Yeah, a set of 150mm cranks would be a pretty cheap thing to experiment with - gives you a bit more control, and more power if the tyre gets a bit stuck in deeper snow (once you’ve got a tyre with a tread, you can put more power through it before it slips in the snow).
Joe
One problem you’ll have is that the Pashley frame isn’t large enough to accept a really fat tire. You might be able to find a studded tire which isn’t very fat; that will help on icy surfaces, but not a whole lot in the snow. You could try a local bike shop; your rim is a standard 700c which will fit a wide variety of tires, as long as they fit within your frame. I assume that bike stores in Oslo have a decent selection of stuff designed for riding in the snow.
Longer cranks will definitely help, and also make it easier to freemount. unicycle.com has a Swedish outlet which might help you with shipping/importing longer cranks. Cranks are measured from center-to-center; the center of the hole for the crank bolt to the center of the hole for the pedal bolt.
I’ll have a look but I know what you mean, there isn’t that much clearance either side.
Well at least I know I am measuring correctly!
Is it better for you to buy from UDC Denmark than UDC Sweden?
Almost anything that could be on a bike (unusual tyres, studded tyres, unusual seatpost sizes…) can be ordered through your local bike shop if they don’t have it in stock. It’s the specialist unicycle parts that they’ll have problems with. For those it may be good to shop around as with the wildly fluctuating exchange rates it could possibly be better for you to order from the UK UDC or Germany or…
I’m probably at the same skill level with you.
–Short background start
I had just turned 42 two years ago in May when I bought my first unicycle (20’’ trainer) at UDC Sweden. That summer I practised with it and learned to ride straight and turn a bit on firm ground.
The 20’’ trainer was no good for commuting which was one of my goals. That’s why last August I bought a Qu-Ax 29’’ Cross at UDC Sweden. It has 170 mm cranks.
With that I have commuted 1-2 times a week for the last three-four months. As I live in Helsinki we also have occasionally some snow
–End of short background
I have Nokian Extreme 294 tyres on (should I say under?)my unicycle. They seem to work well on snow, ice, mud etc. If the snow is really soft it can be somewhat deep also. Naturally if the snow is hard the depth doesn’t matter. The difficult snow is hard enough to almost carry you. Then the tyre sort of get’s stuck into snow (for someone at my skill level at least). All in all I think that tyre should be good for your purposes.
tuomas
A studded tire and some longer cranks are what you need. A wide tire would help you float better and not get bogged down in semi-solid snow but you can only go as wide as your frame allows.
I find a 26" MUni with a 3" studded tire is awesome in winter. I also really liked using my 36 in winter. Big wheels roll and float much better in snow than smaller ones.
Here is a tutorial I wrote up abut making studded tires. Hope it helps.
Last time I looked it seemed like UDC Denmark had a better selection of stuff and was slightly cheaper but I’m quite happy to shop at any of them.
Speaking of that. My cranks, anything special about them preventing me from going to a local bike shop? If I want longer ones what am I asking for besides being 150mm+?
Thanks!! My original plan was to commute to work as well, although it now turns out I only live 6 mins walk away. Of course I can still commute but it will be a pretty short commute! 
I’ll look out for the Nokian Extreme 294s. I haven’t actually gone looking at tires yet. I thought I would ask here first. By chance I was in a sports shop the other day looking at ski equipment and the shop had a small bike section, inlcuding some Schwalbe Winter tires with studs but perhaps the Nokian Extreme 294 are better?
If I had the money (and a convenient way of ordering) I had thought of the Surly Conundrum as a possibility, with an endomorph tire. But sadly that would be too much for me right now in terms of cost, even if it was a good option. Similarly I like the idea of a 36er one day, so you are saying all the things I want to hear!! 
I think I’ll try buying one first … but … I’m booking marking this page for the future! Thanks!
Bike shop cranks will have a spider on the right hand crank for fitting a chainring on. Unicycle cranks don’t. You can grind these off, but it’s usually easier to buy a unicycle specific set of cranks. Bike cranks also usually only come in 175mm or longer, which means they’re a bit long for a unicycle.
In terms of what cranks - you’ll need square taper cranks (square hole in the middle).
Joe
Thanks Joe!
A skinny tire can work really well too. Studs are good for ice, but hardpack snow on a sidewalk or dirtroad is fine with a skinny tire. I even had a friend who preferred the skinny over my muni tire because the skinny would go through the snowbanks on the sidewalk from when people plowed their driveways 
And as always, practice, practice, practice
Extreme 294 is quite aggressively patterned. I am riding Nokian 240’s that have more surface and are skinnier (40mm vs. 54mm). They roll better on smooth surfaces but get clogged in loose snow. Last winter I rode 106’s but they are mostly for clear pavement. Even the 106’s work great on ice though, especially skating rinks!
Take a look at http://www.gazzatyres.com/winter.html. Note that not all tires are available in 622.
I haven’t used the Schwalbes. The Winter Marathon looks too smooth to be useful except on occasional icy patches on clear pavement. Ice Spiker and Pro look bettter.
Happy commuting!
Petri
Ok, since I can’t have a very wide tire anyway and I’ll be mainly riding on the road / sidewalk where the snow is usually fairly compacted (but occasionally icy) I decided to go with the Nokian 240 as suggested by petri. I’ll also see how this skinny tire ‘plough through’ idea (as highlighted by evil-nick) works.
Since it was lunch a short while ago (here in Norway at least) I have already been out and found a nearby bike shop with a good range of tires, including the Nokian 240. So I have bought one and I am all ready to give it a go. It is just a shame I have to work for a few more hours!!
At some point I guess I’ll probably want to try longer cranks but I’ll give this setup a fair run first to see if I can get on with it.
Thanks once again to everyone for your helpful suggestions!! I might post back in this thread at some point to let people know how I got on.
Ok, now I have a problem. Since my Unicycle is 29" I have always thought of it as being 700c. So I bought a Nokian 240 tire in that size. However after struggling for some time to get the tire on the rim I did a bit more investigation and looked more carefully at the markings on old tire and the rim itself.
The old tire and rim both reference the number 635, whilst the new Nokian tire has the number 622 on it. A bit of searching on the internet lead me to Sheldon Brown’s tire sizing page. Sure enough, my rim is fraction too big for the Nokian. 
Now what? I have a tire I can’t use and more worryingly I’m wondering if I can even get a studded snow tire in this size. Thoughts and suggestions would once again be gratefully received!!
Weird, that’s an old size that used to be on dutch & German bikes, and pretty much obsolete. Semcycle used to sell a unicycle in that size.
That is a bummer. If you want, you could rebuild the wheel with a 700c rim, it’d need new spokes and a new rim though. It might give you a little bit more clearance too. The bike shop could probably do it, although unicycle places may have a wider range of 29er rims. I’d find out how much it’ll cost though, compared to buying a cheap new 29er from a unicycle site.
Joe
I don’t know much about the history of the bike so have no idea if the wheel is original or a previous owner put it on but I have seen references to English Roadsters using this size and indeed Pashley do still make classic style roadsters, so perhaps they considered this a ‘normal size’.
What kind of tire is the stock? I used to ride a cyclepro with a street tire on it on the snow, and aside from pure ice it was fine… In fact, my friend who used to plow through snowbanks used that unicycle AND the tire after I gave it to him… he actually wore holes in the tire, and that was in the winter
wha, a 635mm! I have never seen one of those before, ever. I had a 630mm wheel on a uni once and I thought that was a screwy obsolete size.
A skinny tire will work better than a wide one in slush or on perfect ice, and can be fun for trying to navigate the melt water channels in spring. But for anything else I would prefer a big wide tire to float over the snow and grip in loose conditions.
I don’t know what is available in 635mm but it can’t me much. I would either re-build your wheel with a 700C rim or build up a second wheel with a 26" rim (or get a second uni) for winter rides and light Muni and keep your 635mm for summer road rides and commutes.
The “middle” that Joe states is relative, you could say the square hole is in the middle of the end.
Ruari, since your rim turned out to be an odd size, you might as well want to invest in a cheap new uni. For riding in snow you don’t need a splined (strong but expensive) hub, a cheaper “cotterless” one (like on your Pashley) will do. As for wheel diameter, 24", 26" and 28/29" will all work fine under snowy conditions. Depends on what you want: a bigger wheel allows for more speed, especially under more favourable conditions, but you’re somewhat more limited in technical riding. For most snow conditions in my (limited) experience a wide (e.g. 3") knobbly tyre is good, you don’t need medal studs.
If you go for the 28/29" size, you can probably order a new uni without tyre, and use the Nokian 240 you already bought. You could also re-use the seat, with UDC such custom purchases are negotiable.
A new unicycle is tempting. I’m just considering if I can justify the money. Perhaps I’ll have to, otherwise I need to wait until the snow has gone.
Although another 29" would allow me to re-use the Nokian 240 I have I would then have two 29" unis, which seems wasteful. I was thinking of getting into some light Muni at some point so perhaps it would make sense to get a second 26" unicycle. I could use this as my general winter/muni cycle. Also keep the 29" Pashley for a bit more speed on the road when the snow has gone.
The reason I suggest a 26" rather than a 24" is that I don’t want to give up all my potential speed, particularly as it would become my main winter uni even for longer distances.
Any recommendations on a cheap fairly decent 26" for use in the snow and light muni?
26" also has an advantage in that there are masses of tyres for it. For example I doubt you’d find a studded tyre for a 24.
Joe