After ebike conversion, has anyone had a higher rate of broken spokes or bent wheels?

[Deleted member 33385]

Has anyone's bicycle had a higher incidence of broken spokes/bent wheels/other wheel damage, as a direct result of adding an ebike kit to their bicycle? I haven't ever had any broken spokes on my Dahon Helios P8, which still has it's originals wheels... but now I'm thinking of swapping my wheels for stronger (and oh no - heavier) wheels with more spokes.

 

[Trickyh]

Managed to snap a deraileur hanger on the first outing with the BBS02 kit fitted. Last one I snapped was on a mountain in Austria and managed to find a replacement by the skin of my teeth.

I'm putting it down to poor setup (my fault) or super muddy mech (also my fault)






The problem I see in edrive is it just powers on and doesn't give you the same feedback in the same way if you were just peddling. The edrive allowed me to get through terrain that would have been impossible under my own steam which ultimately led to the failure. (which again is my fault)

 

[vfr400]

Anecdotally, stronger wheels break more spokes than lighter ones.

About 10 years ago, there were a lot of poorly built Chinese motor wheels and others with very suspect spokes. When they found all the spokes were breaking, they tried to fix it with thicker spokes (12g), but that made it even worse, with rims starting to break as well. The more astute companies now fit thinner spokes (14g) which don't seem to give any of the previous problems, I guess because elasticity is a very important characteristic for an ebike wheel, and thin spokes can stay functional over a much wider range of tension.

 

[Trickyh]

I agree, the problem is we are putting approx double the power into standard bicycle components (250 watt human and 250 watt e motor) so things are bound to break sooner rather than later. If you beef up the spokes, followed by the rims, bearings, cassettes etc, then we start turning into a motorbike (with pedals!)

 

[mike killay]

Anecdotally, stronger wheels break more spokes than lighter ones.

About 10 years ago, there were a lot of poorly built Chinese motor wheels and others with very suspect spokes. When they found all the spokes were breaking, they tried to fix it with thicker spokes (12g), but that made it even worse, with rims starting to break as well. The more astute companies now fit thinner spokes (14g) which don't seem to give any of the previous problems, I guess because elasticity is a very important characteristic for an ebike wheel, and thin spokes can stay functional over a much wider range of tension.

Does anybody have any idea of just how much weight a single 14 gauge spoke can support before fracture?

 

[Jayfdee]

Has anyone's bicycle had a higher incidence of broken spokes/bent wheels/other wheel damage, as a direct result of adding an ebike kit to their bicycle? I haven't ever had any broken spokes on my Dahon Helios P8, which still has it's originals wheels... but now I'm thinking of swapping my wheels for stronger (and oh no - heavier) wheels with more spokes.

Had a few broken spokes on a cheap Chinese 500w hub motor wheel.
My Bafang 250 w mid drive has done 2000 trouble free miles, and similar on my Yamaha Haibike. So The hub drive was the only problem.

 

[sjpt]

Does anybody have any idea of just how much weight a single 14 gauge spoke can support before fracture?

No direct answer, I think a huge amount of steady weight. What will do it in will be impact from potholes/pavements, and flexing at the hub end (especially if the wheel isn't that well built with insufficient tension on some spokes)

 

[vfr400]

Does anybody have any idea of just how much weight a single 14 gauge spoke can support before fracture?

A lot. My mate was 120kg and had a hub-motor running up to 30 amps. he didn't have any problem with his spokes after I rebuilt his crappy chinese wheel with 14g spokes rather than the original 13g.

Mild steel has a tbreaking strain of about 100kg for a 2mm wire, which is 14g. So a wheel should support a weight of well over a ton.

What makes the spokes fail is metal fatigue either at the start of the thread or at the elbow. Metal fatigue happens when you get a cyclic bending force. Mild steel is fairly resistant to metal fatigue, but other steels like stainless or high carbon aren't. It just depends what metal is in the spoke. Any tooling nick or other discontinuity in the bend will significantly weaken the fatigure resistance.

In summary, poor control of the steel wire that the spokes are made from and poor manufacturing processes are more likely causes of spokes breaking than the choice of spokes or the diameter.

 

[Deleted member 33385]

Managed to snap a deraileur hanger on the first outing with the BBS02 kit fitted. Last one I snapped was on a mountain in Austria and managed to find a replacement by the skin of my teeth.

I'm putting it down to poor setup (my fault) or super muddy mech (also my fault)

Ouch! Shudder! Finding a replacement for mine will be like locating hen's teeth... maybe I should avoid using the gear sensor as much as possible - the resumption of power after cutoff as a result of changing gear is not an assignable parameter in the firmware, but it damn well should be! Do you hear that Bafang?

Anecdotally, stronger wheels break more spokes than lighter ones.

That's a good point! Now that I've thoroughly Dysoned all your minds of all available useful information pertaining to spokes, wheels etc. and damages suffered as a result of use with motors... I've got to decide whether to get similar wheels to what I have now, or ultralight:


https://foldingbike.biz/epages/7665e38c-067c-4fa0-9037-afac2266f927.sf/en_GB/?ObjectPath=/Shops/7665e38c-067c-4fa0-9037-afac2266f927/Products/DAHKINPROWHEELFROBLA


...or "Stronger":


https://foldingbike.biz/epages/7665e38c-067c-4fa0-9037-afac2266f927.sf/en_GB/?ObjectPath=/Shops/7665e38c-067c-4fa0-9037-afac2266f927/Products/DAHKINCOMPSETSIL



I'm loathe to add more weight! I'm quite attached to my 10.7kg bike + 12kg Bafang kit combination. I'll probably try and source the same as what I currently have (because the rimline on the front wheel, is more of a dotted line), and hope I don't kill the derailleur or break too many spokes.

Mild steel has a tbreaking strain of about 100kg for a 2mm wire, which is 14g. So a wheel should support a weight of well over a ton.

What makes the spokes fail is metal fatigue either at the start of the thread or at the elbow. Metal fatigue happens when you get a cyclic bending force. Mild steel is fairly resistant to metal fatigue, but other steels like stainless or high carbon aren't. It just depends what metal is in the spoke. Any tooling nick or other discontinuity in the bend will significantly weaken the fatigure resistance.

In summary, poor control of the steel wire that the spokes are made from and poor manufacturing processes are more likely causes of spokes breaking than the choice of spokes or the diameter.

As usual, a welcome and wild level of in-depth knowledge there vfr400!

My Bafang 250 w mid drive has done 2000 trouble free miles,

That's very reassuring to hear!

I wonder if I could install mag wheels? 74mm hub at the front, 130mm at the back for rim brakes is proving hard to find, but they may be strong as well as light?

 

[mike killay]

What makes the spokes fail is metal fatigue either at the start of the thread or at the elbow. Metal fatigue happens when you get a cyclic bending force. Mild steel is fairly resistant to metal fatigue, but other steels like stainless or high carbon aren't

Some time ago I hazarded a guess on this forum that the advent of stainless spokes was one reason that so many now report spoke breakage.
I don't remember spokes breaking 60-70 years ago. Mine never did, but they were mild steel and could rust.
Lots of sailors do not trust stainless rigging wire for their masts because it has a reputation of suddenly breaking, whereas galvanised mild steel gives years of warning as it slowly leaks rust.

 

[Deleted member 33385]

Some time ago I hazarded a guess on this forum that the advent of stainless spokes was one reason that so many now report spoke breakage.
I don't remember spokes breaking 60-70 years ago. Mine never did, but they were mild steel and could rust.
Lots of sailors do not trust stainless rigging wire for their masts because it has a reputation of suddenly breaking, whereas galvanised mild steel gives years of warning as it slowly leaks rust.

Stainless steel is of course more brittle, but I'm stating the bleeding obvious as usual... I'm intrigued by these Niobium alloy spokes:

https://foldingbike.biz/epages/7665e38c-067c-4fa0-9037-afac2266f927.sf/en_GB/?ObjectPath=/Shops/7665e38c-067c-4fa0-9037-afac2266f927/Products/TERNKINPROWHEELFROYELL

...they get away with 14 spokes vs my normal 20... but there are quite large gaps between spokes , so I'm wondering if that makes them harder to true? I'm resisting the temptation to buy them, but might not be able to for much longer. My Bafang might kill 'em! What's the worst that could happen?

 

[Trickyh]

Certainly a nice looking wheel, but I'm sure an emotor would chew them up in minutes.. i have similar (but not as extreme) on my road bike and the rider weight limit is 100kg . I was very nervous of them for the first couple of 100 miles..

 

[Deleted member 33385]

Certainly a nice looking wheel, but I'm sure an emotor would chew them up in minutes.. i have similar (but not as extreme) on my road bike and the rider weight limit is 100kg . I was very nervous of them for the first couple of 100 miles..

Yes, you're right. I shouldn't have my head turned by their looks... that's always been my problem

Those would most likely shatter.

 

[Edward Elizabeth]

Im 120kg, never broken a spoke in my life.

 

[Deleted member 33385]

Im 120kg, never broken a spoke in my life.

You're 18.89 stones in weight? You must be about 10ft tall! How's the weather up there? It's a good job bicycle wheels are mostly overengineered - I used to break spokes on my racers quite often by riding at pavements - if you hit them square, the wheels were so large that you end up and over onto them.

Most of the stress caused by torque will be on the back wheel, therefore I might go ultralight for the front - it depends on whether I can replace (and obtain) the spokes myself. They hand build those ultralightweight wheels within a few days. I'm so tempted, but I have time for disaster to befall my front wheel first, after which I'll have no choice but to do what I wanted to anyway, and try one of these Niobium alloy ultralights out.

 

[WheezyRider]

I think another reason why there have been more broken spokes is that with larger hubs and a crossing pattern of 2, on a lot of the wheels I've seen there is quite a lot of spoke bend as they reach the rim. Maybe with thinner spokes the bend occurs along the length of the spoke and it's not so extreme at the rim, so is less of a stress concentration point.

 

[Deleted member 33385]

I think another reason why there have been more broken spokes is that with larger hubs and a crossing pattern of 2, on a lot of the wheels I've seen there is quite a lot of spoke bend as they reach the rim. Maybe with thinner spokes the bend occurs along the length of the spoke and it's not so extreme at the rim, so is less of a stress concentration point.

Do they secure/make spoke threads at slight angles to prevent stress concentration at that point? Spoke breakages are probably too rare these days for them to bother.... Mild steel seems very likely to bend near the rim - a stiffer material at the same thickness, might bend more along it's length? 14 spokes don't seem enough on that wheel... on the other hand, it's a small 20" wheel. Without knowing exactly what the characteristics of that specific alloy are, it's a gamble. Each spoke (in combination with the rim) would have to be 1.43 times stronger than usual. I'm betting that those Niobium alloy spokes/rim will shatter when powered by a motor into a pothole, but I don't want to win that bet - at least, not without wearing a lot of safety gear... new BMX helmet arrives tomorrow, next would be spine giard, kneepads, elbow pads, airbag vest...

 

[Deleted member 33385]

I was very nervous of them for the first couple of 100 miles..

Lol, I bet you were! Flimsy looking things... Maybe someday spokes will be replaced by those graphene chains they might try on space elevators:

https://en.wikipedia.org/wiki/Space_elevator

...thin spokes made of that would likely look invisible in a bike wheel.

What wheel did you get anyway? Let's have a look at them - any broken spokes or rims?

I may yet be unable to resist these ultralights, but if it turned out to be cr*p - it'd be yet another object taking up space...

 

[Edward Elizabeth]

You're 18.89 stones in weight? You must be about 10ft tall! How's the weather up there?

I'm 6'5". It's chilly up here, but not snowbound all year round.

 

[Woosh]

Does anybody have any idea of just how much weight a single 14 gauge spoke can support before fracture?

14 gauge (1.9mm diameter): 740 lbs, 336kgf to break it in the middle.
But spokes never break in the middle. They either break at the J bend or at the end of the thread.
Spokes work in extension (tensile) and usually break in compression, that's their weakness. If your spokes are loosened, you'll break them.