Wrong.
Because most rear wheels with motors are badly built.
I've built 20+ rear wheels with motors and no one has ever come back to me with a broken spoke.
A good wheel is 10% rim, 10% spokes and 80% builder.
Chunky monkey needs a kit!
- Thread starter Lardo
- Start date
I've built 20+ rear wheels with motors and no one has ever come back to me with a broken spoke.
A good wheel is 10% rim, 10% spokes and 80% builder.
perhaps some of these 20 customers have lost contact with you.
Badly built wheels will cause the nipples to loosen, leading to broken spokes.
If you fit 36 x 13G spokes to a 26" non motor hub, the spoke length is about 245mm, the wheel is pretty much indestructable.
On a 26" BPM motor wheel, the spokes are much shorter, about 205mm, therefore cannot flex to the same degree, taking into account the lace angle, a 205mm spoke will break with about half the loading (on the rim) of a 245mm spoke with the same lacing pattern.
Nope - in regular contact with all of them.
That's why you don't build rear wheels + hub motors with 13g spokes. Use 14/16/14 double butted spokes and get a competent wheel builder to build it for you and you'll never break a spoke unless you put a stick through the wheel.
The elasticity in butted spokes gives you the oppurtunity to build a stronger wheel. 13g plaing gauge spokes have almost zero elasticity, resulting in an inherently weak wheel, no matter how good your builder is - but that's part of being a good wheel builder - choosing the right components to build a wheel that will do it's intended job.
It's a total myth that thicker spokes equals a stronger bicycle wheel.
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The overal comparison does not change. I am not disputing that a well built wheel will perform better than a badly built wheel. What I am saying is equally applicable to 14/16/14 spokes because the 16G section is still that much longer on a non-motor wheel.
13G can take higher tension, resulting in stiffer wheels. 14/16/14 are better at resisting torsion and better at not loosening nipples. In any case, the choice of spoke size is determined also by the spoke holes on the rim and hole size on the motor. BPM motors are drilled for 13G spokes. If you buy a motor already laced, then the rim is already drilled for 13G. What makes the wheel perform well is the trueing. A well looked after wheel will have the spokes well and equally tensioned, shock to the rim is radially dissipated equally between half of the 36 spokes. A badly trued wheel will have some spokes tighter than the rest, where shock wave is concentrated causing them to break.
13G can take higher tension, resulting in stiffer wheels. 14/16/14 are better at resisting torsion and better at not loosening nipples. In any case, the choice of spoke size is determined also by the spoke holes on the rim and hole size on the motor. BPM motors are drilled for 13G spokes. If you buy a motor already laced, then the rim is already drilled for 13G. What makes the wheel perform well is the trueing. A well looked after wheel will have the spokes well and equally tensioned, shock to the rim is radially dissipated equally between half of the 36 spokes. A badly trued wheel will have some spokes tighter than the rest, where shock wave is concentrated causing them to break.
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How much would the tax/delivery be on that kit, and why would one buy the lipos separately instead of one of bms batteries' packs? the dollar is helpfully weak and I have an old hase tagun that would benefit from the 328rpm version
In your rush to be argumentative you are confusing cause and effect.
Of course disc brakes, a hub motor and high rider weight put extra strain on the spokes - that's the cause.
In a poorly built wheel spokes break - that's the effect.
In a well built wheel, well, there is no effect.
As an expert wheel builder you can probably tell a properly built wheel from 20 paces.
For the average customer it's almost impossible.
Again, as an expert you will be aware of the domino effect, once one spoke goes, others often follow.
Replacing spokes on a piecemeal basis is a nuisance and not a proper job.
Ideally, the wheel should be rebuilt, or at least de-tension all spokes at once and then 'rebuild' the wheel from there.
Few of us have easy access to such expertise, which makes a crank drive the common sense solution.
i (genuinely) dont mean to inflame this thread more (it's getting pretty hot), but - i thought shorter spokes were stronger than longer spokes? i have q rohloff bromptomn i have gratuitously abusing for years without ever even thinking about whether its short spokes might be loose (and their not, their as stiff as can be) whereas spokes on larger wheeled bikes i have have frequently gone loose after heavy use?
the Brompton wheels are 'legendary' for their toughness.
the strength of the spoke is determined by their breaking force, which depends on their elastic modulus of their steel, the spoke angle, dishing, rim, tyres and frame. With all the other factors being equal, the longer the spoke, the more it can elongate before breaking. I'd say the Brompton steel frame has a bit of give, is the major protection against broken spokes.
If the spokes on your larger bike get loose, get it done up or spend a couple of hours learn to true the wheel yourself then you won't have to worry about them again.
Spokes tend to break at the elbow, partly due to torsional metal fatigue, partly due to going past their elasticity in the middle section. The biggest reason for using butted spokes in place of normal spokes is weight saving. Sapim 'strong' is perfectly good but heavy compared to their 'race' or 'laser' version.
the strength of the spoke is determined by their breaking force, which depends on their elastic modulus of their steel, the spoke angle, dishing, rim, tyres and frame. With all the other factors being equal, the longer the spoke, the more it can elongate before breaking. I'd say the Brompton steel frame has a bit of give, is the major protection against broken spokes.
If the spokes on your larger bike get loose, get it done up or spend a couple of hours learn to true the wheel yourself then you won't have to worry about them again.
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D
Deleted member 4366
Guest
As I've said before, breaking spokes is nothing to do with spoke length or gauge. Motorbikes have hubs the size of a BPM motor and 13g or 12g spokes or even thicker, plus the rims are smaller, so the spokes are shorter. The motorbike motor is typically 12 times the power of a BPM motor too. I've not heard of any spokes breaking on motorbikes.
We normally buy lipos from Hobbyking, who have a UK warehouse. BMSBattery do a lot of nice batteries, but not 44v (12S) ones. Nearly all 36v controllers can run on 44v, which gives 20% more speed and torque from the 36v system, so it makes the motor a bit more sprightly. The 201 rpm motors that BMSB sell are just a bit too slow for some of us. There's no other way to speed them up other than to give them more volts.
The 328 rpm small motors are too fast for their power. They're not good in a 26" or bigger wheel unless you're very light. 328 rpm is OK for bigger motors that have the power to take you up to 25 mph. You need about 1000w from the battery for that, which means a 25A controller at 48v or a 30A one at 36v. Then you need a powerful big battery to give those currents for any length of time.
The tax/duty is normally something from £15 to £35 - maybe £40 if you have a battery too.
We normally buy lipos from Hobbyking, who have a UK warehouse. BMSBattery do a lot of nice batteries, but not 44v (12S) ones. Nearly all 36v controllers can run on 44v, which gives 20% more speed and torque from the 36v system, so it makes the motor a bit more sprightly. The 201 rpm motors that BMSB sell are just a bit too slow for some of us. There's no other way to speed them up other than to give them more volts.
The 328 rpm small motors are too fast for their power. They're not good in a 26" or bigger wheel unless you're very light. 328 rpm is OK for bigger motors that have the power to take you up to 25 mph. You need about 1000w from the battery for that, which means a 25A controller at 48v or a 30A one at 36v. Then you need a powerful big battery to give those currents for any length of time.
D
Deleted member 4366
Guest
A brilliant deduction. How many full suspension bikes with hub-motors have you checked? Could it be none?
I know of one - the Woosh Metro will be here in October, so not as yet. It will have rear BPM motor but it has front and rear suspension.
Edit: two, the Woosh Zephyr, full sus, 20" folder, rear SWX motor, no broken spokes while its sister, the Gale, 20" folder too, same rear wheel but without rear suspension, got a few broken spokes over same two year period. Zephyr CDs have no broken spokes yet.
Edit: two, the Woosh Zephyr, full sus, 20" folder, rear SWX motor, no broken spokes while its sister, the Gale, 20" folder too, same rear wheel but without rear suspension, got a few broken spokes over same two year period. Zephyr CDs have no broken spokes yet.
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Irrelevant as the maximum tension on a spoke is limited by the nipple, not the spoke itself. You'll round a nipple way before you snap a spoke and 13g and 14g nipples have approximately the same "rounding" resistance.
It's not "shock" that snaps spokes, it's poorly tensioned wheels and the resulting fatigue that snaps spokes. I concur with d8veh - rear suspension (or not) has no correlation to snapped spokes. I've totally pancaked a wheel with opposite sides of the rim almost touching and there hasn't been a single snapped spoke.
Bent rims ont he other hand...............
thanks for the helpful info, its all very affordable, do lipos give on eteh 800 or so charge cycles typical batteries claim to? more generally i wildly wish you guys woudl become less fundamentalist
Many thanks, that seems affordable, heres to hoping lipos can do 800 charge cycles. I'm afraid i'm non the wiser about wheel strength, spokes and crank and hub drives, but perhaps in teh real world it's not such a burning issue.
D
Deleted member 4366
Guest
Correct. Loads of us us have hub-motors - some very powerful. Do you think we're panicking about broken spokes. I think I've had one in four years and 10,000 miles.
Lipos can't do so many cycles as normal ebike batteries, but once you've got all the stuff, they're easy and cheap to fix when they wear out. Their main advantages are that you can make a battery of any voltage to get the speed you want, and they have a very high discharge rate considering their weight.
Lipos can't do so many cycles as normal ebike batteries, but once you've got all the stuff, they're easy and cheap to fix when they wear out. Their main advantages are that you can make a battery of any voltage to get the speed you want, and they have a very high discharge rate considering their weight.
thanks for teh wheeltruing link, ive bene just tightening, pinging them and dodging potholes so far..
sorry - one last thinig - how many cycles does one get out of lipos and what does "fixing them" involve? many thanks
I've got around 300 cycles out of my zippy compacts so far and still going strong, resistance is around 10mohm per pack so I reckon I've got another 200 reall world cycles left in them before they get relgated to "emergency backup" packs. I do however only charge them to 4.1v per cell and I NEVER let them discharge below 3.5v per cell, which is about 3.65v resting voltage.
You might think 500 cycles out of a battery is poor, but consider that the pack is a 55.5v12ah pack (666watt hours - so 60% more than an equivalent Bosch 400wh pack) and it only cost £200.
Some good value packs from Hobbyking have just landed - they make really good ebike packs - six of those packs in 3s2p config will give you a 44.4v10.4ah pack weighing only 2.6kg and giving 460 watt hours for £127. I'm going to give those a go when my Zippys die. they used to have 6s10000mah packs but they seem to have been delisted now - got really good comments over on Endless Sphere.
many thanks, 500 cycles on a 666 wH pack is at least two years plus in my life, so, while not ideal, survivable..
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