Compare front wheel drive hub systems with rear wheel ones

[kmxtornado]

I'm new to this whole e-bike thing. Mind shedding some light on the differences btw the two systems? I've noticed some conversion kits are rear wheel while others are front wheel driven.

ANALYSIS FROM A NEWBIE:
- I suppose rear wheel drive ones will maneuver much differently than a front wheel drive one pulling the bike. Front wheel allows you to powerside while a rear wheel one can do a burnout. Neither of which I'd want to do, but I'm sure there are some practical differences you guys/gals can share with me such as...
- Removing components off a rear wheel to replace a tube (instead of patching) is a pain already with the chain and derailleur back there. Having a kit with proprietary axles and hardware would be add to the difficulty in removal and reinstallation while on the road. Perhaps a front wheel drive system would be easier for curb side flat repairs?

Ugh, sorry fella's. I did some more searching on the forum and found this: http://endless-sphere.com/forums/viewtopic.php?f=5&t=9302&view=viewpoll
Reading it now....

Feel free to post here if you have more to add though.

 

[dogman dan]

Flats are a pita on any hubmotor. Front or rear. You got nuts that need to be very tight, a torque arm or even two. then the wires have to be unplugged or at least seperated from the frame.

Some get real good at patching a tire while it's still bolted to the bike. Personally, I just run obscene amounts of 4x4 grade slime.

Some really freak out on the "danger" of a front hub. I think it's not so likely that your motor will lock up on you. Chances are much better you find one of the other million ways to crash first. Often a car will suddenly turn in front of you into a parking lot, or you will just find a crack in the road or some gravel. I think front hubs work great on bikes for street commuting, that usually are not so fast or high powered.

On dirt, rear hub is pretty much mandatory. It's too nice to be able to lift the front wheel easily when you have obstructions to deal with. Same for urban riders who need to curb hop constantly.

In a way, it can make sense to determine where the battery will be carried , then choose front or rear. If the bike frame pretty much prevents carrying a battery in the frame up front, then a front motor can be a good choice for a street bike. Such as this.



On a dirt bike, the battery needs to be up front, so the bike still handles ok. In the frame is great, but sometimes it just can't be carried that way. So a saddlebag style carry on the top tube is common, like this.


Many build a bike like this, because for various reasons they want rear hub. Carrying up to 15 pounds of battery on the rack can still work ok. But only ok, handling is definitely worse. For dirt riding this is a lot less nice than a mid battery carry. It can be tolerated, but never enjoyed.


Notice how the rear racks have been braced to the frame by a diagonal. I consider this pretty much mandatory for seatpost racks used with FS bikes.

 

[Pure]

Wile there is the issue of the off chance that you lock up a front hub, the bigger problem is that bicycles are not designed to withstand the stress a front hub motor puts on the frame/fork. High powered systems can break forks and welds. So with that, most people don't put any kind of real power to a front hub. Sure there are the guys here who do, but I sure as heck wouldn't.

 

[d8veh]

I have two bikes, both with high torque geared hub motors. Both are fitted with substantial torque arms. I've high-sided three times on the rear driven one on poor adhesion surfaces and no accidents on the other - just a bit of wheel-spin. I have the batteries on a rear rack on both of them, and the rear driven one doesn't handle as well as the other: It has a tendency to weave, but is still quite controllable. Overall I prefer front drive, which I believe to be safer if properly engineered.

 

[edcastrovalley]

One thing I learned about the 9C direct drive hubs is the rear hub is larger than the front and has more power. I learned that from one of Justin's posts. I'll check but I think the front stator was something like 35mm wide whereas the rear was 53mm? When I read that I ran down to the garage and switched motors (since I had the luxury of having a front and rear motor) and removed front hub installing the rear hub and I have noticeably better acceleration and definitely better top speed. Because of the switch I had to move the batteries forward to a Falcon triangle bag for better handling which is working out great.

 

[kmxtornado]

Dogman is the man! WOw, thanks so much for your super thorough writeup! Much appreciate it. It never occurred to me that curb hopping may determine that the hub/weight should go in the back. That makes tons of sense but I guess I just never thought about that. What I did recently realize though is that most of the braking on a bike (as opposed to a motorcycle or tadpole trike) is done on the rear wheel. It would make sense that braking here is done at the same point as the hub making a rear hub to be the preferred location for a motor.

Thanks also for the tip about locating the battery before deciding whether to get a front or rear hub motor.

 

[Pure]

Overall I prefer front drive, which I believe to be safer if properly engineered.

Seriously? Ok get past the design flaws (forks/frames not meant for these forces) with this setup. No matter what you do you will always risk a hub lock up at speed. This is even a risk for rear mounts. But if a rear mount locks up on you, you will most likely slide a little, at worst lay the bike down. If a front hub locks up on you, you are going over the bars, no doubt about it. Don't blame poor battery location for ill handling. That's more your fault than that of the rear design. The only thing a front hub has over rear is if you are in really loose or slippery road conditions, like riding in sand or snow. In these conditions it's always better to be pulling rather than pushing. Other than that, a rear hub beats a front hub hands down. More power, better handling, and safer, it's really not even a contest.

And I don't know what this "wiggle/wobble" you feel from your rear mount. But as I have one of the heaviest rear motors plus 30 pounds of battery hanging off of my rear rack. I don't feel anything. The bike is actually very stable. I wouldn't want to run a slalom course or a tight single track with it, it is a little top/ass heavy. But for commuting on the street, it handles just fine. If I had to guess I would say more likely you have a poorly designed "fabricated" motor who wobbles on it's own. This is a common thing with lots of hubbies, front and rear drive, coming out of china. After that I would point fingers at your bike's geometry. Just having a lot of weight on the ass doesn't make a bike wobble. Least not mine.

 

[dogman dan]

Usually excess wobble, or tail wag, is caused by the heavy battery up high combined with weak or loose racks.

If you brace your racks the way I do, then you see the entire frame flex when carrying really heavy loads. On a good bike, as Pure must have, it may be completly un noticeable. On a wallbike, carry that battery high, and add the extra mass of a rear motor, and you will see the frame flex alarmingly. But it depends, some cheap bikes, particularly hardtail mtb's or cruisers may have dang strong frames despite their cheap price. While a moderatlely expensive FS bike may have the wobbles real bad.

But really pure, you telling me your front wheel doesn't feel a tad light? Or just that you don't notice what you've gotten used to? A well handling bike is one you would take on a slalom or single track. For sure, I don't have the best handling on my street bikes either, not with those huge panniers. What works for street may work poorly on dirt.

As for braking, you really should use at least some front brake. Even if weight is carried high and back, you can still get the traction to happen on the front by easing into the front brake till the tire starts to grab better. If you have a front hub, the extra traction is always there though. 8)

I'm definitley biased toward liking front hub on asphalt. I loved running 72v 40 amps and going 40 mph in the death race. But I do admit that when I bumped voltage up to 110, and had a 47 mph front hub bike, I couldn't controll it in the corners. I was getting tons of slip, and scaring my self shitless 13 times per lap. So though I love a front hub, there is definitely a limit to controlling one. I still think front hub on a commuter is nice, since I don't need to curb hop since the ADA law.

 

[Pure]

No it doesn't feel light once I'm on it. The problems with high speed single track or slalom is that the bike is slow to react because of the high center of gravity, I think, it just feels pigish.. Other than that it's at least a stable ride and I can take "street" corners at speed with no problems. More than once I've scare the shit out of myself by scraping pedals cause I'm laying it down too low.

I wouldn't call my bike special. The frame on it is a lil chunky. The bike is pushing 30 pounds without hub motor and batteries. It's just a wallyworld Mongoose...It is one that cost over 500 new though. Pitty they don't stock it anymore, cause it would be a perfect FR bike to trash.. It's cheap enough to trash and not care about broken frames yet solid enough it can take some abuse. It would be even better with upgraded suspension and forks. But it has 0 frame flex. Even with my fat ars on it, it's solid.

But my point is...Bikes with hub motors do not handle worse than a front hub as long as you place your batteries in the frame. You can't blame ill handling issue on the motor being in the rear.

 

[dogman dan]

Same point I was making. Rear motor, and carry battery weight mostly forward in the frame is the ideal. I'da swore you were just trying to make the point that carrying the battery high on a rear rack was okey dokey in the previous post. I guess I misunderstood your words. I know what you mean though, about it feeling piggish and slow to react. That is different from tail wag. I think poor traction on the front wheel is part of the issue. My mid battery bike started riding that way last spring. A new front tire was an amazing cure. The tread looked fine, but couldn't compare to a new tire. Nothing happening when you steer results in slow and piggish handling all right.

On this bike, which is the arrangement a lot of noobs settle for at first, I was able to ride single track. 15 pounds in the blue box. But it did not handle well. I am simply experienced enough to ride just about anything, and got away with it. I just rode charging the bars all the time on street or dirt, so I could get a decent front wheel traction and get reliable turning and front braking input. Leaning on the bars would of course fatigue my hands, leaving me the ol familar tingley palms as nerves got pinched in my hands. Rideable yes, enjoyable for awhile, but not for a really long ride.



Sidetracking a bit, this box didn't get the rack reinforcement. So it got this.

 

[SamTexas]

Sidetracking a bit, this box didn't get the rack reinforcement. So it got this.

Not while you were riding, I hope.

 

[DrkAngel]

Ebike (Electric bike) vs EAbike (Electric Assist bike).

If you are going to run as an electric motorcycle, then you will want to go with a rear drive!
Especially with a high power front hub, you are liable to spin during heavy acceleration.
Losing traction with your front tire is extremely dangerous.
Dirty, even wet surfaces, are liable to put you down.

So why would anyone ever want a front wheel motor?

A front drive Electric Assist bike is capable of supplying All Wheel Drive.
A reasonable motor up front, combined with pedal assist to the rear, gives awesome traction and performance.
Skill is required! Possibly, restraint, is a better term.
Front throttle must be matched to road, or trail, conditions!

Spinning the rear tire can be considered fun, on the other hand, spinning the front tire is called OUCH!

So beginners, "lead foots", etc. ... go rear motor.
More advanced, skilled, of if you want to enhance your own performance ... front drive can be awesome!

 

[Ykick]

I enjoy both styles and a good comparison can be if you've ever broke traction with FWD (front wheel drive) and RWD (rear wheel drive) cars for any length of time you'll understand the straight line feel.

I also like the AWD (all wheel drive) approach for slick, wet and winter driving. Of course, YOU MUST BE CAREFUL using power during leans but I like to be pulled through deep snow as opposed to pushed. Too much motive traction during slippery conditions may not always be best - remember, you still need to be able to STOP. That FWD spin at startup constantly reminds me of my road surface traction limits.

Some folk worry about the magnets coming loose and locking up DD motors. Maybe a hot rod pushing tons of heat/power? IMO you'll have more likelihood of a front tire blowout than a magnet ever locking up the motor. Or, a tire simply not seated properly and the tube pushes out from under the bead and wedging itself in the forks/wheel. Yes, that happens to bicycles, electric assist or not.

There's many pitfalls that can befall those of us fabricating homemade vehicles. That's why it's important to define either convert a bicycle to electric assist or build a motorcycle - as DrkAngel mentioned, big differences between the two.

 

[SamTexas]

That's why it's important to define either convert a bicycle to electric assist or build a motorcycle - as DrkAngel mentioned, big differences between the two.

Agreed. But where do you draw the line? DrkAngel artificially set it at 30mph. Why not 29, why not 31? I think it has a lot to do with the quality of the bike in question. For me, I think it's borderline suicidal to do 30mph on an ezip/izip junky frame and components.

 

[dogman dan]

Well, in New Mexico the state draws the line at 30 mph. Above that,you are no moped.

Where the line is drawn in the real world, can you ride it, is it safe decision process varies a lot. As you say, bad frame, bad brakes etc can make even an Izip dangerous at a speed a well put together bike is very comfy at.

On my racing bike for instance, the danger of going over the bars was waaaaaay less than the danger of the rider next to you, and elbowing each other through every corner. Yes, we did take each other out. Specificly, I took him out when I laid it down. Likely the reason I laid it down was too much wheel slip when I put on the throttle. In the heat of the race, I put it full on, and spun the front tire too much to keep it up. But when I was racing in the spring with about 3000w on a front hub, I was not having much problem with wheel spin. It showed up at more than 100v, so that was the line for me, on that bike.

Vids of it if you want to watch it happen, when I cross the line. http://www.youtube.com/watch?v=qnMBlcxVCeE
You can see guys that are slower than me, beat me in the corners because I'm getting more scared in each turn by the past the line power causing the front hub slipping. So I start braking too early, afraid to corner fast.
And rear view of the same race and crash. http://www.youtube.com/watch?v=_59vJNBzLFg&feature=related

 

[kmxtornado]

Thanks everyone for your thoughts!...and you for those crash videos (speaking of which, it'd be cool to have a separate thread of just those). I hadn't occurred to me (until reading other related threads. Sorry I made another. I hadn't realized there were so many already) about the importance of weight balance. If I'm going to have my battery mounted on the rear for sure, it makes sense that a front hub motor would probably be a better setup than a rear one. I also hadn't thought about the fact that having a front hub in a sense means you have two-wheel drive since we're pedaling and pushing the rear.

Sounds like everyone's set on turning sharply on a front hub motor can be scary and takes some more skill to ride. Do you guys find that either the front hub or rear hub performs better specifically on hill climbs?

 

[d8veh]

Overall I prefer front drive, which I believe to be safer if properly engineered.

Seriously? Ok get past the design flaws (forks/frames not meant for these forces) with this setup. No matter what you do you will always risk a hub lock up at speed. This is even a risk for rear mounts. But if a rear mount locks up on you, you will most likely slide a little, at worst lay the bike down. If a front hub locks up on you, you are going over the bars, no doubt about it.

When you apply too much torque for adhesion with a rear drive, everything behind the steering head turns side-ways on, grips again, and you get thrown straight over the handlebars. Just watch the Moto GP and you'll see it nearly every time. It's called high-siding as opposed to low-siding, which happens when you're leant right over, where the back end just keeps going until you're flat on the ground. As I've said, I high-sided three times on my bike, which has the same result as motor lock-out except you get a good idea when it's coming, and,if you're quick, you can throttle back and avoid it. Perhaps my reactions are too slow. The chance of getting a lockout is pretty small, but for me the chance of high-siding is high. That's why I prefer front drive.
My rear drive bike weaves a little because I have a heavy Ping battery on the rack that won't fit in the triangle and so there's insufficient weight on the front wheel. The weave is manageable, so I live with it. It's a GIant NRS and has high quality full suspension.

 

[dogman dan]

Come to think of it, I don't high side as much on the dirt bike now that the battery is up front. Handling great, I don't crash much on it.
This is what the bike looks like, as of this morning. The boxes carry 8 lipo batteries, for 72v 10 ah. I removed the larger boxes, because the bike handled better with just 10 ah.

Regarding the climbing with front drive, for a street bike front is ok as long as it's not too wet. But it can climb fine up to 10% grades at least. So maybe front is not so perfect if you live in the swamps. But I have climbed 6% in the wet with no particular problem. The wheel just spins a lot as you get going, then gets a grab.

For dirt, you want rear hub for sure, and the primary reason is that when it gets crazy steep the front wheel just comes up in a wheelie. So it starts spinning as the weight leaves the front wheel and the shocks top out. It can still work good on a dual motor bike, but not so great on a front only bike. On the flat, power slides with front hub in loose dirt can be fun.

Here's some vid from this week, of the above bike. The vid shows it handles OK. http://www.youtube.com/watch?v=ZEsUvvyOIjk

 

[kmxtornado]

"It handles okay", but don't forget to give yourself some credit. From what I've heard so far, riding a front hub motor requires some skill - especially when you're taking it to the limit and testing it's performance values. It's pretty cool that you're so hardcore with this stuff. As for me, I'd plan to use it primarily for commuting in a city environment. Plenty of hills for sure. I wouldn't ride in the rain nor after it when it does rain.

I have sort of an odd question. I know it would look superweird, but if there's a way I can make having a front rack mounted battery setup look decent, wouldn't that balance out the whole rear hub weight issue? I rarely see front mounted anythings, but occasionally I spot a front rack on someone's bike.

Again, I'm new to this. So perhaps there's wiring issues or something else I haven't thought about that makes a front mounted battery less than desirable (or is it really just the more than possible hideous look of a front mounted battery)?

Oh and if you feel like it, I would be interested to see a new thread on how you rigged your camera! NIce angle!

 

[dogman dan]

You might look at some of the "best frame" type threads. Lots of discussion on which brand or what type of FS frame can still carry batteries up front. Then often a decent battery can fit into a triangle bag such as this. http://www.emissions-free.com/catalog/i29.html

Well no pics. But there are triangle shaped bags that can hold a triangle shaped battery. Usually the best choice for looks and front carry. Wont work of course with the Y frame type full suspension bikes.

 

[miuan]

Unsure whether to go front or rear? Go both and put batts into the triangle. Switch off the front when needed and get away with lower currents and simpler torque arms for same or greater power output. Concerned about weight? Use geared motors that weigh 8kg combined.

 

[oatnet]

Come to think of it, I don't high side as much on the dirt bike now that the battery is up front.

I have found that mounting the battery to the front forks vastly improved the handling of my ebikes. It dives into corners much faster, yet with greater control. The feel is different - more like a motorcycle than a bike - and takes a little getting used to but well worth the effort. Think about a dirt bike and rider, where the mass is pushed up against the forks as much as possible. Anyhow, photo at the end of this post.

As others have mentioned, front motors add stresses to the forks that would not normally be there, and and driven wheel has less traction than a freely rolling wheel, so when traction is low (turns, loose surfaces, etc) you have less margin for safety. I can lose traction on the rear wheel and keep the bike upright, but if I lose traction on the front wheel I'm gonna eat pavement. Front motor does balance out the weight of a rack mount rear pack nicely, so in mild application (commuter bike, slow, steel non-suspension forks) I can see how someone might like the configuration. In any power application, I would only recommend a rear hub motor - in fact I only recommend rear hub motors.

-JD

http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=24329&start=15#p413920

 

[dogman dan]

Example of near perfect bike above.

The point I keep trying to make, is that front or rear depends on your particular needs. I have a stable of ebikes, each one meeting a particular need. I found high power front hub a fun experiment, but I also knew the crashes were coming at some point. :lol:

Front hub works great on my commuter, allowing me to save money by buying an old used Y frame fs mtb for the bike. Then I load the snot out of the rear. But for nearly every other thing, rear hub works best. IF, IF you carry the battery up front, OR the battery is light enough. Rear hub, rear rack, 20-30 pounds of battery or cargo, and a bendy wallbike frame and your bike will be a nightmare to ride. It might feel ok to you, but it's NOT, and you may crash more often. If that is what you are stuck with, a front hub would have helped a lot.

I'm not speaking from theory here, or reading about it, I've tried about 20 variations of bike- motor- battery. Everything from trike to cruiser to hartail mtb to fs mtb to longtail. Only thing I haven't built is a 20" bmx or a folder.

 

[Ykick]

I've only done 6qty various conversions but in complete agreement with Dogman. IF, IF, IF, is the only approach to FWD choice but it can provide for a useable economical ride without the excessive stresses on RWD spokes when also using rear mounted batteries and/or carrying a large rider.

Even under ideal weight conditions (front mounted batteries, low rider weight) most RWD's will eventually need eyelet rims, quality spokes and better construction than what comes standard with the majority of prebuilt wheel motor kits.

Particularly, if you use regen and disc/drum brakes which exert their forces through the hub against the spokes in the opposite direction of the motor power. That constant twisting force in one direction and then the other will also require very, very secure torque arm(s).

 

[CogHog]

I've only done 6qty various conversions but in complete agreement with Dogman. IF, IF, IF, is the only approach to FWD choice but it can provide for a useable economical ride without the excessive stresses on RWD spokes when also using rear mounted batteries and/or carrying a large rider.

Even under ideal weight conditions (front mounted batteries, low rider weight) most RWD's will eventually need eyelet rims, quality spokes and better construction than what comes standard with the majority of prebuilt wheel motor kits.

Particularly, if you use regen and disc/drum brakes which exert their forces through the hub against the spokes in the opposite direction of the motor power. That constant twisting force in one direction and then the other will also require very, very secure torque arm(s).

A lot of useable info in a nutshell. I have a front BMC 2T that I would like for a daily comute, 9% grade for about a mile. And I have a rear V3 for whatever. I have a "Y" frame full suspension so the LiFe PO4 battery is a problem. Maybe parallel behind the seat post for the front motor. And maybe a LiPo setup like Dogmans for the V3. Thick torque arms and eyelet rims. And for the first time in my 58 year life....A Helmet.