Rusty rotors

So my Sram centerline rotors which are only a few months old are showing rust in a few places on the arms (for lack of a better word) of the rotors. I’m wondering why this has happened since they’re made of stainless steel so shouldn’t technically rust.

I’m wondering if they’re just made of a crap grade of steel or I have got a defective batch?

Either way, will probably just get them warrantied. Just wanted to know if this is common with Sram rotors since I have never seen a decent brake rotor rust before.

I’d probably just rub the rust off to be honest.

Stainless doesn’t mean they won’t rust, just it comes off easier. Bit of wire wool will sort them out, make sure your bike gets dried properly and is kept somewhere dry.

….Bit of wire wool will sort them out….

bit of stainless steel wire wool will sort them out – many years since worked in selling stainless steel but I can still spot a urinal that has been wire brushed with a bog standard non stainless wirebrush

Brillo pad works

Although I have wondered if it was ‘leaking’ from the sintered pads down the arms and staining rather than corrosion of disks themselves

Stain-less doesn’t mean stain-never.
There are a number of reasons for and mechanisms by which stainless steels suffer from various types of corrosion.
Also, as has been observed, run off from pad backers etc. might give the impression of or initiate disc corrosion.

Thanks for the replies. Yes, I’m aware that stainless steel is not rust-proof, but a decent quality stainless steel should not rust going through nothing worse than damp mud.

I did think it may have been the pads, but the pads are the same ones I’ve been using for years (nukeproof semi metallic) without any problems, so that rules the pads out.

I know it’s more of a cosmetic thing than anything else, but mtb rotors are put under a surprising amount of stress and temperature gradients repeatedly (especially at inners and the golfie), and as such, the steel in brakes should have a reasonable quality so that the metallurgical structure is more resistant to these large temperature variations and consequently more resistant to effects such as rusting.

I’m probably reading too much into this but brakes are one of the more important parts of a bike imo, and its not something I wish to cheap out on. Probably should have just stuck to shimano, been using them for years and never seen rust on them.

Winter road salt contamination would do it.

Unusual though, I’ve never had rust on an rotors (not even years old rotors) despite bikes previously being stored in a very damp shed. The only time I had some small amount of rust on a rotor was when crc were selling off flood damaged stock a good few years back 🙂

more resistant to these large temperature variations and consequently more resistant to effects such as rusting

Does one follow the other?

Salt causes ‘tea staining’ of stainless steel. It’s worse with brushed/machines surfaces. We certainly see lots of it on stainless building furniture so I’d imagine it’s the same with things like disc rotors.

https://www.plant-maintenance.com/articles/Tea_Staining.pdf

Pleased it’s not just me – I’ve four rotors which have rusted at one heck of a rate this winter. I’ll probably switch to shimano when they need changing, if only to help the bike look less tatty.

I probably should update this thread. Had enough and forked out for a set of discobrake floating rotors and guess what? In the same conditions that caused my Sram rotors to rust, the disco rotors have not even came close to rusting, pleasantly surprised at the quality of their rotors considering that they’re a lot cheaper than the Sram rotors.