Wheelcalc let me down
 

I have used Wheelcalc for determining spoke lengths for years and it had never let me down..........until now.
I plugged in all the pertinent data for some touring wheels and ordered the resultant lengths of spokes.
The are all about 2mm too short! (I did round down all decimals after researching.)
I laced the front wheel and, though I am not fully tensioned as of yet, there are about 3 threads showing at the nipple.
I tried another program on the web using the same criteria and it gave me lengths that appear to be more appropriate.
What a bummer!! (Not to mention the $$$$ down the tubes.) Ah, well, more inventory.
I may be able to use the NDS spokes on the DS of the rear wheel, but that's about it.
I guess I'll just get the longer lengths.
I fear that. since the spokes don't make it all the way to or near the top of the nipples that I may wind up breaking nipples.
I don't want to risk that on a loaded touring bike.

What spoke calculators do y'all find most consistently accurate?

I use spocalc and round up a bit.

Measuring my own ERD's and hub dimensions and using the spoke calculator on QBP's site although I think you have to have an account to get to it.

Don't blame Wheelcalc for what is almost certainly an example of GIGO.

Spoke length calculators don't have minds, moods or whims. They NEVER deviate form being simple calculators running a simple formula. All spoke calculators use the same basic formula, with some variation among the various programs to account for the small fudges such as the allowance for the extra length needed for the over/under lacing at the crosses, or for the 1mm difference between the hub's on-center spoke circle measurement vs. the inside elbow measurement of spokes.

So while various calculators will give slightly different results the same calculator is 100% bulletproof reliable IF proper and consistent data is entered. This is why most wheelbuilders will always use the same calculator. Once they build a wheel or two, they know which way to round, or otherwise tweak the calculated length to get the results they prefer every time.

So when a calculator gives a wrong answer to someone used to it, then the only source to the error if wrong data entered. This can be as simple as calculating 2x and building 3x, or most commonly the result of using published specs. for the rim's ERD instead of an actual measurement. Measured or from a spec, remember that the calculator's answer will have the spokes end at the ERD entered, so it's critical to allow for the nipple when entering the data, or add 2-3mm to the result to correct if the rim's actual diameter at the spoke hole was used.

BTW- spoke calculations are also prone to error from typo's, of forgetting to change the flange diameter when switching front to rear on pairs, so check your work before simply accepting the results and lacing a wheel.

Hmm,
First, the "garbage" I have put in previously has yielded "garbage out" that has always been spot-on.
I have also done several wheels using the same Dyad rims and the same ERD for then and never had a problem.

Second, as I put the IDENTICAL "garbage in" to two different programs, why would I get such different "garbage out?"

Hi,

Is it possible to adopt a different spoking pattern they are the right length with ?

rgds, sreten.

You said you've used wheelcalc in the past, so wheelcalc calculations will be consistent, since the same math is used every time. I explained how various calculators tweak or don't tweak results with correction factors (opinion of the programmer) for cross, on-center vs. inside elbow, or even some nipple height assumptions.

But the same calculator will give the same results for the same data every time, and will give consistent results for any set of data. It's a calculator, it runs the same formula based on the info you feed it, and doesn't have moods or whims. Of course if you're depending on it's internal database for dimensional data such as ERD, that's always subject to a data error in the database, or the rim's spec change over time (not that uncommon).

If you used the same program in the past and want to know where it (you) went wrong, re-enter the data set for the wheels, and if you get the same wrong answer, check the data against the actual measurements. Also take a moment to measure that the spokes are the lengths you think they are.

Of course, you can skip that and assume the calculator has some random whims programmed, or caught a cold.

It's a definite possiblity. The second most common source of error, is not building to the calculated cross pattern. (the first is wrong data, usually the rim's ERD).

However the OP is convinced that it's not him, but the calculator that erred. It could be neither, with the spoke vendor having sent the wrong spokes. But the OP will never know unless he checks everything.

In answer to his original question as to which calculator is most consistent, they are all equal at 100% consistency. However the databases vary in reliability and there I'd say MrRabbit's is the one I'd trust most since he goes to great lengths to find and correct errors. However I don't trust any database and measure everything myself. That way if anything goes wrong I know exactly who to blame.

I have discovered one anomaly:
WheelCalc utilizes a flange to center measurement.
Pro Wheelbuilder Spoke Length Calculator utilized a flange to locknut measurement.
If I use the same dimension for those two different dimensions, the resulting spolke length is much closer, even though inappropriate.
If I put in the dimensions which the program requests, the spoke lengths are much different.
Time to quadruple check in order to find my (other) error.
I have "learned" more than one thing today (although one of those I already knew).........
[h=2][/h]

Ok, dumb question, but have you measured the spokes to verify they are the desired (ordered) length?

I have a ParkTool USA Spoke Length Gauge (NOIBN) and have verified that the received spokes are exactly as marked, at least to the precision possible using that tool and the best of my ability (disclaimer) and are exactly as ordered.

I do have a pair of Velocity Cliff Hangers that have a smaller ERD (advertised 591 vs. 596 for the Dyads) and could use those, but I just think I will get longer spokes.

For the record, IMO (disclaimer, again) there is NO such thing as asking a dumb question.
The only dumb question is the one not asked...

Ronno,

Just to give you some added insight, changes in center to flange distance affect spoke length on a roughly 10:1 ratio. For every 10mm change in CTF distance you'll get 1mm of spoke length change.

Rim ERD changes are 1:1 with spoke length, and changes in cross typically add/subtract 3-5mm but this varies with flange size and the number of crosses.

Hub spoke circle changes spoke length differently depending on the amount of crosses, ranging from zero on a full tangent (36h/4x, 28h/3x, 20h/2x) to 1:1 for radial pattern. On a typical 3x build the change is roughly 1mm less spoke length for every 3mm more of spoke circle change)

Most cases of error as large as yours are either ERD errors because of entry or database error, or building one cross more or less than what was used in the calculation.

You can also get issues if the flanges are built out of phase, but this won't be uniform, and you'll see a classic hi/low effect on alternating spokes on the same flange (or both flanges producing a hi-hi-lo-lo pattern). I'm assuming this is not your problem since you describe the spokes as uniformly short.

Thank you for that information.
Initially I used dimensions given on the manufacturers' websites for the hubs and the rims.
However, I physically measured and verified the hub dimensions before ordering spokes.
I did NOT verify the rim ERD, choosing to rely on the manufacturer's information as well as that
provided by Peter White on his website. And, as I have used this rim in earlier builds without incident,
I chose to use Velocity's number. If that is the error, then my apologies to Machinehead Software and everyone else.
If the rim is that much larger, I will probably not get a tire on it!
But, that still would not explain the differences among spoke length calculator programs.
Of the several I have tried, the majority seem to hit on or around a number 1mm longer (give or take) than Wheelcalc's figure,
but shorter than that derived using Pro Wheel Builder's program.

I have rechecked the build of the front wheel, and have verified the number of crosses (errors in that regard would result in a non-buildable wheel,as spoke length deltas required for alternate # of crosses are far greater than 2-3mm) and I have verified that the stagger pattern between hub flanges has been correctly laced.
I am not above making mistakes,nor admitting to them as I have made many. But the lacing of this wheel is not one of them.

Dunno.

You're first and possibly only mistake is trusting a spec. ERD rather than measuring for yourself. I'm not a fan of published ERD specs. because they include an assumption about the nipple's dimensions, and the builders preferred final height in the nipple. This makes it like the Newlywed Game, where you have to guess what the person publishing the spec thinks you're going to do.

I much prefer having the actual rim diameter at the nipple seat which the rim maker can know for a fact, and which anyone later can prove right or wrong. That lets the builder make his own adjustment for nipple height and be in control of his destiny without guessing what assumptions anyone else might have made.

As to why differing calculators have different answers (within 1-2mm) for the same data, that, as I explained earlier< is because of various little adjustments that are not part of the basic formula.

1- difference between spoke hole center and rim, about 1mm
2- allowance for flange thickness and extra length needed for over/under lace at crosses, about 1mm
3- allowance for spoke elongation, and straightening of elbows at full tension, about 1mm
4- settling of eyelets, nipples or rim itself (distortion) at spoke holes, 0-1mm depending on the rim
5- differences in opinion about the allowance for error (aim high, or low), effects of rounding, and compensation for ERD values vs ideal height in nipple.

Throw all these into the hopper, and various calculators will yield answers ±2mm from each other (maybe a bit more). Unfortuantely most calculators don't tell you their final adjustments, but if you use the same calculator each time you'll know what to expect and can compensate accurately.

The big issue remains the published ERD data for rims, and my recommendation to everybody is to trust nobody on this and measure your own every time.

The calculators are reliable and consistent, but depend on the quality and consistency of the data you feed them.

BSD & ERD are entirely different numbers.

Yessirree, I understand that.
I would have to conclude that, if it is believed given that the extrusion itself has not been altered by the manufacturer, if the ERD is significantly larger the resulting BSD would be also.
However, I guess that is,again, making a supposition that may not be accurate.
For example: if one DYAD had an ERD of 596mm, that is no guarantee that another one will as well..

A couple of visible threads is only a cosmetic problem, not a structural problem. If you use standard 12 mm nipples, and the threads protrude 0.5-1.0 mm below the shank, there will still be around 7 mm thread engagement instead of 9 mm. Nothing to worry about.

A cheap way to fix it is to buy longer nipples. Assuming you are using std. 12 mm nipples, you can just substitute them with standard 14 mm or 16 mm DT Swiss brass nipples to counteract the slightly short spokes. A 14 mm DT Swiss nipple will effectively elongate the spoke by 1 mm, and 16 mm nipple by 2 mm. Notice that because the internal thread on such a nipple is lowered by eg. 1 mm, the spoke shouldn't be flush with the top of the nipple, but should also stop 1 mm below.

Why your spoke calculator gives a different output than other programs can be difficult to say. I always use the "spocalc lite" spreadsheet because it is open source and has been peer reviewed by people who knows their stuff. I won't rely "black box" software that gives out a magic set of numbers.

Some spoke calculators automatically subtract 0.5 mm to compensate for rim compression and spoke elongation under tension, other don't. Some compensate automatically for staggered spoke holes, others don't. DT Swiss's online spoke calculator wrongly subtract 2 mm from spoke length when using 14 mm nipples instead of 1 mm. (hopefully corrected by now). Most rim and hub databases are full of errors, and even manufacturer homepages often give wrong ERD number for rims. ERD, unlike "spoke seat diameter" (Mavic), isn't a number one can derive from the rim alone.

The "ERD" is the point you wish to terminate you spoke*, and that point is usually where the spoke end is flush with the top of the nipple, but that point depends on the length and shape of the nipple. So the ERD changes whether you are using 12 mm or 16 mm DT Swiss nipples. There is some convention, that the ERD is measured with std. 12 mm nipples, but I don't think there exist anything like a fixed definition for what ERD exactly is and how to measure it. I know of at least three competing definitions of ERD, so the ERD that the manufacturer gives out, may be different than the one your program uses.

It is all a bit of a mess, so personally I only count on ERD's I have measured myself. What is really needed is community database project where people can submit hub and rim measurements according to certain, defined standards.


*For one definition of ERD. The correct one as I understand it.

I appreciate the information.
Thread engagement is indeed way more than adequate, but I have read of nipples popping at the base of the head.
This can be attributed to the spoke not threading all the way up into the head, causing a stress point at that location,
especially if that is the point where the nipple contacts the rim. That would not be affected by nipple length.
As these wheels are intended for a loaded touring bike, and I am a big guy, I want to alleviate that possibility.
But, now I need to understand how to measure ERD for future reference. This go round I can just add 2 or 3mm to the spoke lengths.
I guess I need to assemble the rear wheel using the spokes I have just to verify. I'll put compound on then anyway, just in case ;-)

Nipples may break if not engaged through to the head, but only alloy nipples in my experience. I've never seen this occur with brass nipples - one reason I use brass on my own wheels, to allow for spoke lengths to be guessed out of my inventory and +/- 2mm.

- Joel

Absolutely correct, the only threads that count and provide 100% nipple strength are those engaged in the nipple head. 2mm engagement there, which is typically up to the bottom of the slot achieves that goal. Any more is margin for error.

ERD is the diameter at the desired end of the spoke. For a typical nipple it'll be about 5mm more (2x 2.5mm thread engagement in the head) than the actual diameter at the base of the hole, ie. top of the eyelet where the nipple sits. There are a few ways to handle this. Measure all your rims to the spoke holes, and calculate to there, then add enough for nipple head when rounding or tweaking to the desired spoke length. Or measure to the base of the spoke hole, and add 5-6mm for two nipples before calculating, or put two nipples at opposite ends, and measure ERD directly to the base of the screw slot.

The first is how I measure so I have all my adjustments in place together. Those who make DIY rim rods, to masure rims usually use the last method, building the nipple into their calibration.

Whatever method you use is fine so long as you remember that the calculator result will bring the spoke out close to the ERD you entered in the first place.

While breakage is less common with brass nipples, it's anything but rare. Catastrophic multiple nipple failure leading to wheel collapse and injuries was one of the common types of mechanical failures that led the CPSC to take a closer look and ultimately regulate bicycles 40 years ago.

http://bikeforums.net/attachment.php...hmentid=325143I have seen that claim too, but I am pretty sure it is just an speculative urban myth. As explained, every 14 mm DT Swiss has an ideal spoke termination length 1 mm below the top of the nipple (just like an 12 mm nipple with 1 mm too short spokes), I have never heard of anything like stress cracks in 14 mm nipples. Considering that Mavic recommend 14 mm nipples for their popular and widely used CXP 33 rim, there should be loads of problems with that rim, but I have never seen anything. Been using that rim for almost a decade on several wheelset, and never had a problem, even when using +140kgf spoke tension.

I also can't visualise what forces that could wiggle a spoke inside a nipple on a tensioned wheel; either just the spoke would flex from lateral stress, or the nipple and spoke would move together. So I don't believe in neither stress points at the spoke end, nor in nipples popping off because they only had 7 mm instead of 9 mm thread engagement.

Anyway, 16 mm would give full 9 mm thread engagement for spokes 2 mm too short, and saves a relacing and new spokes.


Roger Musson, author of the instructive "The Professional Guide to Wheel Building" has instructions on how to measure ERD and build the tool to do it:
Check this pdf from chapter eight from his book:
http://www.wheelpro.co.uk/spokecalc/calc-measure.pdf
(IMHO his book is worth buying too)

Basically you take two spokes, cut them so they are 200 mm long each. Glue on a nipple on each so the spoke end are flush with the top of the nipple.
You put each "measuring spoke" in opposite spoke holes in the rim, and use a ruler to measure the the distance between the two spokes.
The entire distance between the two spoke ends are the ERD (2x200 mm+ruler distance=ERD)

Put that measured ERD number into Jobst Brandt equation, or a program that uses it like "spocalc", and you will get a correct "raw" spoke length. Round it down 0.3-0.5mm to compensate for spoke elongation and rim compression.

Ronno6

Bottom line - it's always best to measure your own ERD's - even for the same rim.

See my spreadsheet at:

http://www.mrrabbit.net/wheelsbyflemingapplications.php

Open "rimchart" tab...

Scroll down to Mavic section - and you'll see that the Open Pro varies all by itself quite a bit.

Hub changes as FB pointed out - relatively minor. ERD changes - deal killer.

=8-)

1. Glue = bad idea. In many cases, you need to remove the nipple to get rods into some double wall rims.

2. Nipples are set to builders preferences - often driven by thread length, nipple size and type - and MAX / MIN insertion behavior.

There's is no one positional reference for ERD - ERD refers to the distance between the ends of spokes in an already built wheel.

=8-)

Why cut spokes.
Just buy a few pairs of appropriate lengths.
I get my spokes at coloradocyclist.com, by the spoke and just ordered extra pairs of 265's & 290's to cover anything I expect to deal with.