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Safe Dishing

Old 02-27-22, 12:04 PM
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Aardwolf
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Safe Dishing

Hiya Folks,
I'm after some opinions about how much dishing is 'safe'.

I've got some Mavic MA2 32 hole rims with Shimano rx100 hubs (8 speed: FH-A551-8) and according to 10-speeds on a 126mm hub SUCCESS
I should be able to respace to 126 OLD. That thread says 16-18mm of dishing is safe, I'm guessing because the NDS/DS spoke tension ratio is in some way 'reasonable'.

So far my best config seems to be 37.6 / 16.6 mm for the hub flange to centre measure (and 127 OLD) which means the chain just clears the stays:



So basically is 16.6 OK, and would for example 16.35 be ok too ?
I'll be using 2mm stainless steel spokes if that makes any difference.
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Old 02-27-22, 12:43 PM
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Your NDS tension will be 44% of DS tension.
I like at least 65 kgf on the NDS which would mean the DS would have to be 146 kgf.
130 kgf tends to be my absolute max.

Using a 2.5mm offset rim would make the NDS 55% of DS, which would make "my" max right about 120 kgf.

Last edited by Bill Kapaun; 02-27-22 at 12:47 PM.
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Old 02-27-22, 01:01 PM
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Thanks for the reply,
How did you work out the 44% number ?

I have the option of not using the small cog which could get the 16.6 up to about 17.1,
and I'm probably too old to use 52/12 or 52/11 anyway

The rear wheel did have 57.51-85.8 kgf on DS and 25.02-55.02 kgf on NDS, but I'm sure it hadn't been tuned for a while.
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Old 02-27-22, 01:08 PM
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I like using off-center rims which reduce the dishing. I'm not sure about the entire physics on the rims. Torsional? But they seem to work well.

There are a number available.

Velocity
Aerohead OC (discontinued)
A23 OC

DT Swiss
RR411 Asymmetric (and probably a few other models).

I've used 9s with 126mm spacing and the Aerohead OC rims.
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Old 02-27-22, 01:30 PM
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Thanks, but I'm using the Mavic MA2s, I like the look and they're also almost the correct period (1986) for my 1982 Holdsworth.
I also got them for £47 on Ebay (with the hubs).

I've set up a spreadsheet to calculate the hub flange to middle distances from hands on measurements of the hubs,
according to that I could get to 36.6 / 17.6 (127.08 OLD) if I don't use the small cog.

If I knew how to calculate the 44% I could add that in and make a proper judgement.
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Old 02-27-22, 01:38 PM
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Simple trig. Call the spoke length L. Flange distance to CL, drive-side d1. Flange distance to non-drive-side d2. Angle of drive-side spoke alpha, non-drive-side beta.

Now, the forces. The horizontal side force at the rim but be equal from the two spokes. Call drive-side tension A. Non-drive-side tension B. The horizontal component of the spoke tension is cosign of the spoke angle X the tension.

So: We know A X cos (alpha) = B X cos (beta)
From trig: alpha = arctan (L/d1) = arctan ( 300/16.6) = 86.8 degrees. Likewise, beta = 82.9 degrees.

Hence B = A X cos (alpha) / cos (beta). Plug in the numbers and get B = A X 0.44

The end result isn't strongly affected by the exact spoke length. Yes I ignored nipple depth, spoke insertion and that drive and non-drive lengths are different. Real world - answers within say 10% work just fine here unless satisfying OCD is required.
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Old 02-27-22, 01:41 PM
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Doing a half-radial lacing would do a lot towards equalizing the DS/NDS tension.

Further removing every other radial is known as "triplet" lacing & will even the tension even further.
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Old 02-27-22, 01:52 PM
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Yay, many thanks, I can follow that.

Now I've just got to decide what tension to use, Mavic said 70-90 kgf apparently.
But my Mavic Monthlery Route (36 hole) were 61-66 DS and 33-44 NDS when I bought the bike and they are working just fine.
Since I'm respoking the MA2s from scratch I'll probably go for 90kgf max DS (currently 85.8 max).

What's the reasoning about setting a minimum tension for NDS ?
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Old 02-27-22, 01:54 PM
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Originally Posted by Aardwolf View Post
Thanks for the reply,
How did you work out the 44% number ?..
spocalc
https://www.sheldonbrown.com/rinard/spocalc.htm
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Old 02-27-22, 04:23 PM
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Originally Posted by 79pmooney View Post
Simple trig. Call the spoke length L. Flange distance to CL, drive-side d1. Flange distance to non-drive-side d2. Angle of drive-side spoke alpha, non-drive-side beta.

Now, the forces. The horizontal side force at the rim but be equal from the two spokes. Call drive-side tension A. Non-drive-side tension B. The horizontal component of the spoke tension is cosign of the spoke angle X the tension.

So: We know A X cos (alpha) = B X cos (beta)
From trig: alpha = arctan (L/d1) = arctan ( 300/16.6) = 86.8 degrees. Likewise, beta = 82.9 degrees.

Hence B = A X cos (alpha) / cos (beta). Plug in the numbers and get B = A X 0.44

The end result isn't strongly affected by the exact spoke length. Yes I ignored nipple depth, spoke insertion and that drive and non-drive lengths are different. Real world - answers within say 10% work just fine here unless satisfying OCD is required.

I think I'm going to disagree slightly

B/A = cos (alpha) / cos (beta)

But the hypotenuse is the spoke so cos (alpha) = d1/L, and cos (beta) = d2/L
OK the spokes are going to be very slightly different lengths.

So B/A = cos (alpha) / cos (beta) = d1 / d2 = 16.6 / 37.6 = 0.4415


Also I've just checked the spoke holes on the MA2s and they are offset by about 1mm from the centre, I'm going to measure the average tomorrow.
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Old 02-27-22, 05:07 PM
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Originally Posted by Aardwolf View Post
I think I'm going to disagree slightly

B/A = cos (alpha) / cos (beta)

But the hypotenuse is the spoke so cos (alpha) = d1/L, and cos (beta) = d2/L
OK the spokes are going to be very slightly different lengths.

So B/A = cos (alpha) / cos (beta) = d1 / d2 = 16.6 / 37.6 = 0.4415


Also I've just checked the spoke holes on the MA2s and they are offset by about 1mm from the centre, I'm going to measure the average tomorrow.
No arguments here. But it would have taken another hour to refresh my nearly 70 yo brain with that 50 yo trig stuff. Had I been rigorous, I'd have gotten your number. Instead I got .4443. Diff = .0028 or 0.6% I said I was happy withing 10%; this being wheel spoking and not rocket science.
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Old 02-27-22, 05:17 PM
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Originally Posted by Aardwolf View Post
....What's the reasoning about setting a minimum tension for NDS ?
Under sever pedaling/braking 1/2 your spokes get "loaded" and 1/2 get "unloaded". IF tension is already low, the unloaded spokes can have nipples start to unscrew and spokes loosen.
I use linseed oil, but you need heat/warm weather to make it set up within a reasonable time.
With your low NDS tension, I'd use some type of thread prep/locker. Green Loktite may be suitable? You want something "gentle".
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Old 02-27-22, 07:38 PM
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Originally Posted by Aardwolf View Post
........Also I've just checked the spoke holes on the MA2s and they are offset by about 1mm from the centre, I'm going to measure the average tomorrow.
Unless you have a disc brake front, you wouldn't want any offset there.
In my limited experience, the offsets I've seen are 2.5mm for road wheels & 4mm for a 559mm. (Velocity Synergy)
1mm would hardly be noticed unless one was paying attention.
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Old 02-27-22, 09:53 PM
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One thing... when I moved to 9s on the old Colnago, it was pretty quick to discover my derailleur hanger was bent.

After straightening the hanger, it leaves the rear derailleur mighty close to the spokes.
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Old 02-27-22, 11:09 PM
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This is not in response to the safe amount of dishing, but it does relate to trying to get a 130mm FH close to 126mm.

Having 2 126mm Cannondales and a 126mm Specialized Allez Epic, I am a bit familiar with miamijim's 10 Speed Success thread.

I think miamijim used a DA FH-7403 hub. I don't know the specs of your RX-100 freehub. I've used an FH-7700 to get it down from 130mm.

I didn't read all the responses since they were really dealing with dishing and not getting the hub to 126mm. In my experience the goal is between 127mm and 128mm. I see you have calculated a 127mm width. Obviously you don't want to spread your rear dropouts, although I would be inclined to go to 127mm if I felt it would result in a better final result. But inserting a 128mm OLD hub into 126mm should work since mfg's were making 128mm dropouts in the late 80's to accept 130mm OLD hubs.

In my own project, I bought .1mm, .2mm, and ,3mm stainless 10mm shim washers. This helps top dial in the DS spacing to get the best cassette to dropout distance to pick up whatever real estate was possible.

I also did something miamijim didn't try. I used a freehub with a thick freehub body flange and used a body with a thin body flange. The result is a freehub body that sits deeper in the freehub. I needed about .8mm of shim washers to get me about 1.5mm of clearance between the last cassette cog and the spokes.


For me the name of the game was finding whatever excess space I could capture on the DS. If I can get 1+mm, then I only needed less than 2mm from the NDS to get to 127mm. Redishing less than 1mm seemed to be of little consequence to me.

Finally, if I had a steel frame that I wanted to keep pretty much intact and needed 1mm more width to make me feel better, I set the frame at 127mm. There would be no issue with someone going back to a 126mm with a freewheel.

John
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Old 02-28-22, 04:38 AM
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Thanks for the comments everybody,

Yep I'm trying to stick to around 127 OLD max: it's to go on a 1982 Holdsworth (12 speed) and I've measured the dropouts at 125mm but it's obviously meant to be 126.
I didn't know there were 0.1mm shim washers, but ebay has 0.1 and 0.25 I've already got 0.5mm axle spacers.

This is my first go at wheel building so it's almost certain to go wrong somewhere, but I've already got some tubular wheels that work fine so I can always fix it.
It's also my first look at freehubs and cassettes, so I'm actually quite lucky that the rims came with RX100 8 speed hubs as they seem decent quality and about right for
what I'm trying. I tried fitting a 7 speed freewheel on my tubular rims but could only get 6 to fit so 8 would be a nice since I'm an old git and I need help on the hills.

I measured the spoke hole offset at an average of 0.79mm from the centre line, the way spokes are laced that increases the NDS/DS difference very slightly.
And here's the results:




As bought the wheel (at 130 OLD) had average tension at 73.86 / 40.39 kgf so I'm thinking go with row 12 (126.58 OLD, 90/38 kgf) and see what happens.
(I've tried a few 'dry' builds and the measured OLD is slightly more than my plans).

Edit: Obviously the NDS tension column has an errant "/100" in there

Last edited by Aardwolf; 02-28-22 at 05:38 AM. Reason: booboo
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Old 02-28-22, 12:31 PM
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I built up a wheel for a friend who is 225 pounds and strong as an ox. The original wheel had a Power Tap hub and Mavic Open Pro rim. He cracked the rim through spoke holes and along the edge of it. I rebuilt the wheel with an Open Pro rim, and he destroyed it also. I obtained an Open Sport rim (more al. ergo a little stronger) and rebuilt the wheel. Now he was breaking NDS nipples and spokes. Because of the offset of the hub the NDS spokes were low on tension. I replaced the broken parts and raised the tension on the DS to about 130kG and that solved the problem.
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