2 speed Fatboy

[Wildcat]

I now have the parts for my idea. I had a problem with braking, but I think that is worked out too. I already added a laidback seat post, one of the heavy custom ones that "Slowriders" makes. The other change from stock is the seat and handlebars, and the 22 tooth sprocket on the hub. It rides well, but not fast enough with that gearing. With a smaller sprocket, it isn't that good for sand or dirt. So, the 2 speed fabrication is in order. I'm not relacing in a hub, I'm keeping the one speed hub and adding more sprockets up front. Just enough to have two gears fairly close together. I could make it three, but the chain length is a problem then. Yet to be fabbed up is the shifter. I may add a different kind of front brake.
I'll add some pics when I get home.

 

[aka_locojoe]

I now have the parts for my idea. I had a problem with braking, but I think that is worked out too. I already added a laidback seat post, one of the heavy custom ones that "Slowriders" makes. The other change from stock is the seat and handlebars, and the 22 tooth sprocket on the hub. It rides well, but not fast enough with that gearing. With a smaller sprocket, it isn't that good for sand or dirt. So, the 2 speed fabrication is in order. I'm not relacing in a hub, I'm keeping the one speed hub and adding more sprockets up front. Just enough to have two gears fairly close together. I could make it three, but the chain length is a problem then. Yet to be fabbed up is the shifter. I may add a different kind of front brake.
I'll add some pics when I get home.

I wondered about going this route.

 

[Wildcat]

Here is the plan: take the crankarms from the mtb and put them on the Fatboy. Use an old tensioner from a Mossberg tandem (thanks Crassley) to take up the slack in the chain (also from the mtb if it fits the rear sprocket). I have a big rear derailler if that doesn't work. Then make up a shifting mechanism because the usual front derailler won't reach across far enough on the wide frame. The idea is to only have enough slack and keep the tensioner close to the chain line to use the coaster brake. A front brake will take up the slack, another engineering problem. The idea I have right now is Fred Flintstone style, but I'm also looking at a rod brake of some sort. The sprockets on the mtb crank are 44, 34, and 24 teeth, I won't use the smallest one to avoid any clearance problems. I'll have to see if the best range is with the 18 or 22 rear sprocket. It came with 36 front, 18 rear. So, if a 42/22 is about the same, that will work, a good street gear and a good low off road, 34/22. I'm using 36/22 right now and it's too low for the road.

 

[Wildcat]

Progress. I'm using a derailleur because it mounts right up and can take the strain of the braking better than the tensioner. My big cog derailleur had parts missing, so this one works. It also lined up right to the sprocket using the existing stop, so that was easy. I took the chain rings off the mtb using my hammer method. I am waiting for a puller for the fatboy's crank removal because I don't think the threads on the BB will make it if I loosen them again. It might be the bearing cup and not the frame threads but I'm not going to risk it. Next is to check the gear ratios and see how to make a shifter. I might make it without a shifter and do the shift manually, but it wouldn't shift on the fly.

 

[Wildcat]

Took the cranks apart anyway and it's a good thing, they were shot on the right side. I had some old ones from an english bike that worked in place of them.

I got everything together and tried it out. I went back to the original 18 tooth sprocket in the rear because I didn't have any of the right size chain to splice in. The 34/18 is a good street gear, and the low gear is great. There is a problem though. The brakes are good on the high gear, but the low leaves too much chain loose on top, and the chain jumped off when I resumed pedaling. I may have to use the 2 larger sprockets after all. or maybe forget the speeds and leave it 34/18. At least the chainwheels match the bike.

Low gear:

High gear:

Slack chain when braking:

 

[user 135]

I think any tensioner or derailer will have a tough time with the coaster brake. Front brake will allow you to stop but chain management will still be a problem.
The ultimate solution would be a new hub or figure out how to disable the coaster brake.

Sent from my ADR6425LVW using Tapatalk 2

 

[Wildcat]

This is a non-success. LOL! A nice name for a failed idea. With the amount of play in the chain, and the fabrication needed for a shifter, it isn't worth the trouble. A multispeed rear hub may be the only way. So it's a one speed, but the 34/18 works well for me, on and off road.

 

[dracothered]

You just need to add the bolt on brake bosses for the front forks and then fab some posts for the back wheel. After you have that you pull the brake shoes out and put a spring in there to keep the clutch from going over to far to the brake side. Leave the coaster brake arm on and make a bracket for the front derailer to put it out where it is needed.

 

[Wildcat]

I think that would work, but it's too much work for the result. Of course, then It would use all three chain rings for 3 speeds. I don't have welding capabilities so maybe someone else can try this.

 

[Wildcat]

The 34 tooth chain ring is still working well for street and off road. I got a more upright set of bars and found a use for the shock stem I've had for years.