Rear wheel rim off-set (Again - sorry)

I have brought down from the rafters of my garage an old 850 Commando wheel with a view to reusing it.

It has the slots to accept cush drive buffers.

It is fitted with a Akront 2.15" WM3 18" rim and as yet no tyre.

I fitted the bare wheel into my 850 Command without any problems with fittings or spacers.

I stuck a piece of gaffer tape tightly across the rim and marked the centre of the rim with a pen mark.

I taped a piece of rigid plastic across the rear frame loop roughly above the axel and marked the centre
of the frame loop with a pen mark.

I hung a plumb-line from the centre line mark of the frame loop down the the tape on the wheel rim and
found the center of the rear frame loop lined up exactly with the centre mark on the rim.

However, I then measured from the inner edge of each side of the swinging arms to the centre mark on
the tape on the rim and found the centre of the rim is off-set to the LEFT (primary drive side) by 1/8"

The stardard WM2 19" rim is "specified" as being off-set in the swinging arm by about ( ) 3/16" to the RIGHT

My WM3 18" rim is off-set to the LEFT.

Do I need to worry and get the rim moved over,
or have a beer as the centre of the rim is in the centre of the frame loop?

I think the rim being in the centre of the frame loop isn’t very relevant.

Normal procedure AFAIK for wheel alignment is to first centre the front wheel in the forks. And then align the rear wheel to the front.

Staytite said:

I stuck a piece of gaffer tape tightly across the rim and marked the centre of the rim with a pen mark.

I taped a piece of rigid plastic across the rear frame loop roughly above the axel and marked the centre
of the frame loop with a pen mark.

I hung a plumb-line from the centre line mark of the frame loop down the the tape on the wheel rim and
found the center of the rear frame loop lined up exactly with the centre mark on the rim.

Click to expand...

That sounds as if the offset is correct.

Staytite said:

However, I then measured from the inner edge of each side of the swinging arms to the centre mark on
the tape on the rim and found the centre of the rim is off-set to the LEFT (primary drive side) by 1/8"

Click to expand...

Sorry to have to ask but do you mean the rim was 1/8" closer on the left side than on the right as the offset would then be 1/16" as it's a fairly common mistake to subtract one measurement from the other without dividing the result by 2 in which case the wheel might only be out of alignment?

Staytite said:

The stardard WM2 19" rim is "specified" as being off-set in the swinging arm by about D) 3/16" to the RIGHT

Click to expand...

The rim should be offset to the right of the hub which should put the rim on the centreline.

Hi LAB
To confirm :Tthe centre mark of the rim is central in the rear loop
The centre mark of the rim is offset to the left in the swinging arm (which worried me as it is said the standard rim needs to be offset to the right)
Thanks

Fast Eddie said:

I think the rim being in the centre of the frame loop isn’t very relevant.

Normal procedure AFAIK for wheel alignment is to first centre the front wheel in the forks. And then align the rear wheel to the front.

Click to expand...

+1

Here's how they tell you to do it in (forgive me) Triumph Workshop manuals - slightly harder on Norton since the front and rear wheels are usually the same width.

That method is fine when you have both wheels fitted with tyres and on the bike.
What do you do tell your wheel builder to do when you have a hub and a rim?

Staytite said:

To confirm :Tthe centre mark of the rim is central in the rear loop

Click to expand...

And which seems normal.

Staytite said:

The centre mark of the rim is offset to the left in the swinging arm (which worried me as it is said the standard rim needs to be offset to the right)

Click to expand...

Ok, but the rim is offset to the right of the hub centre.

I wouldn't place too much importance on the distance between each leg of the swingarm and the rim as the swingarm isn't symmetrical and which may only suggest the wheel is not correctly aligned with the frame/front wheel as there has been no mention of actual wheel alignment (and you didn't answer my offset measurement question).

Staytite said:

That method is fine when you have both wheels fitted with tyres and on the bike.
What do you do tell your wheel builder to do when you have a hub and a rim?

Click to expand...

In that case you have two options...

If it’s a stock (ish) bike then you go to a knowledgeable wheel builder who will know what offsets to build. You really should still check using the above method when they’re done though, you don’t need tyres for this BTW. This isn’t just blah, blah. I had my wheels done by Central Wheels and they were WAY out!

If it’s a total special then you assemble the hubs into the chassis, work out where they need to be based on sprockets and discs etc, then using a centreline from the headstock, calculate the required offsets. Of course, you then check and tweak them when they’re done cos unless you’re a chassis guru you’ll probably be a bit out somewhere!

My main point in my first reply was that using the rear frame loop isn’t any good as a datum point for the centre line. Use the forks, or a plumb line from the steering head, and some straight edges and work from there IMHO.

Hi LAB

Sorry I did not answer your question with measurements: the centre line of the rim is 2 7/8" from the left hand arm
and 3" from the right hand arm, but my main worry was not the actual measurements rather that the centre of the rim
was off-set in the swinging arm towards the left rather than the right.

My thinking was that if the front wheel is centred in the fork legs, and the fork legs are centred on the steering head
bearing, and the steering head bearing is centred on the main spine tube, and the rear loop is centred on the spine tube,
so the centre of the rear wheel rim should be centred on the rear loop to be in line with the centre of the front wheel.
Does that make sense both grammatically and physically for a Commando frame?

Just been out into my garage and dangled a plumb-line through the hole in the rim for the inner tube valve. The pointer
is just to the RIGHT of the central rib of five. Difficult to measure with a glass of Primitivo in one hand but visually
it looks like the rim is off-set to the right of the centre rib of the hub by about 3\16"

Thanks

Fast Eddie said:

If it’s a stock (ish) bike then you go to a knowledgeable wheel builder who will know what offsets to build.

Click to expand...

The front wheel of my 850 came from the factory laced such that the wheel was about 1/8 inch off center to one side. You could see it just by looking at the tire from the front. I had the wheel laced with stainless spokes by Buchanans years later and it came back dead center between the forks. I spoke with one of the wheel builders there before sending the rim out to them and he said, "Right. Commando. Offset front hub. We know how to do that."

Hi Fast Eddie

Discs? Are they not specifically only for use by racers using methanol in the southern hemishere

Alignment is two fold.. First, things like chains and sprockets have to align so they wear correctly, but they do have a certain amount of acceptable tolerance... meaning that a tiny amount of misalignment between the rear drive sprocket and the rear wheel sprocket is probably not noticeable and the extra chain wear due to that is probably not significant. So, the engine is fixed in the frame by the isolastics. The rear sprocket is therefore somewhat fixed as well with tiny amounts of variation due to shimming and potential frame variation. So your rear "HUB" alignment is based on the sprocket alignment, but your rear "RIM/WHEEL" alignment is based on the frame center, which is controlled by the lacing of the wheels... (complicated sounding, but it works when done right...)

Secondly, in a two wheel vehicle, it's very easy to have a static alignment of the wheels on a centerstand. but that doesn't mean that the static wheel alignment continues to stay in alignment with the movements of the wheels when the suspension travels on both wheels. That would be why a very critical part of alignment is knowing that the steering head axis defines a plane of travel along with the center of the circumference of the front wheel which intersects the plane defined by the swingarm pivot and the rear axle in a perpendicular manner. This way when the swingarm moves up or down, and the front suspension moves up and down, the wheels continue to stay in the same plane

When all the above is set up correctly, and you do a simple static alignment of the wheels, (like Greg pictured above) then, the sprockets align, the wheels statically align, and then they dynamically remain aligned as they travel through their paths dictated by each one's suspension.

Most motorcycles don't have 1/10th of the trouble a commando has since their swingarms aren't part of an engine which is isolastically mounted. For the most part, we all assume our headstock and swingarm have the correctly alignment because to measure that properly, you need an engineer's granite surface plate table plus a lot of patience and skill.

IN my own case, I fitted cast wheels to my commando. I didn't worry about the sprocket alignment until after the wheel/rim was aligned in the frame, then i measured how far off the sprocket carrier was and had to cut it down ~.25" to line up with my gearbox sprocket. Unfortunately, Norton's rear wheel sprocket doesn't allow for any adjustment so your adjustment is based on having to get the hub aligned first so the sprockets are aligned, and then using the spokes to adjust the wheel center to be aligned to the frame center... (harder to do ) Once you are there, you can use Greg's set up, and you are good.

Staytite said:

Sorry I did not answer your question with measurements: the centre line of the rim is 2 7/8" from the left hand arm
and 3" from the right hand arm,

Click to expand...

Ok, therefore, it's off by 1/16", not 1/8".

Staytite said:

My thinking was that if the front wheel is centred in the fork legs, and the fork legs are centred on the steering head
bearing, and the steering head bearing is centred on the main spine tube, and the rear loop is centred on the spine tube,
so the centre of the rear wheel rim should be centred on the rear loop to be in line with the centre of the front wheel.
Does that make sense both grammatically and physically for a Commando frame?

Click to expand...

Yes, assuming the frame is straight and the (offset) cradle is aligned with the frame then with the correct hub-rim offset that should place the rim on the frame centre line and equidistant between the spindle/axle pads.

Staytite said:

Just been out into my garage and dangled a plumb-line through the hole in the rim for the inner tube valve. The pointer
is just to the RIGHT of the central rib of five. Difficult to measure with a glass of Primitivo in one hand but visually
it looks like the rim is off-set to the right of the centre rib of the hub by about 3\16"

Click to expand...

That sounds about right then.

Many years (decades acually) ago I worked in an precision engineering company while I was a student.
There was an old codger there (like me now) who used to say "that'll be about right boy" . He said that
when I had made some really complicated little pins for some sort of safety mechanism for nuclear
submarines

Thanks LAB I'll fit the tyre and go for a pint....or not

Q; is this rim for l.h. brake or r.h.?

Level your bike at the upper shock mounts.

Get a cheap line laser level that carpenters use, and set it up from above and rear so the line runs straight down the spine and the top/rear of the tire.

Then you can see if the tire/wheel is both straight in the frame and plumb.

Also worth checking is that the swing arm isn't warped.
= swing arm spindle and rear wheel spindle in the same plane.

Ok, to recap....

The Commando frame has the engine, gearbox, cradle, oil tank, Z-plates and forks fitted, but not the
mudguards. This makes it easier to set the rims in line in he forks and frame.

The frame has been checked for straigtness by Norman White. The cradle is a new one with the double
cotter pins from RGM and the swinging arm is new. The rear hub is built from all new parts.

The rim is a WM 3 x 18" with a measured width of 2.92" (74mm)

I stuck pieces of masking tape across the large diameter frame top tube and spent a lot of time
puting pencil lines in exactly the centre line of the top tube.

I used masking tape to fix a piece of wood across the rear frame loop roughly above the wheel axel.

Using a long straight edge I drew a line on the wood to line up with the centre line of the top tube.

Using a plump line I dropped the pointed bob down to see where the centre line of the rim (no tyre)
at the valve hole, that's the point used as a datum by the very experienced (lots of decades) wheel builder.

The frame is carefully wedged to be level left to right to ensure correct plumb line measurements.

Using this method I asked the wheel builder to adjust the centre of new rim to be on the line of the top
frame tube.

My thinking being that if the front wheel is exactly central in the forks, the forks are central in the frame
then the centre of the rear rim should be on the centre line of the top tube?

The result....

The centre of the valve hole is now exactly in line with the centre line of the top tube.

The centre of the valve hole is 70mm from the inner edge of the right swinging arm leg
The centre of the valve hole is 82mm from the inner edge of the left swinging arm leg
So the rim is off-set from the centre of the swinging arm by 6mm (sorry for metric I mean 1/4" !)

A plumb line from the valve hole shows its now above the second rib from the right.

The question...

The very experience wheel builder said the spokes on the right side are more vertical than
he would have liked.

It is difficult to accurately measure the spoke angle, but it is about 10 deg off vertical towards the left.

The left hand series of spokes have a greater angle off vertical as the rim is off-set to the right compared to the hub.


Any comments gratefully considered.

Thanks

Wow that a lot of work for a street bike! On a Norton I build the wheel using: https://www.gregmarsh.com/MC/Norton/RearLacing.aspx, install it and get the rear sprocket in line with the front and other than a final check with two boards while not on the center stand (need a helper), I'm done. On a Norton, generally the boards will show the rear wheel straight with the front but a little right or left of center - I don't care - too many variables. On a Triumph it's perfect or something is bent or the nuts/spacers are wrong in the rear wheel.

BTW, on a Norton disk front wheel, the disk-side spokes are nearly vertical.

BTW, I use a piece of thick plate glass that is very flat to get the front forks exactly parallel to each other (needs to have short gaiters, can't do it with full gaiters installed - in that case you have to pull the sliders and check them there. Norton front ends never go together parallel for me when simply assembled and doing the compress and release trick. I recheck after each thing I tighten (top bolts, clamp bolts, spindle nut). I have one bottom triple tree that looks fine but is so bent that the forks cannot be made true.

Hi Greg

Thank you for your reply. Especially your observation that spokes on disc wheel
are nearly vertical.

The comment by my wheel builder about vertical spokes worried me a bit.

I have found in the past that having the front wheel perfectly central in the forks
eliminated the handle bar shake. And much reduced the vibration I thought was
due to the Isolastics.

My thinking is having the centre of the rear wheel rim in line with the frame tube
stops the infamous Commando weave.

Not a lot of work when the bike is partially built and no tyres fitted to the rims.