Author Topic: Which lacing pattern, 2x or 3x for 20"(406) rims  (Read 722 times)

Which lacing pattern, 2x or 3x for 20"(406) rims
« on: July 04, 2019, 06:50:07 pm »
I will be building up my first 20" (406) wheels soonish.  The wheels will have 36 spokes.

The wheel pro spoke calculator comes up with

A spoke entry angle of 6.4 degrees for 2x
A spoke entry angle of 8.2 degrees for 3x

Should I opt to build 2X to deliver that lower spoke entry angle, build 3X with polyax nipples, or not worry about these values? 

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #1 on: July 04, 2019, 07:21:20 pm »
I would.
Never tell me the odds.

Kim

  • Timelord
Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #2 on: July 04, 2019, 07:22:53 pm »
I've always gone for 2x on 406 wheels, seems to work.
Careful, Kim. Your sarcasm's showing...

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #3 on: July 04, 2019, 07:38:06 pm »
not all rims are made equal in this respect and most can be adjusted/modified if needs be. It also makes a difference if you are building 28, 32 or 36 spoke wheels. Thus if you want an informed view you need to say more about what you are trying to do exactly including the likely service conditions of the wheels.


From the numbers you quote I'm guessing that you have a large flange hub; is this the case? What rims/hubs are you  using?

  In general when you reduce the number of spoke crossings you decrease the torsional stiffness of the wheel and increase the loading in the flanges; not every hub will work if it is used with radial spoking but the flange loads can be as bad with a tight build that is x2 on the gear side.

Note that in the wheelpro calculator the 'spoke entry angle' is not quite what it appears to be; it is the predicted angle in the wheel plane only (it does not vary with flange offset value, i.e. hub width). The actual angle is a compound angle which (in most wheels built with SF hubs) comprises mostly of an angle in an orthogonal plane, arising from the hub width rather than the flange diameter/spoke crossings. Even with a large flange hub built full tangent in an undished wheel, the contribution of the hub width to the compound angle is equal to that rising from the crossings/flange diameter.

Thus the wheelpro angles are stated as 8.2 degrees and  6.4 degrees for x3 and x2 respectively but using a typical LF hub, undished, the actual compound angles are  ~11.6 degrees and ~10.4 degrees respectively. Whether this is worth worrying about is entirely dependant on the rim; very few rims are exactly radially drilled and the relative effects of hub width and flange diameter/crossings are affected by quite small details in rim design.

cheers

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #4 on: July 04, 2019, 08:29:58 pm »
It will be a front wheel. Not super large hub. It's a Deore XT M756 Hub, and Sun CR18 rim.  Will be used for Audax / touring. They are for a new recumbent project. Min width tyres I be running on the wheel will be 28mm, not tubeless.  What else do you want / need to know?  They are for my own use.

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #5 on: July 04, 2019, 09:45:43 pm »
It is not widely known, this,  but IME eyeleted Sun CR18 falls into the category of 'tweakable rims' (which includes a lot of single and double eyelet rims)  such that if you fit a close-fitting mandrel into the eyelet and forcibly lean it in the right direction, you adjust the rim so that you can have spoke nipples which more easily sit in the rim at a slight angle.

If you tweak the rim thusly, you need to reset all 36 eyelets. Until you have done this a few times it is best to mark up the rim (using a marker pen) so that the correct direction of 'tweaking' is obvious. Otherwise you could do more harm than good. Obviously it is necessary for the mandrel to have a diameter that is at least slightly in excess of the nipples you intend to use, preferably a close fit in the rim eyelet (which in CR18 is about 4.35mm dia). Once adjusted, the eyelet allows the nipple more freedom to move through an angle before one side of the nipple lifts off its seating (which is what results in the kink/fatigue stresses). Possibly you could further adjust the eyelet by using drift to reshape the nipple seating too, but I've not bothered with that.

Another approach is to use concave washers (*) under each nipple; these can allow a larger articulation too. However in CR18 the space available is shallow, so this may impose extra constraints on the rim tape quality, because it will be almost certain that the rim tape will bear against the nipples directly.

(*) the seating washers from V brake blocks are not far off being right....

Anyway HB-M756 has pretty strong flanges and will work OK even built x2. But with a bit of rim tweaking etc you could build a x3 wheel and this will be even stronger.

cheers

LittleWheelsandBig

  • Whimsy Rider
Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #6 on: July 05, 2019, 07:44:49 am »
I only build my 406 wheels 0x, 1x or 2x for 28 spokes and have never had a broken flange. YMMV

36 spokes could be 2x or 3x but I prefer lower cross numbers for small wheels.
Wheel meet again, don't know where, don't know when...

Socks

  • FFCT rally, France 2012
Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #7 on: July 05, 2019, 08:59:45 am »
I have used 1x and 2x on 36 hole 406 wheels with no problems.  I wouldn't go more than 2x for reasons of spoke angle as already said.

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #8 on: July 05, 2019, 09:36:26 pm »
2x it is then.  Messing around with spoke holes isn't my thing.

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #9 on: July 05, 2019, 10:07:53 pm »
It's a front wheel.  You have to be pretty incompetent to build a bad front wheel.

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #10 on: July 05, 2019, 11:53:26 pm »
2x it is then.  Messing around with spoke holes isn't my thing.

It depends on the rim; the spokes go into the rim at a big angle anyway (which the misleading calculator you have used does not tell you) so it could be good or bad with a  x2 build.

IME the spoke angle arising from hub width is just as important as that arising from flange diameter when using a CR18 rim; this means that the  actual (compound) angle is only ~20% greater for a x3 build vs a x2 build, not nearly double as the calculator suggests. 

 It also means that the actual angle for a x2 build is about double the angle suggested by the calculator.

x2 is not a bad choice per se, but it is perhaps being made in this case for bad reasons; the angle calculation is cobblers and the decision not to address the root of the problem probably arises from something else that doesn't bear close scrutiny either.

Probably the wheel will work OK whether it is built x2 or x3; most wheels that not just thrown together don't just fall apart. But -as is often the case when wheelbuilding-  you have the  opportunity to build a first-class wheel here (rather than a second-rate one) for just a small amount of extra effort. 

cheers

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #11 on: July 06, 2019, 07:55:44 am »
It is not widely known, this,  but IME eyeleted Sun CR18 falls into the category of 'tweakable rims' (which includes a lot of single and double eyelet rims)  such that if you fit a close-fitting mandrel into the eyelet and forcibly lean it in the right direction, you adjust the rim so that you can have spoke nipples which more easily sit in the rim at a slight angle.

If you tweak the rim thusly, you need to reset all 36 eyelets. Until you have done this a few times it is best to mark up the rim (using a marker pen) so that the correct direction of 'tweaking' is obvious. Otherwise you could do more harm than good.

You say that Brucey but you also say, as quoted above, that I could do more harm than good.

The spoke angle difference between 2x and 3x is 27% according to the calculator, 8.2 vs. 6.4 degrees.  Not sure where you got almost 100% or double the angle difference? The reason I asked about polyax nipples is that they say this, which implies the 3x angles might be ok. But you are dismissive of the angles quoted.

Quote
Polyax nipples re-align themselves within a rim hole up to 9 degrees in a radial direction and 6 deg in an axial direction, making for a much superior fit.

So I have a choice between building a perfectly good and strong wheel or trying to forcibly adjust the rim in some pursuit of perfection and potentially wrecking it. 

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #12 on: July 06, 2019, 09:14:40 am »
I explained previously why the angle calculation you have done  is misleading and what the spoke angles actually are (for an undished wheel; the angles are slightly different for a dished one).

 In the simplest terms a radial spoked wheel measures 'zero' for angle using the calculator you have used whereas it is obvious that the spokes must enter the rim at an angle because of the flange spacing (hub width). This matters with a CR 18 rim because the eyelets are set in a flat part of the extrusion and (apart from a slight stagger) the eyelets are set radially. In other words the spoke angles in both planes are equally important with this rim. 

  Having reset CR18 eyelets I would describe any risk of damage as 'small'.

cheers

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #13 on: July 06, 2019, 09:28:28 am »
Probably the wheel will work OK whether it is built x2 or x3

This is the best advice on this thread.

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #14 on: October 25, 2019, 01:02:48 pm »
ICE lace their 406 rear wheels 3X and their front wheels 2X.

After recently ovaling the SA hub on the front (deep pothole made a flat spot on the rim 2-3 spoke holes in length).

I built the new wheels 3X to give a more tangential pull from the spokes.

As an experiment I also rebuilt the ovaled hub 3X and it has made it round again!

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #15 on: October 25, 2019, 01:33:42 pm »
good point about the interaction of spoke tensions with brake hubs; if you have a flat spot or a bump in the rim and you try and take it out using spoke tension, the spoke tension will be variable. If the wheel is built near-tangent a brake drum won't be pulled out of round, but if it isn't, it will be.

You would have to be extremely unlucky to pull a hub out of round permanently but hitting a pothole; however uneven spoke tension can pull a drum out of round elastically, which is probably what has happened here.

cheers

Re: Which lacing pattern, 2x or 3x for 20"(406) rims
« Reply #16 on: October 28, 2019, 06:45:11 pm »
I'd say I was lucky!
I had to tease it back into shape/roundness with a vice to get it close enough to build the wheel and keep the spoke tension even-ish.


The  :demon: "pot hole" was at the bottom of a nice down hill on a bend, I hit it at about 30-35 mph and rolled the trike, twice! according to the spectators :o.
Evidently I was the second person to come off because of it that morning!
I was uninjured but it ripped my pannier bag. :'(
I did a quick (about 3/4 hr) rebuild at the roadside (loosened all the spokes, straightened the rim and re-tensioned/trued, sort of ;) ) then finished the "Sportive" slowly ;D.
But the brake was very grabby and locked the wheel if I used it.

Weirdly it didn't damage the tyre or puncture, even though the spokes were bowed at the flat spot.