How round does a wheel need to be

robjh

Legendary Member
I've replaced a rim, got the side-to-side truing right and the wheel almost round.

I've got the roundness down to about 1 to 1.5 mm variance (in rim distance from the centre) and am getting diminishing returns from further efforts.

Is there an acceptable limit for normal riding, or do I need to carry on to perfect circularity?
 

dodgy

Legendary Member
Location
Wirral
In the Roger Musson book, he says 0.5mm is a good target for radial trueness. I'd be happy with a bit more than that as long as it couldn't be felt when riding.
 

PpPete

Guru
Location
Chandler's Ford
As general point, even-ness of spoke tension is more important than perfection on radial or lateral true-ness.
Is your 1-1.5mm variation a particular high spot or flat spot?
Or just a general "egginess" over the whole circumference?

Some rims (Open Pro springs to mind) have a distinct high spot at the join (opposite the valve)
I don't usually take the spokes in that area up by more than 10% ** over the average tension.... That sometimes leaves the high spot at around 1 mm, and there is no detectable ill-effect at that level.

If you've got significant variations in tension and the wheel is still noticeably oval throughout then I'd suggest there may be something wrong either with the components or with your technique.

** Someone with a musical 'ear' ought to be able to tell a difference in tone between spokes that show a 10% difference in tension on a tensionometer. I'm cloth-eared and can't.
 

dodgy

Legendary Member
Location
Wirral
Radial trueness is a little harder to get right but you should get closer to 0.5mm.

If you have disc brakes,I guess, you won't notice 1.5mm
You will once the road gets smooth, you'll be able to feel the thud thud thud on every wheel revolution. I know this because the wheel on my Day One Alfine needs truing for radial accuracy, it has a low spot that I've had trouble tuning out from new.
 
OP
robjh

robjh

Legendary Member
As general point, even-ness of spoke tension is more important than perfection on radial or lateral true-ness.
Is your 1-1.5mm variation a particular high spot or flat spot?
Or just a general "egginess" over the whole circumference?

Some rims (Open Pro springs to mind) have a distinct high spot at the join (opposite the valve)
I don't usually take the spokes in that area up by more than 10% ** over the average tension.... That sometimes leaves the high spot at around 1 mm, and there is no detectable ill-effect at that level.

If you've got significant variations in tension and the wheel is still noticeably oval throughout then I'd suggest there may be something wrong either with the components or with your technique.

** Someone with a musical 'ear' ought to be able to tell a difference in tone between spokes that show a 10% difference in tension on a tensionometer. I'm cloth-eared and can't.
I'll willingly admit that it may be my technique - this is my first attempt at a full rebuild rather than just a bit of emergency truing, but hopefully I'll be learning from my mistakes.
The good news is that after some more perseverance I've got the radial true close to that fabled 0.5mm - as I'm doing it by sight and improvisation I can't measure it exactly, but I'm sure I've seen worse than that on new wheels before with no obvious effect when riding. The spoke pings* have gone a bit askew with all the fiddling, but I'm going to take the bike out and see how it feels.

*unfortunately no musical ear here
 
You will once the road gets smooth, you'll be able to feel the thud thud thud on every wheel revolution. I know this because the wheel on my Day One Alfine needs truing for radial accuracy, it has a low spot that I've had trouble tuning out from new.
Good to know..... is it possible that it's more than 1.5mm?
 

Smurfy

Naturist Smurf
Beyond the point you've got to, adjustments need to be very small. In my experience, about one quarter of a turn on a set of spoke nipples should be the maximum, before you spin the wheel and check again.
 
I'll willingly admit that it may be my technique - this is my first attempt at a full rebuild rather than just a bit of emergency truing, but hopefully I'll be learning from my mistakes.
The good news is that after some more perseverance I've got the radial true close to that fabled 0.5mm - as I'm doing it by sight and improvisation I can't measure it exactly, but I'm sure I've seen worse than that on new wheels before with no obvious effect when riding. The spoke pings* have gone a bit askew with all the fiddling, but I'm going to take the bike out and see how it feels.

*unfortunately no musical ear here
I find that by eye, it always looks worse.
 
OP
robjh

robjh

Legendary Member
I rode on the rebuilt wheel today, and after 50 miles it is still as straight and round as when I started. I'm slightly bothered by a few uneven pings, but I'll keep an eye on it for a while
 

andrew_s

Guru
Location
Gloucester
Radial trueness is something that you have to sort out near the start of the wheelbuilding process.
If you can feel a radial bump in a fully tensioned wheel, it's probably better to slack everything right off and retension from scratch.
 
Location
Loch side.
I rode on the rebuilt wheel today, and after 50 miles it is still as straight and round as when I started. I'm slightly bothered by a few uneven pings, but I'll keep an eye on it for a while
Pings spell trouble. A ping - usually within the first few meters of riding and then silent thereafter, indicate spokes that twisted in the nipple. This happens because the spokes were wound up whilst tensioning and the builder did not take it out before handing the wheel over to the customer. This means that the original trueness is gone, if albeit only slightly. Nevertheless, it is the sign of an unskilled builder's work.

Spokes, being long slender bolts resist torsion very poorly and as the friction between spoke and nipple increases during the latter part of the build, the spokes wind up slightly (sometimes as much as 1/2 turn, depending on their length and thickness. When that spoke now relaxes at the bottom of the loaded wheel in the load affected zone, the tension is relaxed slightly and the spoke springs to its natural default position of zero torsion. That's what you hear, the spoke turning in the nipple.
 
OP
robjh

robjh

Legendary Member
Pings spell trouble. A ping - usually within the first few meters of riding and then silent thereafter, indicate spokes that twisted in the nipple. Nevertheless, it is the sign of an unskilled builder's work.
I meant that if I ping the spokes with my fingers, the pitch on some varies a bit more than I would really like; but the wheel seems to be running fine

Nevertheless, it is the sign of an unskilled builder's work.
yes I own up to that but I am hoping to learn from experience!
 
Location
Loch side.
I meant that if I ping the spokes with my fingers, the pitch on some varies a bit more than I would really like; but the wheel seems to be running fine


yes I own up to that but I am hoping to learn from experience!
Well, then it sounds to me that you've nothing to be bothered about. Remember, a wheel that is perfectly round cannot have even spoke tension and a wheel with perfectly even spoke tension (i.e. uniform tone) cannot be perfectly round. This is because rims are not perfectly uniform and homogeneous.

It sounds to me that you've created a good wheel then, it is round and the spokes produce only a slightly varied sound when plucked. That's as good as it gets.
 
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