Knard-sized segmented forkage

I’m building a fork (and next, a frame) for the Surly Knard tire and 50mm wide rims.   I am super psyched for these tires to be released, sometime in December. In March of this year, after a couple days with TB in Durango riding fatbikes, I emailed Kenda’s to try (beg) them to create a 29 x 3″ tire. I’m sure they get that kinda thing all the time, and I’m definitely wasn’t the first to think of such a tire, but I offered to help pay for some start-up costs and also help with distribution, marketing, etc.  That’s how bad I wanted it.  My email must have found it’s way to the trash bin pretty quickly since I never heard a word.  But…hey Kenda…look what Surly has done…they beat you to it!  Nice work Surly.

If you’re ridden a fatbike (26″ wheels) and you love 29ers, you know why this new bike and tire size is so cool.  It will not only ride the dirt in a whole new way, but be very adaptable to soft-conditions riding – including snowbiking which is what I’m so excited to try it out on.  My bet is next year they have a 29 x 3.7″ tire and a 29er fatbike frame to go along with it.  We’ll have to wait and see.

So yes, I have no Knard tires in stock to measure and fit to make sure the frame and fork clearances are correct.  But I posted on the mtbr framebuilding forum and alas, MikeSee measured the one he somehow has in stock.  He made me some sweet 29er wheels earlier this year with the Speedway Uma 50mm rims and Bontrager 29-4 (2.4″) tires but now i’ll have to upsize those to the Knard tires. Anyways, here’s the measurements I’ve collected, first from Surly:

“The Knard 3.0 tire on a Rabbit Hole 50mm rim will be 75.8mm/77.7mm (casing/tread) wide and will have a diameter of 779.4mm (at 19psi).  The Knard 3.0 tire on a Velocity P35 (35mm wide rim) will be 72.6mm/76.7mm wide and have a diameter of 778.6mm.”

From Mike C.:  “Just measured my front wheel: Paul Whub laced to Surly Rabbit Hole rim, Knard @ 15psi.  The widest part of the tire is fairly tall–basically it goes from ~13.5″ to 14.25″ from the axle. 14.25″ is axle to the tip of the edge knobs.”

In metric now (mostly for me when I forget and have to come back and read my own blog to remember what I’ve done before): The distance axle to widest point of tire (outermost tread) is approximately 362mm.  Although the tire is very round in profile, the widest point of the tire starts at around 343mm and continues on up to 362mm. This is very similar to their fatbike tires like the Endomorph where the crimp in the chainstays needs to be pretty long to clear the tire.

See the photos of my two drawings for the fork.  The ‘before’ drawing was before I got Mike’s info and was just a guess on side profile and where the widest point of the tire was located.  The ‘after’ drawing is after adapting the tire size and profile to his measurements.  Had I used the first drawing to dimple my chainstays i would’ve had potential issues with clearance!  You can see how round a tire this appears to be.  Should be sweet, especially even only on the front wheel as a little bit of added suspension.

The other pics are random process shots from the mitering of the fork parts. One (expensive) tip is – Alico magnets from MSCdirect.  They’re costly, but man do they help with fixturing a segmented fork. See photos, the fixture is upside down and two magnets are holding the un-tacked leg in place while I finish file the crown pieces to match the steerer and leg. Blue tape doesn’t hold a candle to these magnets. So many uses — braze-on placement, weird fixturing, holding in place while tacking…a great purchase!

I also figured out a new method to get a closer fit on the crown pieces with much much less filing post-milling machine.  It involves the tilt-table set at an angle one way for one side’s crown piece, and the other way for the other side’s crown piece, and then using the angle finder on the 1.125″ tube block set at 25 degrees in the milling vise.  Once one end is mitered, the block is just flipped and set at around 25 or more degrees to miter the other side (angle depends on the drawing — how wide the tire is, as in slacker for narrower tires because there’s more of an angle in the fork leg from steerer to dropout).  I used to file the fork offset angle by hand, but that would take way too long and usually involved me making one too short, then having to file the other side down to match, etc.  This method took simple math to figure out the angle of offset to set on the tilt-table (for 583mm fork length and 47mm rake it was set at 2.8 degrees so when you flip the block the total offset is 5.6 degrees).  Now why didn’t I think of this earlier…?

One Response

  1. Awesome! Can’t wait to see this put together.

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