Disc cross forks

It’s hard to know how beefy to build a disc-specific cyclocross fork, especially when you know it’s going to be ridden on trail, over big washboards, through winter, and with room for fenders.
You want to make it light and ride smooth but strong enough to last.

I first built a lugged-crown fork (Nova 7deg offset cross) and used Nova’s new fork blades that were drawn beefier specifically for disc brake usage.  They are pretty heavy but serve the purpose (28 x 20 x 390 long, wall = 1.1mm top / 1.4mm bottom).  The bottom of the leg is pretty big at 17mm diameter so I used a set of the 1″ Paragon hooded dropouts. Fitting tab dropouts would be possible but IMO would need to be done the “Iglehart” or “Potts” way instead of simply slotting the leg and brazing.  Axle to crown is 395mm and it has 48mm of rake.  I don’t think many would want to race on this fork, it’s just too much heft at over 2.3lbs (without eyelets for fenders).

Robonza Joe in Colorado is getting a Mountain Cross frameset and he wanted a Yo Eddy segmented fork so I built one using True Temper FB4 legs (1.3/0.9mm wall profile, round tapered legs, 1″ diameter at top, 14mm at the bottom).  The crown pieces are 1 x 0.049″ 4130 and it’s a True Temper straight 1.125″ steerer.  The dropouts are from Paragon and have an eyelet for fenders.  Axle to crown is 400mm and it has 48mm of rake. I likely could’ve used the lighter thinner-walled FB7 fork legs but because I know where Joe will be riding and what he will be riding I decided to be safe, especially for disc use.  This is really a MTB fork that only fits 1.7″ tires, or a cross fork that fits 45’s, you choose. It’s still a heavy cross fork at 2.29lbs with an uncut steerer.  As comparison, both forks are over 3/4lb heavier than this random (non-disc) Bontrager carbon fork I have in the shop.

Forks take me a long time to build, but I do love the results. There’s just something about them that is very satisfying and they do top off a custom frame in a way a carbon fork just can’t.

PJMac’s frame progress

I’m 3/4 done building a 29er frame for Paul, mastermind of Cross Propz – portable cyclocross barriers for training rides and practice. Pretty ingenious design where you can literally thrown it on the ground and the bungee cord connected PVC pipe barrier nearly self-assembles itself in seconds.

Paul has been waiting a long time for a frame from me and was one of the first guys to say he wanted one so I’m happy to say he’ll have it just in time for fall in Colorado. He’s getting frame #20, a milestone for me.  The 29er frame is similar to most of my 29ers and what everybody seems to want — slacker head tube angle, short-ish chainstays, more trail, a carvy and more all-mountain handling bike.  This bike will have no front derailleur, Paragon Sliders, and be run as a singlespeed for the most part with the option for 1×10.  It’s got a 69.5 HTA / 72.5 STA, 425mm effective chainstay length, a 43.6″ wheelbase, and a front center of 685mm.  I used a bent downtube from Nova for enough fork crown clearance, a light 8/5/8 OX Plat top tube, OX Plat chainstays, True Temper oversized (44mm) head tube, True Temper seat tube with a sleeve for strength and a cool look. Fits a 2.4″ tire no problem. I think this is his first 29er and his first steel hardtail and I hope he digs it!

He’s putting a sweet new 120mm White Brothers Loop 29 fork on it with tapered steerer and 15mm front axle.  I have the fork in hand and uncut it weighs right around 4.3lbs.   I need to buy one for myself.  The tapered steerer versions of the WB forks come with 49mm offset whereas the straight steerers come with 46mm of offset.  More offset is what I like and look for especially on frames like these with slacker head tube angles.  You also have the option of getting black or white lower legs.  I love options and these guys seem to like to offer options since all forks are made to order.  Located and fabricated in Grand Junction, CO make it even better — US made forks!

Cannondale Lefty on custom frames

It’s strange having this blog come up more than any other site for framebuilding information when I Google anything from welding to mitering questions.  I KNOW other builders blog about this stuff but maybe Google likes WordPress blogs better than Blogger blogs. That’d be funny since Google owns Blogger.  I hope some people find this stuff interesting other than me!

Anyways…

This is a almost straight copy of my text from the mtbr framebuilding forum since I don’t want to write it again but wanted to include it on this ‘archive’.  It’s what i learned about building a custom frame for a Lefty since I found very little out there on this subject plus a little more.

I have a Lefty build coming up and he’ll be using a 2013 29er XLR 100mm. Finding specs online is extremely difficult, at least I couldn’t find anything except conflicting info on mtbr. Eventually my friend found the information HERE, look for the “2013 axle to crown measurements” link.  So for the 29 XLR the ATC is 500mm and the offset is 45mm. Add/subtract 10mm for each different travel version (i.e., 120mm travel would be 520mm atc).  The Lefty manual recommends 20-30% sag for the length of travel (20-30mm for a 100mm fork) with XC builds going in the 20-25% range and All-Mtn going 20-30%.

You need to supply your own steerer for the fork. Cannondale sells a kit with a straight 1-1/8″ steerer and their own zero stack headset (different stack heights than Cane Creek’s). Project 321 also sells a couple of steerer kits – one with a straight 1.125″ steerer and one with a tapered 1.125″ to 1.5″ steerer. It appears to me the Project 321 is higher quality and you get to use your favorite headset as well.

The Lefty comes in two versions – one has 137.6mm between the fork clamps and one has 163mm (XL) between the clamps (#’s from the 2012 Lefty Manual Supplement). Those clamps are set (can’t move them) so you need to have the headset cups and head tube fit within that distance. For example, suppose I am using a 115mm Paragon head tube, and a King inset 7 (i7) headset for a tapered steerer (14mm lower stack height, 8.2mm upper) that would give me 137.2mm total length. That would fit within the regular size Lefty’s clamps but with 0.4mm left over. With that same head tube, you could also use a non-tapered steerer and a Zero Stack headset (4mm lower stack height, 8mm upper) and that would give you 127mm so you’d have to fill the 10.6mm gap above the upper headset cup and the Lefty clamp with some spacers. Obviously you could also NOT use the Paragon head tube and cut your own to 125.6mm (with a ZS44) and not have those spacers permanently lodged there. For longer head tube frames same issue but the total stack height and head tube length has to be less than 163mm.

A straight steerer/zero stack headset would allow for a slightly longer head tube. If you use the tapered steerer option, you need the same headset you’d use on any other tapered build – Cane Creek’s EC44 bottom or the King i7 – both have the same lower stack height. This makes for a shorter head tube (since you have to stay within the clamps).

You could also turn a 1.5″ head tube and use the oversized Cannondale steerer and stem combo but I didn’t do any research into that since I want to use either Paragon’s or cut to length some MHT-44 from True Temper.

Because the Lefty is a double-crown and puts a lot of torque and stress on one side of the head tube, I would think an oversized 44mm headtube is preferred and for it to be cut to the max length it can be with the zero stack headset and using the straight 1.125″ steerer. It seems like a longer head tube would be more important to front end stiffness than using a tapered steerer and a shorter head tube with a lower external cup. But maybe the same reasoning holds for regular forks using tapered steerers and a stiffer steerer would help handling.  I’m not exactly sure of the best headtube, headset, & steerer combination for a Lefty — longer head tube and straight steerer or a little bit shorter head tube and tapered steerer?

For this build I’m going to use a 115mm Paragon head tube and a King i7 headset. I’m pretty sure the MHT-44 stock would be plenty strong for this application, but for a double-crown fork and a 180lb rider that plans to do some bikepacking and general Rocky Mtn riding…I just feel more comfortable with going beefier on the headtube on this frame.  So we’ll try out the tapered steerer option from Project 321 and report back later with any issues or praise.

Fatbike fork for Dynamo hub

This fork is for loaded dirt, snow &/or sand touring once attached to his Surly Necromancer frame. It’s got more braze-on’s than most touring frames! It’s got three bottle bosses on each leg for Salsa Anything cages or for water bottle cages in one of two positions (high/low). It’s got one bottle boss on the middle of each leg and a threaded nut in the lower steerer tube for a Salsa Minimalist Rack. It’s also got one bottle boss at the dropout just in case he wants to use another type of low-mount pannier for bringing more stuff, or a fender perhaps. The last thing this fork has is internal routing for SON (Dynamo) hub wiring which will connect to a Supernova E3 light at the fork’s crown (which doubles as the upper attachment for the Minimalist Rack).

The internal wiring is less complex than it sounds, I just made a hole in the lower inside leg, brazed on the seen cap to protect the wire as it comes out of the leg and goes down to the hub’s tongs. I fed some bailing wire from that exit hole up through the crown BEFORE brazing the sleeve to the lower leg of the fork which made it super easy to fish through the crown. This wire stayed in place for the brazing and then the powdercoating and then I used the wire to guide some derailleur cable-housing liner through the fork leg to serve as the path for the light’s wire. The plastic housing will also protect the wiring from the edges of the fork crown. The wire will momentarily poke out the bottom of the steerer and attach to the E3 light itself. Hopefully Scott will send some pics of it all set up!

It’s an interesting fork that he requested because he wanted clearance for 4.7″ tires on a Clown Shoe (100mm wide) rim. Most fatbike forks that run this sized tire have 135mm axle spacing or even 170mm. Since the SON hub and other Dynamo hubs don’t come in that width we made this fork with the normal 100mm axle spacing.

The fork is built pretty beefy. The crown pieces are 1.125 diameter x 0.058″ wall since they are so long compared to a regular segmented fork. The sleeves and legs are the normal setup, sleeves are the same as the crown pieces and the legs are 1″ diameter x 0.035″ wall. Paragon hooded dropouts and a modified Willits ISO disc tab and there you have it. The color he chose closely matches the text outline on the Necromancer frame but also makes it stand out a bit from a standard black fork.

Testing the fork un-raking theory

There’s a theory, more like a hypothesis, that if you put a disc brake on a raked (curved blades) fork that the blade will ‘un-rake’ itself over time due to the disc brake force on the left leg.  This would result in a lesser amount of rake (less than the 44mm you bend the blades to be) and the fork twisting out of alignment.

I’ve not seen any evidence of this online, but it may be out there and I just haven’t run across it.  It could be like a lot of things framebuilding and otherwise, people develop opinions that become fact without much evidence; just because it seems like it should be true.  That doesn’t mean it’s not true, it’s just possible that this idea has never been tested very thoroughly.  It does seem like disc brakes on some thinner walled road fork blades would not be a good idea, and I have seen a photo or two of fork failures right above where the disc mount was welded to the fork leg. But would some beefing up of the disc brake mount on the fork leg limit any un-raking of the fork leg and prevent fork failures such as using Paragon’s Willit’s style caliper mount?

I wrote about this fork awhile ago and rode the fork as a all-rounder MTB/Cross/dirt road cruiser for over a year.  The fork blades I used were the only available  for that ‘retro’ style fork crown from Nova Cycles Supply (0.9/0.6mm wall i think – pretty thin).  I rode it on the same trails I rode my mountain bike and I was not easy on it.  I linked to another blog that provided the inspiration for using the “Willit’s style” disc tab on a raked fork blade.  Here’s a photo and explanation of the tubing that was used in the fork compared to the newer one I made to replace it.

Anyways, since i made a replacement fork for my 1st lugged MTB/All-rounder fork, I wanted to check how it fared after being ridden hard – to see if there had been any un-raking of the left fork blade from the force of braking.  The gallery below shows the results.  Sample size of 1 doesn’t say much but even with my newbie fabrication skills when I made this fork…it did not move one millimeter — and I rode it hard.  Maybe over more rides and more time it would bend back? I’ll be checking changes in alignment over time for my other forks.

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…?

Lugged mountain bike fork

This lugged crown is from Pacenti (bikelugs.com) and it’s beautiful.  “This crown was modeled after the very rare and highly sought after crown Tom Ritchey designed for Bridgestone many years ago.” 

It fits any sized MTB tire you want (74mm clearance), except for fatbike tires obviously. The only think you have to do bend the 28×20 fork blades to get the proper rake since the crown is not offset. I’ve bent a total of 2 sets of blades so far so I am far from experienced in this, but this time I got lucky and it went very well. I set a ‘stop’ on the wood bending mandrel and bent to the stop, checked what approximate rake i was at, then re-set the stop and inched up to what I was looking for (44mm rake).  I only had to do one bend prior to getting it spot on.  Without a guide to cradle and hold the blade while bending, i worry about getting side-drift in the legs so when you sight down the fork one or both of the legs spays in- or outwards.  I think these turned out though as seen in the photo.  I used the crown and angle finder to get the blade as close to vertical in the bender as possible (not sure how others do this other than just eye’ing it).

The brazing went just OK. For some reason at the last minute i decided to go from Silver to Brass as the filler for the crown and legs.  I thought ‘how hard could it be?’  Well…the left side had messy shorlines until i kinda ‘got it’ and then the right leg turned out really pretty good…minimal cleanup with the Riffler’s file.  The left leg on the other hand…   Bad brazing really makes you want to get good at brazing since there’s little to no filing or cleanup after soaking off the flux.

If you are learning to build frames and forks, I highly recommend Kirk’s 4 part series blog on building a fork and frame just for the stepwise pictures alone.  It’s great to have a master outline his process so that lessers like myself can benefit from his years of experience. Here are my build shots for this fork.  It’s on my frame #10 the All-rounder frame with small tires right now for cross season but it’ll usually have some 2.o’s on it.