Excuse me for insulting you! I figured, any engineer worth his salt would have done the math, saw the 1% figure, and scrapped the idea before proposing it on an international forum. Being that you posted, I assumed you hadn’t any familiarity with the math. So sorry.
And the cost of a “VTEC” sticker is far less than the investment in creating a Ferrari from scratch. What’s the point of that comparison?
Ken Looi on a 29er is still faster than a jet taking off from the deck of an aircraft carrier. The physical shape of these guys is inhuman. Let’s talk about us mere mortals.
I have a major event in the same month that I’ll need a lot of work to prepare for. If I can finish that work before the crit, I’ll be there… but things aren’t looking good.
Okay, so we’re not talking about mass-producing a track wheel. But it seems no one’s talked about the “rideability” of a lighter wheel, or done any work to suss out the cross-over point at which a wheel becomes un-rideable. If someone wants to hack up a prototype and ride it, let’s go! But if we’re talking about sending something straight to production, we need to do some analysis first…
My point exactly. People need to remember that the majority of unicyclists either never heard of this forum, or can’t be bothered to read it, let alone post to it. When it comes to the community here, we’re all pretty gung-ho about such things. But the rest of the unicycling world still dwarfs us. Remember where UDC makes most of its money? From selling the entry-level unicycles most of us would not even admit to using.
Thanks for that much more detailed explanation of that stuff! I never took a physics class…
That’s right, and I’m sure the “right” answer will be a matter of opinion, like everything else. We can only hope that, if a manufacturer gets interested in such a project, they’ll keep this community in the loop for feedback, instead of using some “average” unicyclist who doesn’t know what we’re after…
I would cut one across the thread. I would cut a section out of the other one. I could then use some type of reinforced rubber patch and rubber glue to splice them together (ideas for material?) Assuming I get the dimensions right I could then mount in on my 36" unicycle with an inner tube, and pump it up. It would be weaker than a real tire, but would it be useable?
Here is a reinforced tire patch kit. Would it be suitable for splicing tires together?
Thank you for the link. You talk about a number of different ideas. Would you be willing to summarize your approach to tire building? Did you end up using rubber cement and nylon cloth? Do you have any advice on connecting the bead?
Would drilling my stealth rim save enough weight to make a noticeable difference, and even be worth doing? And would drilling holes the same size as the kh 29 rim make the rim too weak? It would be used exclusively for distance riding on paved roads.
Edit: The impulse 36er rim, which is drilled, is only 3.2 oz lighter than the stealth (solid) rim. Not sure if that would make a noticeable enough difference, and be worth the time an effort to drill the stealth.
@Terry, Try adding a few ounces of extra weight to your existing rim to see if you can feel the difference. Then you’d know if you’d notice the weight savings from drilling a solid rim without compromising the rim strength for your experiment.
Perhaps a length of wire woven between the spokes would represent a comparable weight…
I’ve often considered something similar for training and strength building - riding with additional wheel weight. I’ve just never found the right thing to use as ballast.
Kinda like runners who carry weights! Maybe attaching small clip-on weights to the nipple end of the spokes? Another way would be to simply add Slime to the tube! I’m sure that would net you at least three additional ounces! And afterwards, you should be able to squeeze most of it back out by removing the stem valve core.
This is just what I’m planning to try. It would certainly be light, if it works at all! Lighter than the Schwalbe tyre you linked would be something like a Continental Sportcontact (hybrid slick) - even the fattest, 700c 38mm, is 550g.
My rough estimate of combining two of these to make a 36" tyre is that you’d use 2/3 of each 700c circumference, so 550*2/0.66 = 726g!! Yes please. Even adding a couple of hundred grams to overlap, patch, add extra bead strength etc and it looks feasible to get under 1kg.
I wonder if leaving 10cms or so of bead sticking out to overlap where you cut the rest of the tyre, and then stitching that extra protruding bead onto the neighbouring bead of the other tyre would make a good enough join to mount a tyre and hold pressure? Otherwise you could always stitch on a complete, unbroken 36" bead from an old 36" tyre; that would be sure to work, beadwise - it would be a bit of extra weight though.
I wonder what effect the different natural curvature of the 700c tyre would have when bent outwards to make a larger circle? It may not matter at all, and with a bit of air in it I imagine it would fill out and shape up OK.
… or the lightest I can find is a Vittoria Ranonneur Hyper, available at 700c 38mm at only 440g (though not cheap). It’s kevlar bead too, but I don’t know whether that would make the splitting/joining process easier or harder.
By the 2/3 calculation (above) using these would result in a base weight for 36" of circumference of 581g…
Wow, I hadn’t realized the weight difference was so slight. I’d previously been very attracted to the new rim, but I’m now thinking it’s not enough of a weight loss to justify the holes. Yeah, it’s probably still plenty strong, but the holes must inevitably add some vulnerability to the wheel build and tube. Besides, any significant dirt or wet riding could easily result in more than 3.2 oz of sand and mud getting into the holes and caking between the layers of the rim, so it could actually end up being heavier!
edit: Not to mention that the sand in the rim could be unevenly distributed, resulting in an unbalanced wheel. Although I haven’t seen discussion of this issue with respect to other drilled muni wheels, I suspect the effect could be exaggerated with the large wheel.
Basically I made the beads out of lots of loops of non-stretch ice fishing line and held them together with a piece of tape running their length and folded over. I cut the material at a 45˚ bias slathered a bunch of glue on the material and folded the beads into them sort of like this
so that in the middle the end overlapped. At the seams I just glued and overlapped then folded, that is how it looked in the 24" tire I destroyed so I copied the technique.
waited for the glue to partially dry and mounted it up and pumped to moderate pressure to get the wrinkles out.
I glued on the tread I pealed off a tire (easier said than done), let that set then took it for a test run.
I couldn’t find the materials I wanted so I ended up using polyester material and contact cement. Next time I plan to use room temperature vulcanizing butyl rubber (I didn’t even know such a thing existed until that thread) and silk or nylon.
I really don’t think that joining two beads together would be a very good idea. Lets say that you are running a 1.5" wide tire with a diameter of 36" at 50 PSI Assuming that the bead hook does nothing there would be about 36 X 1.5 X 50 = 2700 pounds of force your beads are holding back. Even more for a wider tire at the same pressure. I would go with an old 36" bead or at least 30-40 wraps of 50# non-stretch fishing line/wire.
I drilled just the outer wall of my Coker rim before building it up. It still feels really strong but I drilled a rim the whole way through once (26") and it felt pretty flimsy after. If you have your wheel apart why not try drilling only the outer skin. It keeps the rim stronger than a full drill and you won’t need to switch to ha heavier rim tape. If the wheel is all built and you are happy with it I would only do it if you were bored and need something to occupy your time. The weight savings are not huge but probably noticeable.
Been there, done that, got the scars to prove it. Makes for an uber stable ride, just don’t go faster than you can handle.
BTW I made a tread about adding weight to a wheel for stability and it turned into a thread about drilled rims. Go figure eh?
I haven’t tried it, but if I remember reading Jobst Brandt (The Bicycle Wheel) correctly, you should be able to ride with a cut bead without any problems. So if you are cutting down two narrower tires to make a 36in tire, do you even need to connect the bead?
Interesting - could you elaborate? I don’t know a lot about clincher bead theory, and what makes it work, but I can’t find much on Brandt discussing clincher beads either (he seems to be a tubular kind of guy).
Do you mean that restricting the circumference of a bead is not important: that it will not pull ‘along its length’ but rather pull outwards from the rim, and simply being the right shape to hook the rim will hold it well enough?
Maybe this is how a Big Apple tyre stays on an old coloured Nimbus 29" rim. It literally falls off the rim until there is some pressure in the tube, but once it is on it seems happy to stay there.
Thanks for mentioning me on this thread.
I was mentioned earlier in the threads as I have drilled rims and tried all sorts of things to make the 36 lighter but I understand there might be a way of saving about 400g soon on the wheel build (secrets not devulged :)). Keep your eye on UDC sites.
The Tire Bead Test does look like a good demonstration. The inspiration for that test came from this thread, where Brandt says:
So if I’m reading this correctly, the bead is just providing shape to the “hook” and it is the pressure from the tube pushing out on the hook that holds the tire on, not the circumference limit set by the bead. This makes sense, because the pressure is in all directions, not just radially out. That’s a good bit of force holding the hook of the bead into the hook of the rim.
I’ve never seen one of the Nimbus 29 rims, but that sounds reasonable. I think I’ve seen the same thing on an old three-speed bike.
BTW: Brandt is an advocate of treadless clinchers on 36 hole MA-2 (classic box double wall) rims for all road bicycling.