Wheel truing: which direction is 'correct'?

[civilisationshift]

Hi all. Apologies if this has been asked and answered already...

I bought a pretty cheap truing stand[1] - not brilliant but it does the job. But one thing I'm really not sure of, in terms of making adjustments, is how to tell/decide which direction is 'correct'? As in, if a wheel section is moving laterally (eg) left, how do I know that it should be adjusted toward the right and not that *it* is true and other sections of the wheel should actually be adjusted toward the *left*? If you imagine a case where a wheel is more or less out of alignment across one half, how do you tell which direction is true? And the same for high vs low spots in radial alignment too.

I don't have a dishing tool, but is that how you should decide which direction is correct (or use the on-frame method Alex shows in his vid)? For radial alignment, does that come down to spoke tension (too tight then you know you've pulled the rim too far toward the hub)?

Thanks!

[1] http://www.ooocycles.com.au/item-20.htm

[jr14]

When you true a wheel, the entire point is to get the rim straight, then worry about dishing. Normally, only one or two spots will be out of true. These are irregularities, and need to be corrected. I would find it very hard to believe that the irregularities would actually be correct, and the other 95% of the wheel is out of alignment. That just doesn't make sense.

So on your truing stand, if a portion of the wheel hits the left side of the arm, adjust to the right. Once the entire wheel is true, then worry about dishing.

And, no, you don't need a dishing tool. Take the wheel and flip it around horizontally to see where it ends up. If it's not centered in the stand, it needs to be adjusted. You will have to tighten/loosen each spoke in the proper direction to get it centered, but this is the easy way to dish a wheel.

[Joe_W]

I repeat myself, but check out Roger Musson's book http://www.wheelpro.co.uk/wheelbuilding/book.php is just great. I have it (only wheelbuilding book I own) and the explanations are great. I finally built a dishing gauge (out of scrap wood), much more convenient than havin to flip the wheel and then worry whether the arms of the cheap stand (Minoura) moved...

nitpicking on cyclerUK's answer (who is usually more correct than I, so forgive me): actually with rear wheels about 90% being wrong at some point in time is highly likely due to the dish of the wheel...

[civilisationshift]

(02-20-2010, 02:55 PM)jr14 Wrote:  When you true a wheel, the entire point is to get the rim straight, then worry about dishing. Normally, only one or two spots will be out of true. These are irregularities, and need to be corrected. I would find it very hard to believe that the irregularities would actually be correct, and the other 95% of the wheel is out of alignment. That just doesn't make sense.

Appreciate the response jr14. In hindsight I didn't explain myself very well -- yep, I do understand the principles and of course it would be exceedingly unlikely for one small section to be true and the remainder 'untrue'. I was just using that (exaggerated) example to try to explain my slight doubt. I did have more of an S shaped wobble, partly due to my own initial poor truing skill, and as I was in the middle of fixing it I suddenly realised I wasn't certain which direction was correct. I do tend to overanalyse things though...


Another, hopefully more useful question. Over on the wheel truing vid, Alex explains that for a rear wheel the left/non-drive side spokes affect lateral movement more and the right/drive side spokes affect radial movement more. Makes perfect sense. Alex then says: "To compensate for this difference, the right side spokes should be adjusted two turns for every turn on left."

So you do this because the right side only has (for example) about half the tensioning force in lateral movement as the left does.

But here's where I'm confused: wouldn't doing this at the same time be applying twice the tension adjustment to radial alignment to the spokes (right/drive side) that already affect that radial alignment about double that of the left?

Clearly I'm missing something simple but I haven't been able to figure this out! I think I have my rear wheel close to true, but initially I focussed on radial and ended up with a rather sever deviation laterally.

Cheers guys, really appreciate the help

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(02-21-2010, 02:49 PM)Joe_W Wrote:  I repeat myself, but check out Roger Musson's book http://www.wheelpro.co.uk/wheelbuilding/book.php is just great. I have it (only wheelbuilding book I own) and the explanations are great. I finally built a dishing gauge (out of scrap wood), much more convenient than havin to flip the wheel and then worry whether the arms of the cheap stand (Minoura) moved...

I think it was your post elsewhere that led me to doing just that. Roger's book is excellent! So thanks heaps for that I'm about to knock up a ye olde cardboard dishing tool myself...

(02-21-2010, 02:49 PM)Joe_W Wrote:  nitpicking on cyclerUK's answer (who is usually more correct than I, so forgive me): actually with rear wheels about 90% being wrong at some point in time is highly likely due to the dish of the wheel...

Almost entirely my own fault, but yep that's definitely what I did. One massive bowed mess...

[Joe_W]

undo all spokes, redo from start. Better to redo the wheel than to try to correct errors. You did use the nipple driver, didn't you?

Lateral and radial are tied up. Whenever adjusting lateral trueness you have also to account for radial trueness (so if the wheel is radially true you tighten one side and loosen the other side to move the rim laterally)

[civilisationshift]

(02-23-2010, 11:06 AM)Joe_W Wrote:   undo all spokes, redo from start. Better to redo the wheel than to try to correct errors. You did use the nipple driver, didn't you?

*cough* this was an existing wheel. one that has more or less served me fine for, erm, 4 years. a 26" factory mtn bike rim. spokes did seem a bit on the loose side and there was some deviation.

(02-23-2010, 11:06 AM)Joe_W Wrote:  Lateral and radial are tied up. Whenever adjusting lateral trueness you have also to account for radial trueness (so if the wheel is radially true you tighten one side and loosen the other side to move the rim laterally)

no I get that. just not quite seeing how the tighten-twice-on-the-right can work. I better just think about it some more

[DaveM]

(02-23-2010, 11:24 AM)civilisationshift Wrote:  no I get that. just not quite seeing how the tighten-twice-on-the-right can work. I better just think about it some more

You're right. But the thing to also keep in mind is that for a given adjustment (1/4 turn, 1/2 turn) you will impact the side to side trueness much more than the radial trueness. (See: geometry of changing the length of a side of an acute triangle). Most of the time, you adjust side to side without paying attention to radial issues because it won't be changed enough to matter. Of course, that assumes your wheel starts out in good shape radially.

The tricky thing about truing is that every adjustment you make affects all four factors (side, radial, dish, tension) and all four are important. You can't make any big changes in any one factor without needing to correct for the others, though you can typically make small adjustments to one without issue.

I find that if you have two issues (like side to side and tension) that need addressing, you have to go back and forth between the two issues. You can't fix one, then the other. So get the side to side a little better, then check and improve the tension, then get the side to side better, etc, etc.

After you do this more, I think you'll find that you can mentally adjust for how one adjustment will affect other factors and work more efficiently. But I doubt you can get there just by thinking about it. You have to let your hands learn to feel it as well.

[Joe_W]

Dave is obviously better at finding good explanations (hm, should I come up with the excuse of not being a native speaker probably not...).
Oh, and truing an old wheel is more difficult than building a new one. There at least the rim starts out being reasonably round. What I do is:

• check lateral (worst spot on the left)
• check lateral (ditto to the right)
• check radial
  

I correct this by finding the spoke where the tension is "off". When truing laterally I try not to affect radial trueness (loosening about the same amount I tightened), when truing radially I try not to affect lateral trueness. If the rim is round I check for dish. Then I try to get the correct dish, so I tighten one side maybe half a turn and after that I tighten the other side maybe one whole turn. I do one side after the other in order to not become confused. After that I try to bring the wheel up to final tension (always "stressing", well stress relieving the spoke in between and checking the trueness). So far the only problem I had was with my first two trailing / two leading wheel...
You could probably get the tension up faster but I don't want to risk messing up the trueness, so I take my time. Nobody is rushing me, this is just a hobby.

[civilisationshift]

thanks to you all, really appreciate your taking the time to go over it.

I did have one more question though. without using a tensiometer -- as Roger Musson's book says is really not necessary or all that effective (h/t Joe_W again!) -- what method do you use to decide the spokes are tight enough? I've been doing the parallel-pairs squeeze and listening to pitch (still a fair bit of variation there), but as it's my first ever crack I'm not entirely sure when tight is tight enough.

[Joe_W]

Well, as a beginner we tend to build wheels with the tension too low. I compare the force I need to squeeze the spokes together to a factory built wheel and hope the best. I usually try to get the tension as high as possible since the modern rims (not the lightweight stuff, though) are quite tolerant...
As Roger Musson notes in his book, there is quite a margin that will make a wheel that is reasonably stable. I only needed to true my first built (yes, tension too low) and the last one (two leading and two trailing). So: when you think it is ok, the spokes have been stress-relieved and they don't have torsion left put it on the bike and take it for a ride, then recheck.