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How sun affects mountain bike tires & covering it would be worse

I think a lot of people just like me when they get back from trails would leave their bikes on the front porch and forget about it and call it a day.

But you should be careful about leaving your mountain bike out on the porch all day long leaving it to get some good amount of sun, but over time the sun will start damaging your bike starting from the paint and seat post and eventually damage the tires as well.

Tires are the treasured trophy of a mountain bike and the sun can get to them faster than you think it might do to be specific.

Tires are made up of natural rubber and synthetic rubber and Uv rays from the sun or heat exponentially increase their deterioration rate by many folds as time passes by, On shorter periods it may seem that nothing is happening but once the tires start detouring the process gets much faster.

So what happens when you leave your bike in the sun what effects does it have on the bike tires as time passes

What happens to bike tires when left in sun :

Over a period of a few months 1 or 2 months you will not notice any significant effects on the tires but what starts happening after 2-3 months is the scary part.

What happens is that the first few months when you are not noticing any effect UV lights from the sun and varying temperatures are eating away at the elasticity and flexibility of the tires.

Behind the scene what happens is that the UV lights are causing the rubber polymers to shrink, rubber polymers are the things that are responsible for your tire’s flexibility or hardness and they are breaking due to extreme shrinking and causing them to break.

Signs that your tires are getting damaged by the sun :

In those first 2 or 3 months you might not see significant damage to your eyes but here are signs that will tell you otherwise.

tires losing weight :

The first sign of the tires detouring in the sun are not cracks but the tires losing their weight, if you leave two brand new tires and store one inside the house and let the other bath in the sun you will see that the tire in the sun will start losing its weight month on month.

Tires becoming porous and air leaking :

When the rubber polymers shrink under the sun the tires start becoming more and more porous and you will often find your tires losing air in the sun.

Because the polymers are no longer tightly held together when they were new and that would cause them to make tiny holes in the tire which you would probably not be able to see with your bare eyes but they are definitely there and to conform it check your bike pressure often and you will see you are losing 2 to 3 psi more than you would normally do.

Well, you might say “ehh” it’s just 2-3 psi I can just pump that back but the problem is it will just get worse and worse at this point in time.

Cracks forming in the tires :

And the other effect you would notice after leaving your bike in sun constantly for 2-3 months is the cracks when cracks start appearing would be the time that you might notice all the effects the sun had on your tires.

tire rotiing

Cracks form on your tires because of the initial effects of them becoming porous as I mentioned above and at this stage, the rubber polymers and molecules are drastically shrinking and the carbon chain is rapidly breaking creating holes that are appearing in the form of those cracks.

If you notice these cracks early on it’s best that you shouldn’t store your bike outside or at high temperatures because if you leave it out there more the process will just accelerate at a much faster rate.

These are the three main indicators that your tires are dry rotting in the sun there are some other signs as well Like

The tires start to lose their strength they start becoming more and more light and fluffy due to the Uv lights from the sun.

in some cases, you will see chalky surfaces on the tires which is another big sign that your tires are deteriorating at a very fast speed and telling you to do something.

Storing bike outside with the cover on it :

unlike most materials rubber contracts when heated can give you a very good idea about leaving your bike outside with a cover on it.

To be more precise Leaving a cover or a sheet on your mountain bike is the same as leaving it in the sun it makes no difference and in some cases, it causes more harm than good.

What happens is that if you put a cover on your bike for an hour or two everything seems fine but then the cover starts conducting heat from the sun and heat has the same effect on your tires as the sun the rubber molecules start expanding again and the same process repeats as you already left your bike in the sun it makes no difference.

How long it takes tires to go bad in sun :

this whole process doesn’t happen in days so you don’t need to worry much that if you left your bike in sun for a few hours the tires will start rotting or cracks will start appearing, No they won’t but if you always keep dumping it in the sun here’s what will happen over time.

It takes 5-6 months for the damage to fully appear on the tire For 2-3 months the tire will slowly fade in color, lose weight and leak air more than it should after 2-3 months the tire will show wrinkles at first but the process will become much faster and it will dry rot in a month or two.

in the next 2-3 months span the cracks will appear rapid fast and from then on the tire will start rotting even if you don’t leave it in the sun anymore.

picture shows rotted rubber tire

if your tires are showing something like this there is a high chance that these cracks you see here will start appearing more and more

The same thing will happen even if you leave it out with a cover on it the outcome doesn’t really change by that much of a margin.

How to store your bike properly in summer :

Summers are slightly longer than winter in most parts of the world and usually, that is the time when you should pay attention to where you should store your bike because the heat can essentially damage your bike and especially your tires substantially.

The correct way to store your in summer would be to leave your bike in shade as much as you can even if you can’t store it inside, rather than covering your bike with a cover and using that cover to make a small shed for your bike that would be much better and productive because air will take care of heat to some extent but don’t leave it under a cover under the sun you will be essentially just doing the same thing as putting your bike in the sun.

But that is not the perfect way to store it because even if you will be saving it a little bit and your tires may last a little longer but still it is something if it’s impossible for you to store your bike inside.

And the best way to get around this would be to just park your bike inside or in your garage if it’s slightly cooler it doesn’t take a lot of time and I would urge you to do it daily it doesn’t take much time to just park your bike in a shady place.

Other bike parts that are most vulnerable to sunlight :

It’s just not your tires that are affected by the sunlight your bike paint and seat are equally or even more vulnerable to sunlight.

Even before your tires take significant damage in the sunlight your paint will be one that gets dimmer and dimmer and fades away.

The same thing would happen with your seat post and all other parts of your bike sunlight will dry out the lubricants you used on your different parts of the bike and they will start wearing as well some of them you might notice and some of them you may not even notice happening.


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  1. Pingback: Why bike paint fades in the sunlight and should you repaint it yourself – TRUSTY SOURCES

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