Bicycle Mechanics - Measured ERD, but still wrong spoke length?

Sorry to add the myriads of posts regarding spoke lengths. I did a search, but didn't see anything specific to what I encountered.

I was attempting to lace the following:

Rim: Kinlin XR-300
Hub: Shimano Tiagra Rear Hub FH-4500 32h
3-cross both NDS and DS

Hub specs are as follows:
WL: 20.6
WR: 37.6
dL: 45
dR: 45

ERD for Kinlin XR-300 lists as: 577

I always want to double-check ERD myself when I receive the rim, especially as it can vary a bit from different size nipples. When measuring multiple spots on the using a 12mm nipple, my ERD came out to 581.

As a result, using spocalc with hub specs above, I got 282mm for drive side and 284mm non-drive side.

When attempting to lace with the above lengths, the spokes were too long (spokes went all the way through the nipples until there was no more threading). It seems like 280mm and 282mm would have sufficed, which would have been the lengths if I in fact used ERD 577.

Any idea where I went wrong in either my ERD measurement or use of spocalc?

Thanks everyone and Merry Christmas!

I use http://lenni.info/edd/ haven't had any issues with using either it's own data, or entering my own following the instructions.
with the info you have supplied, it gave



Hub
Shimano Tiagra FH-4500, rear


Rim
KinLin XR-300


Spokes
32


Crosses
3


Spoke length left
281.8 mm


Spoke length right
280.1 mm


Not sure where you are getting the 282mm & 284mm on spokecalc, as entering the data as you supplied gave me the same info as lenni to within .2 of a mm, which won't be noticed when building (although Lenni looks to have the opposite data for the L&R sides)



Front Wheel
Input Data
Output Data


N, total number of spokes
32
cross
left length
right length


ERD, effective rim diameter
577.0
0
265.6
267.4


OSB, offset spoke bed
0.0
1
267.4
269.3


WL, width from center to left flange
20.6
2
272.6
274.4


WR, width from center to right flange
37.6
3
280.2
282.0


dL, left flange diameter
45.0
4
288.9
290.6


dR, right flange diameter
45.0
3.00
280.2
282.0


S, spoke hole diameter
2.4





X, cross number (decimal allowed)(optional)
3.00





WL_effective = W + OSB

20.6




WR_effective = W - OSB

37.6






Did you alter anything else in the spokecalc data?

Found another calculator site, again gives the same 280/282, put your data in here to give the result below (again, some minor mismatches, but when rounded = 280/282mm)

http://www.prowheelbuilder.com/spokelengthcalculator/

Left spoke length: 282.8
Right spoke length: 281.2

So you used an ERD 4mm larger than the mfgrs spec and got spokes 2mm to long. That makes perfect sense, so I suspect that you somehow mismeasured the ERD. Is it possible that you factored the 2mm thickness of the nipple heads twice?

The other possibility is that you accidentally reduced the cross, oe calculted 3x, built 2x, but this usually causes a greater length error than 2mm.

I usually trust the manufacturer's measurement unless I have a reason to be suspicious of it. I'll usually try a few different calculators just to see if there are any significant differences. The DT calculator is the only one that's given me weird numbers (and oddly that was with a DT hub). I've used the Lenni calculator a few times and so far so good.

When in doubt I suck it up and take the rim to a shop, have them measure, and get spokes from them based on a calculation with that ERD. It's more expensive, but I'd rather spend some money at the LBS (not a bad thing to do once in a while anyway) than pay twice and lace a wheel twice.

When in doubt I suck it up and take the rim to a shop, have them measure, and get spokes from them based on a calculation with that ERD. It's more expensive, but I'd rather spend some money at the LBS (not a bad thing to do once in a while anyway) than pay twice and lace a wheel twice.

I take the opposite approach. I always measure everything for myself, and do so consistently. Then I always use the same spoke calculator because I know how much and which way the answers need to be fudged. If you do things the same way every time, you'll get consistent and reliable results.

I take the opposite approach. I always measure everything for myself, and do so consistently. Then I always use the same spoke calculator because I know how much and which way the answers need to be fudged. If you do things the same way every time, you'll get consistent and reliable results.

This is definitely the best way. I don't have a good way to measure ERD myself yet (comparing my DIY measurements to published ones confirms this).

As I mentioned in the other recent thread I just built my 13th wheel last night, so I would not consider myself experienced yet, nor do I have all the tools I'd like to have.

This is definitely the best way. I don't have a good way to measure ERD myself yet (comparing my DIY measurements to published ones confirms this).

One source of error is in the definition of ERD these days. Years ago we measured the rim diameter at the nipple seat. But sometime along the way Jobst Brandt defined (redefined) it to mean the diameter at the ends of the spokes. There's a difference of about 2mm (per side) because you want the spoke to end near the top of the nipple, or 2-3mm beyond the rim.

Most of the calculators use a formula which will have the spoke end at a diameter equal to the entered ERD, so you have a choice. Either allow for the head of the nipple and enter the ERD (as defined by JB) or do as I do, an measure the actual rim diameter and allow for the nipple at the end by adding 2-3mm to the computed spoke length.

Unfortunately there's no consistency here. Some manufactures publish the rim diameter (at the nipple seat) and others the ERD (RD + approx 5mm). Others might allow more or less for spoke engagement. Having to make an assumption about what the rim maker thought I might want for spoke engagement in the nipple makes the spec useless, which is why I don't bother with it.

Likewise some formulas add more or less to allow for nipple engagement, so if you don't know for sure who's doing what and by how much, you can end up with an answer that doesn't allow for nipple head engagement, or allows for twice.

BTW- this is an old and still running debate. Today most people are used to an ERD that allow for the nipple (don't ask me how much they allow) because that's been common since JB published his book. But many of us who were building wheels before JS's book, prefer actual measurements and prefer to make allowances ourselves because that way we know for sure what we're doing.

Thanks for the input guys. I know I could always count on these forums to give insight from experienced minds to help.

@jimc101, I got 282 and 284 mm spokes because I used 581 as my measured ERD and not the 577 provided by the mfg. Otherwise, I got same as you with 280 and 282 mm.

@FBinNY, I used the following to calculate ERD:

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/Wheels/MeasuringERD.jpg

I used two spokes per the diagram, but instead of measuring 200mm from the threaded end, I measured 250mm from the threaded end. I sharpie the 250mm mark on both sides of the spoke. I thread spokes on opposite ends of the rim with the spoke ending right at the top of each nipped. Pull the spokes together and measure the difference between my sharpie mark.

I measured this at 4-5 different points on the rim, and got 581 every time.

Thanks guys and Merry Christmas!




One source of error is in the definition of ERD these days. Years ago we measured the rim diameter at the nipple seat. But sometime along the way Jobst Brandt defined (redefined) it to mean the diameter at the ends of the spokes. There's a difference of about 2mm (per side) because you want the spoke to end near the top of the nipple, or 2-3mm beyond the rim.

Most of the calculators use a formula which will have the spoke end at a diameter equal to the entered ERD, so you have a choice. Either allow for the head of the nipple and enter the ERD (as defined by JB) or do as I do, an measure the actual rim diameter and allow for the nipple at the end by adding 2-3mm to the computed spoke length.

Unfortunately there's no consistency here. Some manufactures publish the rim diameter (at the nipple seat) and others the ERD (RD + approx 5mm). Others might allow more or less for spoke engagement. Having to make an assumption about what the rim maker thought I might want for spoke engagement in the nipple makes the spec useless, which is why I don't bother with it.

Likewise some formulas add more or less to allow for nipple engagement, so if you don't know for sure who's doing what and by how much, you can end up with an answer that doesn't allow for nipple head engagement, or allows for twice.

BTW- this is an old and still running debate. Today most people are used to an ERD that allow for the nipple (don't ask me how much they allow) because that's been common since JB published his book. But many of us who were building wheels before JS's book, prefer actual measurements and prefer to make allowances ourselves because that way we know for sure what we're doing.

So comparing to the drawing you added 1mm per spoke to your measurement, so that's 2mm. The other 2mm might be from the width of your mark or some other error.

When following someone else's methodology you must follow it exactly, unless you have very specific reasons for modifying it and understand the implications. In this case the instructions were based on the nipple ending shy of the top of the nipple, allowing some room for elongation under tension. By measuring from the top of the nipple you biasedthe calculation to the high side and eliminated the margin for error.

577 for the XR-300 aims for the screwdriver flat of a 12mm standard profile nipple.

It would appear the OP was aiming for the top of the nipple - using box threaded spokes with quality nipples - that usually means you run out of threads before you've reached the desired tension.

Next time OP, aim for the flat of a 12mm.

(Top was used way back in the 70s when 10m nipples were still around...very rarely will you see them - I only run into them when I do a tear down of an old wheel.)

=8-)

and back when 'tops' were used, you usually had to file down the spoke ends after truing a wheel. no fun at all until dremel tools became commonplace.

and back when 'tops' were used, you usually had to file down the spoke ends after truing a wheel. no fun at all until dremel tools became commonplace.

True if single wall - or using long threaded spokes and 10mm nipples in double wall toward the long side.

If you didn't make an effort to go higher than the screwdriver flat - you ran the risk of having threads showing on the barrel side when done.

I remember some of the tear downs being such that they were clearly built using long thread spokes (old school) and 10mm nipples where the excess spoke ends (quite a bit in many cases) were simply cut off with heavy duty wire cutter.

Watched an old timer do this once...back then with traditional box profile rims...it seemed a sure way to get the spoke length right every time for any one category of rim such as 700c.

Wouldn't surprise me if other old timers here on BF have seen this as well...

=8-)

while tubular rims were always doublewall, I don't think doublewall clincher rims were available until the mid 80s. My old Motobecane hanging in the garage, originally a tubular bike, still has 700c superchampion 'gentlemen' rims from the early 80s, and I'm not sure those are double wall, they were about the best rim you could get back then. Its been so long since I slapped any tires on that, that I can't remember offhand what they look like inside.

while tubular rims were always doublewall, I don't think doublewall clincher rims were available into the mid 80s. My old Motobecane hanging in the garage, originally a tubular bike, still has 700c mavic 'gentlemen' rims from the early 80s, and I'm not sure those are double wall, they were about the best rim you could get back then. Its been so long since I slapped any tires on that, that I can't remember offhand what they look like inside.

Mavic 700c models E and 3 go back to the mid seventies. Rigida also had similar double rims in the seventies. I'd guess that other makers like Super Champion, and Ambrosio brought out their versions soon after. (if not first)

and eeek, my 'gentlemen' rims are superchampion, not mavic.

Well, (seat-of-the-pants flying ) if you built up the wheel, and it's not right,
you can see, where the error is,
spokes too long, or short.. and compensate that much.

Order a set of 280's and put the 282's on the left side. On Renard's Spokecalc I get 280 and 282. http://www.sheldonbrown.com/rinard/spocalc.htm