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Spoke tension and dishing

Old 01-14-21, 06:45 AM
  #1  
Mamil Fritz
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Spoke tension and dishing

I have just completed a new carbon REAR wheel with rim brakes. 👍👍👍
I used Sapim CX ray spokes (2mm x 0.9mm x 2mm)
My wheel is rated to 130kgf max

My Dishing is out by 7mm to the NDS (non drive side), but I cannot pull it back as my spoke tension on the drive side is already above limits (Avg tension 15.85). The tension on the NDS is low (Avg tension 6.9). (I believe and was taught should be 60% of DS tension)
I cannot find a tension deviation chart for these spokes but assume my 130kgf has already been exceeded.

Anyone have any ideas?
What chart should I use to calc Kgf?
How low can I go on the NDS?
How High can I go on the DS?

Appreciate all suggestions 😊😊😊
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Old 01-14-21, 07:26 AM
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Geepig
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Originally Posted by Mamil Fritz View Post
I used Sapim CX ray spokes (2mm x 0.9mm x 2mm)
...
Appreciate all suggestions 😊😊😊
My newbie question is should the spokes be the same dimensions on each side?
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Old 01-14-21, 07:43 AM
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Mamil Fritz
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Originally Posted by Geepig View Post
My newbie question is should the spokes be the same dimensions on each side?
The spokes are the same on both sides ... it is just the lengths that vary due to the rear hub...
on the front wheels they will all be the same unless its a disc brake wheel
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Old 01-14-21, 08:10 AM
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If you're using the (most common) Park spoke tensiometer, you should have a chart that will convert tensiometer readings to kgf based on spoke gauge (and the tensiometer should have come with a spoke gauge in the package, too).

If that's the case, I believe you've got a pretty severe case of under-tensioned spokes. IIRC 130 kgf corresponds to something over 25 tensiometer reading.
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Old 01-14-21, 08:26 AM
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Mamil Fritz
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Thanks pdlamb
I hear you and indeed I do have said chart. Unfortunately it does not feature the sapim bladed spokes.... and I am not sure which spokes are similar.

Originally Posted by pdlamb View Post
If you're using the (most common) Park spoke tensiometer, you should have a chart that will convert tensiometer readings to kgf based on spoke gauge (and the tensiometer should have come with a spoke gauge in the package, too).

If that's the case, I believe you've got a pretty severe case of under-tensioned spokes. IIRC 130 kgf corresponds to something over 25 tensiometer reading.
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Old 01-14-21, 08:44 AM
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Originally Posted by Mamil Fritz View Post
Thanks pdlamb
I hear you and indeed I do have said chart. Unfortunately it does not feature the sapim bladed spokes.... and I am not sure which spokes are similar.
Ah. Does your chart have the bladed spoke tensions on the back? My original didn't, but when I lost it, Park sent me a new chart (and gauge!) that had round on one side, and bladed on the other side.
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Old 01-14-21, 08:55 AM
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Mamil Fritz
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Thanks pdlamb
yes it does. Perhaps I am reading it wrong.
the Sapim spokes are 2mm x 0.9mm x 2mm ie 2mm at the nipple, blade is 0.9mm thick and its 2mm at the hub end
I am using the chart column steel blade 1.0 x 2.0-2.2 (as I believe this is the closest) which at 16 gives me 133kgf.
Would appreciate it if u would check my thinking and let me know if I am wrong😊😊😊


Originally Posted by pdlamb View Post
Ah. Does your chart have the bladed spoke tensions on the back? My original didn't, but when I lost it, Park sent me a new chart (and gauge!) that had round on one side, and bladed on the other side.
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Old 01-14-21, 09:05 AM
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The general approach is to build the DS to the target tension. Then let the NDS tension will be whatever thatís dictated by the geometry. If 60%, fine. Otherwise, not much to be done about it. Down to 55% is not unheard of.
It becomes a matter of priority. If the rim is more expensive than a half set of spokes, youíll suffer less from undertension failure than from rim failure.
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Old 01-14-21, 01:04 PM
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nds is what it is, it's determined mainly by hub geometry.
With modern hubs 50-55% is about the best you can ask for.
A basic rule of thumb would be to divide the ds flange to centre distance by the nds flange to centre distance.
F.i. 17/35 would give you a nds tension of slightly under 50%.
You can somewhat improve this with a larger ds flange vs nds and/or an offset rim.

So loosen the nds spokes again until the rim is centred.
This should bring down ds tension too.
As soon as the rim is centred you can bring the spoke tension up again.
Do 1 turn ds vs 1/2 turn nds and the rim should remain centred.
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Old 01-14-21, 01:27 PM
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Maybe I should add that Park Tool somewhat regularly updates their conversion tables with new spokes. It may be worth a look.

Also you should try and find a copy of Spocalc somewhere if you have Excel or a compatible spreadsheet program.
Besides being a pretty good spoke length calculator it can also show you the relative spoke tensions of various hubs/rims/spoke patterns.
Also has a built in database with hubs and rims (albeit dated)
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Old 01-14-21, 01:42 PM
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Originally Posted by Mamil Fritz View Post
Thanks pdlamb
yes it does. Perhaps I am reading it wrong.
the Sapim spokes are 2mm x 0.9mm x 2mm ie 2mm at the nipple, blade is 0.9mm thick and its 2mm at the hub end
I am using the chart column steel blade 1.0 x 2.0-2.2 (as I believe this is the closest) which at 16 gives me 133kgf.
Would appreciate it if u would check my thinking and let me know if I am wrong😊😊😊
I'd probably be inclined to use the 0.9x2.2 0n the chart, which would even make things worse.

Does this rim possibly have an offset spoke bed that you have installed backwards?

BTW, since we're only referring to tension, I describe the spokes as 2.0x0.9mm. The nipple/head numbers just add a bit of confusion.

Last edited by Bill Kapaun; 01-14-21 at 01:50 PM.
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Old 01-14-21, 02:03 PM
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Using the same spokes DS and NDS with highly dished 9/10/11-speed wheels is doable but marginal (as you are seeing. Far better is to go a full gauge lighter on the NDS. (Being thinner spokes, you will be paying a smaller penalty going simple round instead of bladed.

To make this wheel work, back off your NDS to proper dish and true and call it as good as you can do for now. (If you start breaking NDS spokes down the line, consider a re-build, same rim and perhaps same DS spokes (just loosen the DS spokes, don't pull them out of the hub and swap the NDS spokes to a gauge lighter).
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Old 01-14-21, 02:48 PM
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Bill Kapaun
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What rim?
What hub.
What DO spacing.
Knowing those, might help give us more insight, since we can then plug the numbers into a spoke calculator and see what we should expect.
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Old 01-14-21, 08:17 PM
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Just to double check, are you using the tensiometer the right way on the spoke? I don't use the Park but the Wheelsmith version you base spoke tension on the center part, so regardless of the end butting you base it on the thin section in the middle which would be the .9, probably the same is true for the park. If you're still over tensioned you need to loosen the drive side and move it back towards a proper dish. Once you get back to center you may have to tighten all the spokes a touch to keep them at proper tension, unfortunately with 130 spaced rear hubs sometimes ideal NDS tension isn't possible which is really annoying.
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