On my couple of builds- completed several years ago- I mounted my motor sprocks directly to drilled flip/flop rear hubs (smooth sided large flange) Now we can easily and more cheaply get disk brake hubs like these: http://www.ebay.com/itm/Pair-Mounta...7d6db36&pid=100005&rk=2&rkt=6&sd=141707441658 And the ebay guy in Miami at least has alloy sprocks with inner disk brake drillings, http://www.ebay.com/itm/MOTORIZED-B...430839?hash=item3f5bffce77:g:ZSMAAOSwpzdWtlhg plus you can still get them- a little more money, but super nice- from Kings Sprockets http://www.kingssalesandservice.com/ just noticed another item - f you want to go cheap: http://www.ebay.com/itm/30200418287...49&var=600803066188&ssPageName=STRK:MEBIDX:IT It's a disk brake adapter that threads on a rear threading- luckily I already have one of these lying around: http://www.ebay.com/itm/Bike-Bicycl...9a67688&pid=100005&rk=3&rkt=6&sd=222063529655 So for a 99 cent adapter I'll see if it threads up- I think you can reverse the adapter either way? Wondering if the mounting hole threads are right then? Anyway- losing the rag joint and it's long and heavy bolts, and replacing a heavy steel sprocket with alloy- may wear a bit faster- and then using titanium disk brake bolts to bolt it on is a SUBSTANTIAL weight saving If you can also drop the heavy steel tensioner it's another chunk of weight off the kit, and a 415 Industrial trike chain is barely half the weight of a kit chain-(rolls better too) So- new stuff just keeps coming- a little slow though! Still hoping for a lighter 33cc Chna girl for a classic steel road or touring bike. I think the warm days have come for a 15 lbs TOTAL weight kit that will roll along at 22-25 with light and fast wheels.