I just received my new 125 mm Nimbus hub. It came with a small spacer ring (1.5 mm thick) on the inside of the left-hand bearing (between the bearing and the brake disk mount, see attached image). Is that spacer supposed to stay in there when I tap down that bearing? The reason why I am asking is because I noticed there is no such spacer on the right side. Is it present on the left to provide some more space between the frame and the brake disk? Is it optional? I do not plan on installing a break initially.
The bearing should be fitted on the metal piece next to the brake flange. (Which should be press-fit, but on the Nimbus hub probably isn’t). The spacer goes between the bearing and the crank.
I don’t have any disc uni hubs so I can only give advice based on how I would figure this out. If I know that my hub is supposed to fit a frame with 125mm spacing (on center) I would measure my hub to find out what I need to get that spacing. In your case since you have one bearing installed I would measure from the outside of the bearing to the stop where the unmounted bearing should rest. That should be the same as a center to center measurement of the two bearings once mounted, or 125mm’s. If it works out to 125mm’s with the 1.5mm spacer then you will need it when you press the bearing on.
I have never seen that before but I wonder if it is there in an effort to make the hub compatible with both superwide standards.
Some superwide hubs and frames are advertised as 127mm wide (5") while others are advertised at 125mm wide. Realistically the tolerances aren’t that tight on the frames and a couple mm in bearing spacing won’t make a difference.
If not using a brake I would do whatever needs to be done to have the remaining spindle sticking out the same on both sides.
I got my hub today and I didn’t get that. I wouldn’t use it. Check the hub width mesurements before pressing the bearing in. You’ll know if you are 1.5mm off or not!