Hoping this is just the lacquer...

[Globalti]

Just give the forks a good squeeze and tug while listening for creaks then carry on enjoying the bike.

 

[Heltor Chasca]

I agree. It looks nothing like a crack to me, I'd happily forget it and keep riding.

But surely any bicyclist worth their salt should ALWAYS be thinking of N+1. It’s a natural characteristic isn’t it?

 

[srw]

when I was cleaning the road bike.

I think I've identified the source of your problem. Sounds like an excellent argument for a dirty bike.

 

[Drago]

Is that a Tarmac? Anyway stop worrying, it's a witness crack where the thick glossy brittle paint has cracked as the frame flexes. Look at the ends of the chainstays where they join the dropouts and I bet you'll find other hairline cracks like this one on my 2009 Roubaix:


View attachment 452493

That's a forged part of the frame, not something I'd be comfortable with flexing sufficiently to crack the paint.

 

[Yellow Saddle]

That's a forged part of the frame, not something I'd be comfortable with flexing sufficiently to crack the paint.

The frame flexes where it joins the part. The drop-out flexes less. The paint cracks happen at the transition between solid and tube.