Truing wheel for the first time.... Question on spoke tension and egg

[Ricker]

This is a PXC-2 wheel from a Giant Trance 27.5 1.

I broke a spoke and had previously noticed that the wheel was not running very smooth, had some severe side to side wobble.

A couple of places on the rim had dents on one of the rim rails, so I bent these back gently with a spanner.

I then bought a $40 truing kit (budget as all heck), and watched a bunch of youtube tutorials and read through sheldon browns building wheels and truing wheels articles.

Setup the wheel, and started working on it. I feel I've got the wheel as perfectly straight as I can get it so that there is very little side to side. I'd say its around 1mm or under.

Testing my spokes though, majority like 70% feel around the same tension, but 30% of them feel about 20% less tensioned... That gonna cause much issue?


Then I went to check the roundness of the wheel (there are more technical terms I just cant remember them). I noticed that there is a little egg shaping happening at one point. That point is occuring at the seam of the rim. I have made a very quick and dirty video to show. Is this a big problem, or seeming there is a bunch of tyre and air inbetween the rim and the ground it should just negate out this small amount?

http://youtu.be/y-MwGWK42RM

Any help most appreciated.

 

[redbruce]

This is a PXC-2 wheel from a Giant Trance 27.5 1.

I broke a spoke and had previously noticed that the wheel was not running very smooth, had some severe side to side wobble.

A couple of places on the rim had dents on one of the rim rails, so I bent these back gently with a spanner.

I then bought a $40 truing kit (budget as all heck), and watched a bunch of youtube tutorials and read through sheldon browns building wheels and truing wheels articles.

Setup the wheel, and started working on it. I feel I've got the wheel as perfectly straight as I can get it so that there is very little side to side. I'd say its around 1mm or under.

Testing my spokes though, majority like 70% feel around the same tension, but 30% of them feel about 20% less tensioned... That gonna cause much issue?


Then I went to check the roundness of the wheel (there are more technical terms I just cant remember them). I noticed that there is a little egg shaping happening at one point. That point is occuring at the seam of the rim. I have made a very quick and dirty video to show. Is this a big problem, or seeming there is a bunch of tyre and air inbetween the rim and the ground it should just negate out this small amount?

http://youtu.be/y-MwGWK42RM

Any help most appreciated.

Video comes up as private access.

 

[Ricker]

Sorry, fixed now

 

[tomacropod]

Wheel is fine. Seam imperfections are common (and inevitable, if you consider how the rim is made). You've done quite a good truing job - considering you're about to put a massive tyre on it which will have its own imperfections.

- Joel

 

[Ricker]

In terms of spoke tension not being even across all of them, how much impact will this really have? Will I be breaking spokes on my next big drop?

 

[Alo661]

The roundness of a wheel is a lot harder than getting a wheel true. If the rim has been dented, you've got little to no hope of getting it back into perfect round.

You wouldn't notice those hops on a trail, only riding on bitumen. If you really want to fix the hops, either loosen the spokes around where the hop is, or tighten the spokes opposite the hop.

Spoke tension? It looks like a 28+ spoke wheel, spoke tension ain't the end of world on a high spoke count wheel.

 

[redbruce]

In terms of spoke tension not being even across all of them, how much impact will this really have? Will I be breaking spokes on my next big drop?

Spoke breakage is usually caused by insufficient tension, not too much (unless the spoke has already reached its fatigue limit somewhere).

This occurs as spokes tension reduces when they are under compression (ie vertical and below the hub) and then tension is increased again as the spokes tension forces increases.

Having more spokes with and closer to the correct static tension reduces the tension change in a spoke as the wheel rotates and low frequency material fatigue development.

It also reduces the likelyhood of a spoke breakage on drops as more of the extra force is evenly distributed across more spokes.

As already mentioned, if the rim has been dented you are unlikely to get it perfectly round again. Having said that an out of round (within reason) wheel with relatively even spoke tension will be stronger than one closer to round but with significant differences in spoke tension.

 

[T-Rex]

In terms of spoke tension not being even across all of them, how much impact will this really have? Will I be breaking spokes on my next big drop?

Looking at the video, you've done a very good job at truing that wheel.

Regarding spoke tension, getting even spoke tension (+/- 10%) is arguably more important than truing for the wheel's longevity. However, it's very difficult to judge tension by squeezing spokes, especially if you are not very experienced at wheel building. A better (ghetto) measure is plucking them or striking them with a metal object, and judging the tension by the sound. Apparently an ideally tensioned spoke resonates at F sharp..... Whatever that is, I don't have a musical bone in my body, so I use a Park spoke tension meter. However, a tension meter might be overkill for replacing one spoke, so try the sound method.

 

[SummitFever]

On a disc brake wheel I always aim for even spoke tension (eg. all spokes on one side will be within 10% of each other), even at the expense of roundness / trueness. The strongest wheel is one where all of the spokes work evenly together, at that occurs when the spoke tensions are even. Even spoke tension is far more important that slight (eg <1mm) variations in roundness / trueness. As tomacropod says, once you chuck a big tyre on at 20psi, any <1mm slight variations are unnoticeable.

 

[Ricker]

Why only on 1 side? Shouldn't it be 10% of all spokes?

 

[SummitFever]

Disc wheels and rear wheels are dished so that the spokes on one side have a different bracing angle (and tension) to the spokes on the other side. All spokes on one side should be the same tension, and all spokes on the other side should be the same tension.

 

[slippy]

Give the loose spokes a 1/4 to 1/2 turn with the spoke key. The small increase in tension is unlikely to effect the trueness significantly.

 

[Ricker]

Ok, so I spent another 5 hours on it! I bought a iPhone spoke tension app, which works really well. Wasn't that interested in that actual kgf numbers it was showing, but rather than all the numbers were the same or close per side of the rear wheel.

Got them all pretty dam close. Especially on the non drive side.



I got the drive side to 60% more than the non-drive side. 130kgf - drive side, 80kgf - non drive side. Those numbers are what the app shows, with the input of my spoke length, diameter and material type. But not sure its really that good at giving correct tension numbers, but its very accurate on the actual sound and therefore showing a number that is repeatable every time you strum the spoke.

Anyway I then threw the front wheel on, and noticed that its spoke tensions were all over the place, although its trueness was good. I had a good at correcting all the tensions, but this threw out the trueness quite a bit. So is the front wheel also going to have different tensions on each side? Is that because the disc is sitting inside the fork arms, and so it needs to be dished slightly to one side? If the disc is on the non drive side, should those spokes (non drive side), be tighter than on the drive side, because the rim should be dished towards the disc brake?

I think I screwed up the front cause I tried to balance all the tensions on both sides to the same 90kgf. Couldn't get it to happen easily, and got frustrated and quit.

 

[T-Rex]

You are not likely to get the tension the same left and right due to the hub flange offset. This difference is more pronounced on the rear. Don't worry about it, try to get the tension close on each side.

To sort out the front, you need to progressively tighten the nipples, alternating on truing the lateral and vertical runout and trying to keep the tensions even as you go. Don't try to get one of the dimensions completely right first go, you then won't be able to correct the others.

Tell us about your Iphone app... How does it work?