Saturday, February 16, 2013

Homemade Studded Fatbike Tires.

We've had weeks of persistent icy conditions on our local mountain bike trails.  While most were ride able on the fringes of trails, or with extreme caution in a lot of spots, I'm pretty sick of it.  Tip toeing around on really sketchy ice is not generally my idea of a good time.  Spurred on by a recent friend's crash, and with a desire to once again ride quickly, I got the notion to make a pair of studded fatbike tires.

45North does make a set of off the shelf studded tires, the Dillinger.  These are super light, and have a ton of studs.  They represent the current high tech, super go fast option for studded fatty tires.  They also come with a price tag that rivals most nice truck tires, and that is frankly a lot of money for some pretty specific conditions.  I happened to have a set of the less expensive 27tpi Surly Nate tires laying around.  Due to their lower cost, and pronounced, fairly large knobs I thought these would be a prime candidate for some homebrew stud action.

Starting with the tires and a caliper I measure the knob height and casing thickness.  Based on these measurements I determined that a screw between 1/2" and 5/8" would be required to yield a preferred stud height.  Once at the hardware store to compare, it was obvious that the 1'2" screws would be too short.  These would only allow for the very pointed tip to stick out through the knob.  I figured this would be less than ideal, as it appeared it would be very easy to wear that point out.  Conversely, the 5/8" screws were obviously going to be too long.  These screws cost about $3.50 per 100 count box.  Compare that to Gripstuds!  As it's a lot easier to cut things shorter rather than longer I bought the 5/8" ones and headed back to the shop.  These were technically 8 x 5/8" size, with a Phillips flat head.

The stud pattern I chose was to alternate every other smaller center lug, and every other mid side lug.  I figured this would provide enough more straight line traction, while adding the most traction fairly far out for cornering or side hill stability.  The first step in making these is to drill the lugs from the outside in using a small drill bit.  You can see I centered the holes on the outer knobs while opting for a slightly front center hole on the inner knobs.  It's important to use a drill bit that is about half the size of the core diameter of the screw, not the thread diameter of the screw.  This will allow the screw to have something to bite into.

At this point I simply filled all the holes with screws driven from the inside out.  I did this with a hand held screwdriver.  It's the most monotonous part of this process, but it's also one of the easiest.

On the inside of the tire I made a boot comprised of strips of Gorilla tape laid across the length of the tire.  The tape does not stick to the tire itself, as it's oily and slippery.  By applying to layers of tape in an overlapping scale type arrangement I was able to create a fairly durable inner layer that held it's shape well.  It remains to be seen whether this will provide sufficient support to stop the screw heads from poking through to the tube.  Frankly I suspect it will fail at some point, and based on how it failed I'll rethink my strategy.   

After the tires were lined I had to address the issue of the now too long screws.  I took a small bolt cutter and trimmed the screw height over the knobs to about 3-4mm.  This was long enough I felt to be able to bite well, without being too long as to bend the knob over on hard ice or dirt.  The cut actually makes the screw more aggressive than just the point I think.  I had to remember not to snag clothing or appendages on them, they're sharp as hell.

So again to recap.  I used 8 x 5/8" sheet metal screws for studs.  I drilled each knob in the pattern that I wanted.  The screws were then simply threaded into the knobs from the inside of the tire.  I made boots for the inside of the tire by overlapping small sections of Gorilla tape two layers thick.  I then trimmed the screws tips with a handheld bolt cutter.

These worked very well no my first ride with them.  I rode the same trails the next day on my Mukluk with Big Fat Larry's.  The trails we all ride able on both set ups.  On the Big Fat Larry's I had to slow way down on many sections, and I could feel the tires slipping all the time.  The studded tires provided absolute confidence.  I was able to blaze through sections, even standing and sprinting across icy sections.  The studded tires simply out performed anything else I've ridden in these conditions.  I don't doubt that I worked harder with the studded tires.  For the few weeks of the year where conditions dictate their use, these are just the cat's meow.  I only wish I'd made them sooner.

I'll update on how these tires wear, and I'll report any issue that come up with them.  So far I'm impressed, and I plan on testing them further to their limit by attempting my St Olaf hill loop on them this weekend.


Jerry said...

way to go macgyver

FTMN said...

After these wear down, try getting a hold of 410 grade stainless steel screws. That's what I'm using this year, and I'm impressed how well they are holding up to the pavement between home and the snow/ice covered trails. The standard hardware store screws I've used previously wore down really fast.

Anonymous said...

You might try hex headed sheet metal screws from the outside. Makes dealing with the point inside harder maybe but the hex head will wear slower.

Tman said...

I always use #6 hex heads screwed in from the outside. Then, smack the point with a hammer to dull it. I use old tires with the bead cut off for liners. 1000s of miles this way

Anonymous said...

I did the exact same thing on my 2.35" tires about 2 years ago. Next time try using stainless steel Truss screws. they are thin rounded pan head screws with no sharp edges. I'm on my 3rd winter with them and they still grip like Velcro! I also used Gorilla tape! That stuff is TUFF!