All I can say is that they are very close-fitting. My tyres are 700x23 and I spent a fair amount of time getting them to fit without rubbing. I think you may have problems with 700x38 tyres. Hope this helps.

No the manaufactures state a maximum of 700c x 25mm.

I fitted then to a Giant Defy 4. Needed a little trial and error but once fitted no issues

The mudguards are clamped to the brake calliper mounting bolt with a cable tie. You should find that, even if you only have 6 or 7mm clearance between the tyre and frame,they will fit OK. However, a bit of patience may be required to get the perfect fit.

Thanks for response. I've actually fitted them and found: as mentioned they really do need a bolt to attach to so if you don't have caliper brakes the best bet is to install a bolt where the brakes would be and then zip tie the mudguard to that. If the frame is not drilled/tapped for a bolt there, then it'll take some creative thinking to attach the mudguards securely - attaching the guard directly to the bridge in the frame probably won't work as it'll twist the guard out of line.

Don't know about the Feltz35 but on my Roubiax which seems to have a pretty narrow fork, they fit fine. Also note that if they do not fit a narrow fork, they would be very easy to trim a slight notch into so that they would set inside the fork nicely.