Commando Rear Wheel Offset

Previously wrote:

Chaps et chapesses, does anyone happen to have MK3 rear wheel in the shed/workshop? What I've done is to re-spoke the wheels on my bike and I completed the front wheel a month or so ago. Being 'experienced' in these things now I attacked the rear wheel today with gustobut, being a numpty, I completely forgot to measure the offset between the planes of the wheel rim and the brake disk flange. So, having re-spoked the wheel and spending some time getting it to run true in both planes, I do not know whether the hub actually runs in the centre of the wheel, or even if it SHOULD run in the cenntre of the wheel in its vertical plane.

So, would you mind measuring that offset for me - it is explained better by photographs 6 and 7 at http://www.webbikeworld.com/motorcycle-wheels/spoke-wheels/

Thanks again.

Peter.Hello Peter .its your lucky day just stipped a mk3 back wheel today the offset is 15/16 from disc flange to outer rim hope this helps Colin Blundell

Which rims are you using Peter ? My 19" has a WM3 Akront on so my measurements won't give you an absolute figure. However, the height from the disc flange to the very edge of the rim is .750" and on the other side, if I put an edge across the machined face where the cush drive locates, I measure .830"

I don't of course know if this wheel was accurately built and if you're not running the same sort of alli rim, this will add another varuiable.

The front rim isn't central in the hub, as you'll have found but should now be central in the forks. The rear rim should be in line with the front, if you haven't yet fitted a tyre, you can check to be sure.

I've recently had reason to look at where the rear wheel sits in a Mk3 swinging arm and came across this topic (amongst others).

First, a little preamble: In the bicycling world the lateral location of the rim relative to the hub on a spoked wheel is referred to as "dish". And, since all our machines can trace their origin back to the bicycle (https://www.nortonownersclub.org/html/nocclassifieds/oc-content/uploads/18/2028.jpg), I think it would be useful for "dish" to be used in preference to "offset". Central Wheel use both dish and offset interchangeably.
To set the dish, we need a datum on both the hub and on the rim. The rim is pretty easy : the centre line; thereby addressing variations in rim widths. And measuring to the centre is simply accomplished by measuring to the outside of the rim then adding half the rim width.
Finding the centre of a full-width hub is similarly easy but asymetric hubs, like the Mk3 rear, are a little more tricky. So the best datum is a machined surface, such as the disc mounting flange (and hope they've all been machined the same). The datum used should always be stated to avoid confusion.

Anyway, on with some numbers.

I have two rear wheels built at seperate times with different rim widhts by Central Wheel. They identified the hub as Mk3 Commando without any input from me so I assume they know how they should be built. The dish, measured from disc flange surface to rim centre is 57.5mm for both wheels.

On Access Norton I found a report giving outside disc surface to rim centre as 3 1/8" (3.125"). When I measure the same on my wheel I get 79.5mm (3.13"). And another report of disc flange to rim centre as 2 3/16" (2.375"). My 57.5mm, above, being 2.264". There were some other reports but it wasn't clear what they were measuring.

The 15/16" (23.8mm) to the rim reported above by Colin Richard Blundell, when re-referenced to the rim centre and assuming an original WM2 19" chrome rim (68.3mm wide), is 58mm.

There seems to be a consensus then that the dish on a Mk3 Commando rear wheel is 57.5mm to 58.0mm - disc flange to rim centre line. And this equates to the rim being offset by approximately 7mm to the right (disc) side from one centred on the hub.

RGM has the offset info in their tech section.

Other than the offset there are some serious pitfalls in building MK3 rear and Norton disc front wheels. Using chromed steel or alloy rims reduces the chances of encountering these problems, using stainless rims and spokes needs more care to avoid them. 

I have seen 3 stainless wheels where the nipples have been tightened so much that the rim cracks from one piercing to the next on the rim. The use of anti seize grease on the nipples reduces the torque needed to obtain the tension, this can cause undue concern when you have the wheel at the correct offset as one side of spokes will be well tensioned and the other side will be tensioned to quite a low figure - this is normal just check your old wheel and it might scare you. 

The other issue is that you must start from a good known position and pull the rim over to the correct offset, the reason you need a known good starting position is that when you pull the rim over towards the correct offset the spokes you are not using to pull the rim over will slowly tension themselves you can easily increase this tension to very high levels very quickly, that is why the known good start point is critical. 

The spoked wheel is a 'fluid' item, mechanically we ask a lot of it and spokes being too tight creating a rigid disc are just as likely to fail as rim spokes too loose. 

However, it is not beyond the capability of owners with mechanical experience to build a wheel, and it is actually very rewarding when you do. 

I hadn't seen the RGM information. It's in their tech tips section: https://www.rgmnorton.co.uk/dept/tech-tips-help-instructions_d01253.htm

Roger's measurements, assuming a 68.3mm wide rim, put a Mk3 rear rim 1.6mm to the left of the owner reported dish figures I've found. Not a lot but 1.6mm closer to the chain and makes the right side gap 3mm greater than that on the left - on the verge of noticeable.

Hello Ashley, I'd hoped you'd pop by and let us know the definitive answer from the factory specifications you have.

Hi Stan,

RGM`s "offset" of 1" from the drive side concurs with a complete NOS wheel I got from TMS still with original part number stuck on it. Therefore the measurement you "dished" up from this would be correct.

Best regards, Al.

The figures we recommend and have had no feedback from, and I used myself are - 

Front  0.5''  +/- 0.020''

Rear 0.9''  +/-0.010''

Both are from the disc face of the hub. These figures were checked against my old wheels and found to be very close to within a mm. 

In the world of Norton and especially MK3 Commando do not assume original unused stock is correct.  

Hi Ashley,

The NOS rear wheel is exactly the same as my other Mk3 wheel so I think that it is right.

Best regards, Al.

Ashley wrote: "Rear 0.9''  +/-0.010'' ... from the disc face of the hub" . To where please?

To outside edge of rim