I'm new to ebikes but want to get started on one soon. I have a 14 mile commute that I am already doing part of by bike. I would like to do it all by bike but want to try an ebike so I can get it done faster than I can by pedaling alone.
Could someone give me a brief rundown on the pros/cons of front vs. rear mounting hub motors? From what I have read on the boards, torque rotating the axle can be a problem in the front fork, is this also a concern when mounted in rear?
Thanks
Excessive torque is only a problem for very large motors or for medium motors combined with aluminum forks and/or front shocks. Whether you need to be worried about it depends on the motor/battery combination you pick. There are larger issues when choosing between a front and a rear hub motor, however. I would first decide on the system you want and then deal with torque as a question of installation.
Front hub motors are easier to combine with trailers. They give you more choices for the trailer mounting attachment. Front hub motors are also good for snowy and icy weather for all the same reasons that all-wheel drive cars are better on slick roads. Rear hub motors don't have any particular advantages that I can think of, but they are far more common. Kits like my favorite the Bionx only come as a rear hub motor.
"we must be the change we wish to see in the world"
Thanks Dave. I was thinking of going with one of the conversion kits from electricrider.com based on the Crystalite hubs. The BionX systems look really nice, but are priced kinda steep too.
My thinking is that the Crystalite systems seem pretty modular, so I could upgrade eventually without too much trouble as I feel the need for more volts or better batteries. I see Russ put his on the back wheel because of potholes etc. causing problems with the front wheel (http://www.youtube.com/watch?v=zKKvP9wWrlY&feature=user).
No snow or ice here except for maybe one day a year, but I hadn't thought about the possible use of a trailer.
I don't think a hub motor on the rear would interfere with trailers.
A setup like the Currie/Lashout drive where there's a motor mounted on the rear triangle next to the rear wheel -- that clearly will interfere with a trailer.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
I shouldn't have made my original statement so sweeping. I know of two trailer designs that won't work with rear hubs. There's one design that fits over ends of the real axle (the electric wire gets in the way) and then there's mine from Bike Nashbar that replaces the rear skewer with the trailer attachment (hub motors don't have skewers). I'm sure the ones that attach to the triangle that would work fine, however.
"we must be the change we wish to see in the world"
Yes. On my Wilderness Energy setup I have replaced the battery pack at least once a year for one reason or another. That's $300 a pop. My original Bionx is still going strong, although I will cost a pretty penny when I do have to replace the battery.
Crystalite is an excellent system, although some have enough torque to require torque arms to be safe. Once you pick a kit there will be loads of help around here to install it. One of the things I really like about Bionx is the way the battery rigidly attaches to the frame using the water bottle mounts. It sure would be nice to get a similar battery setup for a Crystalite.
"we must be the change we wish to see in the world"
I can think of a few. I have a front, and would prefer a rear, actually. I'd have one if they weren't more expensive, and I'm thinking of converting my BD36 to rear.
Anyway: There of course is the problem with weak front drops, but that can (for the most part) be remedied with torque arms. Rear drops aren't as critical, since they are meant to handle more than the fronts. However, torque arms should still be used with rears if you have a powerful system.
They also won't have the slippage problems with really torquey setups. Powerful front hubs in small tires can make the front wheel spin even on asphalt. Rears don't have this problem, though extremely powerful rears can make you do wheelies (which can be awesome).
Probably the most noticeable is the way the front wheel goes over bumps. Unless they are very small, front hubs make the wheel much heavier than before. Steering isn't affected by this much, but bumps are much more noticeable with a heavy front wheel.
Rears are also stealthier, since they are partially hidden by the sprockets. There's a guy over on ES who fitted his with a small TongXin(I think) motor which is only partially visible through the disk side, and virtually invisible from the sprocket side.
As far as I can tell, most people prefer them. The ones who don't are the ones who need them for their handling in slick situations. The best setup for that, though, seems to be dual hubs, but that can be expensive.
Oh yeah: I'm pretty sure the BD36 has enough power to rip out the drops. I think you'll be okay if you use the stock setup, but I'm using it at 48V and 33A (comes out to like 1300W after sag). Supposedly, it's rated to 96V, but that's insane; about 50mph in a 20" (!!). I don't know where the core saturates, though.
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I wanted rear wheel drive to have good uphill traction if I ride in snow. Rain probably wouldn't be a problem, but...
if you're on an uphill and traction is at a premium, the rear wheel has the majority of the weight on it and therefore least likely to slip.
I have used both a front (http://www.evalbum.com/1152) and rear (http://www.evalbum.com/1203) Crystalyte 5303, so I can compare'em.
FRONT:
+ Steers incredibly smoothly and consistently because the front wheel is heavy and it pulls the bike forward.
+ Doesn't interfere at all with the existing drivetrain.
+ If you pedal while using the motor, you have all-wheel-drive.
+ Symmetrical.
- REQUIRES a good torque arm.
- Probably requires a rigid fork; suspension forks can't take the lateral force, I hear.
- Makes using a front disc brake difficult or impossible, and front brakes are the most important by far.
- The wheel will often lose traction, screeching against the pavement and wearing down the tire a bit.
- Causes very heavy fork vibration that is very audible.
REAR:
+ Lots of weight on the motor ensures it will never lose traction (on dry pavement at least) except possibly on large bumps.
+ Makes it easy to use a front disc brake.
+ Allows you to use a quick-disconnect front wheel.
+ Allows for a suspension front fork.
+ Also allows for a rear suspension, since those *are* designed to withstand lateral force.
+ Steel bikes with good dropouts won't require a torque arm.
+ Wiring is simpler since the rear wheel axle is fixed and the controller and batteries are probably closer to it.
+ A bit more "stealthy".
+ No audible frame vibration at all, at least not on a steel hardtail bike.
- If your batteries are also on the rear, very little weight will be on the front wheel, causing steering to be extremely squirrelly and erratic. The front wheel will not want to remain straight and you have to steer firmly to keep it straight. Also, there can be a lot of stress on the rear axle, and the inertia can cause the rear end to jump up when going over bumps.
- May require that the rear dropouts be pushed farther apart to fit. On most frames they're 135mm apart or a bit less, but they'll have to be around 140 mm apart for the 5303.
- More of a pain to add or remove.
Overall, I think a low-power bike that won't go over 30 mph is best with a front motor since it helps with steering, but higher speeds need a suspension so a rear motor needs to be used.