offsetting cranks

[King Zebba]

Need to know how to offset cranks on a standard bottom bracket to accommodate a 4" wide wheel. Anyone?

 

[scrumblero]

3 piece conversion kit and a custom welded /longer spindle I guess..

 

[c.p.odom]

I am thinking a torch, a one piece crank arm, and bend a dogleg into them.

 

[Bendix]

i wonder what kind of spindle would be simplest to have machined? maybe find a three piece bmx crankset with a simple interface, i.e. fewest splines, and have the spindle duplicated in XL by your local shop. seems i remember a diamondback bmx spindle with just flats in place of splines several years ago......(?)

 

[c.p.odom]

This is taking the hard road to a much simpler solution.
You can buy American to European bottom bracket cup conversions. These are two press in threaded cups with Allen bolts to allow you to use any conventional Road/MTB/Tandem bottom bracket.

I did find this:
http://www.choppersus.com/store/product ... cket-Axle/

 

[Bendix]

This is taking the hard road to a much simpler solution.
You can buy American to European bottom bracket cup conversions. These are two press in threaded cups with Allen bolts to allow you to use any conventional Road/MTB/Tandem bottom bracket.

I did find this:
http://www.choppersus.com/store/product ... cket-Axle/

i've used the coversions many a time, i'm sure scrumblero has too. of course if that stingray spindle gives him the correct chainline it's the obvious choice. i was just thinking out loud (on a keyboard?) about a truly custom spindle if it were to be needed.

 

[c.p.odom]

To go with a custom spindle you would need to be using sealed bearings. It would be very impractical to grind and harden bearing surfaces. Press in cups with through bolts machined for sealed bearings would be pretty simple. The end tapers are 2 degrees but the length and size varies between the ISO and JIS cranks. The even older Type 2 cranks (spindles with male threads) are different as well, some even having a 3 degree taper. Pick the crank and then make the spindle. The problem is that bottom bracket widths for one piece cranks are not very consistent in their tolerances, designing for some bearing shimming would be required.

 

[King Zebba]

Good ideas! Thx Guys!

 

[Bendix]

To go with a custom spindle you would need to be using sealed bearings. It would be very impractical to grind and harden bearing surfaces. Press in cups with through bolts machined for sealed bearings would be pretty simple. The end tapers are 2 degrees but the length and size varies between the ISO and JIS cranks. The even older Type 2 cranks (spindles with male threads) are different as well, some even having a 3 degree taper. Pick the crank and then make the spindle. The problem is that bottom bracket widths for one piece cranks are not very consistent in their tolerances, designing for some bearing shimming would be required.

again, that's why i would say pick a complete sealed bearing BMX three piece crankset with the simplest shape on the ends of the spindle if forced to go custom. not terribly expensive these days, they're designed for the vagaries of american bbs and have no complex bearing surfaces, shoulders, tapers, etc.....only the spindle would have to be recreated, your machinist would have it in hand for his own measuring, there would be no guesswork, and you'd know everything else would be compatable since you bought it as a set. another plus is the abundance of really cool bmx chainrings! shop around, i've seen them as simple as basically 2/3 round with only a flat spot for aligning the cranks. obviously a splined unit would be more complex, and hence more expensive.

 

[Dorian]

ChoppersUS has the wide bottom brackets - and spindles, they also have wide rear hubs. Same specs as the fat tire'd modern stinkrays. No need for special machining when all the stuff is available off the shelf.

Dorian