(Saga of the exploding tires)
I have a dental appointment in a hour. Hmm, manual wheelchair tire feels slightly low, maybe I should top it up a bit. Okay, I'll consult the manual to see what the tire pressure should be. Oh yeah, neither of my chairs came with a User's Manual. Spinning the tire around I see "75 PSI" imprinted on the rubber tire. I trust that pressure applies to the tire in any situation, as used on a wheelchair or bicycle. Is that the maximum pressure or the operating pressure. Then again, does the pressure apply to the innertube or to the outside rubber tire,.....or to both???
(I recall that while waiting for the chair to be put together, the service person sent over didn't know what the pressure should be.)
THE COMPANY'S SERVICE PERSON DIDN'T KNOW!!
I get the air pump and start inflating. Hard to get the pressure above 35 PSI with a hand pump. Sweating and grunting, I repeatedly check the pressure to see it go up a bit then loose that amount as I take the hose off for another measurement. Finally I coax it up to 65 PSI - checked by a mechanical and digital guage (both in agreement). One or two more pumps and.......
So I call up and cancel my dental appointment. I take off the tire and remove the inner tube to get the size (as I have no manual to refer too!!!) . My wife calls around and can't find any bicycle shop that carries that size. Finally one store has it in stock and she runs down to buy a few to have on hand as spares. Get it home and the valve stem is slightly too short and won't stick out far enough from the kevlar rim. Sorry, I'm not a cycling enthusiast so didn't know the stems might come in an assortment of lengths. Never occured to me and the sales person at the cycling shop never questioned me. Asked for the inner tube size and nothing more and he had the blown one for comparison if necessary.
So, not optimal but I could manage to get the pump fitting on and inflate the tire to about 35 PSI. Next stop was to buy valve stem extenders. This way I can use the common size tire/valve stem and not pay the inflated 'medical supply' store price (about 3 times the sports store price). Now the pump hose fitting fits over the stem with ease. Filling the tire is still another matter. My air compressor is a bit to aggressive and I don't have enough control - can overshoot the desired pressure too easily. The hand pump is difficult as the resistance is so great it is difficult in getting the pressure past about 45 PSI.
In the end, I never have gotten the pressure to the printed 75 PSI but manage to keep it around 65 PSI.
More Innertube Explosions:
On two other occasions the innertube exploded on me, thankfully never while I was out and riding in the wheelchair. On time the tire exploded after having sat in our hallway for about 3 days post trip. No use, no stress, not under pressure, not in the sun, - no warning- just explodes mid-day. The next time I had just left my doctor's office and the chair was in the rear of my van. My wife ran into the store for a few moments and suddenly the tire explodes behind me. Thankfully it didn't explode while in the doctor's office where surrounded by cardiac patients and infants. Thankfully too it didn't explode in traffic with my wife behind the steering wheel. Sounds like a shotgun blast going off.
Each explosion was on a different wheel and different innertube manufacturers.
Manufacturing/Quality Control Issue???
So at home I remove the rubber outer tires and inner tubes to check for debris or sharp edges. I may have found both. Some black kevlar shavings fell out, left over from the manufacturing process. also where the two halves of the semi-circle kevlar rims are fused to make an entire circle, the joints are somewhat rough. Perhaps this edge contributed to the explosion while damaging the inner tube while rubbing under pressure. Who knows? Not a big edge but I took what I could down with some sand paper to smooth it out.
Lack of Confidence in Wheelchair:
The tires are on and inflated to about 65 PSI waiting for their next trip. However, after spending $6300, I have a wheelchair I have no confidence in using in public. An explosion could happen at any time and as I have no manual, I have no idea if I can travel on a blown tire without doing permament damage to the rim. I'm sure the wheelchair supply company would be happy to sell me another new rim at their special price! Damned if I'm going to call them up after my previous dealings with them.
... and no confidence in it's usability!