Is my wheel going to explode?!?!

Ok, the title of this message might be a little over the top, but...

I built my first ebike wheel recently from a little geared Bafang and a quality double wall rim that has spoke eyelets (Alex DM18). Since I'm I big guy (200+ lbs) I thought it would be smart to use 12 gauge spokes. I did a ton of reading about lacing it up and it turned out great. Now, I see I didn't do enough reading since there are a lot of threads with people talking about how 12 gauge spokes are a bad idea since it's impossible to tension them correctly.

I've put around 100 miles on it so far without any issues. I'm keeping an eye on spoke tension and nothing seems to be changing yet. This is a light use bike mainly for our local paved bike trails when I want to be very stealthy. Nothing off road, just cruising at speeds less than 20 mph on a smooth path.

Question is, am I just asking for problems with the larger spokes? Will I eventually have a cracked rim because of them?

Sorry if these are stupid questions. I'm very much a newbie when it comes to hub motors.

Your spokes when tightened properly are firmer than regular spokes and less springy/flexy, so they transfer more stress to from the rim to the hub, and increase the peak forces the rim has to take dealing with obstacles. So it will dent or bend easier and the eyelets are more likely to crack.

miuan said:

Your spokes when tightened properly are firmer than regular spokes and less springy/flexy, so they transfer more stress to from the rim to the hub, and increase the peak forces the rim has to take dealing with obstacles. So it will dent or bend easier and the eyelets are more likely to crack.

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Gotcha. I guess I'm really wondering if it's that big of a problem on a low power build like this. Don't most cheap Chinese built wheels come with 12 gauge spokes?

12ga isn't going to explode. Would I go looking for a wheel with 12ga spokes? Nope, had 'em and the constant tightening and truing just got old. I now build motor wheels using 13/14ga butted spokes. Don't touch 'em for years and many 1000's of miles.

Its not going to explode. But it will never be as strong, never be as comfortable, and you will constantly find your self re-tightening the spokes.

If you ride in a harsh environment with tons of potholes, or off road often, you might want to re-spoke with some 14g. However, if you don't abuse the wheel, It might just be easier to leave it alone, accept the higher maintenance, and ride. I'm Lazy, so I would leave it. IF/When it ever breaks, then rebuild it with the right spokes.

Also, the next time you build a wheel, you might want to look at the DM24, or the DX32 if it will fit. Wider rims are much better for Ebikes.

I built my 4.2kW ebike with 12ga spokes on the rear. I'm light only 160lbs, but I ride hard, off-road at times and my bike is a hard tail. I run low tire pressures, and I've bottomed the tired on curbs at least a dozen times, one time I power wheelied into a curb accidentally. Nothing broken yet, no flat spots on the rim, never had to re-tension or re-true the wheel yet in 3500km. Only had to replace the hub bearings probably from all the bottom-outs.

+1 for DM 24

The Alex DM18 is a really strong rim for its size, and I doubt you'll have undue trouble with it. But thick spokes are a maintenance hassle, and they don't allow you to fully reap the durability benefits of a good rim like that. I say use your wheel up and try something different next time. If it's a 26" wheel, take the advice you've gotten about using a wider rim too. There is no better rim for the money than the DM24.

You'll get the best from a sturdy bicycle rim if you use 14-15ga spokes on the tighter side and 14-17ga spokes on the looser side of a dished wheel. For economy and ease of construction, 14-15ga all around works fine. Danscomp had those for $0.40 each the last time I checked.

Straight 14ga were $0.25 each. Those are usually easiest to build with.

The main advantage to 13-14ga spokes is that they fit better in too-large hub holes. In practice, they are not significantly less likely to break than normal 14ga spokes.

It's going to depend on your riding habits:

Some builds can take whatever you throw at them. (good parts AND well built)

Others, will stand up to the rigors of easy cruising, but will start to have issues if ridden really hard like a BMX. (mediocre parts AND/OR decent build)

And if the wheel was a bad build, it will eventually have issues with just normal riding. (Crappy parts OR crappy build)

With 12Ga spokes from a factory lace, you're likely in the last 2 groups, so take it easy and time will tell. (500 miles is a good mark for spokes to do some loosening)

Thanks for all the replies. I think I'll just keep it as is for a bit and if I start having problems down the road I'll rebuild the wheel. This bike isn't going to get a ton of miles anyway.

Interesting advice on the rim. I think the DM18 is probably fine for this build. It's just a little geared bafang (surplus Schwinn Tailwind motor) running at 36 volts. I'm also running street slicks. Here's a picture of the beast:


This was the very first mountain bike I ever owned. Think I got it around 1989 or 1990. A friend of mine bought it off me years ago. I asked him if he still had it and I traded him a case of beer to get it back. lol. I don't think he ever rode it. I updated a few things on it with parts I had sitting around and it's actually a very enjoyable cruiser.

All BS aside, 12g spokes are stronger than thinner spokes, and are the recommended spoke size for 1000W and lower motors. That's what the spoke holes are drilled for. Larger motors like the MXUS 3000 are drilled for 10G spokes. I'm 270 lbs and use 12G, and have never had a spoke come loose or brake on a wheel I built. Now I've only built 2, but I've got over 10K miles on one in a 1000W motor with a max of 4000W. There's more to a wheel than the spokes. Rim choice is big factor too. Personally, I prefer larger stronger rims that weight more. I use these.
http://www.weinmanntek.com/Products/DOWNHILL/DH39.htm

The only BS Wenewell, is your insistence on applying anecdotal evidence to all situations, and in this case the result is bad advice because you don't understand how a bicycle wheel should work. Chalo and I have very different views about ebikes, but when it comes to bicycle wheels, electric or not, I defer to his recommendations with confidence. Not only is he a much larger man than you with extensive experience, but he also helped LFP solve an ongoing wheel/spoke problem at extreme power. That answer was the counter intuitive idea that thinner spokes make for a more durable wheel.

It's a pure ass fact that a thicker spoke made from the same material is stronger than a thinner one. Now you can apply all the BS theories you want, but you can't change facts. Build both wheels properly, and the one with larger spokes will be far superior to the one with thinner spokes as far as strength goes. How many motorcycles do you see using 13/14G spokes? It's just simple logic. Build it right and the spokes won't break. Build it wrong and they will all break, regardless of size.

Easily 80-90% of us have 12 gauge spokes on our motors.

I used to be 270lbs and rode a hardtail with the motor in the rear for ages. No problems.

When you have 14 gauge spokes on a hub motor, that's when you typically run into problems. I've built 2 motors into wheels that way and never figured out how to get the spokes to not constantly loosen themselves.

wesnewell said:

It's a pure ass fact that a thicker spoke made from the same material is stronger than a thinner one. Now you can apply all the BS theories you want, but you can't change facts. Build both wheels properly, and the one with larger spokes will be far superior to the one with thinner spokes as far as strength goes. How many motorcycles do you see using 13/14G spokes? It's just simple logic. Build it right and the spokes won't break. Build it wrong and they will all break, regardless of size.

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Don't try to drag oranges into the conversation about apples. A motorcycle rim is far heavier and stronger, which when combined with heavier loads and faster speeds is why thicker spokes are used. Your example is on par with the idea of putting a motorcycle monoshock on a mountain bike, and your statements only prove that you don't understand how a bicycle wheel works it's best. A bicycle wheel isn't supposed to be a perfect circle with a constant radius from the center of the axle. Of course if you did a bit of research you'd learn these things, and if you didn't ride on such flat smooth terrain, you would have been forced to learn more and wouldn't make half of the bogus, misleading, or just bad advice statements you make.

A motorized bicycle is a motorcycle by definition. And if your wheels aren't round, you will bounce up and down while riding. The only way that wouldn't happen would be if the rim had a constant flex while riding. That will subject everything to metal fatigue and cause the spokes to constantly come loose. Something you don't want to do for obvious reasons. The 12g spokes are stronger. If you can't figure that out I feel sorry for you. There's a lot of difference in the torque angle on the spoke in a hub motor as compared to a regular bike hub. You need stronger spokes for this. And stronger rims.

Wes, we've been over this before. Spokes don't work in isolation - they are part of a system with the rim. John is right, spoked wheels are not rigid, they do constantly flex while riding, just like a rubber tyre, but much less so. This would create the potential for metal fatigue, but propet material selection and design/manufacture to avoid stress raisers prevents this. Handily, steel, is one of few materials that has a "fatigue limit": below a certain magntiude it can be flexed indefinitely without failure. It's not a coincidence that springs are generally made of steel and spokes *are* springs when used properly. If the rim is too weak to support the preload required to stretch those springs then the wheel will fail (rim failure or rim deformation loosening the spokes).

If you happen to have a heavy duty rim that can support the preload required by 12ga spokes then your wheel will work. Also, spokes made of low-grade material will require less preload (but will be of lower strength).

Bottom line is, you cannot tension to the tightness 12g spokes really need, because the rim or the motor flange will fail then.

So keep your spokes tight, but not crazy tight. Don't let them get really loose, IMO running the wheel like that is the real cause of 12 g spokes breaking, combined with just really shoddy spokes some kits use. But pointless to tighten till your rim fails.

Lastly, don't expect to jump curbs all day without damage, unless you have good full suspension.

Anyone with an iq over 100 should be able to figure out that you don't want a rim to flex and you want the wheel to be as round and as strong as possible. And that you want even tension on all the spokes while riding. But do to rider/bike weight, the most pressure is on the upper half of the wheel. If the wheel flexes, the lower spokes will lose tension, thus allowing them to become loose over time. Now since spoke position is constantly changing, all of them suffer if the rim flexes. Use your dang brains. There's a reason most vehicles don't use spokes. And the ones that do use the strongest spokes possible. I'm over this too. For all you people using hub motors, use the spoke that the hub motor is drilled for for best results. And tension them properly. Drill the rim spoke hole at the angle they take to the hub and it will be a lot easier to get the proper tension without the spoke having undue stress at the nipple. Or treat the wheel as if it's a standard hub and live with what you get. I'm done. Do whatever you want, but don't try and convince me that thinner spokes are stronger than thicker ones.

Hmmm, I didn't realize spoke size was such a touchy subject. Some interesting points to ponder.

Wes, you clearly don't understand how a spoked wheel works. Flexing of the rim allows loads to be distributed over a large number of spokes rather than the single spoke directly adjacent to the load point. This makes for a stronger wheel. "Strength" is not usually defined as "stiff".

As has been said repeatedly, the spokes operate in their elastic range as the rim flexes and therefore do not become unloaded during normal operation. This also reduces fatigue.

It may be difficult to grasp this without some understanding of materials science and mechanical principles, whatever someone's I.Q.

Most vehicles don't use spoked wheels because they are too expensive and unreliable for the weight advantages they confer. Vehicles that did/do use spokes clearly don't use the strongest spokes they can, otherwise their diameter would fill the available space in the wheel.

I've got hubmotors with 8000 miles on them, with not one broken spoke. Cheap ass rims, cheap ass spokes too.

But I never tightened them enough to crack a rim, nor ran them with loose spokes. A minimum of attention to your wheel, and a bit of due care about how you hop a curb, and you'll be fine.

It's not an IQ thing, it's a common sense thing. Don't ride your wheels into the ground with no tuning, and you will likely be fine. Sometimes a wheel comes out the door with defective spokes, and if that's the case, you will have to get new ones. But for 90%, even the cheap crappy wheels from china do fine, with just a moderate amount of attention to the wheel. They will need a lot of tuning the first 500 miles, then after than you should be getting at least 500-2000 miles between needing to tune it.

To the OP- Keep an eye on your spoke tension. The bafang flange is plenty strong for 12ga, but your rim won't allow full spoke tension without buckling. Therefore, they will work loose over time. Generally the 1000- 1500 mile mark if they are seated properly at first. If you start hearing any creaks or pings, take care of it immediately. You don't run the risk of catastrophic failure unless you hit an object at speed with tension problems.

wesnewell said:

. Do whatever you want, but don't try and convince me that thinner spokes are stronger than thicker ones.

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Nobody is arguing this. The point is that stronger spokes do not improve a wheel when the bicycle rim or hub flange is your weakest link. Your wheel might not be giving you trouble, but I know it rides horrible compared to a normal wheel. This is where you have experience of building TWO wheels VS folks that have built wheels for decades. Your critical assessment of wheels is immature, and frankly it is inconsiderate for you to spread a blanket notion that 12ga is OK.


Bicycle rims and hubs should be combined with 13ga or thinner spokes for the best wheel. 12ga or thicker into a bicycle hub flange will stress fracture it, and can result in a catastrophic hub failure.


Hubmotors typically have thicker alloy flanges, or steel flanges. If your hub has slightly oversized holes, use 13/14ga. In small hubmotors like bafang and 9c, 13/14ga spokes are a fine choice. In larger hubmotors with very oversize holes (cromotors, mxus 3000, xlyte x5), it is bets to drill a new set of holes when lacing into bicycle rims. You can fix both spoke fitment and insertion angle with this.



mxus 3000 hubs are drilled for 10g, but who laces those sorts of hubs into bicycle rims? Out of hundreds of rear wheel builds, I've had less than five with large hubmotors and bicycle rims. In those cases, we drilled new holes and used 13/14ga spokes with wonderful long term results.





My ideal 20mph hubmotor wheel would have a bicycle rim with tight flange holes and 14/15 on the high tension side and whatever super butted 14/17ga I could find for the low tension side. Just like Chalo recommends! When he has wheel building advice it is a good bet to follow.

Yep. Fat spokes and a bike rim means you can't tension them to the point they never need maintenance. If you hear pings while just rolling straight and level then you gotta get out the spoke wrench and tighten up before they work catastrophically looser.

But my experience with a cheap rim is, you might be hearing some creaks when you crank a very hard corner, if you have not over tightened them. It's a fine line between loose enough for your bike rim, and too loose.

People want to have a wheel that needs nothing for a year or more. Its not really going to happen. I'm used to watching a wheel, when I was young I had to tune a ten speed wheel weekly, I rode it so hard then. So to me, it's not a big deal to look at the wheel at least monthly or so, even if I don't find a problem every month.

Also, where 250 pound people get the idea they can run non suspension bikes through potholes at 30 mph without problems beats me. If it will wreck a regular bike wheel, why wouldn't it wreck a motor wheel?

Again, I didn't mean to open a can of worms when I started this thread. This is just the first hub motor wheel I've ever built and don't know how I missed all the talk about 12 gauge spokes being too thick. This is pretty much a smooth paved bike trail bike so from what everyone is saying it doesn't sound like it's going to be a huge issue assuming I did a decent job building the wheel. I will, however, keep an eye on it. I'm certainly not in the camp that thinks they can ride a non-suspension bike 30 mph over potholes. I personally don't think a normal bike should be going 30 mph anyway but that's for another thread.