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Heat-Related Issues?
#1
I have a question relating to tubes and heat issues. I changed out the tube on my back tire recently because of this and now I find my front tire tube has the same issue. When I would look at each tube, there was a 1/4-5/8 inch gash on the inside of the tube. Nothing outward happened during the ride itself to indicate the tire was damaged, but when I would go out the next morning the tire would be deflated completely and (of course) wouldn't hold any air at all. I checked the rims of each tire and there's nothing about the rims that seems like it would put this hole into the tube (rim tape intact, didn't feel anything sharp spots running my fingers around the rim).

So any ideas on why this happening and making sure it doesn't happen again? The back tube has held up so far, but I want to be sure. Since I'm not finding any outward signs of sharp edges on the rims, I was wondering if it could be heat issues? It's been getting rather hot during the day lately, and I do my rides in the morning (as well as check the tire pressure and put it near maximum). The bike is stored in the heat, which makes me wonder if the air is expanding and popping the tube? Or is there something I'm missing in considering what's going on?
Why is it that they make adult bikes that'll generally work for 5'9" or above, yet when you pedal these same bikes they only work for someone who is 5'4" or so?
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#2
Regarding tyre pressure: Use lower than max pressure for _decreased_ rolling resistance. High pressure actually increases resistance (on non-ideal surfaces) because the bike is "lifted" by bumps rather than the tube being deformed. The tube releases most of the stored energy in a "usable" manner, the energy used to lift the bike is lost. The increase of rolling resistance is actually quite steep with increased pressure after the optimum, so it is safer to err on the lower side.

Regarding the heat: well, maybe? When I last had issues like this it was a hard to see (when deflated) cut in the tyre casing, though.
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#3
Do you ride the same route daily? Perhaps you are getting a pinch flat at a certain point in your ride where you go over an obstacle like a curb or something.
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#4
But a pinch flat leave "snake bites" and not long gashes...
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#5
if your bike is in the sun, and/or parked on black top, with little wind, the tires will get very hot - more than enough to burst if starting from a high pressure at a low temperature.

P1/T1 = P2/T2 -> P1 * T2 / T1 = P2

P is in absolute pressure, so add 14.7 psi or 1 bar to your pressure gauge measurement.
T is in absolute pressure, so add 460°F or 273°C

From what you describe, estimate T1= 290°K; P1= 8 bar; T2=310 air + 50 for sun -> 360°K
leads to about 10 bar in the tire; or stated another way a 24% increase in pressure - probably more than the tire can handle for an extended period.

Not rubber can handle very high loads for very short periods, but not steady state. Think about water, ease into it with little resistance, fall in from 15 feet and hurts.
Nigel
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#6
Wow, awesome posts!!! Thanks again guys I just learned something new. Smile
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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