Opinions on front wheel hub systems

[friendly1uk]

Part of the issue I have with mine comes from the fact it's a typical cheap pedelec. Using the typical speed targeting led display and pedal sensor that always applies full power to reach the target speed. On top of this I have a suspension fork on it. With just 15 amps the wheel spins a bit with every pedal bob, on dry concrete. On wet grass your going down every time. This is on a motor that falls somewhere between 300 and 360 rpm. Using black jack tyres.

 

[Chalo]

[...]That is why so many are willing to endure the weight penalty, to build with motorcycle rims, spokes and tires.

To build lightweight and reliable, you need to invest some time and Art :wink:

To build lightweight, you must eschew all motorcycling vanities. Including rims, spokes, and tires.

 

[Chalo]

Most of problems that you refer to are NOT 'inherent' but rather poor design, material and/or build quality.

Poor design, material, and build quality have been a given since Chinese manufacturers took over the hub motor market. If you suggest the problems aren't inherent, you have to identify an exception. Or perhaps you can provide one to the market?

Note that my criticisms don't all apply to Heinzmann hub motors, which predated the hub motors we can get today. I wouldn't know how to get one now.

 

[LewTwo]

Most of problems that you refer to are NOT 'inherent' but rather poor design, material and/or build quality.

Poor design, material, and build quality have been a given since Chinese manufacturers took over the hub motor market.

They also have the majority of the bicycle parts market as well (with increasing competition from Thailand and Vietnam) . As far as I can determine my Bafang hub is aluminum (i.e. no steel flanges), the holes are on center, evenly spaced, and perpendicular to the flange.

Just to be fair I compared it to a old Japanese manufactured Suntour hub with a pair of the same spokes. I note the holes are a bit oversized in both hubs. The biggest difference is the thicker tapered flanges on the hub motor thus requiring a deeper countersign on both faces of the flange. If anything the Bafang hub has more material supporting the spoke head than the Suntour hub.

 

[Chalo]

If you compare your Bafang hub to your Suntour hub, you'll notice two things:

First, the flange spacing is almost as wide as the space available on the Suntour, while it's much narrower than the space available on the Bafang. That's one of the points I made.

Also, you'll notice that the spokes approach the rim at an oblique angle in the hub motor wheel, while they approach more perpendicularly on the traditional hub. That's another point I made.

All spoke holes must be bigger than the spoke diameter, so the bend of the spoke elbow can pass through. I think if you measure the spoke holes in both your hubs, you'll find that the holes in the Suntour hub are between 2.5 and 2.8mm, and the holes in the hub motor are significantly over 3mm. it doesn't sound like much difference, but there's a small range of spoke diameters that works with bicycle rims. The heads and elbows of such spokes don't fit well into holes 3mm and larger.

If you know of an available hub motor that doesn't have these problems, please tell us what it is.

 

[LewTwo]

... the flange spacing is almost as wide as the space available on the Suntour, while it's much narrower than the space available on the Bafang ....

I have to concede that one:
With the same SUN CR18 700C rim the included angle between the left and right spoke cones is:
13.45 degrees for the Suntour front hub
11.75 degrees for the Sturney-Archer rear hub
10.20 degrees for the Bafang Motor hub
However I do not feel the difference is significant.
If it were then we would all be running around with 16 inch rims.

... you'll notice that the spokes approach the rim at an oblique angle in the hub motor wheel, while they approach more perpendicularly on the traditional hub. ....

If I understand what you are saying then that angle is more greatly influenced by the cross pattern than the flange diameter.
Per Rogger Musson the cross pattern makes no significant difference in the strength of the wheel.

... All spoke holes must be bigger than the spoke diameter, so the bend of the spoke elbow can pass through. ....

That much I understand. I would have to have a set of 'go-no go' gauges to accurately measure the diameters.
I did try with my digital calipers and best I could determine they were slightly less than 3mm.
However they appear to fit just fine.

Neither one of us is going convince the other so it comes down to:
"I respectfully disagree, but thank you for explaining your reasons".

 

[dogman dan]

Though the hub motor may be inherently weaker, that does not mean it has to be as weak as the worst china cheap examples. I've seen an amazon kit, with the weakest possible wheel, a radial laced 20" rim, explode on virtually the first pothole.

Others, like I said, bend a rim somehow, like a lay down or other crash. Then overtightening one side, and slack on the other, hell yeah they have tons of problems from then on.

But use a decent quality spoke, and a semi stronger 26" rim, ( stronger than the 5 buck rim in a bargain kit) and you can ride the rock staircases for quite a few years with no problems, even when it's the fat spoke. But yes, you do have to mind your wheel, mine have lasted fine in pretty heavy use because I do have a look at spoke tensions every half a dozen rides or so. Nothing fancy, I just squeeze each pair of spokes and feel for an obviously loose one. FWIW, the dish on these rear hub motors is not that huge, so they don't have near as much inherent weakness as the older design hub motors did.

Loose spokes, like Chalo said, It may as well be missing. I don't head out to pound the bike through the rocks like that! In addition, I don't fly the bike. When I want to fly, I use a hot air balloon. So little pops is all I put my off road hub motors through. But I still ride harder than average, corner like a mad man, and have no trouble with wheels without needing motorcycle stuff. Bring your 10,000w bike, and I'll outride you on my local trail. I'm not riding dirt like la de da.

To ride like a motorcycle, I do tend to say "get a motorcycle" I just did, for street riding, and keeping up with traffic on the freeway is very nice. Cost per mile on this 10 year old Yamaha is going to level out at about half the cost of any of my street e bikes. And it will do 90 mph when I feel the need for speed.

 

[Tom on 101]

Hub motor wheels are inherently weaker and less reliable than conventional wheels, ....

I will grant that hub motors wheels are inherently less reliable as anything more complex is inherently less reliable.
However I would challenge the statement regarding 'inherently weaker' as they generally have larger, heavier flanges and shorter spokes.
Pray tell what you reasoning is to support that statement.

Hub motor wheels have less lateral bracing angle than normal wheels, which makes them more flexible and easier to bend or collapse. They don't have to be that way, but they are (so that the hubs can fit a bigger range of rim diameters)

Rear hub motor wheels usually have much more dish (lateral tension difference between one side and the other) than normal rear wheels. This makes them weaker and less stable, in proportion to the degree of tension imbalance.

The insertion angle of hub motor spokes into the rim, even when laced cross-one, tends to be more than optimal for the spoke, and promotes breakage at the threaded end.

Hub motor flanges are often made from steel, poorly finished and thinner than normal aluminum flanges on bicycle hubs, and drilled with holes that are too large, all of which promote breakage at the spoke elbow.

Lastly, thick spokes-- such as those which are pervasively used on hub motor wheels-- make a wheel weaker. Spokes can only work to support a rim when they are in tension; the moment they go slack, they might as well be missing (from a structural standpoint). Thick spokes lack elasticity, so they go slack much sooner and in larger numbers than thin spokes. Also because of the same lack of elasticity, they tend to overload and crack the rim at the holes. This in turn rapidly leads to wheel collapse. Again, they don't have to be that way, but they typically are.

Now we are getting down to the nitty-gritty. Gonna take a closer look at the build on my motor considering what you said, very interesting. My wheel has 13g spokes and the tension was set using a specific tension meter. But I'll have to look closely at the rest, great info for evaluating a wheel build, thank you!

 

[heavymetalthunder]

I use my 1000 w front hub bike for commuting and doing the around the town trips. Rides nice and I haven't had any problems. I've taken it into for some trail riding and I can tell you it sucks when you try to go up a hill with loose dirt from a dead stop. Not going go happen. As far as I am concern if you even think you are planning taking it on to the trails a rear drive is the only way to go.

 

[Toorbough ULL-Zeveigh]

They don't have to be that way..

i.e. non-inherent.
ty for the correction

If you know of an available hub motor that doesn't have these problems, please tell us what it is.

 

[Chalo]

That one has the problems of using nonstandard spokes and of being a huge PITA to build and maintain. But if you like those things, then sure. How much extra do you have to pay for the inconveniences?

Allow me to observe that 99+% of hub motors that actually exist make wheels that are inherently weaker and less reliable than normal bicycle hubs built with the same components. 99 plus percent true = true. Hypothetically I could design a conventional bicycle hub that made an even weaker wheel (so you could say they're not inherently stronger for that reason too), but in practice nobody does that.

By using the best method and high quality rims and spokes, it's quite feasible to build a hub motor wheel that is strong enough for most applications. But because front wheels are stronger and have an easier job to do, it makes sense to put the hub motor wheel in front.