The high power front hub thread

[qwerkus]

Hello,

So far, besides that one long john the kids love, I've only build lightweight front driven ebikes (FWD) uprights and would like to move to stronger stuff, to climb steep hills.
Hence I would love to collect infos and advices on high power (1000w) front hubs here, as there are many contradictory statements on this topic. While many online sources wouldn't even consider it and go straight for a rear hub or even better a mid drive, I find that many points raised on ebikes.ca are quite true: the simplest way to electrify a bike is adding a front hub. It's easily accessible, less prone to puncture, completely independent from the human powered drive train and actually improves the overall weight distribution on upright bicycles, where most of the weight tends to sit on the rear wheel. Also in many cases, you can switch to a smaller wheel for better motor efficiency without changing your bike's geometry simply by swapping the fork.

Of course, there are undeniable issues with front hubs, especially on high power devices. The 3 main problems I've encountered so far are:
- traction on loose ground or steep hills
- torque arm design on modern aluminium forks
- handling impairment due to motor weight and stability issues at higher speed levels (>40km/h)

What is your experience with front hubs ? How did you solve the above mentioned issues ?

From what I gathered so far, the ideal configuration for a high power front hub would be a bicycle with a long wheelbase, a small front wheel and the battery somehow sitting on top of it.

Thanks for your input!

 

[motomech]

Front hub motor mounted systems are best left to small mini-motors (>2.5 Kg.). The problem is not mounting the motor securely, nor is it traction. The main problem is the sense of the weight in the frt wheel and as power gets near 1000 Watts, the rider gets the feeling the frt. whl. is pulling the bike though the corners.
I used the tiny (2 Kg.) Q100 (Cute) as a frt. mount for years and one hardly knew it was there and for assist bikes up to 22 to 23 mph, this is a good set-up.
But more speed requires a bigger motor and when I installed a 2.5 Kg. Bafang SWOX2, the added weight is noticeable all the time and starts to erode the "bicycle" experience of a good assist ebike.
Mounting the same model motor on the rear and the "bicycle" experience is restored.
So, to me, it is not an issuse of how much weight and power can be safely mounted on the frt. of an ebike (I have used the 5 Kg. Ezee @ 1200 Watts), but at what point does the frt. oriented system start to detract from the riding experience. With the Ezee, I never forgot there is a big motor up frt.
So at that point, It just doesn't make sense not to take the few extra steps to rear mount.

 

[motomech]

From what I gathered so far, the ideal configuration for a high power front hub would be a bicycle with a long wheelbase, a small front wheel and the battery somehow sitting on top of it.

Adding weight to the steering assembly is, IMO, a bad idea. Although most ebikes can't reach the speeds where oscillations start to occure, adding weight to a hinged pivot point will contribute to undesired handling (and parking) traits.

 

[Chalo]

Both my e-bikes are front drive and both are in the 1500W (electrical) range. Neither one has any handling weirdness or any subjective quality of feeling different from a very heavy bike.

I have built a couple of low powered front drive bikes with Jump motors that felt different on the throttle than off, but these have been the exception. I attribute the difference to quirks of front end geometry, but I'm open to other explanations.

I do like that front drive bikes don't ever push the front wheel in low speed maneuvers. When traction is poor, they can spin the wheel a little, but it's always pulling where it's pointing.

Adding weight to the front rotating assembly causes awkward handling, but only when that weight has a significant inertial moment (mass at a distance from the steering axis). Thing is, hubs are always very close to the steering axis. Putting a battery on a front rack will goof up your handling somewhat, but a heavy hub doesn't. The better-handling of my two e-bikes has a front hub weighing more than 22 pounds. It handles and maneuvers better now than when it had a mid drive.

I helped one of my buddies set up an electric conversion on a Crust Clydesdale fork. Everything--motor, battery, controller-- is on the rotating assembly, along with whatever's in the cargo bag on top. But because that fork is designed to move the load closer to the steering axis, he has no issues with it. I'm sure it's different to ride now than when it was a regular rigid MTB, but he has no complaints.

(Not his bike, but only a representative photo of the fork he's using.)

 

[qwerkus]

Very interesting replies - thanks your your time!
How come some would report weird handling experience with high power front hubs while others won't? I always thought it's a matter of subjective appreciation - you like it or not. But perhaps there is an objective way to see it, as Chalo pointed, by considering the bike's geometry. Maybe the front wheel trail has an impact ?

As of additional front weight (to increase traction), it seems two smaller battery packs on a low rider rack would be a neat solution to avoid impairing handling too much. You'd still feel the additional weight while turning though!



Very interesting fork you mentioned, Chalo but I'm never riding a rigid fork again (on an ebike).

 

[electric_nz]

I ride a rebuilt Juiced u500 v3 which has a 500w bafang front motor in a 20” wheel. With a diy 14s 4p battery, it peaks at over 1000W, which is then geared down by the hub, top speed is only 40kph or so, which is fast enough on small wheels with no suspension. Handling is a little heavy but you get used to it.

Torque and hill climbing are great and it is not powerful enough to spin the wheel when you’re underway. However at a standstill on the wet it can easily do a burnout

Any more power/torque on the front and I’d be concerned about skidding out inadvertently.

 

[dogman dan]

My best guess is that the bikes that handled shitty with front hubs were shitty bikes. Or rather, perhaps just shitty for use with a front hub.

I ran front hubs for many years, but did transition to rear for one reason. Dirt riding. Thats when the traction issue rears its head.

As for traction issues with higher powered front hubs on pavement, again, the issue was dirt on the pavement, wet paint stripse, muddy street, that kind of thing. But the same conditions can cause your rear motor to push the front wheel beyond its stick, resulting in a laydown. Basically, if the paved gets slippery, you can crash either setup easy peasy.

On dry clean paved, I did not lose traction enough to crash till it was like, corning at 35 mph, hitting throttle with 4000 watts, and starting to power slide the front wheel. Easier to power slide the rear, for sure.

Bottom line, build very strong torque arms on rigid front forks and you are all good, till you are running a bike that hits 40 mph+.

As for front hubs on alloy suspension forks, it just depends on the fork. Again, you need the proper install, good c washers to fill the cup, and solid, preferably one piece torque arms. You can tack weld a two piece TA after its fitted for a soild arm. The forks may handle the motor, or not. My general experience was that lower cost forks just lean forward and bind or stick under power. So when you get to the rail road track crossing, you let off and coast over the bumps. Really good forks should be fine, but if you are putting a motor on $1500 forks, put a rear motor on it. You'll want to ride that bike on dirt.

 

[qwerkus]

I ride a rebuilt Juiced u500 v3 which has a 500w bafang front motor in a 20” wheel. With a diy 14s 4p battery, it peaks at over 1000W, which is then geared down by the hub, top speed is only 40kph or so, which is fast enough on small wheels with no suspension. Handling is a little heavy but you get used to it.

40km/h on 20" with no suspension !?! You are my new hero. Past 25, you can forget about me... I can feel every mm unevenness pushing through my body right towards the spine. Ouch.

Here is what I had lasered for my cargo bike. I agree that torque arms are paramount, and that you can just as easily squid with a rear traction. @dogman My worst accident in years was actually exactly what you described: bbs pushing the front wheel away from the pavement. Still would like to investigate that front-hub-worse-handling question further. There has to be an explanation. If I had road/cruiser frames, I would test the same hub with different trail setups (mtb, road, cruiser) - would surely be instructive!

 

[amberwolf]

How come some would report weird handling experience with high power front hubs while others won't?

Geometry, riding style, riding conditions, controller design (throttle / PAS response), specific motor used, power levels, tire choice, etc.

My cargo bike and trike are both quite long (about 11 feet), with low rider positions, so they have very different handling from "standard" bikes, even disregarding motor placement and cargo loading.

My SB Cruiser trike was frontWD for a while, and it was alright, adequate not amazing; it's RWD 2WD now, and handles great for a big heavy delta trike; at some point it will be 3WD and I can do more experiments with handling F vs R.

CrazyBike2 was RWD originally and 24" front/rear; it evolved to 20" rear 26" front, and using FWD which worked fine, even racing on the kart track (though I'm not a racer so I managed to crash it in hairpin turns, but the front didn't lose traction or cause me problems with handling). Eventually went to 2WD and it was pretty amazing in handling vs anything else I'd ever ridden before that...but it had it's limitations due to the way I built the tie-rod remote-steering mechanism.

My one short trike (Delta Tripper) was not a very good design, too short and too high a rider position, but it would probably have been ok for a FWD system as rider weight was about centered between front and rear. Never tried it though; it was just not good enough to keep around to experiment with, whcih is why it got chopped up to turn into SBC.

 

[calab]

Not much of a big market for huge power hub motors, mostly the 35h Leaf (1500w) fills the minor gap 1kw-2.5kw (w/statorade) with 3kw+ bursts....maybe the mxus 45h "3000w" squeeze a bit more out of it, hub trickeries.

What would an ideal motor be for hobbyists like ourselves?
More poles, more magnets, more hub diameter for more torque, to big means to heavy who's your markets power range.

 

[dogman dan]

No problems with running 2000w through a "1000w kit" type cheapo direct drive front hub. 30 mph on 52v, but perky!

52v 40 amps controllers can be dirt cheap too.

It would only melt if you start towing trailers up mountains, or up the mountain and you weigh 300+ pounds.

 

[2old]

I had a 350w, 36V front hub on a MTB and it was possibly the most fun I've had on an e-bike. When ascending in the dirt it was necessary to stand and put more weight on the front wheel. Sadly, my daughter absconded with the system. Then, I built a three-speed cruiser with a 1000w, 52V, DD hub and it just wasn't fun for some reason although it handled fine. So, it's gone.

 

[qwerkus]

No problems with running 2000w through a "1000w kit" type cheapo direct drive front hub. 30 mph on 52v, but perky!

52v 40 amps controllers can be dirt cheap too.

It would only melt if you start towing trailers up mountains, or up the mountain and you weigh 300+ pounds.

Agreed. My FH212 is rated for 800-1500W on ebikes.ca though I routinely pump 2.5Kw through it, although for 5min max. Ferrofluid helps keeping things cool.

 

[Bigwheel]

If you don't want a rigid fork and are looking to alleviate your issues list just get a Grin AnyAxle hubmotor. You can set it up for completely tooless take off easily, yet especially in a thru axle version it should never fail. I have put mine through all kinds of different terrain including steep loose trails and while it won't blast uphills on motor alone with a good amount of pedaling in proper gearing it will climb just fine. On road climbs I usually set it a 350w and crank along in the right gear to go at a satisfying clip and get my speed ya yas out on the DH part.

Key for me is as you mention it separates the motor input from the human pedal input. It works like a row boat with a motor going so that you never have a dead spot in your pedaling in effect. I would never use any type of PAS with a front hub as a throttle and cruise control work just fine and provide for the most natural pedaling experience of any ebike I've ridden. However on steep loose terrain there may be a bit of a momentary loss of traction at the top and bottom of the human pedal stroke it is manageable. But for cruising on road surfaces of all types it is just fine as long as you don't ask too much of the motor/controller.

I never have noticed any handling quirks in thousands of miles with this and a 9c either.

 

[JohninCR]

Geez it's been a lot of years since I analyzed this one, but front hubs absolutely do change the bicycle dynamics, but it's so easy to become accustomed to the difference it can go unnoticed. It has to do with the dynamics of how a bike turns. Think about a very sharp turn at low speed and the difference with a front drive is obvious. because it creates forces that act on the lean of the bike. It's just very slight, since we typically turn the front wheel only slightly.

The reason I even posted about it is because you mentioned high power on the front, and I wanted to make the you aware of the actual difference in handling. That is, when you accelerate out of a curve the front hub applies a force to bring the bike back toward vertical, so it has the tendency leave you a bit left when curving to the right, and right when curving to the left under acceleration. That's where oncoming traffic is, so just be aware and it's easy to compensate.

Anyone who thinks otherwise, just put a mark on the road near the finish of a curve. Then ride through the curve a few times both just coasting and accelerating out of the curve to see the difference.

Back when I had one bike with a front hub one of my every day use routes had a big treacherous hole right after a curve. I know my routes like the back of my hand, and I noticed that I kept ending up closer than intended, but only when I rode that ebike. It was a head-scratcher at first since I never noticed a handling difference, but after going back to bicycle dynamics 101, and a bit of testing to prove it out, I confirmed my analysis.

Hmm, how'd I dredge up such an old thread? Aha, I must have clicked on something in the "similar threads" at the bottom.