lightweight 36" inner-tube project

I know others have used 28" tubes in their 36" to reduce the weight of the wheel, but I have not had good luck mounting the 28" tube. It turns out the the 28" tire is about 30" too short in length around the diameter for a 36" tire so that 28" tube is really stretched. I thought I’d try splicing 26" tubes together to provide a full 36" tube. Basically add 30" from one tube to the other. The resulting tube weights nearly half of the standard 36" tube.

I came up with a good way of evenly gluing the tubes at each joint.

I’ve used rubber cement and overlapped the tube pieces by about an inch at the splice.

First Joint: I didn’t get the overlap right, only about a half inch. The splice was weak from the beginning.

Second try: Got both joints with a good 1 inch overlap. The tube held air lbs and I rode for 2 miles. At 2 miles the tire went flat and left me with a mile walk back to the car…

The joined inner tube weighs (256gram) nearly half of a standard 36" (487gram) tube. The wheel did feel lighter.

I’ve been using standard inner tube bicycle patch kit rubber cement. I don’t think that is going to hold permanently. I’d like to try this again, but am looking for a better adhesive for the inner-tubes. I’ve searched the web a bit and didn’t really recognize what would work better. Maybe there is an industrial strength rubber cement. Or better something like that plastic pipe solvent that would fuse the rubber together.

If you have suggestions on the adhesive please let me know.

Ken there isn’t a need to join two tubes together, a single 28" tube will fit on easily. Just over inflate it beforehand (to slightly larger than the diameter of a 36" wheel) and leave it like that to stretch for a day or two. Then just let a little air out to fit it on the 36" wheel.

Or, go tubeless of course.

Trying to join tubes sounds like a lot of unnecessary hassle.

You mean 29" inner tubes? That’s hard enough to get on without killing the tube, let alone trying 28" :astonished:

Yeah maybe you have been using tubes that were too small. A 28" tube will be smaller than a 29" tube, and won’t allow for as much stretch.

I sort of think that just stretching a tube would be a better choice but for connecting the tubes did you thoroughly wash and roughen the inside of the tube that you overlapped over the other tube?

The tubes usually have a coating on the inside to prevent them from sticking to themselves, I am sure it could not help in the binding process.

Hey thanks for the feedback guys.

Maybe I should try the 28" tube again, this time with the pre-stretch you mention. I also thought if I could join these tubes together right they would be lighter than the standard 36" and be more durable than the streached 28".

I had thought the 28 and 29" tubes were the same, thought they were all 700C, but just did a web search and did find 29" tubes.

ok, see previous.

Yeah, I didn’t clean the first joint well, and I think that did weaken it considerable. The coating felt like talc. The second try I wiped it clean with a damp towel and sanded both rubber surfaces. That helped a lot. Next try, I’ll be sure to clean it even better, and use alcohol.

Common misconception. Most 700c tires fit on similar rims. There are different widths. 700x23c is very narrow and is designed for road riding/racing. It has a very different outer diameter than a 29" tire which will do better on wider rims. 29er might be 700x50c. Blowing up/stretching a 29er tube will have much more rubber available due to the high volume tire than a 28" which is designed for minimal weight and width.

I think that is a great idea Crashing, and it shows how easy it is to innovate in that area while the tire companies keep selling us what we don’t quite want. I like the puncture protection a coker innertube gives but the weight is unnecessary! I’m not keen to experiment with 29er tubes.

You might try acetone instead of alcohol. A lot of denatured alcohol will leave an oily residue behind. The acetone won’t leave a residue plus it will slightly disolve the butyl rubber leaving a cleaner surface.

Like painting, a good bonding job is 90% preparation and 10% application.

If you want the best possible bond, you’ll need to nerd out: go to an adhesive manufacturer (such as 3M or Henkel) and look in their application guide to find the best adhesive for your application.

Then check out the data sheet for your adhesive. There’s usually a recommended preparation method (including recommended cleaning solvents) and bonding method. Follow the instructions to the letter for best results.

I remain psyched about trying to join these tubes again, at least to be sure I gave it a good shot. Thanks for all the helpful comments.

Thanks for the encouragement. I don’t understand why the 36" tubes are so thick. If a nail or thorn is going through the tire (which most my flats are), the tube thickness isn’t going to stop it.

Acetone sounds like a great idea. I’ll make sure I get this right next try.

Yeah, I certainly can improve my preparation. Next try I promise get and follow the instructions.

I found chemically vulcanizing cement to try. If this ‘vulcanizing’ is real, it has to be better than the Schwinn rubber cement that I was using. Presently, I’m looking forward to making a third try.

Yeah, getting a few shots of JD (or whatever your preferred tipple is) down your throat first always makes a difficult job seem easier :smiley:


My third try joining tubes, ordered all stuff to do it right. Ordered: the REMA Pre-buff Cleaner, the REMA Cold Vulcanizing Fluid, and even the REMA brass bristle brush for cleaning up the area.

Result: I got REMA’ed.

I was careful to clean, roughen, and set things up to bond. The resulting joint was weaker than my first try. No vulcanizing at all. That ‘cold vulcanizing fluid’ seems no better than common rubber cement.

I’m a bit bummed out, I’ll call the vendor to see they if they can explain my results.

I just took that last joint apart, looks like I could have roughen the surfaces more for a better bond. I don’t think this vulcanizing fluid is any better than Schwinn cement so I don’t think it will ever do better than that bond that lasted 2 miles.

The tube of ‘glue’ which comes in every cheap as chips puncture repair kit is in fact self-vulcanising fluid. So its not surprising that you had the same results with that Rema stuff.

The puncture protection I mentioned was more like avoiding any problems that 29er tubes or tubeless kits give rather than actually preventing glass or nail punctures. Most of my punctures come from glass shards- which no amount of rubber and air will prevent, but a thick tire helps fight off the smaller attacks.

I think the weight of the Coker wheel is part of what makes it what it is- the maximum rolling momentum monster wheel. Sometimes you are saved from falling by the virtue of the massive weight bearing down over unexpected bumps- the inertia having a balance of it’s own. I appreciate this after switching between a 28" unicycle and the 36". Having said that I’d love to lose a few uneccessary grams in the innertube cos lightweight= spinning fast -and it will still be plenty heavy.

And sometimes falls are caused by the inability to control the weight of the wheel. Getting over bumps is a function of wheel size, not wheel weight. Really, there’s no plausible way that heavier weight is better than lighter weight; that’s why bikes don’t run 36" tires with way too much tread, like Coker riders do.

Your analogy isn’t very good! Since when have unicycles been made like bikes? There are 36" bikes… And they aren’t as common as 36" unicycles because they are funny enough, over twice as heavy!

The wheel weight does have an effect in my opinion. Try riding straight up a curb without taking your weight out of the seat, first on a 28" wheel (which is easily big enough diameter) and then on the 36" with the tires pumped up hard.

There have been discussions where people add weights to the wheel for extra stability. The weight (and it’s inertia) is good on downhills and with tailwinds but not if you are turning sharp or changing speed or climbing big hills.

I’d be interested to try a 42" or 44" unicycle with a similar width tire to a racing 700x23c - to see how much the weight vs size really effects things cos I can only speculate from the different available sizes. I imagine a really big narrow tire might be hard to mount to the rim but I don’t know.

Be serious: you don’t think there’s any difference in ability to roll over obstacles on a wheel with an 8" larger diameter?

How about this: Try it on a 28", and on a 20", and see how that goes.

Or accelerating, or decelerating, or basically doing anything else. The only time extra weight on your wheel really helps is if you’re dropping it off a cliff.

I am serious. Ive tried lots of different sizes! Try a 20"x2.5 compared to a 700x23c and it will be similar or easier. Ok to be more fair try it on a narrow 24" then on a 24x3" fireball pumped up hard. Only a couple of inches different diameter but the weight and volume of the bigger tire makes it easier to bash its way over big bumps. Still not as easy as a bigger/softer tire but the weight and volume has a measurable effect. Another easier comparison is the higher volume 29" tires compared to the 28" racing slicks. We don’t have anything in the 36" range to be able to do proper comparisons cos all the other big narrow wheels have solid rubber tires as far as I know.

So how is accelerating or decelerating different from changing speed? And what are these “anything else” conditions that you mention- I think we’ve covered most factors. I agree with you that light weight is good, but in the case of the 36" the weight is good because it enables us to be bigger than 28" and we have to use what is available unless we want to make custom projects.

I guess what Im trying to say is that without weight you don’t get volume- and the volume is what makes it easier to soften bumps- and this is very obvios in the biking world with the comparisons between road racing bikes and mountain bikes. Road unicycles face more of a problem from bumps than road cyclists cos of their tendancy to fall on small bumps, so the higher volume can pay off, carrying a bit of extra weight can save you time spent getting up off the road.