tire pressure Q

[bluedress]

A friend of mine (I use the term *very* loosely here—turns out he is kind of a jerk—maybe a very big jerk—I am venting—sorry) says to release the pressure of your tubes between rides to maintain their ability to hold proper pressure. Make sense what I am saying? Anyone else ever heard of this?

[SadieKate]

Huh? Does he does this to his car, the basketball, the football, etc., etc., etc.?

[madisongrrl]

I'm not sure what your friend is talking about, but it is a good idea to release the tire pressure between rides. I left my road bike in the back of my truck on a hot summer day. As the day wore on, the temp increased and my tubes popped. 5-10 dollars down the drain. If the temp goes up, then the pressure goes up.


Take it from a chemist PV=nRT (Ideal Gas Law)

[RoadRaven]

The only time I deliberately let air outta my tires is on really hot days (like MadisonGrrl) when the bike is stored in the car - the heated air in the tires can expand so much it can burst the tube... yes, its happened to us...

The air naturally "seeps" out of the tube anyways between rides - and a general rule of thumb should be to check tire pressure / pump your tires up at least every 3 days...

I find your friends advice interesting and wouldn't hold to much time in your thoughts for it.

[bcipam]

I know of no one who does this and alot of my friends are real bike geeks. I'll ask around.

[DebW]

There are butyl tubes and latex tubes - one leaks more slowly than the other, I don't remember which. Checking your tire pressure every 3 days or at least once per week is recommended. If you let out pressure between rides, well, you get more arm exercise before each ride. But it's really unnecessary. Even leaving your bike in a hot car is unlikely to blow the tubes unless you normally run your tires within 10% of the maximum rating for your tire. In the ideal gas law, P is linear with T, so a temperature change from 70F to 120F is only a 10% increase (convert T to Kelvin).

[madisongrrl]

In the ideal gas law, P is linear with T, so a temperature change from 70F to 120F is only a 10% increase (convert T to Kelvin).

10% can be very significant...especially if you are racing at multisport events which generally start in the wee hours of the morning.

A perfect example would be the Green Bay Duathlon that is held in Wisconsin in early October. You set up in the transition area between 5-6:30 in the morning. It's sucks, it's cold, there is stinking frost on the ground (I absolutely hate fall!) and the temps in the low 30's. You pump up your tires to the pressure that is correct for you....based upon your weight, bike, tires, course etc. The race starts at 7pm, but your run wave doesn't go off until 7:30. (I generally finish up the couse before 10, though there are plenty of people who finish up at 11:30-noon+...you really have to applaud them for being out on the couse so long). Now the temp is topping out in the low 70's (this happend in 2004).

If you run your tires at a 115 psi, even a 5% increase puts them up at 121 psi. Your bike will ride differently (harsher), you might be more prone to flatting and your traction will be reduced. I have noticed that my Cervelo rides differently even when I change the tire pressure 5 psi. The first year I had that bike I ran the pressure way higher than it should have been and gave myself a harser ride than was unnecessary (and when riding in the aero position.....boy does that hurt the bits and pieces). Lessons learned...

I don't think we need to obsess over tire pressure, but just the same its an important consideration on race day. I'm generally not worried about pressure and temp when I do shorter mountain bike races. But I still can't figure out which tires and pressure I should be running based upon my bike, my weight and course conditions. It seems like the longer I'm at this sport, the more I realize that I have to figure out.

Best,

[madisongrrl]

Even leaving your bike in a hot car is unlikely to blow the tubes unless you normally run your tires within 10% of the maximum rating for your tire.

I had my rode bike in the back of my truck. We were mountain bike camping at the Kettle Moraine, WI in late September. It was very cold at night (jackets, pants etc.) and very hot during the day (shorts and tanks). I had pumped the tires up to the max (120psi), but I did it when it was cooler. We spent the day mountain biking and the rode bike was locked in the back of my enclosed truck, baking in the parking lot. Both tires were flat as a pancake (we actually heard one of them go).

My two questions are: Do you think the heat caused this or was it something else? How many psi's would it take to pop a tube in an average 23mm, 120psi max tire?

[Melody]

There are butyl tubes and latex tubes - one leaks more slowly than the other, I don't remember which.

Latex leaks considerably faster than butyl. Typically with latex my understanding is you want to pump up your tire each time. To offset that, however, latex is (supposedly) more puncture resistant, stretching instead of being penetrated by sharp objects.

It can be difficult finding latex tubes now though. I wanted to play with latex tubes but I went to 4 LBS' in the area and none had latex but I could find low weight butyl racing tubes.

Mel

[maillotpois]

This from Sheldon Brown, debunking a myth with some humor:

> 4) Deflating my tubulars after riding them will allow me to ride faster
> through curves the next time.

No,No NO! This is an old husband's tale!

Just as training at high altitudes improves your oxygen uptake capacity
for riding in the lowlands, you should pump your tubulars up 20-30 psi
(13.605-2.041 bar) _over_ their normal pressure for storage. This will
get them acclimated to high pressure. When you let the excess air out
to actually ride on them, they will be livelier and faster!

Carapace Completed Umber
Liège, Belgium

----------

And another, on a related topic, what to fill the tires with:

Re: CO2 tire inflators
rec.bicycles.tech 1997/02/15

redmist wrote:
>
> As far as weight and efficiency go these seem to be the way to go vs. frame
> or mini pumps. Any drawbacks?

CO2 is heavier than air, you will make your bike heavy and slow if you
use it. Helium is lighter, the only way to go if you want speed and
safety.

If you are willing to live dangerously, Hydrogen is lighter and cheaper
than Helium, but don't smoke while riding your bike if you use
Hydrogen...

Carapace Completed Umber
Lakehurst, New Jersey

[SadieKate]

It's also very important that you use CO2 cartridges filled with European air if you're using tubes made in Europe.

[CorsairMac]

It's also very important that you use CO2 cartridges filled with European air if you're using tubes made in Europe.

Wow - guess I need to find some French CO2 cartridges for my Peugeot then no?

[SadieKate]

Mais oui.

[madisongrrl]

Just as training at high altitudes improves your oxygen uptake capacity
for riding in the lowlands....

This statement is absolutely true, but what a lot of studies are pointing to now is "Train Low, Sleep High". Your recovery is severly slowed down at altitude. If you train low, you can get more training in, recover faster so you can get more training in etc.

I've been doing a lot of research on this topic because I live in Wi (flat as a pancake) and I'll be racing in at a Norba Nationals event in CO this summer (elevation 8500-10,000 feet...yikes) . So if anyone has any experience with this, I'd like to hear your stories. Perhaps I'll post this on another thread.

----------

CO2 is heavier than air, you will make your bike heavy and slow if you
use it. Helium is lighter, the only way to go if you want speed and
safety.

If you are willing to live dangerously, Hydrogen is lighter and cheaper
than Helium, but don't smoke while riding your bike if you use
Hydrogen...

Are there really people that fill their bike tires up with Hydrogen and Helium? I've never heard of this... What is the weight savings on a 40psi mountain tire Helium vs CO2 (If you are not sure, maybe I'll try to figure it out later....I on lunch, but gotta head back to work now...)

I've never heard of this, so it kinda blows my mind!

[maillotpois]

This statement is absolutely true, but what a lot of studies are pointing to now is "Train Low, Sleep High". Your recovery is severly slowed down at altitude. If you train low, you can get more training in, recover faster so you can get more training in etc.

I've been doing a lot of research on this topic because I live in Wi (flat as a pancake) and I'll be racing in at a Norba Nationals event in CO this summer (elevation 8500-10,000 feet...yikes) . So if anyone has any experience with this, I'd like to hear your stories. Perhaps I'll post this on another thread.

----------


Are there really people that fill their bike tires up with Hydrogen and Helium? I've never heard of this... What is the weight savings on a 40psi mountain tire Helium vs CO2 (If you are not sure, maybe I'll try to figure it out later....I on lunch, but gotta head back to work now...)

I've never heard of this, so it kinda blows my mind!

Um.....

As noted in my initial post, this was taken from the humorous part of Sheldon Brown's website. (I'm one for injecting a little smart aleckyness in whenever possible). I don't think any wrench would advise the Hindenberg effect on your bike tires...