For USA purposes, there aren't that many TTs where you can't use a beam bike. National Championships, and a few other UCI races. USACycling permits beam bikes. I've seen them in the TT stage of the Valley of the Sun Stage Race, for example.

Aero data on bikes without storage is pretty erroneous even if you're a pro. But the only ones that stripped down aero scores would matter for would be pros at the 70.3 distance and not 95% of amateur racers. If Aero is your number one priority because you think you're "there".

Biggest factor for me remains cost since most front end bikes are "close enough". But once you spend 8k on a bike you keep it for a long time.

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Washed up footy player turned Triathlete.

USA cycling requires a double diamond frame for time trials. That’s the rule, but I don’t know how much it’s enforced.

It's not a USACycing rule. Section 11 of the USACycling regs makes no mention of double diamond.

USACycling does have a regulation where they're required to add in UCI regulation for some types of events.

Below was stolen from 2023 Masters Nationals rules.




But for all non-nationals, non National Team selection events, it's not a USA Cycling requirement. You may run into race directors who decide to add it in as their own rule, at their discretion. I've raced against P5Xs and Dimonds in USAC events for sure.

Got it. All
Makes sense. Thanks.

Interestingly, Ceepo have re-released the Shadow, not with the weird fork but the standard one and they've now hidden the front brake cable. It would be great to see some aero figures on the Shadow and the Dimond Mogul/Ikon, just to see whether there is anything to be gained by these frames now that they've had a few iterations in their design. From what has been said here, the Ventum isn't all that slippery so perhaps removing tubes (such as seat tube or seat stays) is slightly overrated (with weight and handling issues - but maybe their application is on flat courses), and the focus should be on optimal tubes or placement thereof, such as the Ku.