Bicycle Tutor

I figured out how to get the 700x35 -44c tube onto my 700x35 - 37c tire.

In the past, I have always put the tube on the rim first, and then put the tire on top of it. However, in this case, the tube was falling off the rim because it was so loose. To solve that problem I stuffed the tube into the tire first, then stuck the tire with tube inside onto the rim (aligning carefully with the valve stem hole in the rim), then inflating slowly to make sure the tube didn't push the tire bead out of the rim channel.

I wonder if this technique would work on a tube that fits the rim snugly to begin with. I'll give that a shot on my racer next time.

Also, should a tire be inflated to it's maximum capacity? My racing tires have a max inflation of 150 psi, but the guy at the bike shop said 120 psi is plenty - which is convenient because their pump won't go over 120 psi. Is he right?

On another tire that had a flat, the maximum inflation is 80 psi. I mis-read the gauge and put in 90 psi, and after about 30 seconds, the tire burst like a gunshot. It seems to me that putting 90 psi into an 80 psi tire should not have burst the tire, especially when not even put under the additional stress of riding on it yet. Opinions please?

150 PSI ??????? WOW, that is a lot of pressure for a bicycle tube let alone the 120psi. I am wandering what kind of tire/tube holds that much pressure? Most I ever dealt with is 65psi. Again I am no expert, but I am very curious. Can tell this I really don't go the max pressure, usually around 5-10psi lower then the maximum. I just thought of something, what measurement are you using?

Well, 150psi is just a bit more than 10bar, I know that there are some tyres that can be inflated to even more. This is "normal" for road bikes.

On the first thought, it might seem as if higher pressure will reduce rolling friction. This is true only on really smooth underground, maybe on a track inside. On normal roads this is different. Higher pressure has not only the disadvantage of giving a rough, bumpy ride, but will actually increase rolling resistance. This can be understood in the following way: (careful, handwaving argument follows)

When encountering a small bump, a tyre with lower pressure will just roll over it, dissipating some energy in tyre flex, but not too much, actually, due to that flex being elastic deformation, quite a bit of the energy is "given back".. A tyre with very high pressure will bump up and dissipate the energy in the next part of the system that is available in that direction: the riders hands, arms and shoulders. I saw a measured curve a while ago, but cannot remember where. When increasing the pressure, the rolling resistance at first decreases a bit, and, after reaching the optimal pressure, increases quite sharply. I used to ride in the 9-10bar range until that point. Now I usually inflate to 7.5 - 8.0 bar (~110 psi). Tyre: Michelin Lithion with Conti latex tubes.

A rough rule of thumb in the metric-system-using part of the world is rider (some say+bike) weight in kg, divided by 10 in bar.

If the tyre burst after over-inflating it by 12.5%, it probably was damaged / weakened before.

The max pressure listed on a tire is based on the strength of the body of the tire and cannot really account for how well it sits on the rim. Different tire/rim combinations have different fits and might be able to handle higher or lower pressures. That all said, what is printed on the side of the tire is probably well below what the tire can handle (see: liability lawyers). Going 10psi over on a tire definitely shouldn't have popped it unless the tire was damaged or wasn't seated properly.

Joe_W has it exactly right about pressures. The "fastest" pressure depends on the road conditions. I think I read somewhere that on normal smooth pavement, anything over 100psi probably doesn't make much difference. Usually you put about 10% more in the rear as it has more weight on it.

@jdohe - I always put the tube in the tire first. Pump it up just enough to take its shape, put it in the tire, and then mount the tire. I think you are much less likely to pinch the tube when putting the tire on or to get it stuck under the bead so it pushes the tire off the rim when you inflate. I know other people disagree. But this is how I learned when I worked in shops and it's worked well for me.

The 150 psi tubes I have are 1" diameter tubes for Mavic rims on a Softride Powercurve triathlon bike. I suppose that without the carbon tube suspension system for the Softride bike, hitting even gravel at 150 psi would be a very rough ride.

The International Cycling Union - UCI - has ruled that a bike frame must be of the 2 triangle design, so the cantilever tube system of the Softride got pushed aside. People who use Softride bikes love them, people who have had them that think the carbon tube will last forever without breaking hate them, and of course people who don't have them hate them to justify their lack of having one. Its not a super light bike, but the carbon tube does absorb quite a bit of shock and might just prevent an avid bicycle enthusiast from going impotent or aggravating or inducing prostate cancer. If riding the bike can break a space age carbon fiber tube, imagine what kind of damage a rough ride on a bike does to your crotch.

Softride discontinued making that type of bike in 2007. Zipp made a similar type bike but they stopped making theirs in 2002.

Ok thank you for explaining that. I am in US and that is what I was wandering.

Posted this in the wrong thread, sorry. This link should have gone _here_

I also found the website with the resistance data and explanationes: http://www.slowtwitch.com/Tech/...