Bridgestone Albelt

Question

For reasons that have nothing to do with bicycles I retired in the Philippines. I needed transportation and due to traffic density and poor infrastructure a bicycle made the most sense. It's a poor country. To get a decent quality bike at a price that won't break the bank you pretty much have to buy used surplus from an importer. Most of it comes from Japan.

That's how I ended up with a fairly nice Bridgestone Albelt. Like this one only mine is more of a yellow/orange color.

Model specific spare parts were never available here. I'll be getting a set of 622 rims laced up so I can use locally available tires. (currently has well worn 27 x 1 3/8 on 630 rims) The belt drive is working Ok for now but when the belt goes I'll have to either source one from an industrial supplier or go to a chain.

I'd like to have a "splitter" to break the three speeds into six smaller jumps. How hard is it to mount a pair of cogs and a small derailleur on a Shimano Nexus SG-3R45 hub?

The front cog is also internally geared, making less than one full revolution for each one of the crank. The crank shaft looks like a square taper with (rusty) nuts holding the arms on. Can I simply swap it for a conventional sprocket?

Thanks in advance for any suggestions.

Rear Cog

Answer 1

I'll be getting a set of 622 rims laced up so I can use locally available tires. (currently has well worn 27 x 1 3/8 on 630 rims).

You'll need to make sure your brake calipers have sufficient reach, obviously the brake track on 622mm rims will be 4mm further away from the caliper than n 630mm rims.

How hard is it to mount a pair of cogs and a small derailleur on a Shimano Nexus SG-3R45 hub?

Pretty much impossible. The hub does not have a mount that can accomodate a cassette or freewheel, and the hub is not designed to allow room for more than one sprocket.

If you want more gears, are rebuilding the rear wheel and ditching the belt (which is going to require a new crank, shifters anyway), why not just switch to a derailleur drivetrain?

Answer 2

I followed the sprocket link on the Sheldon Brown hybrid gearing section.

https://www.sheldonbrown.com/internal-gears.html#sprockets

If you look at the photo of my current setup you can see the rear belt cog is deeply dished. It uses practically all of the mounting surface on the Shimano Nexus 3spd, covering the snap ring groove. The drive surface is 16mm plus flanges. Removing it will leave more than enough room for a pair of sprockets.

There is enough of a stub outboard of the snap ring groove to support a second sprocket, especially if the inner side is beveled slightly to fit over the snap ring that retains the first sprocket. If I drill and tap for a couple of screws I should be able to install the inner sprocket, snap ring, and then secure the outer sprocket to the inner. Since power is transmitted through the three lugs on the sprocket bore, the screws should be under almost no load and the outer sprocket can double as a snap ring retainer.

Either I no longer have teenage legs or my present gearing is atypical. Second is at the edge of discomfort, first could be lower, and third is useless without a downhill or tailwind. If I add three more ranges between 2-3, 1-2, and below first the bike should be much more rideable. I grew up driving farm trucks with a two speed axle behind a conventional gearbox so shifting with a splitter feels natural. I should be able to mount the lever on the underside of the bar that holds the rotating Nexus shifter. Because I'm only using two sprockets I can swap them to get the right high-low position of whatever shifter lever I use.

So, with the exception of drilling and tapping a couple of non-critical holes, it looks like a straight bolt up of readily available second hand parts. Still not sure what to use for a derailleur or how to mount it. There's no rush. It works as is and even if I snap a drive belt I've found an industrial supplier who'll sell me something that should fit for under $10.

Thanks to everyone for their suggestions and comments.