I just installed a set of Pirelli PZero Velo 25mm tires on my 2017 S5. The front tire clearance and frame clearance is fine but the rear caliper clearance only appears to have about .5mm clearance. I think the plastic mounting piece sits too low. I was thinking adding some spacers might "raise" the caliper. Previously I had Continental 4000s II 23mm because the 25mm had the same issue. (I think tire rubbed while riding and hitting bumps)

Also considering installing Shimano r8000 brake caliper (seems to have more clearance). Any other suggestions? (see pics below)

Not only that, it will also rub the chainstays under hard pedaling. Remember a 25MM tire is probably going to measure 27 and the S5 is designed for 25 max. The conti 23 when used with widght rims should meassure 25. I had the same question last week and a cervelo rep explained that to me on this same forum.

Here is the post https://forums.cervelo.com/forums/t/16534.aspx

Thanks for your reply...I ordered a DA brake caliper as I think it has better clearance. When I had the 25mm Conti's my only concern was the brake caliper, chainstays seem to be OK. I'm not a "powerful" rider more of a spinner.

 

When I had the 23mm Conti 4000s II, I had about 2mm of brake caliper clearance, currently only have less than 1mm.

If you want to be sure, put a black take in the inside of the chainstays and go for a ride. Come back and check the tape and you will see the tires mark on the tape. Better safe than sorry :)

I'm sure it will be fine...

I already rode a few times with the Conti 4000s II 25mm when I first got my S5, no marks inside the chainstays, just the brake caliper clearance at the top the issue for me.