cyberbellum said to add tension until the rim potato chips, and then take a little bit off. i just got my pretty pretty new dm24 rim today, laced it, and started tensioning. it wasn’t until i had some serious tension on it that i realized i had no way of telling if i had enough tension because i didn’t remember how curved the rim was to begin with. is there any way to tell if i have enough tension without undoing all of my work?
Your DM24 won’t potato chip via tensioning AFAIK and if it does, it is probably ruined. Most likely you won’t be able to taco it that way because the nipples will strip before you get the tension that high. Unfortunately, most (all?) tensiometers won’t fit on 24" wheel spokes and give an accurate reading.
That “potato chip” advice was an incorrect reading of a basic wheel building text. The correct reading is “becomes untrue in two large waves” which is not a taco, but a slight wave in the rim. However, for beefy rims, not the rims that the text focuses on, that approach is suspect anyway.
The best way to get the overall tension right is something like this: a) compare the “feel” of the spokes with the feel of the spokes on a perfectly built larger wheel; b) realize when spoke windup is causing serious tensioning difficulties; c) realize when higher tension is making the wheel a bit weird.
“how curved the rim was to begin with” – if the rim wasn’t basically perfect to begin with you should have returned it, because you are likely to have serious problems getting it right if it wasn’t.
I think it’s a good thing to figure out if you are just a rider, or a rider/builder. If the former, you can save a lot of money, time, and frustration by getting your wheel work done by someone who does it all the time. If the latter, prepare to dig into some texts and spend some money on good equipment and start building wheels and experimenting. It’s a misconception to think that wheel building is trivially easy and just a matter of finding the right size spoke wrench.
there are also some good sites about figuring out tension based on the pitch of a plucked spoke (comparativley with a tuning fork) good luck with your wheels.
“how curved the rim was to begin with” – if the rim wasn’t basically perfect to begin with you should have returned it, because you are likely to have serious problems getting it right if it wasn’t.
by ‘curved’, i was refering to the cross-section of the rim, because of the potato chip advice
and i can’t compare the tension to another wheel because all i have available are a pair of wheels from a cheap mtb, which are both rather loose
The “curved” that counts is the coming-untrue curve, which can be seen by spinning the wheel on a truing stand and watching the rim wall go by the calipers. The DM24 has a vertical machined braking surface, so any deviation from flat will be quite obvious.
Re: measuring tension
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
If the rim starts to mysteriously go untrue when you know you are truing it right, back off every spoke 1/4 turn IMMEDIATELY!! That’s the sign that it is at immenent collapse.
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
There was a Calvin and Hobbs comic once when Calvin asked his dad how they determine the load limit for bridges. His dad answered, “They drive bigger and bigger trucks on it until it breaks.”
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
DON"T POTATO CHIP THE RIM!!! IT WAS A JOKE!!!
What U-Turn said.
(Except for the mis-read bit. IT WAS A JOKE! Sorry about the confusion… )
And I’ll add, watch the spoke holes in the rim. The other failure mode from too much tension is that the nipples pull through the rim. This isn’t common on road rims but happens sometimes with wide MTB rims.
If you see visible bulges at the eyelets you’re in a danger zone. If you see cracks the rim is toast.
If you see “the waves” and you didn’t hardly twist the wrench you’re in a danger zone. If the rim tacos it’s a gonner.
There were quite a few other things about wheel building I neglected to mention, like stress relieving and bending kinks out of the rim (yes, it is possible to cold set minor bends out of a rim, but only if the spokes are slack and you have the proper tools.)
So again, what U-Turn said. Might not be a bad idea to get a good wheelbuilder to help you with the first couple. There must be a cool shop near where you live. Build your wheel in slow steps and take it in for them to give you comments.
But please DON’T taco your wheel. I’d feel so guilty!
If you plan to build enough wheels to justify the cost, you can get a spoke tensionometer from bike catalogs. I have one, but then I’ve built lots of wheels over the years. It wouldn’t be worth the cost for one or two wheels.
The pitch of a plucked spoke isn’t a reliable indicator. If the spokes are crossed then friction between the rubbing spokes damps out the sound. Also, the plucking energy is quickly distributed to the other spokes so it’s tough to figure out which one is making the noise.
The only reliable way to judge tension is to feel the force required to deflect the spoke. Tensionometers do this with three pins - two “anvil” pins with a force-measuring pin in between.
Most experienced wheel-builders use their hands to do the same thing. It’s not as accurate but it is much faster. There is a step in wheelbuilding called “stress relieving.” It’s misnamed. What it really means is overstressing the spokes. The best way to do this is to grab two spokes that are reasonably close together and squeeze. This WAY overloads the spokes and causes them to deform the holes in the hub flanges, which seats the spoke in a nice form-fitted aluminum cradle, and bends the spoke into the most efficient shape for resisting spoke-like loads.
If you don’t buy a tensionometer then check tension when you stress relieve. Feel for mismatches in resistance to bending, and for the total resistance to bending. Also watch the rim - if it starts to do unnatural lateral moves when you stress relieve then the rim is near it’s limit and it’s time to back off a 1/4 turn.
For a bicycle wheel with few lateral loads this is about when you want to stop - just below immenent rim collapse. For a uni wheel that will see large lateral loads (e.g. side mounting) that are perfect for sending the wheel into a potato-chip shape, then you want LESS tension in the spokes. You still want a lot of tension, but you don’t want the rim to be anywhere near immanent collapse. (I’m pretty sure that is why Uni wheels have so many spokes compared to a bicycle wheel.)
Best of luck,
Tim
i went to my lbs to see what they thought about my tension. every single bicycle on campus has incredibly loose spokes, so i couldn’t compare those, usefully. i spent my entire morning hunting down parked bikes, and they all suck, even the one that had disc brakes. the guys at my lbs said it was about right, which is a good thing, since i’ve been riding on it
Sounds like you built a pretty tight wheel. Congradulations!
Good riding,
Tim
yes, very happy, me. too bad for me that i don’t have any reason to build any more wheels in the near future. my next project, however, is electrostripping the chrome from my frame, since it looks horrible with my aluminum rim. and since i know that it’s a very bad idea for me to do this, i’m gonna need all the luck i can find