The quest for a lighter 36er...

This old chestnut has surfaced again!

I too would love a much lighter 36" tyre and I agree that a narrower width would make the best progress on this. I think the rim is less of an issue; we could use 40mm tyres on current Stealth/Airfoil size rims and it would be a massive change. The rim needs to be extra strong at the large diameter size; it’s the tyre that’s really overweight.

I understand that the reasoning behind keeping 36" tyres so thick is to maintain a bigger contact area for riding stability (avoid squireling etc.) and minimise the side-to-side deformation that thin sidewalls would give you (which bikes don’t worry about, not steering/driving/braking with the same, single wheel).

I do mean to (some day) try building a normal width (about 40mm) tyre for a 36" wheel - possibly out of two touring tyres and a pair of beads cut from an old 36 tyre. That would ensure that the bead would fit (as opposed to making new bead loops from other wire/kevlar cable). The two bike tyres could then be stitched on to the old beads at each side (obviously this wouldn’t have the weight benefit of kevlar bead!). I’m sure that part would work, I just don’t know how good a join could be made at each end of the half-tyres. It may be possible to get a nice, smooth ride, but I suspect it would be quite hard to! Bumpmmmbumpmmmbumpmmmbump?

Only when we have a good prototype of a thinner tyre can the questions about ride quality be properly answered. But real production tyre prototyping is hugely expensive.

This all means: get bodging!

Sam

Anyone running Titanium spokes and a drilled rim? I believe that coupled with a Ti hub and 29er tube would yeild a very light 36er wheel that one could actually acquire with easy.

That’s an interesting idea, sam. eric (saskatchewanian) has made his own tire before, using some kind of glue and long strips of thick nylon material. He then glued a tread down the middle which he’d pulled from an old mountain bike tire. I think it was only a 24" tire but the concept is the same - he said it was rideable, though I’m not sure for how long!

I’d never thought of using the beads from a 36 tire though, that might make this kind of idea possible for a low-profile 36 tire. Summer only, of course :wink:

What’s broken with the current 36er wheel design?

Yes, it’s heavier than it could be, but what’s the need to go superlight?

Are we trying to shave seconds off our split times for next year’s Tour de France?

Will we be backpacking the 36er into a remote region so we can ride an exclusive paved course?

Is it worth sacrificing the comfort of the existing 36er wheel? Distance riding is painful as-is… why make it more painful?

I don’t see any reason to go lighter.

I ride on a drilled airfoil rim with a 29" tube. No titanium spokes though. Even with this set up, I’d love to take another 500+ grams off the weight of the wheel. Although a Ti hub would decrease the overall weight of the uni it wouldn’t have as big of a benefit in reducing the rotational inertia of the wheel.

Decreasing the rotational inertia is potentially one of the best ways to improve a rider’s efficiency. Although I’m sure it could be improved, I can’t envision a huge decrease in frame or handle bar weight. Carbon fiber, maybe? I’m already skinny, so reducing MY weight isn’t going to happen. After 3 years of riding my 36" guni I don’t think my skill will increase dramatically, so I probably don’t have any great efficiency gains to make there, either. What’s left? A more aerodynamic helmet?

Maybe “onebyone” has some ideas. I look forward to any and all “new developments”.

Geoff

Changing out components at the center of the wheel will make the unicycle lighter, but it does nothing to affect how the wheel handles.

See: http://en.wikipedia.org/wiki/Bicycle_wheel#Rotating_mass

Swapping 6 gram spokes for 5 gram spokes won’t make much difference either. How does 200g worth of spokes compare to 3000g worth of tire and rim?

Ispokes = 1/2Mspokes(1/2Rwheel)^2 = 5.2 gm^2
Iwheel = 1/2
Mwheel*Rwheel^2 = 313 gm^2

By this very rough estimate, the spokes make up 1.5% of a model wheel’s rotational inertia.

Sam drilled his rim and saved but 50g. Compared to the 3000g tire/rim combo, this is just another drop in the bucket.

See: How to drill a nightrider 36 rim?

Your suggested improvements might add “bling”, but they won’t do much for performance.

Yeah, you’re right. What was I thinking? Nor do we need faster computers with bigger hard drives. I remember deferring on the 60 megabyte hard drive because I couldn’t imagine filling up the 30 megabyte hard drive. We don’t need more efficient cars because we’ve got plenty of gas to go around…

We want skinny and light wheels because we love speed. Because we want to kick ass at the next criterium and the next marathon. Because we want to do the next century in less than 9 hours instead of 10. Because faster is inherently better! (Until I fall.)

I just couldn’t resist ribbing you a little Maestro8, because you are so good at dishing it out when people desperately deserve it. I knew you’d appreciate it. :wink: We’ll have to get together for a ride someday. Someday, like maybe the Cool criterium on May 1st. I can show you the virtues of a drilled rim with a 29" tube.:slight_smile:

Geoff

I like the idea but I also love the stability that all the weight gives. It would make hills a lot easier.

Have you got a Nimbus Nightrider? It’s only 2 ply sidewalls instead of 4 like most of the others. I’m a bit new with stretched 29" tubes and now I endorse them so far. I rode one around the mountain the other day with no problem, and it was not too hard to get on even though it stretched a bit unevenly. Maybe I am yet to get my problems. I like reliability too but if something does the same thing for lighter its worth a shot.

After yesterday I got the feeling that my 36" is very small. I rode Andy Fraser’s 58" custom hand built Penny farthing for a few hours. He says you can get aluminium rims any size now but he made his rim out of wood. Bigger is definitely faster. Better for falling harder too. The solid tire is very bumpy over bumps but Andy made it around lake Taupo (100 miles of hills) in just over 8 hours on it. He uses clip in pedals.

I’d like a narrow pneumatic tire 42" or larger, to see what properties it has.

Blaming equipment is what one does when he hasn’t trained enough. :wink:

I understand that our sport has progressed quite a bit in the past few years, especially given the increasing number of races in which we’ve been able to participate, but I don’t see it having progressed to the point where a shaved tire is the difference between a winner and a loser.

Granted, we’ve seen some close races (i.e. UNICON XV’s 10k) but we’ve seen many, many more where there are minutes of difference between winners. This doesn’t tell me that we’ve got to look to technology to close the gaps.

We might also consider the possibility that some riders’ performances will become degraded with a rougher ride. There must be some cross-over point where the benefits of a lighter wheel are lost to discomfort and/or lack of control. There is something to be said about the smoothness of a heavier wheel…

I am wide open from anything between a ribbing and a stern talking-to. It is a direct consequence of my behavior and I’ll stand and take it when delivered, especially from a respected member of the community such as yourself.

And I can show you the virtues of being incredibly lazy. Um, when I get around to finding them.

Unless I make a “quantum leap” upgrade such as a geared hub, my riding will not improve much without an order or two of magnitude increase in training time. I think the same could be said for many riders, except for those who are naturally gifted.

One thing that is missing from the desire for a narrower 36in tire is that unicycles need wide tires for shock absorption. (John Foss and maestro8 have mentioned this too…) Sure, road bikes use 23mm wide tires, but bicycles are designed to absorb shocks, unicycles aren’t. Road bikes have forks that are designed to assist the tires in smoothing the roughness of the road. The 36in unis I have seen just have straight forks that aren’t designed for shock absorption. (The V2 is a heavy frame I wouldn’t consider as built for soaking up bumps.) Additionally, the wheels of a bike are not directly underneath the rider, so you don’t feel the entire shock at once. On a hard and smooth surface, a narrower tire will be more efficient, but on real roads, you need the extra width for shock absorption. So there is a minimum tire width where a narrower tire takes more energy to ride because you must absorb the shocks with your body instead of letting the tire dissipate the impact. This is why the large diameter wheels with rubber tires give a rougher ride than a Coker tire. A rougher ride takes more energy and wears you out faster, so a tire that may give a fast ride over short distances may slow you down past a certain distance. For non-racers, a road bike with a 25 or 28 mm tire is fairly common.

Given that the Coker tire was originally for a 36 inch cruiser bike, I assume the tire width was chosen to match the normal tire width of other cruiser bikes. This means there is probably still room for optimizing the tire width. Since road bikes (racing) typically use 23mm wide tires, I’d guess a good minimum width for a unicycle tire would be ~46mm (1.8in). This matches well with the 1.75 to 1.95 inch tires found on entry level and freestyle unicycles. Because the frame acts less as suspension on a uni than a bike, I’d maybe add a little width, and say a 2.1in tire as is typical on mountain bikes.

If I assume a Nimbus 36in Stealth Impulse rim, I can do some quick calculations for different tire widths. I’ll compare several theoretical tires to the Nightrider 2.25 inch (~57mm) tire:

Nightrider --> 50mm
volume change = -13.70%
rotational inertia change = -10.26%
rollout change = -4cm

Nightrider --> 46mm
volume change = -21.27%
rotational inertia change = -15.79%
rollout change = -7cm

Nightrider --> 40mm
volume change = -32.50%
rotational inertia change = -23.83%
rollout change = -10.7cm

The change in rotational inertia should really only matter when you are accelerating. It is also worth noting that the 40mm wide tire will require more revolutions than the stock Nightrider tire.

So, it’d worth trying a 50mm or 46mm wide tire, but I’m not sure about going any narrower.

Terry: the shape of road bike rims is largely a marketing decision, not a strength decision.

I am an engineer, I understand the math. I was simply stating if you want a light weight wheel as of right this second your only options are a ti hub, ti spokes, drilled rim, and 29er tube, and helium in the tire if you’re nutzo. The amount of money it takes to purchase those parts is far less than the investment in creating a tire from scratch for the 35 people in the world that need a lighter 36er.

I was just describing a more obtainable path to achieve a lighter wheel.

You mean I can’t blame my fourth place finish in the 2010 U Games/Naucc marathon on my equipment? Next you’re going to tell me that my going “splat!” on the pavement halfway through and the fact that Corbin is just plain sooper dooper fast on the descents and everywhere else were the deciding factors. Well OK, I had a decent lead on the flats at the beginning, but then he smoked me.

I agree. I think that crossover point is somewhere between 4 and 5 cm.

I’m almost disappointed here. You are far too conciliatory. That “respected” bit makes me feel down right old. Ouch! Would it help if I stuck out my tongue and blew raspberries?

Well then, get the geared hub. It’s much easier than training. That’s what I thought until the 2nd and 3rd place finishers in the marathon were on ungeared hubs. It’s soooo not fair to not have an unfair advantage because of all the money I spent on a fancy hub. Where’s the payback? Those young whippersnappers. Darn them. Darn them to heck!
See you at the crit?

Hey nordicnoel, how did you come up with the % change in rotational inertia?

Geoff

I think you misunderstand the market for these wheels. Most of the people who have 36" unicycles use them to “show off”, not to ride marathons or centuries. Most of that majority probably don’t care how much the wheel weighs. Of course, the casual users are not the ones who spur the innovations either…

Well said. Really, if you want a more responsive wheel you’ve got to make changes in the tire, tube and rim for them to be noticeable. Tube is the easiest, followed by a new rim, followed by a new tire. Unless we can talk someone into doing a lighter version of one of the existing tires on the market.

Oh, yeah. And for MUni durability I wouldn’t want to take much off of today’s 36" wheels. But those are available now, so they don’t do much for this thread.

That’s what I have on my new 36", but the wheel on that one feels heavier than the one on my 48-spoke Coker did. This might have something to do with the Schlumpf hub and Moment cranks, though those are basically non-rotating weight.

If I remember correctly, all but one of the 36" tires on the market have very similar weights. The light one is the Coker Button. The difference is probably that the others have the thickness of the buttons all the way around, which probably makes them last longer. Anyway, I classify all of them as “very durable, but very heavy.”

Yes and yes, to a point. A 54" unicycle is probably less crash-prone than a 36" Schlumpf in high gear. And of course bigger means heavier. That penny farthing wheel looks relatively lightweight for its size; kind of like what we’re talking about in this thread. If you make a bigger unicycle, you magnify the problem of rotating weight. But it looks cool. That bike sure dwarfs your 36"! I’ve ridden a 63.5" unicycle, once. The wheel was very light, but it was made more for demonstration riding than cranking out distance. It was a rectangular cross section, solid piece of aluminum, with a solid piece of rubber stuff of similar dimensions glued to it. And the seat was built into the frame for the lowest-possible seat height. Even then I was barely able to reach the pedals (the builder was a tall guy!).

Impressive. When we passed Taupo last year, I could see how it must be a beautiful ride, like our Tahoe ride only longer. And that day it was really windy! Almost like the Unicon Marathon day. :slight_smile:

I don’t think that’s what this thread is about. Just about having a lighter wheel. I’d like something about halfway between the current offerings and a Track unicycle wheel. There is a possible market for such a thing. But if you go full-on racing, you’re talking a really tiny market, and a really uncomfortable ride. No thanks!

Good point, and the reason I wouldn’t want to go super-skinny. I think something similar to the 1.75" tires I was raised on would be perfect for riders who want something lighter yet still enjoyable for performance riding. You would have to run higher pressures, but not crazy-high.

And you’re right about unicycle frames; they are not made with inherent suspension in mind. They could be, though at the cost of added weight. A cantilevered frame of some sort could add a level of suspension. But whatever is done there, the pedals will still bang around with the wheel.

BTW, the V2 was intended for anything but soaking up bumps; it’s the most rigid 36" frame out there. I think it’s intended for soaking up looks. :slight_smile:

Sounds nice!

– and decelerating, and making corrections. Basically most of the time, especially when riding on anything other than smooth pavement. That’s why it would make such a big difference to lighten the wheel!

Some might say you guys are obsessed with this 1-wheeled madness… :wink:

Duh.

Only “some”?

My impression, from the few 36"/29" riders I know, and, from the many posts on this forum, is that the majority of 36" riders use them for riding- maybe not necessarily for marathons or centuries, but, certainly, the main point of getting a 36-er seems to be riding (longer distances than on 29/24).

I doubt that many people fork out £200-500 (more in the case of geared hubs) to ‘show off’ :slight_smile:

Oh, yeah, methods… There is plenty of room for improvement if anyone wants to post more accurate measurements to plug in.

I used weights and dimensions from the UDC website:

Nimbus Stealth Impulse Rim: 2.2 lb, 787 mm diameter (BSD)

Nimbus Nightrider 36 inch Tire: 4 lb, 2.25 inch wide

To calculate the volume change, I assumed the tire was a torus with the inner edge touching the rim. I used a rubber thickness of 4mm. I multiplied this result by 3/4 because a tire is U' shaped, not O’ shaped. This gave me a rubber density to use for the smaller tires. I repeated the same math with the other tires to estimate their weight.

For the rotational inertia, I used the weight of the Stealth Impulse rim at its radius and calculated its rotational inertia as ( mass * radius^2 ). I added this to the rotational inertia of the tire with its mass centered at half its width further out than the rim. Then I just found the percent change from the Nightrider tire.

Yeah, the fact that the pedals move with the wheels really limits the suspension options. If suspension worked well, I think we’d see more unicycles built out of mountain bike forks or with suspension posts. Any method to make the wheel move independently of the pedals would complicate the design enough that I’d just ride my bike, saving the uni for when I don’t mind the rougher ride.

Hmm. On pavement, the main benefit of a narrower tire may be saving energy when dealing with the typical cambered road. I’d really like to compare the current 36in tires to a 46mm (1.8in) tire.

How about a current 36er tire with a strip cut out of both side-walls and stitched back together? I know Saskatchewanian made a super-wide tire by cutting two mountain-bike tires and stitching them in the middle, but it seems to me that riding on the stitching on the road at high pressure would be both not smooth and very wear-prone. Could stitches in the sidewalls hold up to high pressure? Would the tire’s profile round out a bit with shorter side-walls or would it just be shorter and still wide? Is there significant weight to be saved in the sidewalls or is the real issue at the tread?

To go further with someone’s comment about acceleration: one is always accelerating the wheel on a unicycle, it’s how we stay balanced. I don’t know if the benefit of a lighter wheel in terms of efficiency is quite as direct as that though, since pushing against the inertia of the wheel can also contribute to correcting balance to some extent as well – when you speed up your wheel, you’re pushing with the foot that’s in front. Since you’re pushing against something that’s ahead of your axle, and, (I’m assuming, in most cases), ahead of your centre of gravity. I think that in itself contributes to balance correction along with actually speeding up the wheel to move it back under you. Seems to me that a heavier wheel would show less variation in speed in normal riding, but I don’t know if this means less energy spent, since you have to push harder to change the speed. From my own experience, I find a lighter wheel easier to control, and most performance-driven riders on this forum seem to have taken some steps to reduce the weight of their wheel.

I’m going to call John Foss out because now twice in this thread he’s stated that

Kind of. You’re right in a way because the spokes are longer and have to be thicker, so you add some weight there. But the same weight of tire/rim/tube out at a different radius actually has no effect on the amount of energy it takes to change the linear velocity of the wheel by a given amount.
And from a practical sense you are right, since larger wheels are heavier… because they’re larger. But the fact that they are larger doesn’t make that weight count more.
Bigger wheels rotate at a slower rate than small wheels for a given speed. This reduced rate of rotation cancels out the increased radius.

For less “perceived rotational inertia” as I’m calling it, we need lighter wheels period. Smaller wheels help us get there, but c’mon, size doesn’t matter.

inertia = massradius^2
energy = 1/2
inertiaw^2, where w=rate of rotation in rad/s
linear velocity (ie, your speed) = w
radius
so w = (linear velocity)/radius
then energy = 1/2*(massradius^2)(linear vel/radius)^2
The radius cancels out:
energy = mass*(linear vel)^2/2

So the energy in your wheel is proportional to its mass, increases with the square of your linear velocity, and is independent of its radius.

Assumption: I assume the mass representing the wheel is a thin ring of constant radius. I think this is reasonable for normal wheels used for racing and distance, but it does not factor in the spokes, hub, cranks, etc. It also doesn’t take into account the movement and energy stored in ones legs, which would be affected by a different wheel size, since you’d have a different cadence.

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?

FTFY.

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…