My bike is only 6 months old and I typically don’t ride in wet weather, but my rear Shimano caliper bolts look terrible. Is this corrosion and should I be concerned?
I thought about getting stainless bolts from the hardware store but then went down an internet rabbit hole with people advising against that. I’m just worried these will corrode and I won’t be able to remove or adjust them down the road.
Seems odd. I’ve never seen caliper mounting bolts corroded so badly, no matter how old, and I’ve seen a huge number working as a bike mechanic for 5 years, not to mention all the bolts on our personal bikes. IDK what could be causing that, but you should try to figure it out. These bolts typically have thread-locker on them and are installed dry. If you use stainless steel and especially Ti, anti-seize would be called for.
Glad I’m not going crazy then 
Bought the bike at the end of November 2024. It was on my trainer for a few weeks over the winter but I can’t imagine that much sweat got under the rear caliper! Otherwise my bike has always been stored in a dry garage.
I’m leaning towards Ti for now I think and will plan to use anti-seize. Thanks for the tip!
I had thought maybe sweat, but on the rear caliper? I guess maybe a fan would blow it back, but there’d be a lot elsewhere. I’ve seen some really bad corrosion due to sweat on some bikes. I figure some riders sweat a lot more than others, and some sweat seems to be more corrosive than others. Looks like you have a ‘perfect storm’ going there.
Why is the tip of the corroded bolt have a special little nib?
Personally, I’d clean it up and then put a drop a paint or clear coat on the bolt head for protection. Or just use a dap of grease and then wipe off excess. You’ll get another lifetime out of it.
Not my pic, but it sticks out through the 160mm adapter so you can use a small retaining clip as a little extra insurance I guess.
Yeah I thought it was weird. I only had this on the trainer for a few weeks to dial in the fit. I usually use a dedicated trainer bike (aluminum hardtail with drop bars) and none of the screws on that bike look corroded. 
But do you sweat a lot?
Sweat can kill bikes and bike parts. I killed a pair of Speedplay pedals. It’s sweat.
I had sweat in surprising places.
I guess? Not saying you’re wrong but it just seems weird. This bike was on the trainer only for a few weeks and I have multiple fans. No issues in 18+ months on my dedicated trainer bike (no rust/corrosion on those bolts) and it seems strange there would be that much sweat making it to my rear caliper, especially with a fan blowing from the back.
I sweat ‘a lot’, and I often had puddles around the seat area, and under the bar ends, and when I started riding Zwift 6 years ago often had parallel rivers of sweat that ran out of my shoes, water that splashed out as I pedaled apparently. Enough sweat that it would tsunami off the mat and seep under it making moving it interest, it was nearly glued to the floor.
I killed the Speedplay pedals, and at least 2 chains (early in my career, and using ‘white lightning’ lube, since switched to waxing). But I don’t remember ever having corrosion on bolts/screws, but the damage I created was bad enough. I’m sure that sweat can cause all kings of problems. (Plug for smart bikes) Riding a Neo Smart Bike means I don’t have the exposure to (somewhat) delicate bike parts that aren’t normally exposed to the amount of sweat they got every time I rode. (Wondering how ‘sweat resistant’ the Zwift Ride is)
