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.