2008 Specialized Fatboy Conversion

[Jax Rhapsody]

WHy would you spend 1800 on a bike that doesn't excel in anything but goin slow? I think disc brakes are wasted on it. It's a cool bike and with a powerful motor would be fun to ride. I remember when the sting ray came out I was like I know that back tire can be used for something else.

 

[1968gtcs]

If you do choose to go with a HT - that jackshaft kit that GhostO has looks like it uses a lot of the same components that I use & it would be an easier install. I just looked at the specs . Your bike is Aluminum. welding another bottom bracket will be a trick. Can you weld AL? If so then it is possible. It also has a 3 piece crank. The Grubee wide one piece crank won't work on that because your front bottom bracket is smaller in diameter. Are you going to install gears? All these things must be considered before committing to a finished design. I posted before I looked at your bikes man. specs. Sorry bout that. I can't weld AL or I would build one of these too. Very good start for a motored. I really like the way this bike is made.

Which jackshaft kit is GhostO's? Do you have a link? Where can I buy the jackshaft kit? Yes, I tig weld aluminum. I'd like to keep to 1 gear because its illegal here in TX to have a geared motored bicycle. The way the bottom part of the frame is designed doesn't look like it gives me clearance to put a jackshaft on it?

<img src="http://www.motoredbikes.com/attachment.php?attachmentid=9188&stc=1&d=1216102195">

 

[1968gtcs]

WHy would you spend 1800 on a bike that doesn't excel in anything but goin slow? I think disc brakes are wasted on it. It's a cool bike and with a powerful motor would be fun to ride. I remember when the sting ray came out I was like I know that back tire can be used for something else.

It doesn't use a stingray tire.......this bike has 24'' wheels, the stingray has a 20'' back tire. This isn't a kid's bicycle like the stingray. This bike is built with VERY high quality, thats why it is pricey ($1800 was the 2007 Fatboy price, this is a 2008 Fatboy with a MSRP of $2800).

 

[Zomby Builder]

plenty of room

You could do it. See how close this one is.





The problem that I see in doing one like mine is your crank will not be wide enough to clear the motor unless you machine another longer center shaft for your crankarms.

Here is one of GhostO jackshaft kits.

http://motoredbikes.com/album.php?albumid=165

He & Pablo are selling these as a kit. Looks pretty impressive. Would work fine on your bike to transfer the drive to the crank sprocket. If you choose this design you will have to use the HT motor.

That is a really nice looking bike.

 

[1968gtcs]

So with this kit, its just transfers the engine crankshaft sprocket from the N.D.S. to the D.S. of the bike? Isn't the stock sprocket too small to allow any pulling power? Shouldn't I have a 36t sprocket or something that then engine turns, or does that jackshaft connect to a sprocket on the crank sprocket that turns the rear wheel independently from pedals?

 

[Zomby Builder]

transfer

Yes all this kit would do for you is transfer the drive side. They use it on shifter bikes, but you don't have to have a shifter to use it. You should ask GhostO about gear ratio options. I think they have the ratios correct the way it is -- Too bad that this kit only fits the Happy Time. It is made to work with the three piece crank.

 

[1968gtcs]

great! This will allow me to keep my disc brake and I won't have to weld canti bosses on the frame for v brakes. Does the crankset come with the jackshaft kit?

 

[Zomby Builder]

jackshaft

I think it comes with everything you need. Ask Pablo & GhostO.

 

[1968gtcs]

Using a jackshaft will allow me to keep my rear disc brake. Thanks for pointing me in the right direction.

 

[1968gtcs]

I've done some research on the jackshaft for my bike and it seems that from my current gearing I've calculated from the following assumtions:

Engine max RPM under load----5850
10 tooth 1.6inch diameter engine crank
18 tooth rear freewheel 2.9 inch diameter
24 inch wheel

Top speed came out to be 73.86 mph......which is nonsense because that gearing would never get the bike moving. I've adjusted these assumptions in my model and find that this would work out a lot better:

8 tooth 1.3 inch diameter engine crank
23 tooth rear freewheel 3.7 inch diameter

This gives me a theoretical top speed of 46.2mph, meaning that I think I will be ok on low end torque and still be able to pedal it @ 50 rpm @ 2.08mph.

Any bigger freewheel and I can't comfortable get the bike up to speed.

I also think that the kit that guy is selling is going to be very bad on low end torque.......it leaves the front crank spinning at 1330 revs/min which is going to tear that china freewheel crank up very quickly.......and the rear freewheel in the lowest 28t gear is spinning at 2089 revs/min.......26 inch wheel going at 51.4 mph in that gear, going to obliterate a cheap freewheel cassette in no time......in 18t gear bike is going 80mph........this is just not a feasible gearing setup......going to be very interesting to see what people think about the kit. Plus, there isn't really any reason to use a freewheel crank.......why not just use a freewheel on the jackshaft kit and you can use your stock crank?