Spoke Tension Gauge and dishing with very short spokes?

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rberger
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Spoke Tension Gauge and dishing with very short spokes?

Post by rberger » Tue Nov 14, 2017 2:15 am

My spokes started pinging the other day when the trike was under load, so I got a park sw-3 spoke wrench and tightened up my spokes based on trying to make them sound the same. But I have no idea if they really are the same. The pinging did stop though when trike was under load.

My winter project is going to be properly dishing (or undishing I still not sure which is which but I got to move the rim about 5mm away from the drive side) my rear wheel on my trike to actually be centered in the rear fork and make sure its all nice and true. Dishing/Truing a wheel is one of the last of my fears of DIY on the trike. Figured its time to get over it.

I picked up the park TM-1 Spoke tension meter but discovered that the width of the tool is bigger than the total length of the exposed spoke on the 20" rim radially laced to a crystallite 3540. They are VERY short spokes. The Wheel was built by Grin Tech and uses what seem to be high quality Sapiem Strong spokes. It wouldn't even fit in the normal front 20" wheels ether due to the cross pattern of the spokes on the front wheel. So sending it back.
Rim and Motor.jpg
Rim and Motor.jpg (66.92 KiB) Viewed 130 times
So I'm wondering:
  • Is there a spoke tension meter that would fit (probably can't be wider than about 60mm or so) and not cost too much (ie < $100)?
  • Can such short spokes withstand being dished 5mm without over stressing them?
  • Is there anything else I should be concerned about or be considering?
2011 ICE Adventure Trike Converted to 1500W DD Hub Pedalec in 2017

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amberwolf
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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by amberwolf » Tue Nov 14, 2017 3:23 am

Why exactly do you need to move the rim over that far? Is it not centered between the rim brake pads? (or the stays, if they are symmetrical (not all stays are).


Dishing is when you center the rim by using shorter spokes on the side it's got to be closer to, when using equal length spokes would leave the rim off-center.


It's possible to move a rim over by loosening spokes on one side (that the rim will be farther from) and tightening them on the other side (that the rim will be closer to), but at some point you'll wind up with spokes too slack to do their job, and either they'll start breaking or unscrewing the nipples from the spokes, or the extra load on the other side starts breaking spokes there.


How far you can dish with existing spokes depends on the spoke gauge and length and the rim itself, distance between spoke flanges, etc.

If you haven't already, I'd recommend reading this
http://www.sheldonbrown.com/wheelbuild.html


FWIW, I use a similarly-built HSR3548 as the rear wheel of CrazyBike2, with rim brakes, and equal-length spokes results in a centered wheel (no dishing needed). Presently that motor / wheel is on SB Cruiser's right side, until I get a different one rebuilt for it, but it served a long time on CB2 without issues (other than a split rim from a serious pothole impact, replaced the rim and rebuilt same as it was before).

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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by motomech » Tue Nov 14, 2017 10:39 am

My spokes started pinging the other day when the trike was under load,...
Sounds as if they may have been over-tightened.
I've never used any sort of spoke tension gauge.
If the spokes start to "squeak" as you are tightening them, they are getting too tight. Keep doing that and the rim will go out-of-round. Once that happens, it's usually best to loosen all of them and start over.
Try and get the rim located where you want it without getting the spokes overly tight, install the wheel and monitor the tension by squeezing them w/ your hand and noting the deflection.
After riding it for a while so the wheel will "take a set", go back and ck. true and add some more tension. You may have to do it a third time to get all the spokes "bedded in" and the wheel true.
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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by Drunkskunk » Tue Nov 14, 2017 7:51 pm

Since the pinging stopped, it sounds like you got it right by sound alone, Which is fine.

Spoke Tension Gauge isn't going to work very well when the spokes are that short and that thick. Listening to their sound is a better method.

A Spoke Tension Gauge is about like a torque wrench. it's very useful when it's difficult to tell if you've reached the right tension, However, you have eliminated the pinging in the wheel, so you have already reached the right tension. The only other purpose serves as a way to verify you have the spokes evenly tight before you try to true the wheel.


It's not clear what you're trying to accomplish by dishing the wheel. Is the wheel not centered in the frame? 5MM isn't much, unless the tire is rubbing or the brakes don't work, I wouldn't bother with it, especially on a trike. It's just added work with no real gain.
A 5mm offset dishing of the wheel isn't very difficult in most cases, though it will stress the spokes more than a non dished wheel. You can pick up about 5mm of offset if you swap the spokes from exiting on the outside of the hub's spoke ring to exiting on the inside on the drive side.
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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by rberger » Wed Nov 15, 2017 1:29 am

Yeah, the Ice Trikes seem to expect a different dish than most bikes/trikes from what I understand. Right now the rim is centered over the flanges, it is not in the center of the 135mm "hub" and on the ICE trike it is not in the center of the frame.

Its not critical that I fix this unless I want to put the rim brakes back on to use for "parking break". I was hoping to put a disk brake on it but there may not actually be enough clearance with the motor wires to allow for a disk brake. It bugging me esthetically as well :P
Left Offset New Wheel.jpg
Left Offset New Wheel.jpg (55.27 KiB) Viewed 87 times
Right Offset New Wheel.jpg
Right Offset New Wheel.jpg (56.26 KiB) Viewed 87 times
offset visual.jpg
offset visual.jpg (23.25 KiB) Viewed 87 times
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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by Lurkin » Wed Nov 15, 2017 5:08 am

I read various books/texts, Sheldon Brown, Roger Mussons, Jobst Brandt, Gerd Schraner.. the list goes on. Most make reference to the listening technique for identifying even spoke tension. However, I had two issues with doing this. Firstly, it does not define the correct spoke tension - it just assumes you have the right tension and after making them sound the same, they are all even - but it could be either too high or too low.... Most seem to have an equally rule of thumb means of deciding that they have the 'correct' tension which was insufficient for me.

The second issue was that the wheel I built with the listening technique sounded equal and ensured they sounded similar to bike with the same hubs, rim and consequent spoke length. The spokes didn't ping or do anything unusual. Within a couple of weeks, the spokes pulled though the rim, splitting the rim down the middle and allowing the tube to poke out! Made for pretty entertaining ride home but definitely not something I'll be doing again.

The conclusion drawn from this was: I had all the tensions relatively too high and either the listening technique requires development of skilled hearing over time.. not suitable for someone doing it the first time round. I've relied on the park tool measurement and I have built a number of wheels which have been subject to a decent amount of use/abuse. No issues since!
Is there a spoke tension meter that would fit (probably can't be wider than about 60mm or so) and not cost too much (ie < $100)?
The only tension style meters I've seen since which are thinner (meaning the distance between the points which touch/bend the spoke) were textile or wire tension meters. I'm not sure if it will apply well as the ones I've seen would force the spoke to move at more aggressive angles and I'm not sure if they would cope with that higher tension. I imagine google is your friend here.
Can such short spokes withstand being dished 5mm without over stressing them?
Its hard to answer that definitively because its a function of the spoke seat angle as to how far they can be angled without bending. Grin actually has a decent explanation and points out the max angles on their calculator from memory in relation to choosing spoke length and I think the same concept applies here. The dishing should be coming from the position of the spoke nipples and spoke head direction, not bending or stressing the spoke. I've gotten away with bending before, but really, faced with this issue again I would be looking to get a rim with the correct spoke hole angle or potentially filing it a little to allow it to correct it more than relying totally on bending spokes. The better option is to choose rim/spoke/motor combos that steer clear of these stresses leading to avoiding premature wheel part failures.
Is there anything else I should be concerned about or be considering?
I have been blown away with the power to weight ratio difference between DD and geared motors and I wonder if it would be worth considering a lower power geared motor which also has a smaller dimension - allowing you to get away with longer spokes. Bafang BPM motor has historically been known to put up with a fair amount of abuse... food for thought anyway.

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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by amberwolf » Wed Nov 15, 2017 1:58 pm

Lurkin wrote:Within a couple of weeks, the spokes pulled though the rim, splitting the rim down the middle and allowing the tube to poke out!
That's definitely too high a tension--for the rim.

Not necessarily too high a tension for the spokes, depending on their gauge (and possibly length).

If they were heavy gauge spokes (12g+) it's possible that in order to tension them correctly the rim (if thinwall/normal and no eyelets) could be damaged. I've had this with various OEM ebike wheels, for instance, where the 12g spokes that came with it were too thick for the supplied rim, and tensioning them sufficiently to not keep having spokes loosen up or break would crack the rim.

This might not have been the problem you had with your wheel--but it can definitely be a problem with them under those condtions.

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Re: Spoke Tension Gauge and dishing with very short spokes?

Post by Lurkin » Wed Nov 15, 2017 4:53 pm

I only use 14g single butted spokes, but its still pretty easy to over tension thinner spokes to be beyond the maximum tension of a alloy rim.

Again, unless you have experience to tell its over tightened or some other method of knowing its over tension - its entirely possible to create a wheel well over the tension specifications of the rim, yet true and perfectly even.

Interestingly, there is commentary in here about pinging or noise which has 'gone away'. that isn't necessarily a sign that the spoke tensions are correct or even - it could be stress relief on the spokes themselves... I've owned wheels which do not run true (uneven tension) which make no noise - the reality is, listening to sounds is symptomatic if the wheel makes them. Its not a measurement of the tension of the spokes!

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