steel vs alum ?Schwinn Transit -power this bike can handle?

[usa_electrophile]

I have a Schwinn Transit. It's a great old bike from the 1990s I picked up last year for like 20 or 30 dollars used

Before making it an ebike I would upgrade the tubes/tires/brakes (such as with some Avids)

just curious what sorta power this frame / fork can handle with torque arms etc, considering both front and rear

http://www.bikepedia.com/Quickbike/BikeSpecs.aspx?Year=1995&Brand=Schwinn&Model=Searcher+Transit&Type=bike#.UEwdTFG8SbI


I noticed this was steel frame, my other awesome bike (Specialized Demo 8 is aluminum)

Should I have reservations about how much power /torque / speed each of these bikes can accommodate without damage to the bike themselves (from the motor)
?

thanks all in advance

 

[wesnewell]

I've never used torque arms and have never had a problem putting up to 4kw into a 1000W rear motor using 24s rc lipo and also using regen braking. I put a jam nut on the inside of the left side dropout so I could torque the axle nut real tight. Before that, I crushed the long spacer that goes between the motor and the dropout on that side. But that was because I didn't have a washer between it and the dropout. I do have torque washers on both sides also.

 

[superdave]

I wouldn't run a front hub motor on any typical consumer fork without torque arms. The steel forks won't get fatigue cracks in the drop-outs the way Al forks do, but that doesn't mean they won't spread and destroy themselves (and your motor's axle) if the nuts loosen. And thats assuming a 90's bike new enough to have lawyer lips on the drop-outs. Without those, there's nothing to keep the hub from twisting right out of the drop-outs (which are often very shallow on older bikes) causing a pretty ugly crash scenario. Some folks will tell you they've run steel forks without torque arms with no problems, but I just can't justify the risk for the relatively small cost savings (a top of the line front torque arm from Ebikes.ca is only $30 plus shipping).

On the rear, I think folks would need to see close-up photos of the drop-outs to give you an opinion.

 

[dogman dan]

Nearly any bike can take 800w from a direct drive motor or 400w from a gearmotor, Provided you haven't mis installed the motor.

Torque arms advised for front motors, two if the fork is not steel at the dropouts.

Wes is correct, that a properly tightened nut can resist quite a bit of torque. Trouble is, newbs often don't get it quite right, the nut loosens and then you get real glad you used a torque arm. Particularly in front, it's just so much nicer if you do have a problem, for the wheel to stay on the bike. My first ride lasted a few blocks, the nut loosened, and I ruined a motor and controller. Luckily, I didn't go over the bars.

I can't stress enough to newbs, get the right washers to fit your bike. Grind down the ones that come with the kit, or get C washers. The motors come with oversize nuts and washers that often don't fit into the cup in the forks. Grinding little tabs off the fork might work, but a QR hub bike will have the cup. The first washer must fit flat and perfect inside that cup. Then the additional washers, torque arm, or nut bears only on the washer, which bears on the part of the fork designed for it. Alloy forks and frames can be broken just by tightening the nut on a mist fitted motor.

What's your top limit? Say you got great torque arms and are thinking in terms of 40 mph club? That depends more on the frame than anything. Some frames are not so strong from side to side, and will start high speed wobbling if you get much over 1000w and 30 mph. Cheaper Schwinns, Next, Mongooses, etc may have really floppy frames in aluminum. Yours is steel, so that might help a lot. The better steel frames are much much better for stiffness, due to the better quality tubes used.