Disk Fork for my Porteur

As I mentioned in a recent blog post I’m building a new commuter frame and fork.  I’ll be moving all of the parts over from a Novara Fusion that I bought.  That includes the disk brakes.

I don’t like most disk brake rigid forks because they are either straight blades or have a really ugly bend to them.  I wanted to build something that looked a bit more traditional.  This presents an interesting design challenge though, since disk brakes are known to “unrake” forks with a tight bend.  My solution was to make some custom dropouts that extend far above the disk caliper into the more stout portion of the fork.  The dropouts had the match the bend on the fork blades.  I still consider this an experiment until I’ve put some hard riding on the fork.

I love the results!   It still isn’t as elegant as a nice flat crowned fork with a brazed on centerpull, but it doesn’t look half bad.

The brazeon count is a bit out of control.  There are eyelets near the bend for fender mounts, eyelets at the midfork and embedded into the crown for mounting a porteur rack, and a simple cable guide for keeping the brake cable out of the way. 

I did use a trick.  The brake is a “rear” disk brake because those are mounted inline with the dropout.  “Front” ISO disk brakes are offset by 4mm from the dropout, and that wouldn’t have allowed me to make one piece for both the dropout and the disk mount.  I wanted a single piece because it saved me from making a fixture for the disk brake mount or making a really complicated dropout.

NOTE: This trick doesn’t work. Read the comments for more details. I got away with it with a BB7 that is highly adjustable, but don’t think it will work with other disk brakes.

The dropout has Keith Anderson TITO stainless inserts brazed in.

Next up: finish up the new frame jig and build the frame.  A rack might come out around the same time.


  1. Joe Broach says:

    That is probably the best-looking disc fork I”ve seen. Tony Pereira’’s look nice, too, but I haven”t looked closely at how he handles the mount and reaction force. I”ve never totally understood the “wheel ejection problem” with front discs. Does your design mitigate that, or are you taking other steps to keep the wheel in? Maybe it’’s not really an issue in “normal” riding.

    Commuting for a year on a bike with drum brakes really made me appreciate non-rim brakes on a utility bike. It was really nice not getting filthy every time something brushed the wheels/fork/frame. A longer reaction arm seems like the logical solution. I guess it will stiffen up the fork a bit, but probably no big deal with fat tires. Best, Joe

  2. Alex Wetmore says:

    Joe: Thanks for the nice words. I angled the dropout forward (instead of straight up and down) to handle the disk ejection issues. This seems to be standard practice on rigid mountain bike forks these days.

    I”ve been enjoying commuting on this bike too. I”m not sure if the disk brakes are doing anything to help me, but they don”t hurt either. I”ll probably like them on some snowy days.

  3. Jimmy Livengood says:

    Alex, when you say “unrake the fork” do you mean permanently? I can see how under braking you would lose the suspension effect of the curved blades.

  4. Alex Wetmore says:

    Yup. This thread on the framebuilders list has comments from Mark Bulgier and Brent Steelman saying that they”ve seen examples of it:

  5. Dan Plaster says:


    Very nice fork. I”ve always wondered about a nice looking disc fork. No ugly uni-crown thing and graceful (if stout) blades with a nice bend. Very nice. I take it the frame will come later in the winter?

  6. Alex Wetmore says:

    Thanks Dan. Yeah, the frame should be done this winter (hopefully, I have a history of getting distracted).

  7. christopher says:

    Very elegant!
    SOMA has a traditional fork with a disc brake on their site, I wonder if they did the research you did.

  8. Alex Wetmore says:

    I checked the Soma page here:

    I only see forks that are very beefy (the two mountain bike ones) or with straight fork blades.

  9. Joel says:

    Great curves, Alex!

  10. christopher says:

    Ah I see!
    It is not a SOMA fork.
    However, the fork I was looking at is in their store, and it is a Tange fork.


  11. Andrew says:

    It was my impression that thin forks were prone to breaking under strong braking with disc brakes. You appear to have solved this with your elegant extended dropout. This should stiffen the left blade significantly.

    Isn”t the idea behind traditional forks that they are flexible enough to absorb bumps? I would be concerned that when you hit a bump, this fork will flex significantly on the right blade, but not the left. On the other hand, I have read of even suspension forks twisting unnervingly under hard braking. Maybe the asymmetrical flex could even be bad enough to occasionally cause the tire to rub on the side of the fork or fender.

    I”m interested to find out how this fork performs!

  12. Alex Wetmore says:

    Traditional forks with tight radius bends and lightweight tubing do flex a little bit on bumps. The blades that I used on this fork are large enough (comparable to the Kogswell P/R prototype forks that I helped test the stiffness of for Bicycle Quarterly) that I didn”t expect to get that type of suspension out of them. That is not a major concern on this bike since I run 35mm tires. The left fork blade will be stiffer due to the special dropout, but the right one is still pretty stiff.

    I”ve put about 30 miles on the forks so far and it’’s been performing well. I”ve tried a few hard braking stops and haven”t had any issues with flex.

  13. Beautiful fork! I like the extended brace and the use of a rear brake, as well. Keeps things simpler, it seems.

  14. Rick Isham says:

    I have been interested in using disk brakes on road forks (and bikes) for a while. A while ago, I came across the work being done by Canyon with two front disks. Have you thought about this approach to even out the forces on the fork?


    It seems that road bikes need to progress from rim brakes. The rim brakes today are not much better than the brakes I used in the early 1970′’s. My mountain bike’’s brakes are so superior to my road bikes rim brakes. I hope that your new bike is a great sucess. I follow your blog, and enjoy reading about your work.

  15. Greg Walton says:

    Alex, that is a really elegant design solution to a challenging issue. Kudos to you. What rake did you put on the fork and what will your final trail be on the bike?

  16. Alex Wetmore says:

    It has about 65mm of rake, just over 40mm of trail on the current frame. I plan on just under with the final frame (which will have a steeper head tube angle).

  17. Jono says:

    Alex: This looks really great – nice job!

    I just sent you an email to get your thoughts on a similar project that I am being forced to undertake since I couldn”t find a curved-blade disc fork that had the correct A-C distance I need.

    My thought is to have a curved blade fork raked and disc tab added along with a brace, perhaps on the inside of the curve. It certainly won”t be elegant, but should by stout. Would love to get your thoughts on the plan.



  18. Erik Rodstrom says:

    Beautiful fork!

    I have a question about your additional braze ons – For your lowrider rack mount, I”ve been unable to find anything on the usual framebuilder sites listed as such. Are water bottle bosses used for front rack eyelets? Or, are they not strong enough?

    Sorry for the slight hijack, since I”m not exactly asking about the disc brake portion of the post. Beautiful fork, either way!

  19. [...] to me as an option till I went to NAHBS and saw it on quite a few bikes. I was more influenced by Alex Wetmore’s solution which was to machine a curved [...]

  20. Adie says:

    Hey Alex,
    I just want to start off by saying your site is a great inspiration for me, just getting into frame building. I have been slowly working on my first frame, a disc brake equipped off road tourer. The fork was directly inspired by the one you show here, namely, raked steel fork blades with a CNC milled disc tab. mine isnt as integrated (or pretty) as yours, but never mind.

    Today I went to install the brakes for the first time, to check clearances etc before finishing work and paint. Unfortunately I encountered a problem. The rotor ends up too close to the brake tab, so that the brake adapter interferes with the rotor (by a couple of mm, by the looks of it). Copying you, I am using a “rear” adaptor (on 160mm Avid bb7s).

    I expected this to work, given that the inside face of my disc tab is in the same plane as the dropout (built a jig for it), and I am using a rear adaptor. Any thoughts? My brake adaptor does look considerably thicker than yours, could that explain it? or do wheels vary in how far outboard the disc rotor ends up? its a sram x7 6 bolt hub, 100mm spacing, 9mm axle.


  21. Alex Wetmore says:

    Fred Blasdel also had a copy of my setup made (using the same dropouts) for his new Elephant and ran into the same issue. It caused me to go back and look at drawings again.

    The standard for rear hubs has the rotor 5mm farther from the locknut than a front hub does. This means that my trick doesn”t really work very well. Since I used an Avid BB7 which has a very adjustable mount I was able to make it work, but I don”t think it will work on some other brakes. I think Fred is using a Shimano brake.

    I thought that I had made my mount follow the fork blade too closely and that is why things seemed tight. I modified my brake mount (it is one of the original Avid ones) by milling off about 2mm. That was enough, and hopefully that will work for you as well.

    My brake and Fred’’s are both working well.

  22. Adie says:

    Thanks for the prompt reply.

    Thats the solution I was looking at. I am going to have to do some careful measurements to figure out exactly how much extra room I need. Unfortunately if i have to take off more than, say, 2mm, i think the strength of the adaptor may be compromised, because the other set of holes (to which the brake body mounts) are drilled all the way through, and I dont want to mill off so much material that those are left open. In that case, I will probably CNC mill a new bracket which mates to my disc tab, maybe out of stainless steel for strength.


  23. Hi alex!

    Beautiful work and inspiring documentation!

    I was referred by Kris Henry of 44 Bikes to http://www.hayesdiscbrake.com/support/ which has .pdf documents that show all the relationships and specs of different mounts and hubs. It seems like the main issue with this type of front tab is that the front hubs have the rotor too far outboard. The rear standard is to have the rotor mount 15mm inboard of the non-drive side lock nut and the front standard is 10mm. I guess that’’s what you were saying to Adie above.

    I”ve been trying to sort this stuff out all night. I think I”m just going to buy both of Don Ferris” iso tools and get on with it. At this point it seems like the easiest way for me to do business since they”re not actually that expensive and any tool I make is going to eat time and inevitably still be inferior.

    Anyway, thanks for the documentation of your fork. Definitely a successful proof of concept, but I think I will find an alternative way to mount an iso disc tab that can reinforce the fork. It seems like having a long tab and tight fit up for brazing will be important.