My stretch bicycle project (Stretch-e-bicycle phase 1) is getting further along but I ran into a snag. I'm using a 48v crystalyte motor and it's wide enough to rub on the forks. The motor barely moves. Dang wish I'd noticed this before now. Good thing about the project is I've got the brakes sorted out and all the welding and stuff is done.
In any case I need a different front fork. I went to the vendors listed on the Support VisForVoltage page and while they carry a variety of forks none appear to be suitable.
I've removed the fork from the frame and the measurements are:-
dropout width - 4 1/4" ... I'm seeing many forks that are 100mm and many other forks don't list a width. Whatever. Obviously 4 1/4" is about 113mm (or so) and 100mm would be too narrow and I'm guessing 130mm or more would be adequate.
steerer tube - 1 1/8" and it has threading at the top to attach it to the frame -- that is, it's a threaded headset and a stem to match. Just looked through Zinn & The Art of Mountain Bike Maintenance -- it's clear if the fork were threadless then I'd have to replace the headset as well as fork.
To catch up on this ... Comparing the forks with those on another bike where I'd mounted this motor successfully - the shape of the fork arms are different. On the other bike the fork arms are skinny for enough distance that the motor fits in, whereas on this fork the arms are thick with the dropouts in the center of the arm.
According to the Electric Rider website this motor is 90mm thick (it's the Sparrow) so the fork arms have to leave enough room for this thick motor.
Unfortunately the bike parts merchants usually aren't giving enough details.
I just found Nirve (nirve.com) who sells some custom bikes plus parts and their forks are the right size except I'm not certain enough about the distance between fork arms. Have sent them a question ...
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
Is this that blue U-style non-shock fork?
If so, use an automotive floor jack between the fork arms and spread them out just enough for the motor and the torque arms you plan to use.
I've had no problems with the (cheap!) steel rear triangles I've spread like this, even with the super-torque motor system I have on there now, which has enough power to begin ripping the motor itself off the 3/32" thick steel mounting plate I welded across the center triangle of CrazyBike2. :roll: Oh, and to partly taco-fold a front chainring.... But no issues with the dropouts or stays, even though it was all a brazed together Schwinn Sprint frame from the late 70s / early 80s.
I've also spread front forks like this, though I have not put any motor power thru them. With torque arms (highly recommended on *any* front fork modified or not), I can't imagine any failures due to bending them this way.
The failures you might see in dropouts and such would be from either drive torque or braking (regen) torque, both of which would be taken care of by proper torque arms, and would be the same problem regardless of width of fork or modifications to that width (or the very slight angle created in the dropouts from the bend).
Really, if my 150-pound monstrosity's frame hasn't broken after all the crap I put it thru, including the most recent "crash" where I hit a vertical post with the rightside cargo pod (taking me from 17mph to 3, instantly), I'd have to say that widening them this way is fairly safe. ;)
--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com
Yeah it is.. I hadn't thought about spreading the forks because I'd read previously it was a bad idea to do so. At least by very much. The page I read recommended that spreading them by more than 1/4" (??? maybe less ???) would threaten the integrity of the forks.
hmmm.... but in this case it wouldn't be very much spreading required. hmmm...
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
You wouldn't want to spread much, especially if cold-bending, but a little shouldn't hurt. No way to tell unless you try--just do some bench testing before any long trips. ;)
If you have a blowtorch, you could heat the area where the U welds to the vertical tube; since it's welded and not brazed it won't come apart. I don't know exactly how hot but slightly red-hot is likely minimum. Keep it that hot until you're done bending, then dunk the whole thing in an oil bath or water to quench it, to re-harden it.
I dont' have a torch so have not tested if that makes a difference, but when I weld I always quench; I know THAT makes a big difference to the hardness of the metal afterward. Some things I welded without doing that are hand-bendable afterwards; if I quench I have actually had trouble *drilling* some of them!
--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com
Yeah, if I'm gonna throw these forks out anyway might as well experiment a little.
This evening I took a long bolt, put a couple nuts on it, put the bolt through the dropouts, and did the bolts so they would spread the fork arms. Seems like a more controllable way to go than a floor jack. I let it sit for a couple hours and took out the bolt. It seems to be wider enough to give some clearance to the motor and that I should be putting a couple washers on the axle to ensure the fork arms stay spread.
One thing I'm not certain of is whether each arm is bending the same. I'm thinking each arm might bend differently depending on the condition of the metal in each not to mention depending on the phase of the moon.
Anyway this looks promising.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki