Big Wheel vs. Geared Small for High-Speed; Performance

Unicycles and Equipment
21

Dave is a climbing machine.

137 geared up on a 29 is about equal in gain ratio as 114s on a 36.

I think Magnus has a point with that solid orange angle but I don’t think he is explaining it right. It is really just the same as a giraffe being easier to keep in the “balance envelope” You just have a higher center of gravity.

One thing that his diagram does show is that you can have your body at steeper angle and still keep yourself in the balance envelope on a larger wheel if all else is equal. Of-course the balance envelope shrinks when you are less able to get the wheel back under you (larger heavier wheel) so it is probably a wash.

22

Alright Rob you haven’t convinced me I’m wrong but I think I understand what you’re trying to say, and I think you could be right. We’re looking at the problem two different ways.

I do want to call this one out. We’re talking about different frames of reference here, and I think you know that. Yeah, the point doesn’t move if you’re an observer standing on the ground, but from the rider’s perspective (who presumably has rotated forward with the frame), the contact point absolutely moves forward. Yes, the universe revolves around me when I ride my unicycle! Or at least when I do physics with it.

It’s similar to riding up a hill. Since the wheel is round, the contact point moves ahead on the slope. The bigger the wheel, the more the movement.

So this is where we’re seeing the problem differently. I think you have a good point about balance being from the axel rather than from the contact point, in which case wheel size doesn’t matter. In reality I’m thinking it’s probably more complex than both of us are describing it:
First, the reason I’m using the contact point instead of the axel is because the rider has pedals to control the rotation of the wheel in relation to the frame. If you sit on top of your wheel with the pedals horizontal, don’t allow them to rotate (in YOUR frame of reference!), and then fall forward, you fall rotating around the contact point (which moves forward in both frames of reference).
But then, when riding is taken into account, I guess one is not so solidly connected to the wheel, especially when the pedals are vertical. So you’d be balancing on the axel to some extent.
Further, I think my defense might prove me wrong, because someone on a larger wheel with the frame at the same angle as the one on a smaller angle has still fallen the same angle from vertical around the axel, so maybe they are in the same trouble. I’m not completely convinced.

Just for fun I want to throw in a bit about the wheel’s inertia. If the wheel is very heavy, pushing down on the pedal in front (assuming your centre of mass is behind that pedal) restores your balance by both the normal force coming back from the pedal who is “pushing back” because of the wheel’s inertia, and also by accelerating the wheel, pushing it back under you horizontally.

On small wheels with longer cranks this might be a pretty small effect, but I think it might actually contribute on a heavy 36, especially if it’s geared up. Maybe this is why use words like “floaty” to describe them: the wheel changes speed less to make similar changes in balance. I wonder how this affects efficiency.

23

That’s what I don’t agree with. You can only rotate around the contact point if you’re balanced on top of a knife edge, otherwise the wheel would have to dig into the ground. When you fall forwards as you describe, you rotate around the axle (and move forwards slightly as the wheel rolls).

If you fall sideways, then you do rotate around the contact point (almost, but even then only with an infinitely narrow tyre).

A giraffe is easier to balance (in the fore-aft plane) because it has a longer frame above the axle, not just because the rider is higher relative to the ground.

(don’t take this personally, by the way - I’m disagreeing in a friendly way because your thread got me thinking about it :))

Rob

24

Rob, you haven’t convinced me but I don’t know if we can ever agree. Oh well. But thanks for challenging though, it’s great to have some friendly debate.

From the Woods, wow, Austria sounds intense! The big climbs in the rockies are mostly blasted down to around 8% if I remember right. Mind you, the big climbs can be much longer than 5km. Dave’s in St John’s now so I can’t comment on his current terrain. But I was referring the to 29 in high gear as Saskatchewanian pointed out, so he has more leverage now than then.

Saskatchewanian, you’re right about the reduced envelope and maybe that effect makes the whole discussion pointless.

I was just thinking: maybe the amount the envelope shrinks is limited by length of the cranks. As long as you’re between them shouldn’t you be able to balance no matter how high the wheel is geared? Or maybe that envelope alone is too small to be useful, at least in the “real world”. Every so often I definitely have to recover from being leaning forward hazardously far, way over the front pedal. That said, I’m only riding 110s. Maybe in ideal conditions like a velodrome with very long cranks the limiting factor on gear ratio is not the balance envelope.

25

It’s very possible to climb climb 10% grades in high gear on a 29er. I do it all the time when I don’t feel like shifting. It’s above the grade where I can climb at speed, but I can still do the Funky Chicken and get up quite steep stuff.

As for bikes, I would be surprised if any bike in the Tour de France even has a gear as low as 44". Certainly all the top climbers climb in gears much higher than that.

26

hi mag,
Yes, I have lots of long distance on road, and offroad miles. My wife and I each rode the geared 24 through Africa on tour. There were some pretty long days. I didn’t have much trouble keeping up with the geared 36’es (and ungeared 36’ers), although the geared 36’ers could easily pull away from me on the flat and downhill sections of pavement. On the bumpy stuff I was pretty fast, but I was also pretty confident at riding offroad at fast speeds. video: http://www.corbinstreehouse.com/blog/2009/11/africa-unicycle-video-unimoon/

Also, do realize that I’m a fairly strong rider when I’m in shape (I’m the current marathon world champion from the last Unicon).

Comparing a geared 24 to an ungeared 36: In my opinion, a geared 24 is an adequate replacement for an ungeared 36. However, the guni 24 takes more energy to ride. No one has mentioned this, but the planetary system does consume more energy (say a few percent, due to the gearing), and it does start to effect you when you are riding long distances. This in particular affected my wife, and she had a hard time riding the guni24. Since the tour, she decided to not ride the guni 24 anymore, and just stick with an ungeared coker, which was faster for her. The thing she did like about the guni24 is the ability to easily mount it (she is 5’2", and mounting a coker is sometimes hard for her).

Your question was a “big wheel vs geared small wheel for High speed and performance”. For high speed and performance, an ungeared 36 will be easier and slightly faster to ride than a geared 24.

For real high speed and performance, you want a geared 36. It will always be faster, unless you are doing a pure hill climb (like Mt Diablo in the Bay Area).

I’ve done the same 100km ride (Strawberry Fields in Santa Cruz, CA) on three different unicycles: geared 24, ungeared 36, and geared 36. Guess which one was the best?

corbin

27

I guess maybe the ungeared 36? Due to the percentage of energy lost which you mentioned. The geared 36" would be faster if you are strong enough to enjoy a long ride like that on it. The ungeared is best for minimum maintenance and price hands down.

Nobody has mentioned rider leg length. Ken Looi and Corbin both save weight on the length of their leg bones but make up for it in leg muscles. The dynamics of wheelsize and cranklength and gears must all change slightly with different sized riders.

Interesting discussion.

28

Actually the geared 36 :). It saves overall energy by being better suited for more conditions. High gear on flats is easy. High gear downhill is easy, and fast.

I think it is also more comfortable. By pushing more with your legs you are taking more weight off the seat, which is actually more comfy. Louise thinks it is more comfortable for me simply because the ride takes me less time. That’s probably true too…

corbin

29

Hi Corbin,

Would you be willing to post times with the three unicycles?

I agree that minimizing seat time in a long ride would add to the comfort level.

Scott

30

I just put this up on my flat screen for the family to watch! :slight_smile:

I’m thinking about getting a 24" guni, and seeing it keep up with the 36’ers helps me believe it’s a good choice for me.
Thanks!

31

heya thanks. I hadn’t gone back and read that article since last September - my point of view hasn’t changed much since then.

The feel of 24 GUni in high gear (virtual 36’er) can’t really be replicated on the single speed 36. As Sam mentioned in the Total Gear Ratio thread the closest thing to riding high gear on a GUni is a bike e.g. riding an MTB in a gear that creates a similar load on your legs.

On a single speed 36’er there’s a lot of spinning lightly and making use of that giant flywheel. It almost rolls itself along once you get it going.

Compared to the single speed 36’er there is minimal flywheel effect on the 24 GUni in high gear - there’s a lot more pushing on the pedals, through the gearing, to keep buzzing along.

For road riding it would be hard to imagine a circumstance where a single speed 36’er wouldn’t be a ‘better’ i.e. more efficient choice than a 24 GUni. Off road though it’s a different equation.

There are a bunch of other differences that come into play when comparing a single speed 36’er to a 24 GUni. I guess rather than generalizing too much, which one has better performance etc depends more on the rider, terrain, situation etc.

Fwiw, since putting the hub into a 24" last September I pretty much haven’t ridden the 29’er at all, and the 36’er not that much. Of course the 24 GUni is still a compromise, but for me it’s just a lot more satisfying/fun to ride - that’s my performance criteria :slight_smile:

32

Hey scott,
it is a leisurely ride, with lots of stops – not a race. It takes all day…and I tend to ride “with the group”. Except a few years ago when chuck and I raced through it on our geared 36’s (this was not too long before RTL).

corbin

33

yesterday I rode with enaddi (Nadine) about 10Km in urban periphery.
she rode a 26" x 3" Gazza, Triton Schlumpf, 125mm cranks and I rode a 36" Schlumpf 150mm cranks.

  • She was faster upphill when i had to shift down (Ok, that depends on the power, but if both have the same power its just a question of the grade of ascend) and
  • she was much faster in speeding up - altough using only high gear! (she is trained to ride her fixed gear 1:1.75 29")
  • I had more maximum speed but at all - in this surrounding of up and downs and traffic lights a 26" x 3" or 29" Schlumpf is faster and makes more fun than a 36" even with schlumpf - (mostly the gazza is no good choice for road but thats my offroad setup)

@michael
If you would ride 100 miles with Dave - [SIZE=“1”]I mean he rides 100 and you about 50:p you would understand words like “fast” and “uphill” in his understanding;) [/SIZE]

34

This discussion has been really informative. Thanks for all the feedback so far!

I swapped out my 36" inner tube for a 29" on my kh36 the other day. At first I really liked it, but it seems to wobble a lot more. It makes me want to ride with shorter cranks.

I can’t say how much it’s related, but I did a 30k ride on Friday and found my backpack swinging back and forth almost uncontrollably on many downhills, and on straight stretches if I was going at just the right speed, which seemed to be right in the middle of my comfortable range. I had a bit more weight than I normally carry, so maybe that’s the problem more than the lighter wheel, but man, it sure freaks drivers out. Maybe it’s just time to get a brake.

It got me thinking though, how does the amount of wobble compare between large heavy wheels and small light wheels? On a 24 in schlumpf high-gear you’d be pedaling the same cadence as someone on a 26 for a given speed, but I’d imagine the stabilization from the wheel would be much less.

Do people have trouble with this at all? Are backpack oscillations more extreme?

35

I can’t comment on the geared 24 but when I go to a lighter wheel of any size i loose some smoothness. and yes you can get some of that smoothness back from going with shorter cranks, which translates into a faster setup. Bonus.

what helps with backpack oscillation is straps, lots of straps. You should be using the shoulder, chest, AND waist straps. If your backpack does not have them you can sew some webbing on and add clips. If setup right they will not interfere with the movement of your body and keep the backpack firmly planted on your back.

Next i also like having compression straps on the backpack so I can tighten up the load so it does not move within the pack.

36

Pedaling technique

Can you pedal and maintain a straight tire track? Wobble can come from how we apply power to the pedals. When we push forward across the top of the stroke the force pushes the wheel into a wobbling tire track. Larger wheels are harder to track straight. It becomes really noticeable when riding a ordinary bike (penny farthing) up a hill.

37

For what its worth, a geared 29er feels more squirrely than a geared 36er, probably due to the wheel size/weight.

38

Thought I would dig us this thread since this is sort of big wheel vs small geared wheel related

Went for a couple back to back rides today with a G24 and my 32" just to compare how they compared.

Critical stats:

24" GUni
24x2.25 tire
47mm rim
125mm cranks
3.7:1 gain ratio (in high gear)
7.20 kg

32"
32x1.75 tire
28mm rim
114mm cranks
3.5:1 gain ratio
5.89 kg

First I took the GUni out for a spin, went down the highway, took a gravel road then went back through town. The thing felt a little sluggish getting going up the first hill but I soon got a good pace going. The wheel was pulling a tiny bit because of road crown but not too bad.

Got onto the grave and was doing great until I hit some washboard and ended up doing a running UPD. Jumped back on and kept on going. Once I got into town I had to do the “pothole slalom” Our streets are more pothole than pavement in the spring and this year is no exception. Going uphill dodging the potholes the GUni was excellent, nice fast and nimble. On the downhill pothole dodging though you could feel the slop in the gears, which didn’t really affect anything but gives sort of a disconnected feel.

Before getting back to the house I hit a patch of mud which really slows down the GUni but didn’t throw me this time. Got back to the house and checked the time. The loop took me 21 minutes.

Brought out the 32 and mounted up. First thing I felt going to the light 32 from the GUni is how light and “refined” it feels. No slop at all and very responsive. I should mention that I only have about 3km of riding on this wheel so far.

I had no trouble getting it up to speed climbing the first hill and was cruising right along. I could not feel the road crown at all on this unicycle but was blown a bit more by the wind. Though the gain ratio is not all that much different than the G42 I really felt that I should loose a bit of length in the cranks (which I did not feel on the G24).

I wasn’t sure how the skinny tire would handle the gravel but it just cruised right along. I guess the large diameter made up for the skinny width of the tire. Hit the washboard section and had no problems, the wheel seemed to flow through it better than the 24 which more bounced along.

Got to town and the pothole slalom course. I was expecting the light wheel to be really nice and flickable, making it really easy to do all the sharp little turns while keeping the speed up, It didn’t. I felt comparatively unstable navigating between the holes and felt much more precarious being higher up than the GUni. Something I never felt with a big heavy 36.

The big wheel cut through the mud patch with barely a notice and when I got home checked the time, 19 minutes.

So no good hard evidence for anything there but I would have to say that I preferred riding the 32 over the G24 on everything except in town dodging potholes. I should have done a ride with my 36 next but it doesn’t have a seat at the moment.

Light weight big wheel (32 is sort of big) feels really good but I need to go bigger on the wheel or shorter in the cranks. If/when I get bored I will have to make up a light 36" tire and see how that handles compared to a standard 36.

I am not really that impressed with the G24 as a wheel size. I think the hub would be great in a larger wheel though.

39

+1

I’ve ridden 24, 26, and 29 munis, plus have a 36er. I can more of less use my 29 and 26 interchangeably since the tire diameter is nearly the same (Larry 3.8 and RR 2.4), but find a 24x3 to be quite twitchy. The 29 x 2.4 in contrast to a similar sized 26 x 2.5, the 29er feels like it bridges obstacles better, but feels slower to respond.

I have ridden my 36er mostly on jeep roads (dirt and gravel) and find that it rolls great ONCE IT GETS GOING, but it is SLOW TO STOP. The 36er has a huge amont of rotational inertia, so it can get to be too much, esp at slow speeds, so not exactly graceful. If I were riding just open road, I’d use a 36er, but if I knew I was going to have mixed surfaces or have to do some agile movement, such a riding in traffic, a geared 29er would be my first choice. Also, the geared 29er is going to allow a low gear for climbing, whereas in the 36er you are stuck with a high gear or a higher gear.

Off road XC, 29er fixed or geared, hands down the best choice.
Off road technical/DH 26, add a guni for making the connecting roads go faster…