Spoke length woes

[Duroon]

I am really new to building my own wheels and having a bit of a dilemma. I downloaded the spocalc excel spreadsheet from http://www.sheldonbrown.com/rinard/spocalc.htm and according to my measurements and its calculations my '74 Varsity's rear wheels should be using 298mm spokes on the left and 296mm spokes on the right (drive side).

I went to my local bike shop and asked for these spokes, he told me that if it were him he would just use 295mm on both sides, you only need two different sizes if the wheel is being built by a machine instead of by hand. If that is the case why do I need spocalc to figure out two different sized spokes? I had previously built this wheel with spokes he had given me (turns out they were 300mm) and I ended up having to file down all the drive side spokes inside the rim as they were too long. I got the wheel built and dished, even rode the bike around quite a bit on the wheel, having to file down so much of those spokes was nagging me though, I felt that the drive side might be weaker due to having too few threads, so I took it apart and went to measuring with a set of calipers.

So the question is, do I really need two spoke length's that are all of 2mm difference from each other to build this rear wheel?

[DaveM]

You can probably get away with using the same size if there is only a 2mm difference (though I would use 297's or 298's, not 295's).
the problem with using too long a spoke is that even if you file off the extra, you no longer have complete thread engagement between the spoke and nipple so you get a weak point. But being 1-2mm off on a wheel with 32+ spokes shouldn't be an issue.

I assume there's a price issue with buying 16 of each size versus 32 of a single size?

[Duroon]

There is no price difference between the two sizes of spokes, I just want to make sure I am building the wheel properly. It is a 36 spoke rear wheel and when I built it before with the 300mm spokes I ended up having to file off close to 4mm from each drive side spoke, I am pretty sure I had some other issues with the build as I ended up with some low and high spots when I finally had it true from side to side. I have a truing stand coming (a Park TS 2.2) this week that I had to order from Performance Bike's website as my local bike shop (a Park tool distributor) didn't want to sell me one, along with several other tools he has told me I don't need over the past couple of years.

[DaveM]

Taking out high and low spots is a normal part of lacing, so it doesn't indicate a problem with the spokes or how you laced it.

4mm too long is definitely getting into the questionable range. I can't verify your length calculation, but if 300 was about 4 too long, 296 should be right. If there's no price issue, get the right sizes. Pretty much any multi-speed wheel should have longer spokes on the non-drive side. No reason to fudge if you don't have to.

[Duroon]

I was fairly certain the high and low spots came about during my attempts to true the wheel without having much experience or a truing stand to work with. It is also possible that I would not have had to file off as much of the drive side spokes if I had gotten the wheel properly true before adding tension (I didn't do this step correctly I am sure). Regardless my measurements are as follows;

ERD = 622mm
Flange diameter = 62.5mm (both sides)
OLD = 125mm
Lock nut to flange left side = 24mm (making WL = 38.5mm)
Lock nut to flange right side = 46mm (WR = 16.5mm)
Spoke hole size is 2.6mm

[nfmisso]

Hi Duroon;

Get the correct lenght spokes. I have built a few wheels, and have always followed SPOCALC; and it always worked correctly.

Also; I always use Wheelsmith spokes after reading Peter White's site: http://www.peterwhitecycles.com/spokes.asp

[Duroon]

Thanks for the link to that article, I am looking at getting some Wheelsmith spokes, my local shop doesn't carry them but I can get them online for $23 per box of 50.

[nfmisso]

I purchase most of my Wheelsmith spokes from an eBay person in Arizona, and only purchase what I need. He does not have DH13 spokes, which I purchase custom cut for my lengths from Peter White.

$23 for a box of 50 is a good price, what do you do with the excess? Properly tensioned Wheelsmith spokes last a lifetime.....

[Duroon]

I don't do anything with the excess at this point, I am just getting in to wheel building. However I am working towards a career as a bicycle mechanic and have been doing volunteer work at the Community Cycling Center in Portland, OR. One of the jobs I am working towards there would involve me spending a good deal of time truing wheels that have been donated to the center. The center has programs for that give underprivileged kids bicycles during the holidays (around 500 a year are given out), teenagers and adults can also earn commuter bikes through their "build a commuter" program.

I am also in the process of refurbishing another old Schwinn that has an identical wheelset to my '74 Varsity, I could always relace that rear wheel as well.

[nfmisso]

That is great !!!

[Duroon]

My truing stand showed up yesterday, we built a workstand for it from scrap metal we had at my family business.

[attachment=2333]

Good thing one of my family members is a welder!

I got the rear wheel rebuilt today with the proper size spokes and it looks great, did take a minor bit of dishing but nowhere near what it took to build the first time out with the wrong size spokes! I also spent some time truing up three other wheels in between working on call all day. So far I think I am off to a good start at least!

[nfmisso]

Nice shop

[tgmmartin]

I know this is an old thread...
Correct me if I am wrong. But as long as you can get enough tension in the spokes before the nipples is wound to the end of the thread (ie can't do nipple up anymore) then there should be no problem. If the end of the spoke protudes through the end of the nipple and you grind some off this must mean that you have a lot of thread in the nipple (the most you could possibly have in fact).

[DaveM]

spoke thread are rolled instead of cut. This means that you can thread the nipple all the way on to a spoke and actually go past all the threads (it won't bottom out like a nut on a bolt.) So if you thread a nipple too far onto a spoke, there actually won't be that much thread engaged between the nipple and spoke and it could strip. If the spoke sticks out a mm or two, it's probably fine. But much more than that and you don't have good thread engagement between the two. Spokes that are too long or too short produce the exact same problem strength wise.

You can get longer than standard nipples that have more threads, this helps for too short spokes, but not too long. For too long, you can put washers under the nipples, but it doesn't gain you much.

[danny1962]

Duroon, I'm almost sure that you've used an incorrect ERD. Your result would be the correct one if your rim is really a 622 ERD, but I'll bet you it is smaller than that.

622 is the rim size, but this is not the same thing as an ERD, and ERD dimensions vary a lot even for wheels that are notionally the same size.

To get a "quick and dirty" approximation of your ERD with your tyres in place, simply put a tape measure between two opposite spokes. You won't get it to go straight, but this will give you a sanity check measure that you know the ERD cannot possibly exceed. Then run a string or about 2 metres of masking tape around the rim, with no kinks or stretching. Mark it, cut it, remove it, straighten it and measure it. That measurement is your circumference. Add a couple of mm to allow for the rim thickness. Then divide the result by 3.142 . The number you get should be less than the measurement you got with the tape measure. It will be a pretty reasonable approximation of your ERD. Once you know for sure the number is correct, record it.

Rim, wheel and tyre sizing is ever so confusing, and what doesn't help is that the dimensions that are expressed bear no relation to what the dimensions are in reality. There are some good internet sources (eg Sheldon Brown) if you wish to find out more. It's surprising how often forum posters can get ERD and rim size mixed up, so explore forums with care.

[danny1962]

Thinking more about this, the more precise description for that 622 number is the Bead Seat Diameter. This number is used for ensuring tyre compatibility between different rims. There is a very significant difference between Bead Seat Diameter and Effective Rim Diameter and these two dimensions must never be interchanged.

Imagine a rim viewed in section. The tyre does not sit right at the bottom of the rim, instead it sits on a ledge. There is a recess in the rim where the spokes are attached, and the Effective Rim Diameter is the diameter of this recess. You can therefore conclude that the Effective Rim Diameter must always be less than the Bead Seat Diameter. See this page for a diagram http://sheldonbrown.com/tire-sizing.html about a quarter of the way down the page.

If you did a spoke calculation using an ERD that is too high, your spokes will be too long. That's why you needed to shorten them.