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Tuesday, May 12, 2009

Flat Tire Again, 26" Tube In 24" Wheel = Bad Idea

Remember my bright idea of using the 26" tube in the 24" tire? Not such a bright idea after all. Only a week and a couple of days in, and it began to fail, though as it turns out not from the same thing causing the other tubes to fail (still undetermined).

When it started to fail, I was on my way home from work, and could feel the tire slowly getting softer. I stopped and reinflated it, hoping the Slime would fix it, and it did help, but not enough--a half-mile later, it was soft enough to feel problematic again. Having little choice at 10pm on a Friday night, I continued to reinflate it two more times before reaching home. I estimate it would have lasted a mile and a half before being totally flat each time, but I didn't want to damage anything with the massive weight of the bike on a flat tire if I could avoid it. I expect the rim could actually cut thru the tire itself, and certainly the tube, with me plus the bike pressing on it for any length of time.

The failure this time was because of the folds themselves, and the thick rubber. As it was stressed in a direction not designed for, it actual *tore* holes at the corner of the fold on one side.
This hole is long, but is pinched together by the rubber around it for the most part, and the chunky tubeless-style Slime is able to seal it, amazingly enough, when I tested it in a 26" tire.

This hole, however, looks rather like a hole chewed in something by a mouse.

It's not actually just a tear, there's material missing; presumably rubbed away by friction with the inside of the tire sidewall. It's not fully sealable by the Slime, and is probably where the majority of the air leak is from.

I taped it with packing tape to hold a temporary patch of rubber just placed over it, then placed it inside a 26" tire (not on a rim) and inflated it, and the first hole could be sealed by Slime, and so could this with the patch over it, but not without it. I dont' think the Slime could actually *stay* in the hole as the tire rotates against the ground, though, so it probably wouldn't stay inflated long during a ride without a good permanent patch on it.

The other is intact, though you can see creasing on it.

It does not bulge out or appear misshapen when inflated, so it is likely the only real damage on this side is the scuffing from rubbing against the sidewall, which is only visible on this side.

This is the problematic wheel, which I have again closely examined and found nothing that could cause a problem in the rim, spoke head/tensioners, rim weld, tire bead/sidewall/tread, Slime protector strips, or spoke cover strip.

The red ellipses are the approximate locations of the two folds in the 26" tube to fit it into this 24" wheel.

I'll be taping up my patched-up 24" tubes and trying them again, since I can't afford new ones at this time. I have to tape the patches because the holes are not where the patches will press evenly against the inside of the tire, and thus aren't held down against the tube. As my patch kit consists simply of rubber cement and patch pieces and/or old innertube slices, it doesn't seem to hold as permanently to the tube as a really good patch kit would, unless it's helped by the pressure of something external holding it on, even after several days of drying/hardening. Wrapping tape around the tube after slightly inflating it seems to help tremendously for holes in places where it does not press against the tire.

I'm tempted to try out the method at this Instructable:
which essentially consists of two innertubes placed in one wheel, with the stem of the second exiting the rim via a second hole drilled partway around the rim from the first.

It would at the least let me quickly get back on the road after a flat bad enough for Slime to be unable to fix, but before I do it I will need good tubes to start from that don't have problems on their inner circumferences.

If I have good tubes, I suspect I won't have flats in the first place, as I have not had any in well over a year on the upright bike using Slimed tubes plus Slime protector strips, as I now have in the rear tire of the recumbent.

The problem might be rendered partially moot if I can quickly design and build the wheelchair-based trike, especially if I use the "solid" tires that came with it until I can afford better ones, at which point I'd be replacing the wheelchair rims and tires with bike rims/tires/tubes.

That will require unlacing the wheelchair rims from the hubs and relacing the bike rims to them, and a decision of whether to use 26" or 24" rims. I think 26" rims might be better mostly because it seems easier to find road-tires with slicker treads in 26" size than 24", especially with recycled stuff.

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