Vixar

Does it fit 25 mm tires ? What about 28 ? Also, should I be worried about such an old carbon fork ( Slice Ultra prodidy SI) ? Snap, crash… you know. Thank you !

Iride01 

Do you have the bike with tires on it already? Just measure the distance to the nearest part of the bike that they might rub on if they were bigger. Tire diameter increases about the same as the width is increased. Though if you go from a smooth tread pattern to a aggressive tread pattern the diameter might increase more. But between essentially the same model of tire the increase in diameter holds true.

Seat tube, brake calipers or bridge and fork crown are typical interference points I've found. Not so much the stays or fork blades.

You do want some clearance though. If you've ever ridden through some of the gumbo mud here that sticks like crazy to tires, then you'll find a small gap will bring you to a halt quickly.

Vixar

No, it's a bike I'm thinking to buy.

tFUnK

I've not been able to fit 28mm on a Cannondale R900 2.8 (pre-CAAD) nor on my Six13 (CAAD7 rear triangle). The limitations were on the rear, not the fork. With 25mm tires, they fit on narrow rims for sure; on wider rims, maybe.

25mm GP4k on a 14mm inner width/21mm outer width rim (26-27mm actual width). Picked up enough grains from the road (from dusty tarmac surfaces, not gravel or dirt) to wear down the FD clamp.

Just enough clearance here.

Camilo

I used to have a CAAD7 R2000. It would fit 28 mm tires. Actually I don't know if they actually measured 28, but they were some sort of Schwalbe labeled 700c x 28. They had little clearance in the rear against the seat tube, so little room if the tire picked up something that stuck to it. I perfected the pro skill of reaching my gloved hand back there to clean off the tire while rolling without getting said hand caught in the brake caliper.

Since I took the front wheel off regularly to use the fork mount in my vehicle, I had to put the wheel back on frequently. Unless I deflated it partially, it was tough to get the 28s past the front brake pads. It could be done though, just a learned process to pop it past the brake pads while aligning the axle and dropouts.

I switched to 23s just because I got a good price on some Michelin Pro Race back then in 23 and they served me well. I'm happy with 23s in general (yes, I've used 25s, they're fine too).

SoSmellyAir

I am (very slowly) building a CAAD4 and there is just enough clearance under the rear brake bridge for a 25 mm GP5000 mounted on a Mavic Ksyrium Elite wheel with an internal width of 17 mm. A 28 mm tire on the same wheel may be cutting it too close.

Lombard

I believe the limiting factor will be the chain stays. What tires are on the bike now? You really should have at least 3mm clearance on each side. Less than that and you risk rubbing when climbing hills.

To answer your other question, no carbon does not degrade with age. However, if the bike has been in a crash, that's a different story. Examine carefully.