disc brake road/cyclocross fork

[NBC]

hi all

i've got a fairly nice lugged audax frame from a few years back, but it's really showing it's old age now, and i feel it's time to upgrade and modernise it a little,

i'd very much like to convert it to disc brakes, which instead of adding a tab to the existing forks (i haven't a clue what wall thickness the blades are), i think it would be far safer to manufacture a new set (i'd like the steerer tube a little longer anyway !)

i only plan on running a 35c tyre with mudguards (fenders !) so i shouldn't see any issue with using a long shen LC-27 fork crown (47mm between the tangs)

the bike currently has a 1" threaded steerer and headset, and i'd like to keep it this way,

the reynolds catalogue is showing threaded steerers in 2.3/1.6mm butted, is this ok, or will i need to use the heavier 2.9/1.6mm they also list ?

as regards to fork blades, i don't have a blade raking tool as yet, and wouldn't feel comfortable bending them without some tuition, so i will probably purchase pre raked blades from reynolds too,

i can get 1.0/0.6mm fork blades, and also 1.2/0.7, however i understand some people producing these forks use a heavier left hand fork blade, is this necessary, or is using 1.2/0.7 blades on both sides adequate or preferable ?

i was going to use a paragon willits style disc tab on the fork, but was wondering how you builders out there solve the problem of mounting mudguard (fender) stays ? could i use a normal RH dropout with an eye, then file the LH dropout eye off, and mount the mudguard stay using the lower disc caliper bolt ? suggestions please !

i hope i've covered it all, but any insight, reccomendations and general pointers into this would be hugely appreciated

thanks very much in advance

nathan colman

[jon_norstog]

nathan,

Road forks and disc brakes are kind of a new thing and i don't think there has been enough experience with them to say for sure what works and what doesn't. Soma and Tange make CX disk brake forks but they are 1 1/8". The Soma unit is pretty cheap, it's a cro-moly unicrown. Perhaps you could drill it out and braze in a 1" steerer? Following Soma's lead, perhaps a set of unicrown blades would make a basis for a fork?

If you decide to build using road fork blades, use the heaviest ones you can find and let us all know how it works out, OK?


jn


"Thursday"

[Mark Kelly]

An elementary free body diagram will show you that there's basically no difference in the forces transmitted to the steerer between disc and rim brakes so there's no need to do anything special with the tube.

I can't give you any useful advise regarding blades - talk to the suppliers about what's been designed for disc use.

Regarding mudguard mounts, I rebuilt a Kinesis carbon Audax fork to use discs and I just kept the existing mudguard mount points on the dropouts. You may need to get creative with the mudguard stays to clear the brake but that's part of the adventure.