Rims and Wheels

Why Special Rims?

Part of the problem is pounds per square inch (kg per square cm).   Riding on semi-frozen snowmobile trails or single track, or crusted-over lakes, you will break through the softer portions, your front wheel will sink, and you may do an Endo.  The surface simply can not support the amount of weight you and your bike apply.

At 40 PSI, 200 pounds of bike and rider will we carried on 5 square inches on the bottom of your bike tires.  This will be split roughly evenly between the two tires.  The trouble is, the snow can not bear 100 pounds on just 2.5 sq. inches.   So you sink.  You keep on sinking until the amount of tire in contact with the snow spreads the same amount of  weight to more and more square inches of snow.  Once you have enough inches of tire on (under) the snow, you stop sinking. 

More square inches on the ground helps.

The other part of the problem is the shape of the tire.  In cross section, the mostly rounded shape of the typical bike tire causes it to slip sideways rather than just straight down.  Down would be bad enough.  Sideways requires steering input at the very least, may cause falls, and is ultimately unmanageable.  Snow tends to "squirt" out towards the edges of the tire, rather then being packed down as the tire rolls over it.

A flatter tire cross section helps.

Finally, when on really bumpy hardpack, or other uneven surfaces, high pressure tires can tend to follow ridges, (diverting you from your intended course), and bounce, breaking contact with the ground, reducing your traction, and allowing sideways momentum to be built up while the tire is in reduced contact with the ground.  Softer tires tend to roll over small ridges and bumps, absorbing the bumps by deforming, while as the same time maintaining contact with the ground.

Lower tire pressure helps.

Each of the above aids to off-road winter cycling has its own place.  On rutted ice, lower pressure and a flat cross section are better.  Glare ice calls for higher pressure.  All three at once would be ideal for many off road situations in winter.

The only way to get all three at the same time is to run wide tires with a flat cross section at low pressure.

The problem is this is virtually impossible with a narrow rim, because if you lower the pressure enough to get a flat cross section you run the risk of snake bite (pinch flats) as the rim will bottom out inside the tire.  Additionally, much of the tires potential width it "consumed" by having the tire form a circle (in cross section).   If the tire only had to form half of a circle, it would be a much wider circle.  If you have ever spread a bike tire flat (pulling the beads away from each other) you were probably amazed how wide it was.

A Brief History of the
Snow Cat Rim.

I designed the Snow Cat for snow riding but there had been hints of interest in them for downhill racing from the beginning, so I didn't go ultra-light on the cross section.

That turned out to be a good idea. For a few years DH sales exceeded winter sales. I started doing serious promotion at major DH events about five years ago and spent the next few years watching over my shoulder for the big companies to pick up on the idea and crush me. It took a surprisingly long time.

The bike industry is cash starved and very conservative. DH rim widths crept upward for a few years with Sun, Mavic and a few others watching each other and giving out BS reasons why really wide was a mistake.

Yet, people from the big rim companies would tell me they were glad I was making such wide rims because it took pressure off them to do it. I got lucky when Sun's first really wide rim (Fat Albert) flopped. It was fun being on the right side of the rumor machine.

My product worked, the big company's knockoff didn't, consumer accounts about why it was bad were wild and widespread.

Nokian tire designer Jorma Tikka got interested in DH and came up with the idea of a tire sized to really fit on the Snow Cat. Nokian took a bigger chance than I've seen any other large company do in the bike industry. They made a three inch tire (the Gazzalodi) when there was only one rim and NO BIKES to fit it. They introduced it at the '98 Winter X-treme Games. Within a few weeks there were plenty of bikes to fit it. I was swamped with calls from small DH frame builders wanting to know dimensions. The standard changed overnight.

So the little kitty led the DH world onto big rims and big tires. Eventually they got it right and there are now wide rims more suitable for DH than the Snow Cat.

But the monster rolled right past me and I didn't get crushed. DH rims are very heavy, so the Snow Cat is the lightest of the big rims. Disc brakes are the standard for DH so very few of the wide rims have brake surfaces.

The market isn't big enough for even one winter rim. I could only get it in production by doing silly, egotistical things with larger lumps of money than I should have. God bless the oil economy. Rim manufacturers are smarter than I am and don't seem to want to waste capital on a product with such limited appeal. So they try to do double duty with a DH rim. We'll see where it all goes but I'm not afraid of competition. I took last winter off; went away and did no marketing and had no product. It would be amazing if no one tried to move into the (small) void.

One more thing I like about Snow Cats: I can drill them in any crazy way anyone wants (see photos) even, (gasp), dishless rears. I mean really dishless, with identical spoke angles and tensions on both sides.  This is how Charlie Beristain (pictured below) just got his.  (You can see the offset spoke holes in the side-by-side pictures below). Ritchey may have "invented" OCR but I'd been making 0-dish Snow Cats for years before he did. Standard width rims can correct for dish by a few mm. Only a big flat rim lets you shift the (w)hole pattern the 10 mm needed to completely compensate for eight or nine gears.

Simon Rakower All Weather Sports