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bluedress
03-17-2006, 04:36 PM
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 :mad: 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
03-17-2006, 04:39 PM
Huh? Does he does this to his car, the basketball, the football, etc., etc., etc.? :confused:

madisongrrl
03-17-2006, 05:07 PM
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
03-17-2006, 05:07 PM
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
03-17-2006, 06:07 PM
I know of no one who does this and alot of my friends are real bike geeks. I'll ask around.

DebW
03-17-2006, 07:02 PM
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
03-17-2006, 11:56 PM
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
03-18-2006, 12:13 AM
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
03-18-2006, 12:32 AM
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

DebW
03-18-2006, 04:48 AM
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?

If you pumped to 120psi at 32 degrees and your truck went up to 120F sitting in the sun, that's an 18% pressure rise, or up to 142 psi. Not surprising that would blow tires. I believe that the pressure printed on the tire is the max you should ride at, though you don't necessarily need that much. There must be some margin above the printed max, otherwise tires would blow when you hit a bump while riding, but not sure how much. BTW, it's not the tube that's critical, it's the tire bead blowing off the rim, which will of course blow the tube because the tube then expands very suddenly. With tubulars, it's the strength of the stitching.

Nanci
03-18-2006, 05:05 AM
I don't have anything to contribute, but this is a really interesting thread!

Didn't the guy in the Tire Pressure Article a couple weeks ago say that max pressures were based on a 135 pound rider? (They were recommending riding at 90psi) I've been riding at 95psi since then, and it seems fine to me.

I've never heard of releasing tire pressure. Not saying you should/shouldn't, just never heard of it.

Nanci

bluedress
03-18-2006, 08:16 AM
This is an interesting thread! Thanks for all the input, ladies. I love all the information and stories. The article posted by Nanci a few weeks ago was interesting, too.

(...now if only I could unscrew a little valve and let some of the hot air out of my "friend"... ;) Meow.)

RoadRaven
03-18-2006, 10:45 PM
Dunno if I can clarify anything - but we keep our road bikes with "normal" tubes pumped to 100... and thats the pressure they're at when in a car on a not summer day they go pop.

Never had a prob with mtn bikes which we keep at less pressure...

maillotpois
03-20-2006, 02:18 PM
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
Ličge, 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
03-20-2006, 02:20 PM
It's also very important that you use CO2 cartridges filled with European air if you're using tubes made in Europe.

madisongrrl
03-20-2006, 07:05 PM
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!

DebW
03-21-2006, 04:35 AM
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

I did some numbers. For a 700x23c road tire inflated to 120 psig, you would add 5.5 g (0.19 oz) by inflating with CO2, and save 9.6 g (0.34 oz) inflating with helium, save 10.25 gm (0.36 oz) inflating with hydrogen (H2). Of course, one presume that if you inflate your tire with CO2 while on a ride, you were carrying the CO2 cartidge already and thus you have a net decrease in bike weight of 11 g when you use it (replacing the 11 grams of air in your tire with 16.5 grams of CO2 which you were already carrying). Compare these weight differences to carrying a pump which weighs several ounces to half a pound.

maillotpois
03-21-2006, 07:39 AM
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...

:D

CorsairMac
03-21-2006, 09:32 AM
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
03-21-2006, 09:39 AM
Mais oui. :p

madisongrrl
03-21-2006, 10:50 AM
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...

:D


I was wondering....I wasn't sure if the second part of your post was supposed to be humerous also or not. I wouldn't put filling bike tires up with helium past most of the weight weenies that I know!

bcipam
03-21-2006, 12:36 PM
Ok checked with the "bike geek" squad. Skinny on tire pressure: Check the pressure recommend on the tire itself. Use the appropiate tubes (not all tubes are meant to be blown up to 140 psi). It is not necessary to let the air out between rides but it is important to check air pressure before a ride. A properly inflated tire means less risk of puncture and offers a smoother ride.

Mountain bike tires (wide, knobby tires between 1.9 - 2.4 " wide) generally take much less pressure. If using the bike on road or trail it can be inflated to around 40 - 45 psi but no more. On trail, singletrack etc. and depending on surface materials (ie sand, loose dirt, hard packed) use run at 25 - 35 psi. Where I ride there is alot of sand so I run my tires at approximately 30 psi. Less pressure gives you more trail "grip" but something you lose alittle control. Higher pressure gives you ability to ride faster but can be "squirrelly".

As to road bikes depends on the tire and tire size. Very high quality racing tires, at 21 - 23 cm can be run up to 140psi. normal tire pressure is 100 - 120. I used Gatorskin 25's on my road bike. I inflate them to 100 psi. They can go to 120 but I like the smoother feel of lighter pressure. Some tires, especially if they are 25's or 28's can run at 85 - 90psi. Basically the bigger the tire the lower the pressure.

Just alway remember to get a couple of things before a ride. 1) tire pressure, 2) condition of drive train and 3) proper adjustment of wheels, brakes etc.

I thank you "bike geeks" !