Wheel build paranoia - too much tension?

graham_g

After my somewhat embarassing (and expensive!) mistake of blowing a tire off the rim of a wheel I'd just had built, I decided to rebuild the wheel myself with a new rim (Mavic CXP 33). I put it on last night and had a few 'pings' on my ride in this morning but after getting the tire up to pressure last night I starting pinging the spokes and this front wheel is producing quite a high pitched note compared to the rear. It's a trad 3 cross pattern 32 hole, and the pitch is comparable (maybe slightly higher) to a radial laced factory rim that I compared to whilst building. In comparison the rear wheel, which was built a good year or more ago and has seen plenty of use is a veritable baritone in comparison!
Have I taken the tension up too high rebuilding the front or is it time I ramped it up a bit on the rear after probably 2000 miles?

Kléber

Sadly you can't play them as musical instruments!

Seriously and I don't mean to be rude but if you don't know what you are doing here, please be careful. Getting the tension wrong - too high or too low - can cause broken spokes, cracked flangers and rim failure, a nasty accident could happen. Wheelbuilders end up knowing the right tension but see if you can borrow a spoke tension meter from a good bike shop, just takes a few seconds to check.

If you're unsure, maybe you're safer playing tunes on them

graham_g

Fair point - I have to say that comparing with the other front wheel I have it seemed OK but I got a bit paranoid when compared to the rear! I'll take it in to the shop for an opinion, thanks.

one_bad_mofo

Spokes usually tend to ping on the initial ride due to them bedding in and releasing a bit of tension. A quick once over with a spoke key should sort things out. If your at all unsure ask your local shop to give the wheel a once over. Take some doughnuts and the machanic may even let you watch as he goes ove rthe wheel so you've a better idea of what to do next time.

leighz

the pinging is twisted spokes untwisting themselves as you first ride off. You can avoid this by overtightening each spoke as you true the wheel and then backing the nipple off a quarter of a turn or so. You can also release the twisted spokes by grabbing two pairs of crossed spokes in each hand either side of the wheel (where they cross) and squeezing as hard as you can. Go round the entire wheel like this.

sheldon also recomends using an old crank arm to relieve the spokes

tension wise you want them as tight as you can go without rounding the nipple off or thereabouts - and the drive side of the rear wheel will be tighter than the non drive side to get the dish right.

....and you can play them like a musical instrument - a tonally challenged one anyway

imho

meagain

"tension wise you want them as tight as you can go without rounding the nipple off or thereabouts -"

Maybe. The wheel-man at what is probably the most used LBS by race folk around here once told me a matter of personal preference/rider! I asked him whether some I'd built were sufficiently tight. He said he'd go tighter for actual racing and/or for average weight riders and above - but for my sub-9st would be fine - and comfortable!

aracer

meagain wrote:

He said he'd go tighter for actual racing and/or for average weight riders and above - but for my sub-9st would be fine - and comfortable!

The old looser is more comfortable myth rears it's ugly head again. Rider weight or what the wheels are going to be used for has nothing to do with it - the strongest and best wheels are made by tensioning the spokes as much as the rim will take. The limit for a normal box section is the rim tacoing, for a stiffer deep section rim normally the spokes pulling through.

In any case, it's extremely unusual for wheels to be overtensioned - most home builders will stop well before that point as it feels like something's going to break. Much more common to have undertensioned wheels (my very first attempt at wheelbuilding resulted in all the nipples coming undone on the first ride I'd put so little tension in it :oops: )

rustychisel

Excellent post!!!! I agree on all points ('cept my first wheel was just wobbly and sh!t).

graham_g

Thanks for the reassurance - if I can duck out of work suitably early then I'll have a word with my old LBS guy. I'm still well chuffed that I got it perfectly true (both ways!) and there's no flex honking up hills on it either (it's on my fixed wheel commuter).

Definitely the most satisfying bike fettling job I've ever done, equally frustrating though as it took me three attempts just to get it laced up right before even putting any tension in!

Kléber

Many spokes (and some rims) come with tension limits. Just "turning it up to 11" will result in trouble too. Of course, slack spokes create their own problems, they are more likely to break.

So it is like a guitat string, you have to get the tension right to play it!

graham_g

I'm a bassist - not used to those horrible trebly sounds

Hugh A

It is also possible that the rear wheel has been built on the slack side. You would expect the non-drive side rear spokes to be slacker than your front wheel spokes. If both wheels have been built correctly then I reckon you might expect the front spokes to be marginally looser than the drive side ones, but not too much in it.

Normally, tighter tends to be better as long as there is even tension and you're not getting to the point where the nipples start to get very difficult to turn or are getting damaged. I find oiling the threads first can help with this. The semi- deep section of your rims should make them pretty strong and able to take quite a bit.

I'm not sure how much comfort is affected by the tension. Spoke profile and the stretchiness of them seems to make a difference.

If the spokes aren't de-stressed first you get pinging. It's also possible that they will be slightly out of true after this. Normally when building some re-alignment is needed after de-stressing.

aracer

Hugh A wrote:

I'm not sure how much comfort is affected by the tension.

As I alluded above, not at all. Not that wheels flex significantly in a vertical plane anyway compared to tyres and saddles.

If the spokes aren't de-stressed first you get pinging. It's also possible that they will be slightly out of true after this. Normally when building some re-alignment is needed after de-stressing.

Just to clear up a bit of misunderstanding (I'm repeating Leighz here to some extent), the pinging when first riding is due to spokes being twisted when building, and is the sound of them turning in the nipples. This does result in the wheel going out of true. However the solution isn't de-stressing (or more strictly stress relieving) but rotating the spoke key past where you want the nipple to be and then backing off to de-twist the spoke. With flexy spokes like CX-Rays I've found you need up to half a turn over and then backed off - though those do also have the advantage of an easy visual indication of whether the spoke is twisted.

Stress relieving (presumably what you mean by de-stressing) is something else entirely, and is done to remove the stress peaks in the spoke at the bend. If you don't do this then your spokes are more likely to break due to the stress concentration. My preferred method nowadays is the one suggested by Sheldon - an old crank twisted between the spokes (see his site for more details and a picture). It's a lot less painful than the traditional method of squeezing spokes together by hand!

Meanwhile I'm still unconvinced that any home builder is likely to get near the maximum allowable spoke tension for a CXP33 - maybe for a box section where the max is lower, but unlikely for one of these. The spokes will just get too hard to turn and you'll get far too much windup well before that stage. Tension limits on the spokes are just silly - yes maybe they do have them, but they're so high that you'll never get anywhere near.