Weird misalignment

General
1

Since I swapped my 29" tire for a Maxxis Hookworm, I noticed that my wheel is not aligned in the frame. It never occurred to me before as I had a knobby tire, but the Hookworm being so round, I couldn’t help but see it:

It’s not shocking from the center of the tire, but if you look closely, the center mark on the tire (from the mold) is not aligned to the seat post:

Yet, if you compare both sides, it’s pretty clear:

A good 3 or 4mm difference!
Of course, as I’m completely OCD (aren’t all unicyclists?), it had to be the explanation to my problems with going in straight lines. Blaming the equipment is easy, hey…

It became an obsession, so I had to come up with a fix. So I thought: maybe my wheel is not true. I figured that turning the wheel around would tell me if it was the culprit. I could always swap the cranks if it was better. But it didn’t make a difference: the offset was still exactly the same. Well, the frame had to be the culprit then.

And it became obvious when I took out the bracket from one side only, leaving the other side pretty tight:

The wheel was perfectly aligned, with no play. I tried to retighten the side I had just unbolted, the wheel went off right away. More than a bent frame (that can happen, I bought that uni second hand and have no idea what it went through in the past), I thought it was probably a badly made frame, with one leg longer than the other.

For a while, I’ve been looking for an excuse to get a 2015 KH uni. That was the perfect opportunity - CDK has started to offer 2015 KH frames, so I figured I could have a new uni for cheap. Just swap the frame. I have a Zero saddle and a disc brake I could install later (my “bent” frame doesn’t have the disc mounts). Got the new frame, and today I got the tools out to do the swap.

And it’s exactly the same problem…

It doesn’t make any sense, does it? Same offset. I even measured the bearings diameter, in case, and they’re identical.

So I ended up cutting a little insert to put in the bearing bracket. First one I made (.5mm thick) was too thick and the offset went all the way to the other side. Found thinner material (.25mm) and now my wheel is exactly in the middle.

Might get a wheel and build a spare 29". After all, I have all the necessary parts laying around.

Is your wheel perfectly aligned?

bad habit: riding twisted?
2

I have about the same amount of an alignment issue on my 24 nimbus muni, but with such a stout wheel, I’m not particularly worried about it.

Just check to make sure that it’s not a tire issue, either from the tire being wonky itself or more importantly, the bead not being set.

After that, I would take the wheel off and measure the actual distance from the inside of the frame to the rim to convince yourself that yes, it is indeed off.

A wheel can be true, but not centered as well, in fact all bikes have dished back wheels, which may be what’s happening, even though the spoke length is the same, if one side is screwed in slightly more than the other, you’ll have a slightly (very slightly) dished wheel, causing the misalignment. A wheelbuilder can fix this if you take it to a bike shop.

3

I seem to have the same problem. I only noticed after installing a rim break, and it is really annoying, because on one side my lower leg pushes against it while hopping or mounting the unicycle.

What material did you use? I should try that, too.

Edit: I just put in a new wheel, built by UDC (Nimbus hub/KH rim), so I assumed it’s true and centered.

4

As I wrote (but maybe it got lost in translation, english is not my first language), I first thought that the wheel was the culprit and that I would need to readjust the spoke tension to shift the rim within the frame - I had to do that on the 36" I bought second hand last year: the previous owner had readjusted all the spokes by ear to have an even tension… except that the wheel was dished (disc brake) originally. By doing so, he centered the wheel perfectly with the hub, but it was off in the frame by almost an inch.
In my case, I turned the wheel around - left pedal went on the right side and right pedal on the left side. If the wheel had been not centered, or the tire uneven, then the offset with the frame would have changed. But it was exactly the same, showing that both the wheel and its tire are perfectly centered with the hub.

I had some hard plastic laying around so I used that. Since it’s a thin strip pressed between the bearing and the holder, it shouldn’t have a chance to be compressed or move around. I might replace it with a metal sheet to make sure it won’t move at all.

I will check the 24", but it’s probably less of a problem as the tire is a big Duro. Also, the diameter being smaller, a longer leg on the frame won’t give such an offset at the top of the wheel.

5

The average person has more difference in leg length than that, and some scoliosis as well, not to even get started on right or left dominance (we all turn to one side when learning, right?). It is hard to imagine that a tiny wheel tilt will matter more than that.
You could test this by moving your contact on the seat a bit to the side and see how that affects your riding, or by turning the seat around and riding backwards.
I suspect that if this asymmetry doesn’t break your wheel or frame (which it probably won’t) then it doesn’t matter at all.

6

Me too. Not to ruin a perfectly good OCD thread, but if I see something’s not perfectly lined up, yet I can’t detect any effect on my riding, it’s not worth worrying about.

Unless I really have nothing else to do and I like to tinker. :slight_smile:

7

Cdo

I am now refusing to look at my Sun Classic 29’’ unicycle’s wheel for fear it will reveal the same fault. Please oh please don’t be the same. My brother says I have CDO - Obsessive Compulsive Disorder, only alphebetized, like it should be. I won’t look. I cannot afford to. Literally. I cannot afford to repair it right now if it proves off.

Is your uni fun to ride? Take a bow to the gods of CDO and just ride it. Or your shim.. an excellent solution. I may check my wheel tonight. NO! I will check it in the morning, in 6 hours, 42 minutes, 53 seconds. That would be a good time to check it.

8

…as long as you don’t have a rim brake…:frowning:

9

You nailed it! :smiley:
Also, I was looking for a perfect excuse to get a KH2015 frame…

10

But whatever you do, don’t measure your leg length!:slight_smile:

11

I won’t… Especially as I know they’re both different, as mentioned by two different osteopaths I see!

I swapped the plastic insert with a metal one. Had an empty can in my recycling bin, so I measured it and it’s .25mm thick. Perfect!

12

me too

I have the same problem with a brand new KH2015 29" frame. I built and trued up a new carbon rim in the frame yesterday, and was congratulating myself when I thought I’d just check it was the same with the wheel the other way around. It was way off (yes with the bearing cup holders tight).

I can true up the frame with 3.5 strips of tin can (red bull) in one of the bearing cup holders for perfect alignment, but this almost fills up the space between the lips of the holder, so it could force out sideways more easily. I’m probably more worried that the reduced diameter could damage the bearings though. Any thoughts on these problems?

Am I being OCD in expecting tighter manufacturing tolerances? Should I return it, or are they all this bad?

13

Flipping the wheel around during the wheel build is always a good idea. Did you use a wheel building rig or just build it in the frame?

14

3.5 strips from a can? That seems a lot.

I achieved my .25mm (hardly anything I know, but it shifted the rim by the required 3mm to align it perfectly) with a piece cut from a can of mushroom I had in my trashcan. The strip of metal only covers half of the bearing holder (on the frame side) as I don’t need to add any at the bottom.
I view it more as a shim than a bearing reduction - if that makes any sense.

I too was a little disappointed by that. Ok, it’s “only” a unicycle, but still it’s supposed to be the top of the best…

15

If the wheel was built with dish to compensate for the frame installed one way, then when it flipped it seems like it would show twice the error - a true one would show half as much when inserted either way.

16

One quarter of a millimetre is a very tight tolerance in any welded object especially of that size.

I expect the KH welding jig was very precisely dimensioned. The small variation would arise due to uneven temperature rise and hence thermal expansion during welding. Even to achieve this tolerance would have required a well controlled welding process.

The precision solution would be to machine the bearing holders after welding.

17

Indeed it’s precise… on my two KH 29" the shift at the top of the wheel is exactly the same… :slight_smile:

18

It might be worth examining the bearing holder on the non-shimmed side.

I recently got a (non-KH) frame where the weld melt had penetrated deeply enough from the outside that there was a slight bulge on the inside where the bearing was supposed to sit. Wasn’t pleased, but a stone on a dremel tool cleaned it up.

19

Hmm… Robotic welding? Maybe that’s something that should be taken for granted these days, particularly on aluminum bike/unicycle frames.

Somewhere in a thread around here I remember Roger from Nimbus giving this as one advantage of the D’Brake disc caliper mount. Every time you heat metal by that much, it changes shape when it cools. Welding a caliper mount onto one leg is one more chance for it to go out of alignment that needs to be controlled.

Excellent job locating the source of the issue.