We own a 2014 coupled Co-Motion Supremo that is 8 months old, with approx. 1500 miles. It has seen 6-7 hours in light rain & has been washed with soap and a hose 3 times.
When relocating the Di2 battery this weekend I noticed a light brown substance (rust?) in both seat tubes. I was not totally surprised to find this. What I was surprised to find was rust in the top and boom tubes. Some of it comes off with just a good rubbing from a towel. Some is quite stubborn. When I put the bike back together, I will use Frame Saver in hopes to stop this issue. Has anyone else had rust issues with Co-Motion steel bikes & should I be worried. I contacted Co-Motion, but have not heard back yet.
Much thanks

Easy way to determine if it's rust, brush a little naval jelly on it and see if it turns black.

Owned a custom (steel) Co-Mo tandem and rode it for 56,000 miles. Never had a rust issue but then we don't do much rain here in AZ.

if a steel frame hasn't been painted on the outside or coated on the inside in some way it will rust. the nice thing about rust on the inside is that the rust is well protected from the elements. and that rust can somewhat protect the inside from more rust, like titanium oxide protects the outside of titanium frames if not disturbed too much. it's just doesn't protect as well as titanium oxide or aluminum oxide. of course if water is forced into the frame or allowed to drain into it and disturbs the rust, new rust will be created and over time the inside of the frame will disintegrate.

if i were planning on washing my bike with a hose and did not want take the trouble to avoid water penetration points like the headset, bottom bracket, water bottle holes, chainstay holes, etc. i might look into having the inside of the frame coated with some sort of rust-preventative, as mentioned.

No. It doesn't work that way with steel. There is no protective coating, the rust cycle just gets worse.

I NEVER use a hose on my bikes! I use a small spray bottle and spray a diluted solution of water and simple green on the frame etc. being very careful to not get water in any of the bearings. Why use a hose on a bicycle? If you take about 10 minutes after every ride to wipe it down it will stay amazing clean.

Noticed rust in my steel frame a few years ago and used this coating. It has an available 24 inch spray tube with a four way nozzle. A little messy because it is thin and runs out of the frame. Immediate clean up is necessary.

[h=1]Eastwood Anti-Rust Aerosol with ext Nozzle Amber[/h][h=3]Item #26018Z[/h]
Eastwood Anti-Rust Aerosol with ext Nozzle Amber

LOL. Our bike gets "hosed" quite frequently in the winter. In fact it comes back from a heavy rain ride a lot cleaner than when the roads are merely wet. I have to wash it after those rides, and yes, I use a hose.

But that's the reason I use a good chain lube and sealed bearings.

How to wash a bike:
https://www.bikeforums.net/road-cycli...ash-yours.html
Yup, I have the chain holder thing and all the brushes.

I once used one of those anti-rust coatings on a bike without totally stripping the frame first. Ruined the BB which wasn't sealed on the inside.

Our tandem only gets the "wet rag" treatment. When we first purchased the bike, we hauled it home on top of the van, it rained for three hours, very unusual in CO, but when we went to do some seat adjustments, guess what I found in the seat tube? (water) I try to keep the water away, Carbonfiber has no chance, but, "that's the reason I use a good chain lube and sealed bearings."
R&J

I heard back from Co-Motion today & I believe they are in Hueyhoolihas's camp. They state: "The rust inside is superficial and actually adds a protective layer, despite that sounding counterintuitive." I don't know enough about metals to have a valid opinion, but it seems to me $5,000 frames should be protected against the possibility of rust in some way. That said, I knew it was not and am sorry I didn't use Frame Saver when new.
Thanks for all the comments.

Steel needs a high chromium content to form a protective layer (chromium III oxide), which is why stainless-steel exists. "superficial" rust will continue the rust cycle, surface rust leads to pitting corrosion. You can stop it with frame-saver or something similar by cutting off oxygen from reaching the metal (whether you remove the rust first or not). If you want to remove the rust, try the classic/vintage forum for threads on the topic. I flushed out a paramount with phosphoric acid with good results. There's a pretty good article on the Sheldon Brown site covering rust removal.

We rode our coupled speedster for 13 years prior to selling it last summer. That bike rode through rain, snow, salted roads, along the ocean, and never showed a spot of rust. Each year I removed parts that could allow penetration of moisture to the inside of the frame (seatposts, water bottle bolts etc.) and applied a good coating of Phil Wood grease. I regularly rubbed down the outside of the frame with turtle wax, so I suppose that was my version of bike wash soap.
Hope you enjoy many good miles on your new tandem.

Joe