# someone PLEEZ give me an explanation

The scenario: I am entering a relay (bike) race on one of my uni’s. My favorite uni is my 26" with 125mm cranks and my average speed has improved to 14km/h with a maximum of around 17km/h (on the flat). However I figured over 40km a 29" would eat up the road quicker. So I dusted off my 29", put on 125mm cranks as on my 26", thinking I would average at least 16km/h.

I was BADLY mistaken. My average speed on the 29" is slightly less 0.02km/h over the same terrain (same weather conditions) I don’t get it! I need to decide which uni to train on, but why give up the smooth handling of the 26" if my 29" can’t deliver???

Seriously, I have ridden bikes and fixies for a few years so know about cadence, spinning smoothly and so on and this is what I aim for on the uni. My bike computer is setup properly for the different wheel sizes. Why is the bigger wheel with the same length cranks not significantly faster?

It seems you have lower cadence on 29". As you say you don’t feel it that smooth as 26", so probably you feel better on 26 and then you can pdeal a bit faster.

What is the actual wheel sizes you have in your computer for both wheels? The ratio between the two should be comparable to speed ratio.

My Wheel size for the 29" is 2355 (I measured the wheel diameter and timesed it by pi.). The wheel size for the 26" is actually 2166, but I have it as smaller in the computer due to a miscalculation 2135, thus I am probably going even faster on the 26"?

The difference is about 10%, so you should reach something about 15,5km/h on 29".
Now it seems you have 10% lower cadence.

Measure the roll out distance of your wheels. Get on your unicycle with the valve stem at the very bottom. Mark that point on the ground with some chalk, pedal one revolution until the valve stem is again at the bottom. Mark that spot with chalk. Measure the distance between two points. That is the true length of one revolution. Your weight will deform the tire and change the distance of your circumference. The PSI of the tire will affect the roll out distance. Use these numbers for your cycle computers.

Also keep in mind that a 26" wheel will wiggle back and forth more frequently than a 29" wheel. Therefore, despite what your computer says, the actual distance traveled of the 29" wheel will probably be greater than the distance traveled of the 26" wheel. Does that make sense? Another way to put it: There is a certain percentage of inefficiency of travel with unicycles because we don’t go in a straight line. If we are riding from point “A” to point “B” and these points are 1 km apart, a 26" wheel will probably travel a greater distance between these two points (say 1.08 km) than a 29" wheel would (maybe 1.07 km)(I’m just making these numbers up to illustrate the concept).

Another approach is to not be fooled by your cycle computer at all. Measure the time it takes for you to travel from point “A” to point “B”. The actual distance doesn’t matter, just use the same distance and ride it on both unicycles. Then you can compare your two rigs. Remember, in a race, nobody cares what your odometer says.

Of course, in your situation my preference would be to sell both unicycles and buy a 36" Schlumpf.

Geoff

The difference between 26" and 29" isn’t that much, so the fact that you’re more comfortable on the 26" is balancing out the fast that the 29" is inherently a little faster. If you train on the 29er it will be faster in the race.

For 40km in race conditions I would probably go to shorter cranks than 125mm.

That’s funny (well not really) but I have been riding my 26er for weeks and took my 29er out this past weekend and ended up posting on my Facebook that I was averaging 1 mph slower then when I take my 26er out. I thought I might average at least .50 better with the 29er.

Another factor could be the type of tire you are riding, and if one is more adapted to the terrain than the other. My average speed on my commute went up when I switched on my 29er from a Big Apple to a Crossmark tire, on mostly gravel trails, even though you’d think the BA would be a faster rolling tire.

I have a schwalbe big apple on my 29" and a kenda k-rad on my 26", so would have thought the 29"has less rolling resistance?
Someone suggested that the 29" takes longer to get to cruising speed, whereas the 26" is easier to accelerate.

Would any of you guys do a 40km race on a 26" or is that nuts? (like turning up at the local bike racing club on a beach cruizer )

So you’ve been riding the 26" a lot while the 29" has gotten dusty? You might need to give it some time, to get comfortable riding it again. Other factors could be seat height, seat comfort (different seats?) or a different tire; maybe one that doesn’t cruise as nicely.

Perhaps your question should also be, why are you pedaling significantly slower on the 29"?

That depends on the relative weight of the wheels and other factors as well; a light 29" wheel might wobble more than a heavy 26". I think there is too much attention paid to the whole “wobble factor” anyway. Some people wobble a lot, some not so much. With practice, you can improve your spin to reduce the wobble, but otherwise it’s a fixed component of your riding. Better to just compare the time it takes to get from A to B, as you said. This also eliminates any inaccuracies that may stem from computer settings.

Definitely. Unless your course is very hilly (as we know NZ can be), try something shorter. I’ve ridden a Marathon race on a 36" with 102s. And no, that was Unicon XIV, NOT XV!

Same thing. You’re going to tend to be more efficient at what you’ve been riding a lot. The other unicycle may need a little saddle time for you to get it “up to speed”.

It depends on wheel weight, especially at the rim and tire. The heavier wheel should accelerate slower, but the difference will only be a handful of seconds.

My first really long ride was 75km on a 6’ giraffe (20" wheel and 140mm cranks). Ride what you have. If you borrow a 36" the night before this event, don’t expect to be faster on it. You’ll need time to get used to it. I recommend riding the 29" some more, and comparing times as Naturequack suggested. In the end, ride the unicycle you’re more comfortable with. The longer the ride, the more that matters.

Thanks for all the info guys! I have decided to ride both unicycles on training runs I do at least 4 a week, so can do 2 on my 26" and 2 on my 29" and see which one I am fastest on 2 weeks before the event. I am also going to put a different tyre on the 29" as I’ve heard there’s camber(?) issues with the big apple tyre, Anyone got suggestions for what would make a good tyre? Can I stick a 700c tyre on there? (I’ve got a 2010 (?)Nimbus 29" wheel)

The Big Apple 28x2.0" version is great on camber; it’s the 2.3" version that has problems with it. The Schwalbe Marathon Supreme is also good.

Your tire needs to be fat enough to fit on the rim; a narrow 700c road tire might not grab the rim sides. It’s also better to have a little more cush in the tire. I’m running a 28x1.5" right now, which is about as narrow a tire as will fit on the KH rim; you probably want something between 1.5" and 2.0" for road racing, although fatter tires can be OK as long as the tire profile is rounded enough to work OK on camber.

Absolutely would! There are folks on this forum who’ve gone much, much further on smaller or same sized unicycles. I’ve personally done 50 miles of hilly XC riding at a 12 hour mtn bike race on my 24" w/o any real problems.

I’d agree that you should go with as short of cranks as you can get away with, regardless of which sized uni you end up using. For road you’ll be better off with as narrow a tire as you can comfortably ride and fits your rim. A bit of “cush” always helps. I really like my Maxxis Hookworm 24x2.5 road tire that I used to ride ~50km along Route 66 a couple years ago. No problems with camber and plenty cushy enough…

Good luck!

Thanks John, yes I was going a bit faster the next day and I also attribute my slower speed to the trail being pretty busy the first day I rode again with the 29er. At first it was entirely me being slower, I think the saddle is a bit wider than on my 26er which takes a bit to get used to being I’m small. Also, I had to slow down several times for dog walkers or people just meandering, which being a nice fall day in NY is entirely understandable, just good to be out on a day with good weather.

Hi,
“So I dusted off my 29”, put on 125mm cranks as on my 26", thinking I would average at least 16km/h. "

While there isn’t a big difference between the diameters apparently, but you are still effectively pushing a bigger gear. One crank rev = more distance on the road.

At least it’s easy to see that concept when you are only changing the wheel size…

I was thinking about this issue on another thread (unsuccessfully) but as I understand it, on an ungeared (poor ) unicycle we change the crank lengths to change our gearing, which in our case is not about the distance covered but the load on our legs.

I don’t run faster when I run up hills…

So a longer crank will not necessarily make you slower? Especially over longer distances where speed is only one factor in getting to the finish…

Cheers

Some people ride pretty fast with long cranks. Like Bill Purcell, who beat the other five riders in a recent XC MUni race, with 165s on his ungeared 36" (and clipless pedals). Though on that course, the longer cranks enabled him to stay on the uni up all the hills (unlike the rest of us), one would think it would make him slower on the flats and downs.

But the difference with longer cranks is that you’re lifting your legs up and down more. Larger leg movement=more energy required to do it. As with everything else, give it some time to get comfortable with it. If you only try it for a few days you won’t get a fair picture of your potential with equipment changes.

I agree, I need to give the 29" more time. If I find however it is not getting significantly faster, perhaps I should stick shorter (114 mm) cranks on my 26"; or would that give it the same feel as the 29" ?

I did a 10k speed test yesterday and I’m only just faster on the 26". My speeds were:14.97km/hr vs. 14.6km/hr - my average cadence (on the 26") was a 117!!! I don’t have a cadence sensor on my 29", but obviously I am pedaling slower due to confidence issues. I don’t think I can pedal much faster without loosing it (on the 26") and I doubt I can keep up that cadence over 40k’s. So my option is to go with shorter cranks, however would that make it feel/handle the same as the 29" ???

Playing with different crank lengths on different wheels can have surprising results. It can have a dramatic impact on the “feel” of the ride but may not have as big an effect on your average speed.

I haven’t experimented much on 26 vs 29 but I have done a lot on 29 vs 36 (both ungeared). In a series of controlled experiments I found the cruising speed for me on a 29er over varied terrain was not that much different from that of a 36. The 36 certainly felt faster and smoother but when Tony and I did our time trial experiments we found out that changing crank length and wheel size didn’t effect our speed over a middle distance length very much at all. Tony was marginally faster on some combinations while I was almost constant across all combinations.

Crank length and wheel size did effect how the ride felt though! Our conclusion was to go with the combo that felt nice and enjoy the ride. At the time my favourite setup was a 36" with 125mm cranks. I still like this combination although since the experiments I’ve been doing a lot of riding with a geared 29er (125mm) and more recently a geared 36er (165mm cranks).

I haven’t had a chance to do controlled experiments yet (wind is a big factor in my daily commute, which stuffs up my stats) but it appears like the geared 36er is going to be noticeably faster once my fitness improves.

Is this what your cycle computer says or what the sign posts and stop watch say? Did you ride the exact same course twice or did you ride two different 10 k lengths? As you know, I don’t trust cycle computers to reflect reality. They just approximate.

I did the exact same course - 5k’s riding and back again, one after the other.
I used a huge pile of dirt next to the road as my turnaround marker.
I did a warm up and went on the 29" first to give it a ‘head start’ (fresher legs)
I had 2 different computers on my uni’s, and the distances on them were more or less the same, so I am sure they are fairly accurate.
We’ve also done other tests with my husband riding next to me and we’ve had similar readings distance wise. All 3 computers are different brands/makes. He has a sigma wired (not sure of the model), I have a sigma BC1609 wireless on my 26" and a topeak Comp 150 wireless on my 29". To be sure cycle computers aren’t a fix-all training tool (unless you have a power meter ) as it doesn’t reflect things such as terrain, wind, mental condition etc. However I find it useful to roughly track my progress.