Cycling UK Forum

I bet someone can point out the fundamental error that I am making. I am not a experienced builder but have managed to do a few and can get to within a mm laterally and about the same off round. Just put one together which I was pleased with, stuck a tyre on and put it in the bike. Its about 4mm to the right or the frame centre line yet was dead central in the jig.
Jig is set up properly as is the hub etc. Other wheels have the rim central to the hub locknuts but if this is set like that its all to cock.
What am I missing? I have always assumed that rims were central to the locknuts but this doesn't want to work like that.
As I said I am sure I am missing something but what?
I suppose I could true the wheel in the frame but what a pain.

Is the wheel centred when you put in the jig the opposite way around?
If it is then the frame is out.

Frame has a distinct kickout to the the right dropout so a non symmetrical set up would make sense but I swap in several other wheels which as central between the locknuts and they are fine. It all seems as if I have an extra spacer in the left side except that its all cartridge bearings with just one spacer and they cannot be swapped side to side.
Sort of thing that some one else looks at and says, "you silly thing, why have you done that?"
Hmm. Too cold to trail up the garden, unlock the garage and check if the wheel is the same in the jig reversed.

Is this a front wheel, or a dished rear wheel?

Dished rear.

mattsccm wrote:Dished rear.

Which the rim still should be centred OLN.

A number of "Orbit" frames were built with the rear triangle offset 4mm to the right......others, too, have some deliberate asymmetry. **
The best test (as said already) is the "turn it over" test........put the wheel in the frame and "turn it over" so the cassette is on the "wrong" side.......if the rim ends up in the same place in the frame, then the wheel is symmetrical, and the frame isn't.
Have you got the wheel that was in this frame before?....do the same turn it over test with that, both in the frame and in the truing jig.

**....to reduce wheel dish.....a stronger wheel for nothing.....well, nothing more than a bit of head scratching!

531colin wrote:A number of "Orbit" frames were built with the rear triangle offset 4mm to the right......

Mind reader

reohn2 wrote:

531colin wrote:A number of "Orbit" frames were built with the rear triangle offset 4mm to the right......

Mind reader

Pace did some as well.....I'm sure there are others?

get a piece of thread and tie it to one dropout. Run it from there to the opposite side of the headtube, round the head tube and back to the opposite dropout. Measure the gap from the thread to the seat tube each side. If it is different each side then the frame is offset. If the frame is offset, it either means it is bent (damaged) or it was deliberately built like that.

cheers

Right then.
Tried Bruceys trick. Extra 4mm of space on right of seat tube to string and you can see the offset in the chainstay. No damage. Its a modern steel frame so over built.
Checked with two other wheels that are regularly used in this frame. Both are symmetrical (rim is central to locknuts) when checked in the jig and the bike. Both sit central in the frame. Neither came with the frame and both as standard. One a Deore hub, the other an old Hope XC. The mystery one is a On One that came with another bike, was stripped and a Deore hub put in and is now back to its old hub.
To my simple mid the fact that the frame is offset shouldn't match the symmetrical hubs but they are fine.
The only thing I can think of is that the spacers are in wrong thus pushing the whole thing to the right but I cannot make them swap, they have different diameters.
Another look with more time then I reckon.

If you have to leave the house to access the jig, something is clearly not right.

The whole point of an Orbit-style offset rear triangle is that the rim is central (or nearly so) between the hub flanges, /not/ central between the locknuts.
If you reverse such a wheel, in either frame or jig, it will be way out.

If the rim is centred between locknuts, and reversing the wheel in both frame or jig leaves the rim in the same place, and the string shows an uneven gap at the seat tube, that implies that the rear triangle is symmetrical, but it's at an angle to the top tube - i.e. the frame is bent.
The fact that you've been riding it with no problems just shows that you can get used to riding just about anything.

If frame bent why would 2 other wheels fit and run perfectly? As said, they are central between the locknuts and central in the frame.
Coming to conclusion that at some point i have done something silly with hub bearings and spacers. I am dead certain that the chainstay isnt bent. Everything else is true, even the dropouts are parallei.
Will check my measuring. The string placement was a pain to get 2 clear runs with dic brake stays, bottle cages and non identical dropout design.

Heres a thought. Cant check as the first thing i did was start messing with the offending rim. If my tensioning was crap would the rim move with tyre fitting and leaning on it etc. Didn't think it was loose, squeezed spokes but no tension meter used. Plenty of care, or so i thought, checking tension by feeel and sound