brakes in the future which will make you even slower.

The H3 is called the GT3. It is the wider format for newer tires. He has the older one, an HED 3. Essentially only really aero with the 19mm tires fitted. They CAN fit 21mm tires, but at that point you threw out the benefit. I emailed some HED folks a year ago about tire suggestions since I owned one, and 19mm was the go-to size for aero on an old HED 3.

On tires that size on some roads you're bouncing all over the darn place.

Also, there is actually data that shows with a fair combo of tire and CdA that most things like a modern Jet 6+ are faster in TT scenarios than an old-school HED 3. And arguable a 6+ is same speed as a 9+ at low yaw angles.

He should either get a 6+, 9+, or newer wide trispoke. I'd go with the 6+. I own one and love it.

He's stated that he is using a 20mm w/latex on his front. Not sure how much faster, if at all, a Jet 6+ would be? Splitting hairs?
And his current rear disc is likely just as fast or faster than a Jet 9+.

I love the Jet black wheels, but I think his gains are gonna be marginal or nil by making the switch.

In ideal conditions, right.

How are the roads there? I can't afford to own wheels I use when the one day a year hits that it's brand new tarmac and the yaw is going to be nil.

I guess I'm looking at it from too much of an overall point of view than an "absolutely optimized" scenario.

Looking at my power data from rides on both those exact wheels on the same road I had to "ease off" for probably a whole 30 seconds out of a 10mi TT on the skinny tired wheel. The plus model on modern tire, I was in the beans for the whole time. 30 seconds of "near zero" power during a TT is a mammoth problem.

So, sure..........it's faster if in an optimal scenario. I've not found that scenario I could use one in with a skinny tire.

Point of order that the GT3 is the tubular version. The clincher version is the H3+. They stopped making the rear H3+ a couple of years ago and it looks like they no longer make any tri spoke.

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I come to that same question occasionally, and am reminded of this chart (which you probably have seen before, given your tire and tube choices). I'll keep using a skinny-tire h3, and I haven't heard of any plans to discontinue the ss20, so I don't think availability is a problem.

http://bikeblather.blogspot.com/...ng-caught-up-ii.html

Thanks everyone, I appreciate all of your replies. I’ve always thought that the narrow H3 was a fast wheel but at the same time I’ve been interested in trying wider rims and tubeless setups. I guess I’ll have to think about it a bit more!

Good find on that chart. Looks like the H3 w/20mm supersonic tire would be at least as good as the Hed Jet, probably better. Then it comes down to the rear wheel, the wider Jet would have a rolling resistance edge but the disk probably would overcome that advantage with superior aerodynamics. Thus, based on Tom A’s data I would say the older setup is faster.

The H3/Disc setup is really hard to beat aerodynamically. It doesn't handle as well in crosswinds, and us unforgiving stiff (both due to the narrow tire, and the fact that the spokes work in compression [vs a spoked wheel that only works in tension])...but damn it's fast (esp. in crosswinds).

I have some J6+ wheels on my roadie, and they are great (aero, comfy, awesome cornering); but I wouldn't swap out the narrower wheels with better aero profiles for them in a TT/Tri.

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If you have a stash of the older 20mm GPSS tires, you won't beat the H3 up front. This is an absolutely killer combination. I've never tested the newer GPSS20mm but it might be fine? If you really want to update, why not go Jet9+ up front? That's a very good replacement -- lighter than the H3 so faster uphill, faster at high yaw, slower at low yaw. Also IMO no real point in replacing your disc, but if you really want an 11sp the HED Jet+ disc is a great replacement. Jet6+ will be slower than a disc.

Keep in mind that everyone is switching to disc brakes right now so it's probably not a great time to buy new rim brake wheels, though it could be a great time to buy used ones.

Also, just a note to help clear up the confusion above: the H3 (or Hed3) is the older shallow trispoke available since like 1990 (under Specialized way back). It came in both clincher and tubular models. The H3+ is the wider/deeper clincher version that was made for only a few years ~4-5 years ago. The GT3 was a wider/deeper tubular version that was also only made for a few years ~4-5 years ago.