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I keep my bicycle on a trainer in a 'cool' room during the winter months. The tires don't seem to maintain pressure after days of non use. Does this matter, and should I be checking/filling the tires often? What pressure would be recommended?

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There's no reason for the tires to lose pressure more rapidly in this scenario. Most likely it's just that you automatically pump up your tires before use normally but are not doing so on the trainer. Re pressure, don't let them run too low as that will result in too much sidewall flex and possibly "wrinkling" (which is quite bad for a tire). –  Daniel R Hicks Dec 31 '13 at 22:26

3 Answers 3

up vote 4 down vote accepted

Like car tires, bike tires can lose some pressure at colder temps (see: Why do tires "lose" air during the winter?) although I'd be surprised if your 'cool' room is cold enough for this to be a significant factor.

More likely, you are just seeing the normal slow loss of air pressure that bike tires experience all the time.

Since your trainer is a relatively "controlled" environment compared to a road, tire pressure is of less importance than it is on the road. If your tire is under-inflated you really don't need to worry about a pinch flat or the tire coming off the rim as you corner. Conversely, if it's a little over-inflated, you won't suffer bone jarring bumps or benefit from lower rolling resistance.

At worst, I think you might experience some accelerated tire wear. Of course, my trainer seems to eat tires no matter what pressure I run my tires at...

Sheldon Brown has a nice write-up about Tire Width and Pressure which you might find interesting even though it doesn't specifically discuss tire pressure when using a trainer.

Edit: I overlooked the What pressure would be recommended? part of the original question...

To me, the answer to this depends on what tires you are using. My current tires have a maximum pressure of 120psi and I run them at around 100-110psi. In the summer I check my tires and re-inflate before every ride due to the various reasons I've listed above. In the winter, I only check the tires occasionally as there is minimal drawback to riding a trainer with under-inflated tires.

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If the room remains at the same temperature, the change in pressure due to temperature only happens once (when the bicycle is moved into the room); it mostly two effects: leakage (inevitable) and the temperature change (from the ideal gas law, roughly, Change in Pressure = (nR/V) Change in Temperature where nR/V is a constant which depends on the shape of the tire (determining V) and the temperature and pressure it was initially pumped at (determining n), both of which are independent of the temperature at time of observation). So its probably some leakage in the tire (natural/tube damage). –  Batman Jan 1 at 1:05
    
I think the question was about the recommended pressure while on the trainer, not when riding... –  Alexander Jan 4 at 17:13
    
@Alexander After re-reading my answer, I agree it's not completely clear. What I meant was that I run my tires at the same pressure for riding on the trainer as I do for riding on the road. –  Jason Braucht Jan 4 at 18:02

While the other answers talk about using your current tires for use on a trainer, I'll take a bit of a different route. Tire manufacturers make special tires for specifically trainer use, such as the Continental Hometrainer (plenty of other manufacturers make similar ones, but the pricing locally for this one isn't bad - they typically run 25-35 dollars each if you shop around). These prevent you from wearing out your road tires prematurely (especially since only your rear tire wears on a trainer), are quieter and are more durable on trainers than most road tires (but are NOT suitable for off trainer use). You can run them up to the pressures suggested by the manufacturer on the sidewall or how much your rim can bear or possibly a bit more (though these are not necessarily optimal - play with them) - since there are no bumps or terrain on a trainer, you don't need to worry about overly bouncy tires or pinch flats or other hazards. See the link from Sheldon Brown in the other answers. I'd recommend buying a tire designed for trainer use, putting it on the rear, running it for the winter months, then swap it out for the usual tire when spring comes along. This should reduce your tire expenses over a few seasons.

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I have a single trainer tire in use for the third season now. Before getting one of these, my trainer ate at least one road tire per winter. Here in Germany, trainer tires are even cheaper than good road tires. –  arne Jan 2 at 6:20
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One thing that might also be useful is running a separate wheel with the tire for the trainer, if you have weather such that you want to ride outside somewhat often. This can also be useful if your rim and trainer tire choice are a tough combination to get on, though likely not worth the expense if you don't have a spare wheel (plus, you can hide the garish colored trainer tire a lot easier this way). –  Batman Jan 2 at 14:02
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Actually, getting a used wheel as trainer wheel shouldn't be too expensive. You don't need the high-end carbon fibre wheel anyway because nobody will see you and the aerodynamics are more or less negligible in the basement. –  arne Jan 2 at 14:19

I would recommend the normal tire pressure, because lower pressure cause unneeded vibrations, noise, tire slips over the trainer, tire excessive wear, and also different resistance if you using speedometer as a powermeter.

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