When are spokes too short?
 

Newby question... Yeah, I know if the spokes don't reach the rim they're too short... Here's my story:
I bought a bike off ebay. Among other problems (which have been settled with the seller) when I
took the bike to my lbs to check the true & tension of the wheels they were quite PO'd at the quality
of build on the wheels (I'm a clyde- ~300# - and I worry about wheels). Almost every spoke (way
over half) had 3-4 threads showing before going into the spoke nipple. The seller says they are fine
'cuase he trued the wheels himself and he's a "professional bike mechanic". I don't want to get into
the quality of lbs work here, I just want to know if the wheels are safe. They are true, my lbs says
they won't last , the seller says they are fine.
I will be getting different wheels but would like to ride these till the budget is a little better. So are
they safe enough to use short term? Or should I not trust them at all? TIA.....

Oh yeah... they are the wheels from a 1987 TREK 560, i.e. Matrix rims, 32 hole Sansin (sp?) hubs. I'm
not sure if the spokes are original.

You mean they have 3-4 threads sticking out of the nipple (on the un-tensioned side)? No problem with that. Any threads sticking out of the nipple are useless, assuming that the wheel is properly tensioned.

If you mean on the tensioned side, that is also fine, assuming that the nipple threads are all fully engaged. (Could that be what your LBS was *****ing about?)

I'd ride the wheels. What's the worst that can happen, a broken spoke or two?

With the tire, tube, and rim strip (tape) removed. Look to see where the end on the spokes are relative to the end of the nipples. This is where you may have an issue with the builder. This is what DMF is calling the un-tensioned side. All or at least most of the nipple threads should be engaged.
If this is a rear wheel all of the spokes on either side of the wheel should have the same thread engagement. But if the spoke engagement on the right side (drive side) is different from the left side that may be OK. Due to the rear wheel being asymmetrical on most bikes to make room for the cassette or freewheel the drive side spokes are shorter and with more tension. Ideally the spoke engagement on both sides should be the same but some differences may be acceptable.

Al

They will be fine, now get out there and ride.

Thanks for the quick replies. The threads are towards the hub and have about the same amount of threads showing on both sides of both wheels. I haven't removed the tire and tubes yet, but will inspect the spoke length before using them.

Look at the screwdriver flat portion of the nipples:

1. If spoke end has passed it - result = ok
2. If spoke end has reached the flat - result = ok
3. If spoke end has come up to within a millimeter of the flat - result = ok

...however...

4. If spoke end is 2mm, 3mm, or 4mm short of the flat - result = not good.

2mm is a judgement call...bottom line is that the spoke isn't penetrating the rim wall enough...and in those cases where the spoke end is only reaching the inner edge of the rim wall or even shorter - the nipples are being relied upon to act as spokes which is not what they were designed for. They will eventually suffer from barrel separation leaving the head inside the rim.

=8-)

3-4 threads is not a terrible concern, but it means fewer threads are engaged in the nipple. As mentioned above, it's not a safety issue. You might have a spoke pull out of the nipple and have to either replace it or scrap the wheels, but they're not all going to fail at the same time and take you down or anything. If you want, you can have them rebuilt with nipples that are 2mm longer. I would feel safer with that (and that's what I did with a recent build where the spokes came up a little short), but I've seen wheels with a few threads showing hold up just fine for a long time.

Longer nipples just hides the problem. It doesn't provide more threads for engagement.

Maybe there's a difference between different manufacturers, and maybe even in nipple versions - but current versions of DT nipples will most certainly have the threads beginning closer towards the hub when you switch to a longer nipple.

....Which of course is a moot point if you share mrrabbits belief that a nipple will be significantly weakened unless the spoke continue well into the nipple's flange.

The issue with spokes isn't thread engagement, or whether threads show at the end of the nipple. The issue is that except for the steel nipples used on dime store bikes, the nipple itself doesn't have structural strength comparable to the spokes.

Think of a nipple as a nut with an extension tube for access from the inside (hud side) of the wheel. The spoke must extend into the head (nut) of the nipple to ensure that the system is as strong as the spoke itself. Ideally the spoke should extend into the head by an amount equal to the diameter of the spoke. It's no accident that spoke nipple heads like most other nuts are about as thick as the screw they're made for.

As dabac said, there are in fact more threads, but you're still right that it doesn't address the real issue, which is that the spokes should reach the head of the nipple. I checked my build with a flashlight and they are barely in there. My choice to go with longer nipples was purelyaesthetic (the 1-2 exposed threads are unsightly to me), but had the build been for anybody except myself (a 160 lb guy with little leg power). Had the wheels been for anyone except myself (160 lb with little leg power), I would have ordered longer spokes just to make sure they came all the way through the nipple heads.

I'm a clyde too and I personally would be concerned with spoke engagement. Until I learned to pay attention to these details that seem mundane to lighter riders, I had spoke breakage issues. At ~#300, I would want the wheels as strong as I could. That being said, you will probably not see a catastrophic failure if and when they should break. You most likely would break one or two and need a ride home.

As far as the seller saying that they are fine, I would take that with a grain of salt. He has a vested interest in that answer. He may also not see this from the clyde perspective.

It seems obvious that more thread engagement would make nipple failure less likely... but I propose their are three distinct possibilities for spoke engagement in the threads of the nipple - 1. The spoke does not reach the end of the wrench-flats-area (nipple has the smallest cross-section area there, and so is least able to withstand force); 2. The spoke reaches beyond the wrench-flats but not to the increased diameter at the entrance to the rim (larger cross-sectional area); 3. The spoke threads in to the large head of the nipple (largest cross-sectional area).

Obviously the third possiblity is the ideal scenario. From experience I know that possiblity #2 most often results in a reliable wheel. The third possibility is less common, as most people who built a wheel with a whole lot of threads showing would see it as an abvious mistake and fix it, but one or two threads showing is debatable.

^ Mine fall in scenerio #2 (actually they reach the expanded portion, but not really into the head). Like I said, I'm not afraid to ride it and don't expect any problems, but I wouldn't let them go to customers except for scenerio #3.

edit: Actually, looking at the longer nipples, the expanded portion comes down further as well. So you do get some strength benefit from them. However, the head of the nipple is the largest section, and spokes that are too short might not reach that at all.