I recently took a framebuilding class. I wanted to be able to use the frame with a carbon fork that I have (brand new 2019 Trek Emonda compatible with direct mount rim brakes). The fork (tapered 1-1/8 to 1-1/5) has an integrated crown race. The instructor suggested that I use a 44 mm headtube because it would be easier to find a headset. Well, I can’t find one. The issue appears to be that when using a bottom EC44/40 the lower bearing is too short and the fork comes in contact with the cup. I went to two LBS, the first one said they couldn’t help, the second one suggested to add a crown race on top of the integrated one, it works but leaves an unsightly large gap between the fork and the cup. I did find an aftermarket bearing that appears to be slightly ticker but I think that the bearing angle (45) won’t be compatible with the angle from the molded crown race (apparently 36). I’m waiting for the bearing the arrive to test it out. Has anyone been into that situation before? Any suggestions?
This is my first post so I’m not sure if it’s in the appropriate section.
44mm headtubes certainly have the most headset options so if there is a way to make it work 44mm is the way to go. What headset do you have on the bike now?
That said, many frame manufacturers have gone off script for standard bearing depth measurements in their headtubes and bearings themselves. This means that often standard forks aren’t compatible with their frames and standard headsets aren’t compatible with their forks. I came across this all the time when I was at ENVE.
If you still have the frame I would recommend trying to isolate if the headtube or the bearing are out of the norm.
Headtube - If you still have the frame, take the measurement of the straight wall inside the headtube. It should be 7mm or 7.5mm.
Bearing - I would try to source the exact bearing that trek uses for this bike/fork just incase is uses some sort of proprietary sizing.
If the trek specific bearing doesn’t work then I think you’re going to have to sand down the headset to make it work. No big deal though, especially if you have a silver headset.
Not Recommended - I would urge you not to put a standard crown race over the integrated crown race or use a 45 bearing on the 36 crownrace. both of these solutions would put a ton of force into a very small surface area and will cause either rapid bearing wear or a broken fork.
This is a very rare bearing standard. All of the headsets and headtubes I have come across in framebuilding use 45deg ramps and crown races.
putting a crown race on a molded fork crown is a bad idea
you will need to match the angle of your headset cup as well
This bearing might work, it is 52mm diameter, 45deg external, 36deg internal:
I would not worry too much about the bearing height. If the headset cup bottoms out on the fork, just throw the cup in a lathe and take off 1-2mm. I just did this yesterday!
