oooh, thanks for the tip, dmb.
However, the large wheel's inside hub spacer is shaped like a wooden spool used for sewing machine thread.
It is 50mm long, has 27mm ends, a 22mm OD body and 15mm (not 16mm) inside diameter.
With 10mm by 35mm bearings, the bike's weight would only be on the bearings, not the hub and its spacer.
I'd still need a spacer for support in the center.
Update:
The inside hub spacer for the large RM125 wheel does NOT provide support to the center of the hub.
The hub's center is about 26mm diameter, so the 22mm hub spacer floats in there.
Therefore, the only reason for the spacer is to provide inside lateral support for the wheel bearings.
So I can't have my fabricated tube spacer extend THROUGH the bearing's ID.
To prove it, I removed one bearing and the inside hub spacer from the smaller 1990-something RM80 wheel.
Its wheel bearing is 12mm ID and accepts a larger, much stronger axle, which is excellent.
This inside spacer is a simple steel tube. It is 50mm long; the larger wheel's one is 52mm long. Perfect.
The spacer is 16mm OD, so its walls are 2mm thick. The wheel hub is 26mm ID, and there's a 19mm center ridge.
So the 16mm spacer also floats inside the smaller wheel's hub.
Like dmb shared, 35mm bearings come with smaller ID holes.
I found 35mm bearings with 12mm ID and 10mm wide. OEM ones were 11mm wide, but no biggie.
So I'll use the 12mm axle, its OEM inside and outside spacers and washers to secure the larger wheel.
FTR, I have a 1986 Suzuki RM80 fork. 1986-1988 forks are drilled for a 10mm axle. 1989-up RM80 forks use a 12mm axle.
Reaming mine to accept a 12mm axle should fix this. Then installing the RM80 outside & inside hub spacers and
two 35mm x 12mm x 10mm bearings should get this large RM125 wheel on the fork.
Once securely installed, an adaptor to mount the larger caliper to the smaller fork can be fabbed.
Both bikes use the same hydraulic system except calipers, so that's comforting.
