I just heard someone say that riding in cold temps and then bringing your bike inside tour house will make condensation form on the inside of your bike, causing rust if it's metal.

Is this true?

Yeap, that why you use a product like Frame Saver or linseed oil inside your frame.

yes.

To a point. Generally a heated house will have more moisture in the air. When you bring in your cold bike, the cooling air surrounding the cold metal can't hold all the moisture that it contains causing condensation around the tubes.

One way of preventing such condensation is to store your bike in an unheated space like a garage. Honestly, however, unless you are taking your bike in and out a lot I wouldn't let it upset me.

I wonder how much of that holds true when you look at it in detail.
Sure, warm air can hold more moisture than cold air. So bringing a cold item into warmer surroundings can cause condensation.
But you asked about inside of frame.
Question then becomes - what's the moisture content of the air inside the frame?
If the air inside the frame is "outside" air, cold air, it'll have a lower moisture content already. Anything wanting to condense would have done so already.
Bringing it inside shouldn't do much, if anything.
To get any heavy condensation going, you'd first need to fill the frame with moisture-loaded air, which then gets cooled to condensation point.
How well do you think a frame "breathes"?
On top of that, air expands when warmed. Bring a bike inside, and it'll breathe OUT - not in. When brought back outside, then it'll try to suck some air in. But that'll be cold, fairly dry air.

there are many 'metals' where this would not be true.

My feeling is not much condensation, maybe none. But I can get a lot of water in the frame from riding in the rain, especially without a rear fender.

Opposite, hotter, humid, damp, vapor, condenses on surfaces, when it is cold enough (@ Dew point).

water or whiskey, same physics..

I agree with dabac that this would be a very minimal problem at worst. Bringing the bike inside will certainly result in condensation on the outside of the frame when the cold metal surface comes in contact with warm air containing more moisture. But that moisture will evaporate pretty quickly as the bike warms up and the outside of the tubes should be protected by paint. OTOH, the air inside the frame would be the colder, drier outside air and bringing the bike inside wouldn't result in condensation unless you blow warm moister air into the interior of the frame tubes.

There might be some minimal condensation inside the frame when the bike is brought outside after a long period inside so the air inside the tubes has gradually mixed with the more humid air inside the house. But I'd expect the amount it be minimal since 1) there isn't all that much air volume inside the frame tubes and 2) even the warm interior air in most homes will be pretty dry during cold weather.

Really? Are you guys for real? The absolute optimal place to keep a bike would be inside a space with conditioned air. However, those spaces are usually reserved for humans, not bikes. Duh.(How old are you, kid)? (Sounds like somebody's Mom is trying to keep their kid from bringing their bike into the bedroom to me).

Fietsbob has it.

Yep, it is so true that you ought to go out right away and drill some holes at the lowest point on the frame so you can drain all of the water out of the frame before it becomes a pile of ferric oxide unless of course it is aluminum and then it turns to goo.

This is a solution in search of a problem. For most homeowners, the heated space inside a home has a humidity level approaching that in the desert during winter unless you install a humidifier on the furnace. Cooking and washing do add some humidity but not much. Cold outside air contains little water vapor and when it comes inside the house (all houses leak outside air or you would suffocate) and is heated, the relative humidity plunges as the air is heated.

I've had steel bikes that were up to 35 years old, ridden frequently in the rain, and never had a problem with the frame rusting from the inside. It has to be really rare. I also don't know anyone who has had a frame rust from the inside. If you live along the ocean with the salt spray, it might be a different matter as salt water is much more corrosive.

Before I get a bunch of nasty replies, I hope you realize that I was being facetious with the first paragraph.

If you keep it in a shed/garage without heat, it will still be exposed to condensation from changing temps, but it won't dry away like it would in a heated home with a warm air, ventilation system. My bikes always come inside the house. No way I would leave them in a cold damp place to get and stay wet.

This maybe true for you, according to your location you live in a desert. The rest of us who live in high humidity areas condensation can be a problem. It is not so much as how much damage some condensation can cause, it is the fact that it gets the damage started. Condensation can lead to rust inside a steel frame. I do not mean to trivialize or offend any person with cancer, but rust to steel is very similar to what cancer is to a person. You want to do what you can to prevent it, not find a cure after it has happened.
Most bicycle will have weep holes to allow for some air circulation and or evaporation, but some will still get trapped in the frame.
I wonder just how many old steel frame bicycles have been ruined by the steel seat post rusting together with the seat tube?

Vegastriker is correct. While condensation might lead to rust, it will be a minor problem. The physics of air works against it. First, as others have noted there is less humidity in the air anywhere during cold weather. When it is cold (or when the altitude is high), the amount of water that can be carried is much less. You won't be near the dew point when you take a cold bike into a warm building when the outside air is already carrying less water. Heating the air drops the dew point even lower so the inside air has an even lower relative humidity.

Simply put, taking a bike...or anything...from cold air to warm air doesn't result in condensation of the water in the air inside the bicycle frame.

The "weep" holes you see in frames...usually in the chain and seat stays...aren't there for evaporation. They are there to allow for gases to escape during manufacturing of the frame. If you didn't allow the gases to escape when the frame is heated, you'd pressurize the inside of the frame and the joint could be compromised.

Lots of frames are ruined from seatpost corrosion of some kind or another. It's more common for it to occur when using an aluminum post and a steel frame or a steel post () in an aluminum frame. But this is easily preventable by providing a barrier of grease. However, the froze posts that I've seen aren't the result of simple condensation but are the result of water infiltration due to rain. A bicycle stored inside and not ridden in the rain is highly unlikely to ever experience a frozen seatpost.

Just get a ti frame.

Good try, but wrong. Steel + air + moisture= rust. Most all tubes made today are treated to combat/ slow the process. That along with products like Frame Saver or linseed oil will go even further. Riding in the rain can add to the problem. The weep hole is there for two reasons. 1: not to blow the weld out with gas pressure built up inside the heated tube; 2: To allow for condensation to escape. It would be super easy to weld up the weep holes if they were not necessary.

Aluminum and steel create galvanic corrosion, it happens a lot with dissimilar metals.

And the vents through which the air must be exchanged are quite small, meaning it will take some time for the water vapor in the air outside the frame to reach equilibrium with the water vapor in the air inside the frame, and by that time it is likely to have thoroughly warmed, limiting the degree of condensation.

Perhaps you should revisit your chemistry. Yes, steel in air in the presence of moisture does cause corrosion but there is also the matter of concentration. At the freezing point of water, the amount of water that can be carried in air at the dew point is 3.8g per kilogram of air. A kilogram of air has a volume at standard temperature and pressure has a density of 1.3 kg/cubic meter or 1.3kg/1000 liters. So on a liter basis, saturated air contains 3.8 mg...that milligrams...of water. The volume of the tubes in a bicycle is, roughly, 1 to 2 liters. Let's assume 2 liters.

If you could wring out every last drop of water from the air in the tubes of a bicycle you'd have almost 8 mg of water. 1 milliliter of water weighs 1g. You have 0.008 g of water available in the air in the tubes of a bicycle. It's not much and certainly not enough to cause much rusting.

Additionally, the air in the tube is warming so the possibility of condensation is going down.



Think about that some more. In order to "weld" the weep holes closed, you'd need to heat the tube and the gas inside the tube so you'd need vents elsewhere. On the other hand, you can close up the vents with sealant and never have a problem with rusting.

By the way, aluminum has the same "weep holes" and there is no need to worry about water corrosion with aluminum.

pardon any duplication, I didnt read the entire thread.

But this is NOT true.

Bringing a cold steel frame indoors will cause condensation on the OUTSIDE, not on the inside.

However, bringing that bike back out from a warm, humid environment to the cold outdoors will cause internal condensation. The key here is the rapid chilling of moisture laden air, by contact with cold steel. The issue depends on relative humidity, and may not matter in places like Colorado, but may in places like New York, or Boston.

Also, keep in mind that heated indoor air has low relative humidity, and that modern frames are closed systems, so this worry may be a relic left over from an older era. When I first riding 50 years ago, we did see some steel frames rusted from the inside out, but I haven't heard so much about it in the intervening years. That may be because it's no longer as much of a worry, or that folks are better at internal frame prep.

PSA: if you ride in conditions where you end up with water in your frame, and you live somewhere the temps drop down to below freezing, do not store it outside or in an unheated space without getting all that water out, especially from the chain stays, regardless of material your bike is manufactured with...

This is the most important point of your post. I would go further and say that winter air that has been warmed to heat a building has a low absolute humidity since the cold air doesn't have much moisture in it to begin with. This is the reason that taking a warm bike from a building out into the cold air shouldn't be of a concern either. As pointed out above, unless the building is humidifying the air, the amount of water in the air is going to be low as well.

Additionally, any air that is trapped inside the frame is going to warm and moisture doesn't condense out of cold air on warmer surfaces.

I think that it was more common to open up older frames so that water could drain out of the frame. There were a lot of bikes made with cutouts in the bottom bracket which, if you think about it, is not the best way of keeping water out of the frame.