26" wheel spoke advice

[Cuprani]

I'm having troubles with my home build Vector Ebike.
The wheel keeps bending.

I've re-tensioned and aligned the spokes several times, but after a few miles the wheel is bend again.
Resulting in wobbling and hopping of the rear wheel which is really annoying.
I really go easy on the bups and drops, but I think the problem is partially caused by the torque of the motor.

My bike is about 80Kg's and so am I, so bike+rider is about 160 kg (350 lbs)

Because of regulations my bike must look as much as a bicycle as possible, that's why I only can ride with normal 26" bicycle rims.
I don't want to mount a motorcycle wheel in my bike.

The wheel currently mounted is a Sunringle MTX39.
Now I'm in doubt what I should do to fix the problem.
So some advice would be great.

I could keep the original wheel and let is respoke by a wheel specialist.
This would cost me about € 200 to € 300 euro's.
But is this wheel still good when aligned again?

Or I could go for a new wheel and spokes (but which ones?) and let it re-spoke by a wheel specialist.
With a good downhill wheel that would cost me around € 350 to € 450 euro's.
This would be the best option I think, but right now I not really want to spend so much an a new wheel.
If this could be cheaper it would be great.

 

[ZAXBÎX]

I've had a couple of bad mtx39s over the years, 3 out of about 20. What size, gauge, spokes did you use; length correct; use a tension meter; spoke butter or linseed oil? With 39s I like to use 12/13ga. butted spokes, on old school double tracks the same or 12 strong's, always brass nipples.
Remove the tire, re-lace, use butter, tru wheel, over tighten a bit, mount tire, give it a gentle ride, recheck true & tension, go ride it like a senior prom queen knowing your headed to boot camp the next day, recheck true & tension, then recheck every ride for a week.

Best of luck, Z

 

[motomech]

I weigh 250 Lb.s and my heaviest bike was 80 Lb.s, although the motor was mid-sized (5 Kg.s).
I use a Alex DX32 rims w/ 14 Ga. spokes, no problems.
Lighter spokes allow some flex

 

[ZAXBÎX]

For 32s & rhinos, 13/14 are great. I do like butted spokes & the compromise of stretch to what the hoop can take. It's gotta stretch. Haven't found a bicycle rim that will reliably hold 10ga. spokes, even double tracks.
My 2 cents for the OP: spend some time with the setup on hand; as long as nothing is damaged & doesn't have 10ga. spokes. Z

 

[amberwolf]

what spokes are you using?

what wheelbuilding methods are you using?

what is the lacing pattern?

I've re-tensioned and aligned the spokes several times, but after a few miles the wheel is bend again.
Resulting in wobbling and hopping of the rear wheel which is really annoying.

if the spokes are loosening, then it is usually because of spokes taht are too large a diameter for teh rim, and they have damaged (cracked) the rim because of too high a tension for it, so they cannot remain tensioned.

when it is not that, it is that the spokes are not tensioned sufficiently, whcih can be caused by nipples binding during tensioning, so they *appear* tighter than they actually are (sometimes by a lot). there are lubricants made for this purpose (even linseed oil can work, which also can act as a form of loctite to keep them from loosening once they're correctly tensioned).

if those are not the problem, and the rim is not actually damaged, then the msot likely problem is the rim is simply not strong enough for the impact forces and sideloads being placed on it.



as a note, on my 500lb+ (with me on it) trike, that carries 300lb+ loads, even on potholed roads at 20mph, the spokes and wheels remain intact (except sometimes bent rim edges where the bead of the tire sits), using 20" alloy rims and 13/14g butted spokes, radially laced on large heavy hubmotors.

so to bend up a regular non-hubmotor wheel that's laced normally with normal spokes and rim, it'd take fairly intense forces.

 

[Cuprani]

I have 36 spokes.
They measure about 2.5mm thick, so that's around 12 Ga. already
Don't know if they are butted or not.

 

[serious_sam]

IMO, 12g is too thick for a bicycle rim. You can't adjust them to their required tension without destroying the rim. So the spokes don't act like springs, and the rim takes a larger shock loading. The rim will always get bent, and spokes will always come loose.

Check the rim for permanent damage, then re-spoke with some quality 14g or 13/14g.

 

[Cuprani]

OK, but how can I check for permanent damage?
There are no cracks or something, but some spoke holes look a bit wide.

Here is how the spokes are arranged.

I'm not going to respoke the wheel myself and will outsource that to a specialist.
Because the biggest part of the costst will be the labor, I think I'm not going to take the risk of investing in a broken wheel.

What is a good downhill wheel? Because I can't find the MTX39 anywhere available in Europe.

 

[john61ct]

go ride it like a senior prom queen knowing your headed to boot camp the next day

Please, ELI5 what that means?

Having a hard time seeing how the prom queen going to boot camp would affect how she rides her bike?

 

[Balmorhea]

Your spokes are too thick. They are laced on alternating sides of the flanges. Both these things reduce wheel strength.

You need to rebuild your wheel. It should be more than strong enough for what you are asking of it. That’s a good rim, if it’s still straight. If it’s not, replace it. Rebuild with 2.0/1.8mm butted spokes, using 2mm washers under the spoke heads to keep them from pulling through the hub flanges. Lace all the spokes on the outsides of the flanges. Tighten them to at least 1200N of tension. Stress-relieve them by prying spoke pairs with a flat tool at their crossings.

A wire wheel is much more than just its component parts. Build quality is more of a factor than any other part to how durable and reliable the wheel is.

 

[serious_sam]

OK, but how can I check for permanent damage?

Did you (or your wheel builder) drill out the eyelets from the rim, to be able to fit the 12g spokes at those angles ? I can't really see in those photos. If the eyelets have been drilled out, then you'll have some fitment issues going down to a smaller size nipple. You could use washers around the nipples to fill out the larger holes, but the rim is double walled and deep, so it will make it more difficult to assemble.

MTX39 is a good rim. There are better (and more expensive) options, but you also need to consider availability in 36 hole. Worldwide have the 36 hole MTX39, and they ship to Europe: https://www.worldwidecyclery.com/products/sun-ringle-mtx39-rim-26-36h-presta-black

I strongly recommend rebuilding your wheel yourself. It's piss easy. You just need a little patience. Take your time. It's kinda like meditation. Very relaxing. Fck paying someone €200 to €300. That's out of control. Spend the €200 on a fck-tonne of beer and snacks, and have a solo wheel building party. Enjoy yourself. What else are you going to do with your spare time at the moment ?

Lacing in exactly the same pattern you have now is fine. Lacing on opposing sides of the hub flange (like you have) is perfectly acceptable. It is very common.

If you're worried that you really can't do it from scratch, (and if your current rim can be re-used), then leave the wheel assembled as it is now (minus the tyre), and replace the spokes two at a time.

For your reference, I used MTX39 rims on my ebike. I used the Sun Ringle listed ERD of 525mm which worked fine. Round the results down to the nearest available spoke length.

Most online spoke calculators will all be within about 1mm of each other. I found Sapim's calculator result was about 2mm longer than the rest. Discarded. YMMV.
https://www.ebikes.ca/tools/spoke-calc.html
https://spokes-calculator.dtswiss.com/en/calculator
https://leonard.io/edd/

Buy any brand name spoke and nipple. Sapim. DT. Whatever. For example, these are good basic spokes and come with brass nipples: https://www.jejamescycles.com/sapim-leader-plain-14g-spoke-silver.html

You'll also need 2mm stainless or brass washers for the 14g spokes to fit centred into the 12g holes in your hub.

 

[amberwolf]

Did you (or your wheel builder) drill out the eyelets from the rim, to be able to fit the 12g spokes at those angles ? I can't really see in those photos. If the eyelets have been drilled out, then you'll have some fitment issues going down to a smaller size nipple.

There could also be cracks that you can't easily see around the nipple holes, allowing the spokes to detension. If this is the case, you'd need to replace the rim itself to fix that, along with getting the correct smaller gauge spokes.

That is the sort of damage I usually see that causes the specific problem the OP is having.

Typically it takes a very bright light (sunlight at midday on a good clear day at minimum) to see the small cracks, and a magnifying glass or better may be required.

Sometimes using a fine white powder like talc and rubbing it deeply into the nipple hole area all around the rim, right up to the edges of the holes and inside, will help you see the cracks. Sometimes it will take a liquid with a dye or color in it that greatly contrasts with the rim color.

 

[dogman dan]

Once you do bend a rim, its just not going to work to over tension spokes to bend it back.

Get a good rim, and rebuild it. Lacing is pretty easy, once you grok the pattern. Each set of four is a group. And you just repeat that group of 4. Start at the hole, so you don't land the valve in the middle of a group of four.

 

[Cuprani]

So for the last months I kept driving, until now.
I have a leak tube and a worn tire, so I'm not going to fix that anymore but build my new wheel.

I checked the spokes again, they weren't loose and I can not discover any cracks so I decided I want to rebuild on the same rim.
Yesterday I took one spoke out and did some measurements.

Spoke hole in motor hub: 4,5 mm
Spoke hole in rim: 5,1 mm

Spoke diameter: 2,55 mm (G12)
Spoke diameter at thread: 2,7 mm
Spoke length: 160 mm

Spoke nipple length: 12,9 mm (inc head)
Spoke nipple length: 11 mm (exc. head)
Spoke nipple outside diameter right under the head (where they seat in the rim): 4,7 to 4,8 mm
Spoke nipple outside diameter at spoke end: 4,1 to 4,2 mm

Can anyone tell me which black 13g spokes I could use?
And what kind of washer and nipples I can use in my situation if I switch to smaller spokes.