A while back I bought a Mountain bike to get fat tires, full-suspension, and a front disc brake. I didnÃ¢â‚¬â„¢t like the posture, so I modified it to be more of a semi-recumbent, similar to a beach cruiser posture. I was pleased except that when riding uphill, the rear weight bias made the bike somewhat wheelie-prone.
There is a longtail bike thread with many examples, and oldhaqÃ¢â‚¬â„¢s bike inspired me to attempt adding a rear suspension arm to a hard-tail Downhill (DH) bike. Half of cheap MTBs have the bottom bracket (BB) as part of the frame, and the other half have the BB on the rear suspension arm (thats the kind I needed). I wanted to try attaching the BB square tapered spindle to the drop-outs on the rear of the hardtail bike.http://endless-sphere.com/forums/viewtopic.php?f=1&t=9673&start=15#p151589
Most cheap bikes have integrated non-removable studs extending from the ends of the BB-spindle (the pedal axle). I found some mid-range Schwinns that had threaded holes on the spindle ends, which would allow me to use bolts (of my chosen length) to attach the BB-spindle to the drop-outs. I could then shim the odd bold length with washers (which I have).
My local bike shop (LBS, a big thanks to Big Poppi bicycles in Manhattan, Kansas) informed me that sealed spindle/bearing cartridge sets are available for $16 that also use end-bolts, and the spindles are available in several different lengths. The end-bolts for the spindle I acquired were M8-1.00 (metric diameter and thread-count) and the hardware store had high-strength "8.8" bolts of that type. Chose a length for maximum insertion, ended up shimming the excess bolt length between the drop-outs with two washers on each side. This bike had 8 gears and a rear disc, so the drop-outs were widely spaced, the spindle I used is 5" long.
Of course hub-motors can be fitted, and the extra frame space provided allows several types of non-hub systems to also be fitted. If someone desired to use a 24Ã¢â‚¬Â or a 20Ã¢â‚¬Â rear wheel, the shock mount could be extended to rotate the arm down so that the pedals wouldnÃ¢â‚¬â„¢t strike the ground on turns.
If you have a rear suspension arm that uses the larger diameter bearings for the one-piece crank (found on many of the cheaper range of bikes) Sick Bikes makes a $20 adapter so that you can use the 3-piece crank-set with the square-tapered spindle.http://sickbikeparts.com/catalog/product_info.php?cPath=23&products_id=56