Bridgestone Albelt drive transplant
08-21-19, 09:53 PM
#1
Junior Member
Thread Starter
Bridgestone Albelt drive transplant
I bought my Albelt more or less on impulse. To get within my budget I had to go with Japanese surplus. My biggest gripe with my last bike was getting my leg greased on a regular basis. Local conditions strongly favor enclosed drives and IGH. After I bought it I discovered that they have been on the domestic market in Japan for over a decade. Junk doesn't hold market share that long. If your primary need for a bicycle is transportation, cleanliness and nearly zero maintenance is more important than how well it fits you or your riding style.
However.
I've always been a bit of a "gear head", and was taught to take the long view. Minor mods and proper adjustment offer a good return in the form of how much I enjoy using a piece of machinery. The Albelt drive makes gear ratio changes expensive in Japan and impossible here without imported parts that if I can even find them would quickly exceed the value of the bike. So, I shopped online and found a good deal on a couple of cogs and a single ring crankset that should let me make the swap. While waiting for delivery, I had a rear flat and had a chance to take a closer look at the current set up. I decided to post this as sort of a specialized FYI.
My Albelt uses a Shimano SG-3R45 IGH. The only place I've found any mention of this hub is the list of models covered at the front of the SG-3R40 service manual. While it has an axle length of 189mm the shifting push rod measures only 87mm. Everything seems to function so it may be OEM rather than a shorter than spec replacement rod. The other noticeable difference is the hub driver. The belt pulley is much wider than a conventional cog. It is dished deeply enough to work with the hub's 120mm LOD but could not be thin enough for the usual retaining ring. The visible end shows the grooves that accept the tabs on a normal cog but the driver has been threaded (35mm x 1?). There may be a retaining ring groove hidden under the pulley. If not my least expensive source for a replacement driver is breaking up a complete bicycle for parts. ($40). While I would like to preserve the parts I remove, my best option may be to saw a slice off the old pulley and fabricate a retaining ring from it.
The front pulley is described on the Bridgestone website as a "Floating Gear" system. This is marketing speak for "Total POS". Ok, I understand what the engineers did. The outer shell is hollow, molded in two parts with a vertical split and held together with screws. The outer surface has the belt teeth and the concentric inner surface has conventional gear teeth. These mesh with a gear mounted on the crank arm that is smaller than the inner circle of teeth on the shell. With the belt off the shell has enough clearance to rotate free of the crank gear. Under tension, the front teeth of the crank gear engage the teeth on the front inner shell, keeping them meshed while the shell "floats". This gives a built in gear reduction. It also moves the front pulley center of rotation about a half inch behind the crank spindle center slightly shortening the chain (belt) line. The actual tooth count on the rear pulley is 25. The effective tooth count on the crank pulley is 55. With my wheels and cranks, the Inter-3 IGH ratios work out to 3.5 - 4.8 - 6.5 meters development, (confirmed by measurement) or 43.8-59.8-81.6 expressed as gear inches.
While I've heard that belt drives don't tolerate heavy loads on small pulleys very well, the front pulley would have been more than double the tooth count of the rear without this added layer of inefficient complexity. I'm old, I need two usable gears with a bail out low more than a top gear that's useless to me without a downhill. The parts I've ordered are 36x20 for 35.9-48.9-66.7 with an alternate 18T cog for 39.8-54.4-74.1 A waxed chain with a guard shouldn't throw any more grease than a belt or require much more attention. It will certainly be easier to source a replacement when needed.
We'll see how things work out.
However.
I've always been a bit of a "gear head", and was taught to take the long view. Minor mods and proper adjustment offer a good return in the form of how much I enjoy using a piece of machinery. The Albelt drive makes gear ratio changes expensive in Japan and impossible here without imported parts that if I can even find them would quickly exceed the value of the bike. So, I shopped online and found a good deal on a couple of cogs and a single ring crankset that should let me make the swap. While waiting for delivery, I had a rear flat and had a chance to take a closer look at the current set up. I decided to post this as sort of a specialized FYI.
My Albelt uses a Shimano SG-3R45 IGH. The only place I've found any mention of this hub is the list of models covered at the front of the SG-3R40 service manual. While it has an axle length of 189mm the shifting push rod measures only 87mm. Everything seems to function so it may be OEM rather than a shorter than spec replacement rod. The other noticeable difference is the hub driver. The belt pulley is much wider than a conventional cog. It is dished deeply enough to work with the hub's 120mm LOD but could not be thin enough for the usual retaining ring. The visible end shows the grooves that accept the tabs on a normal cog but the driver has been threaded (35mm x 1?). There may be a retaining ring groove hidden under the pulley. If not my least expensive source for a replacement driver is breaking up a complete bicycle for parts. ($40). While I would like to preserve the parts I remove, my best option may be to saw a slice off the old pulley and fabricate a retaining ring from it.
The front pulley is described on the Bridgestone website as a "Floating Gear" system. This is marketing speak for "Total POS". Ok, I understand what the engineers did. The outer shell is hollow, molded in two parts with a vertical split and held together with screws. The outer surface has the belt teeth and the concentric inner surface has conventional gear teeth. These mesh with a gear mounted on the crank arm that is smaller than the inner circle of teeth on the shell. With the belt off the shell has enough clearance to rotate free of the crank gear. Under tension, the front teeth of the crank gear engage the teeth on the front inner shell, keeping them meshed while the shell "floats". This gives a built in gear reduction. It also moves the front pulley center of rotation about a half inch behind the crank spindle center slightly shortening the chain (belt) line. The actual tooth count on the rear pulley is 25. The effective tooth count on the crank pulley is 55. With my wheels and cranks, the Inter-3 IGH ratios work out to 3.5 - 4.8 - 6.5 meters development, (confirmed by measurement) or 43.8-59.8-81.6 expressed as gear inches.
While I've heard that belt drives don't tolerate heavy loads on small pulleys very well, the front pulley would have been more than double the tooth count of the rear without this added layer of inefficient complexity. I'm old, I need two usable gears with a bail out low more than a top gear that's useless to me without a downhill. The parts I've ordered are 36x20 for 35.9-48.9-66.7 with an alternate 18T cog for 39.8-54.4-74.1 A waxed chain with a guard shouldn't throw any more grease than a belt or require much more attention. It will certainly be easier to source a replacement when needed.
We'll see how things work out.
