February 2015 Trail Conditions

[GB]

The tire says not to exceed 70psi. I pumped it to around 60 (10 miles is pretty far at 40psi).

I actually blew out this tire when mounting it originally. I figured that was due to careless mounting. I’ll take it to a shop (FB is next to the office) and have it professionally mounted this time.

I have 100% had an MTB tire blow form over heating before. It was on the roof of the car on a hot sunny day – not the same as in the office, but then again I inflated that one on a hot sunny day.

I’d guess that MTB tires were more susceptible to this bece of there increased volume.

[dasgeh]

Does anyone else feel a little alternate-universe-y when the trail conditions thread is talking about blowing tires and the morning commute thread is talking about ice on the trails…

[rcannon100]

@dasgeh 108039 wrote:

Does anyone else feel a little alternate-universe-y when the trail conditions thread is talking about blowing tires and the morning commute thread is talking about ice on the trails…

And the cemetery thread is talking about puppies…..

[dasgeh]

@rcannon100 108040 wrote:

And the cemetery thread is talking about puppies…..

I thought it was talking about do sh*t

[hozn]

@GB 108038 wrote:

The tire says not to exceed 70psi. I pumped it to around 60 (10 miles is pretty far at 40psi).

My guess is that pressure is too high for your rims. I would just inflate to max 45psi.

Edit: a brief googling suggests this may be wrong. Or, more specifically, it depends on the volume of your tire. Larger the tire, lower the psi that the rims will be able to handle.

[dkel]

@Tim Kelley 108027 wrote:

Someone once told that one Bar is about the equivalent of one Atmosphere, and that one Bar is about the same as 14 PSI, so if you took your bike from sea level to the moon, the most you could lose was 14 psi. I stopped worrying about changes in temperature and over inflating my tires after that.

Can anyone more science-y confirm that I’m fine riding my bike on the surface of the moon?

I asked the interwebs about this, and you would be gaining (so to speak) that 14 psi of atmospheric pressure inside the tube when on the moon. That 14 psi was in the tube on earth, but counterbalanced by the atmosphere; now without the atmosphere, that 14 psi is added pressure on the inside of the tube. If your pressure is already high enough that 14 more psi would blow the tire off the rim, that’s what would happen on the moon, but if the tire could hold the added 14 psi anyway, you’d be fine.

[dbb]

@dasgeh 108039 wrote:

Does anyone else feel a little alternate-universe-y when the trail conditions thread is talking about blowing tires and the morning commute thread is talking about ice on the trails…

And an economist is talking about real (as opposed to dismal) science? The apocalypse may soon be upon us.

[DismalScientist]

@dkel 108043 wrote:

I asked the interwebs about this, and you would be gaining (so to speak) that 14 psi of atmospheric pressure inside the tube when on the moon. That 14 psi was in the tube on earth, but counterbalanced by the atmosphere; now without the atmosphere, that 14 psi is added pressure on the inside of the tube. If your pressure is already high enough that 14 more psi would blow the tire off the rim, that’s what would happen on the moon, but if the tire could hold the added 14 psi anyway, you’d be fine.

Obviously, this depends on whether you are on the light or dark side of the moon. Some quick googling suggest the dark side of the moon has a temperature of about 60 K (K is for Kelvin), meaning if the tire were inflated to 14 psi on Earth (at room temperature), the pressure on the moon would be a little over 2 psi (assuming constant volume, of course). On the other hand, the temperature on the “day” side of the moon has a temperature of about 400 K and the tire, if inflated on Earth, would have a pressure of about 20 psi. Of course, you could wait until you reach the moon to inflate the tires, but that would seem to be a waste of your atmospheric resources.

[mstone]

@dkel 108043 wrote:

I asked the interwebs about this, and you would be gaining (so to speak) that 14 psi of atmospheric pressure inside the tube when on the moon. That 14 psi was in the tube on earth, but counterbalanced by the atmosphere; now without the atmosphere, that 14 psi is added pressure on the inside of the tube. If your pressure is already high enough that 14 more psi would blow the tire off the rim, that’s what would happen on the moon, but if the tire could hold the added 14 psi anyway, you’d be fine.

This is why deep sea diving is harder than space.

[mstone]

@DismalScientist 108050 wrote:

Of course, you could wait until you reach the moon to inflate the tires, but that would seem to be a waste of your atmospheric resources.

You’d be pumping all day, but the guy with the co2 will finally be vindicated.

[dbb]

Wouldn’t this be the bike for the moon?

http://surlybikes.com/bikes/moonlander

[dkel]

@DismalScientist 108050 wrote:

Obviously, this depends on whether you are on the light or dark side of the moon. Some quick googling suggest the dark side of the moon has a temperature of about 60 K (K is for Kelvin), meaning if the tire were inflated to 14 psi on Earth (at room temperature), the pressure on the moon would be a little over 2 psi (assuming constant volume, of course). On the other hand, the temperature on the “day” side of the moon has a temperature of about 400 K and the tire, if inflated on Earth, would have a pressure of about 20 psi. Of course, you could wait until you reach the moon to inflate the tires, but that would seem to be a waste of your atmospheric resources.

I don’t think you can assume constant volume, though, regardless of temperature, because of that pernicious vacuum. Otherwise, we could have found that sweet spot between the light and dark sides, landed there, and played golf in real golf clothes instead of a pressure suit.

[Anonymous]

@dkel 108055 wrote:

I don’t think you can assume constant volume, though, regardless of temperature, because of that pernicious vacuum. Otherwise, we could have found that sweet spot between the light and dark sides, landed there, and played golf in real golf clothes instead of a pressure suit.

A bike tire doesn’t have to worry about pesky little things like breathing in oxygen (which the moon’s non-atmosphere doesn’t have), or about keeping the water that makes up large percentage of human bodies from evaporating/boiling away as pressure drops to around 5 psi and you approach the vapor pressure of water at room temperature …

The pressure of the moon’s atmosphere, which is more or less non-existent, doesn’t change between the light and dark, hot and cold sides. It is approximately zero, it contains basically no oxygen (or anything else), and is non-hospitable to human health, everywhere. The bike tire is built to withstand comparatively large differentials in pressure between inside and outside and will be just fine. A pressure suit for a human to play golf on the moon needs to hold about 14.7psi higher pressure inside the suit than outside. A bike tire, depending on the tire, will hold up to 110 psi (or more) higher pressure inside the tire than outside. It doesn’t need its own pressure suit, because it basically is a pressure suit.

[dkel]

@Amalitza 108059 wrote:

A bike tire doesn’t have to worry about pesky little things like breathing in oxygen (which the moon’s non-atmosphere doesn’t have), or about keeping the water that makes up large percentage of human bodies from evaporating/boiling away as pressure drops to around 5 psi and you approach the vapor pressure of water at room temperature …

The pressure of the moon’s atmosphere, which is more or less non-existent, doesn’t change between the light and dark, hot and cold sides. It is approximately zero, it contains basically no oxygen (or anything else), and is non-hospitable to human health, everywhere. The bike tire is built to withstand comparatively large differentials in pressure between inside and outside and will be just fine. A pressure suit for a human to play golf on the moon needs to hold about 14.7psi higher pressure inside the suit than outside. A bike tire, depending on the tire, will hold up to 110 psi (or more) higher pressure inside the tire than outside. It doesn’t need its own pressure suit, because it basically is a pressure suit.

Right. This is why Dismal’s example shouldn’t assume constant volume. If volume remains (magically) constant, then the person in the temperate zone of the moon wouldn’t need a pressure suit because the water in their body would (magically) not evaporate away in an attempt to equalize the severe pressure differential. That person would only need a source of air for respiration. It is also why Tim Kelley’s bike tires may not fail, but their pressure (and volume) would increase.

[GB]

Dkel, I think Dismal replaced the word mass with volume because most people are used to thinking of the volume of a gas rather than it’s mass. But (AFAIK) you are correct, assuming constant volume isn’t technically correct in this hypothetical.

*edit* actually you need mass and volume to get pressure, so your both right.

[Author]

Posts