My current ebike has a steel frame, front hub motor, rear battery pack (36V x 12AHr), front and rear racks, internally geared rear hub and suspension seat. All that and few things like a lock and small tool kit makes it tip the scales between 60 and 75 pounds. It works well as grocery getter and running my few errands but I would to put something together that is a tad bit lighter. My profound ignorance complicates the task thus I am requesting comments, thoughts and/or suggestions.
I live in Houston, Texas. That means that the terrain is 95% flat. To get a change in elevation of 150 feet would require crossing an Interstate via an overpass or riding up a number of levels in a parking garage. The other relative point is that the street pavement is bloody awful and sidewalks are worse. So skinny, high pressure tires are not an option. Lastly it would be at least 50 mile round trip ride to get to anything that resembles woods, forest or dirt trails. So this bike is strictly an urban hybrid.
The idea is to build something light weight, but still full size and reliable that can be ridden either as a short range ebike or normal urban hybrid without paying a severe penalty for including the motor assist. I am going to set a ridiculous target of under 30 pounds (13.6 KG).
I happen to have acquired a stripped 54cm 1989 Miyata CT-7000 frame and fork. This is a carbon-fiber/aluminum composite frame with a aluminum fork that weights just under four founds (1.8 Kg). I have been looking at building a rear wheel with a light weight geared hub motor. It seems that QT75 and 85 are in short supply so at this point I am considering a QT100 (4.6 pounds = 2.1 Kg plus controller). My understanding is that these motors have almost no drag when not powered. However they do require a 36 spoke wheel. The range of 36 spoke, rim brake wheels designed to mount 700Cx32-40mm tires is somewhat limited (and heavy). In the 650C range they are almost non-existent (I did locate some 450 gram Alex Assault Rims on Ebay but they have 13.5 grip width). However being realistic I am not likely to save more that one pound (2.2 KG) with the lighter Rims and spokes. Thus I am considering Sun Ryno Lites (0.565 KG/each).
However the though occurs to me: just how much of weigh penalty would be involved in using a 36 volt Bafang Mid Drive. I have not seen any accurate weights for the drive system. It also includes the Crank, Bottom Bracket and Motor controller. Thus the weight of all these items would be offset as well. This would also open up the range of rims that could be used not to mention the advantage of the motor operating through the gear train. I have also not seem (or forgotten) how much drag this system adds if the motor is not powered. Can someone comment on their experience in this regard?
Tires – Kenda Kourier 700Cx35 (480 grams = 1.0 pound/each)
Battery – 36Volt x 5.8 Ah (24 each Panasonic 18650 = 1.5 pounds)
Other comments, thoughts and/or suggestions ???
Edited by LewTwo
on Sat Jun 27, 2015 1:42 am.