The Conti 4K 25mm definitely rubbed in the rear wheel cutout. I have pictures to prove it from IM CDA 70.3 two years ago. Was powering against my frame the entire bike ride.

After playing with multiple brands and types (including Conti Force 25mm, GP4000s), I had rubbing issues with all 25mm tires so far. I’d stick to 23 to be safe

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MS: Exercise Science
Your speed matters a lot, sometimes you need to be very fast, where sometimes you need to breakdown your speed.

I run the 23s since the 25 rubbed

i can confirm i used conti TT 25mm (at 95 psi) and now put conti 5000 28 mm (at 85-90) and do not rub ...

i had to back out the drop out screws

There is a set screw allows you to move the wheel back 2-3 mm. It is located near drop out. We have been running 25mm Conti GP 4000, since day one, and now the 5000.

Why not just back it out a little by unscrewing the bolts in the rear drop out

It will fit easily

Yes I have no problems with running 25mm for most brands in the rear by backing off setscrews. It is the front where there is no adjustments and the tires rub on the top. I would love to see pictures of your 28mm wheel tire setup on front. I am trying to put larger tires on my ENVE 7.8s for a local race this weekend where the road conditions would warrant use of a Cross bike and not a Tri bike... guy I talked to said he did this race last year and recommends carrying 4 spares....

The Conti 5000 in 25mm is not as tall and wide as the previous GP 4000, so it will fit. In fact, the Conti 5000 has exactly the same height as the Corsa Speed in 25mm.

I run 25mm Gatorskin hardshells for daily trainers on my p5-6 and have no issues with rubbing. Race day I use 23 mm 5000s for the front and 25 for the back