Too tight spokes causes wheel buckling.

[zerodish]

I've done this twice the first time was an experiment. The arguments never end about tight spokes should be so I did a wheel build making the spokes as tight as possible. I build dishless wheels though I expect this also applies to a real wheel with dish. In order to get the spokes as tight as possible I did a standard build then adjusted the out of round 1/4 turn at a time using both a spoke wrench and a screw driver. The spokes were checked for equal tension by comparing the sound of opposite spokes on both the left and right sides and the top and bottom sides. After a certain point the wheel buckled into potato chip shape. This did not hurt the rim and after backing off on the tension I ended up with a useable wheel. The second time was an accident. I used a combination of transmission fluid and Mobil One to lubricate the nipples and the wheel potato chipped while stressing the wheel by squeezing the rim and the chainstay. This did not photograph well but you can see the wheel here after backing off on the tension. I estimate the spokes were twice as tight as the store bought Stay True front wheel by squeezing the spoke and comparing the deflection at the cross. I'm leaving this one tight and will inform you if there is a problem. The wheel is being ridden with 160 pounds on it. Nothing special there is a fh475 hub refitted with a 7 cog freehub. Generic stainless steel spokes of 2 types. A Weinman 519 clone rim. !0mm solid axle. Search for zerodish and spoke protector on flickr to the the wheel.

[Bikinchris]

While you are experimenting, I have a few facts for you. Spokes are three times stronger then they need to be to build a strong wheel. If the spokes are a "little" too tight, they will crack the rim. The hub is the next strongest component and would crack next. The spoke would not break if too tight. Spokes break on wheels because they are not tight enough. The wheel rotating with a load cold works the spokes until they become so brittle, they snap.
So spoke too loose, the spokes break. Spokes too tight, the wheel fails.

[Old Guy New Hobby]

Thanks, Bikinchris. I had heard this before, but I didn't understand why it is true. How tight should spokes be? Does it depend on the spoke pattern?

[Bikinchris]

It depends on:
The total number of spokes; imagine the tension on 48 spokes if you make them as tight as a 28 spoke wheel
The weight of the rider; A tandem or loaded touring bike needs more tension.

The reason is this: the wheel is only as strong as the tension on the spoke the wheel is STANDING on. If those spokes go slack as the wheel rotates, the wheel is likely to fail.

Spoke pattern and other things are lesser reasons for a wheel to fail.

Typically, for a 32 spoke wheel an normal rider etc, most people try for 100kgf. This is below the tension where if you grab the spokes and squeeze real hard, the wheel will take a "set" and be crooked. Kind of like you did in your experiment.

You should read Sheldon Brown's website. It is a no bull or marketing spin place:
http://sheldonbrown.com/wheelbuild.html

[DanE]

Quality rim manufacturers will publish in their specifications a maximum tension. Here is a link to a rim suitable to touring made by DT:

http://www.dtswiss.com/Components/Rims-Road/TK-540

In the specifications you see the maximum tension is 1200 Newtons. When you build a wheel measure the tension on the wheel and do not exceed this level.  Hubs also have a maximum tension, but at a higher value than rims. Rims will crack around the eyelet over time if the maximum tension is exceeded.

I only am using this rim as an example to point to the tension specification. I am not really endorsing this particular rim over any other. It is just an example to show a published specification.

[Pat Lamb]

How tight should spokes be? Does it depend on the spoke pattern?

Spokes should be tight enough, as Chris said, that they don't go slack.  That will depend on the rim and the load. 

Worst case, with a lightweight box rim, the entire wheel load may be taken by the bottom spoke.  Say it's a loaded bike with a heavy rider, 300 pounds total bike load, and 2/3 of that is on the rear, so 200 pounds is "standing" on that spoke.  If the spoke was tensioned to 190 pounds, it's now slack, and at least one of the spokes is likely to fail within the next few hundred to thousand miles.  If all spokes are tensioned to 100 kgf (kilograms force), or 220 pounds, they all stay tight, you don't have fatigue failure, and the wheel lasts a very long time.

If you have a deep section rim and a light rider, the rim doesn't flex nearly as much.  If the rim distributes the load over four spokes, and it's ridden with a 150 pound bike-rider-power meter load, then each spoke only needs to be tensioned to 25 pounds.  (Of course, the drive side tension on the rear wheel will likely be higher.)  The manufacturer will be tempted to reduce the spoke count, e.g. from 36 to 24 spokes, and the wheel will still be solid with the load distributed over three spokes.  (Until I get on that bike!)

All that said, I usually shoot for 105-120 kgf tension on 36 spoke wheels, and try to make sure the rims I buy will handle that much tension.

[chrisx]

rim Manufactures give a tension recomendation.  find yours, then use a
Spoke Tension Meter
http://www.parktool.com/product/spoke-tension-meter-TM-1
to loose is better than to tight.
with the correct tension your wheel will last a long time
wrong tension    short wheel life

[zerodish]

The wheel buckled. I hit an oil slick and the back wheel went sideways. I managed to get it true enough to ride but the rim will need to be replaced. I use Araya VP 20 or Weinmann 519 rims or no name copies of these rims. They have never cracked at the spoke holes keep in mind I have 110000 loaded miles on wheels I have built. The wheel was not heavily loaded at about 160 pounds. I did this once before only it was wet leaves on a board walk. That wheel only needed minor truing.     

[Pat Lamb]

Not too surprising; all bets are off after a crash.  The impact is what bends the rim.  That is, on the way down you can bend the rim and then that bend hits the road, changing a plastic deformation (that could be reversed) into a permanent bend.

You might be able to bend it back to the point it could be used by detensioning (or even despoking) the rim, bending it back close to flat, and then rebuilding.

[zerodish]

It's true but I have several spokes at close to zero tension with the rest being too tight. Generally I allow this for front wheels but not for the back.

[staehpj1]

It's true but I have several spokes at close to zero tension with the rest being too tight. Generally I allow this for front wheels but not for the back.

I am tend to be one to run things until they break, but I'd probably replace a rim that is in that condition if I couldn't get it true with at least somewhat even tension.  If on tour, I'd probably wait until back home though.