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Front wheel rim offset on a 850 mk 2a Commando #74775
05/17/08 5:26 pm
05/17/08 5:26 pm
Joined: Aug 2006
Posts: 730
Dordogne, SW France
johnnyrvf Offline OP
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johnnyrvf  Offline OP
BritBike Forum member

Joined: Aug 2006
Posts: 730
Dordogne, SW France
Hi All, just had the wheels rebuilt with std dunlop chrome rims and s/s spokes the rear wheel is fine but the front rim is not central in the forks, the hub is perfectly spaced in the forks as the disc is perfectly central in the caliper. If an off set is needed I calculate the rim centre has to come over by 5.5 mm ( sorry it's in metric ) , is this normal? the guy who respoked the wheels normaly does modern motoX bikes and may well have not measured the offset before he dismantled the old wheels. Johnny confused


What d'ya mean it won't rev to 10?
1965 BSA A65D Lightning Rocket
1976 K*w*s*ki Z900.
1978 Triumph Bonn3ville (930 T160 Powered T140)
1988 H*nd* RC30
1990 Moto Guzzi California 3
1993 Y*m*h* TDM 850
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Re: Front wheel rim offset on a 850 mk 2a Commando #74776
05/17/08 6:28 pm
05/17/08 6:28 pm
Joined: Dec 2004
Posts: 9,553
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,553
Scotland
The Commando front disc rim is one of the worst rims to true, on one side the spokes are nearly vertical. Sounds like your guy couldn't beleive how much they needed to be vertical.

From Oldbritts The front disc rim to hub offset is approximately 1.4". The hub is approximately 4.5" wide and the edges of the rim are the same distance from both ends of the hub.

More info here http://www.oldbritts.com/lacing_info.html

Re: Front wheel rim offset on a 850 mk 2a Commando #74777
05/17/08 7:45 pm
05/17/08 7:45 pm
Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
J
John Healy Offline
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John Healy  Offline
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J

Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
Using a Dunlop/CWC WM2 rim width of approx. 2.680", the rim offset is 1/2" from the face of the hub where the disc mounts to the edge of the rim.

This is a rim you have to do like a lot of automotive wire wheels. You have to true the rim with just 20 (disc side) near verticle spokes until you have about 1/2" LESS offset than required (the actual amount varies with the stifness of the spokes being used). You will want to get them as tight as they will be on the finished wheel. The other 20 spokes are left loose.

Typically when you start trying to get the required extra offset you will have to place the hub on a block and place both feet on the rim. I have been told by Brian Slark that this is how they did it at the factory.

Actually once you get the concept it isn't such a bad rim to do.

At this point the disc side edge of the rim will be flush, or a little bit outside, the disc mounting surface of the hub. Now, using the non-disc side 20 spokes you pull the rim back until you have the required 1/2" offset. You will not be able to get these spokes anywhere near as tight as the near verticle set. If you did a good job of getting the rim true on both planes before you pulled it over the rim should require very little tweeking.

I would check the rim in the forks making any adjustments required before mounting the tire.

Hope this helps.
John


Re: Front wheel rim offset on a 850 mk 2a Commando #74778
05/17/08 9:07 pm
05/17/08 9:07 pm
Joined: Sep 2002
Posts: 554
belgium
ludwig Offline
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ludwig  Offline
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Joined: Sep 2002
Posts: 554
belgium
johnnyrvf , this ridiculous offset is one of the absurdities of a Commando . The rim HAS to be exactly in the middle of the fork . To achieve this , and at the same time get suficient tension on the nondisc side spokes is allmost impossible . Short of making a one off hub ( as I did ) , you could remove 2 mm of the disc flange and/or remove 2 mm of the hub face .
Remove an equal amount of the wheel spacer .this extra 2-4 mm will make centering the rim so much easier . (For liability reasons , a workshop may refuse to turn off the disc )

Re: Front wheel rim offset on a 850 mk 2a Commando #74779
05/17/08 9:34 pm
05/17/08 9:34 pm
Joined: Aug 2001
Posts: 1,285
Hamilton, Mass. USA
D
Dave Comeau Offline

Crew Chief
Dave Comeau  Offline

Crew Chief
D

Joined: Aug 2001
Posts: 1,285
Hamilton, Mass. USA
My measurements agree with John on this one.

However, the Old Brits tech article wheel pix, on the disc side, show a transposed (inner vs outer) spoke pattern from original. I would think it goes down the road OK, but since Fred admits to not lacing rims this detail may have eluded him.
On a properly pierced front disc rim, this wheel MUST be correctly oriented on the hub.... left/right must be respected or it will not even lace up in a mechanically sound fashion.
help


dynodave
BSA 3 1961-1963
Ducati 3 1992-2002
Norton many 1951-1975
87 Serv-Equip 100HP MC brake dynamometer,
Re: Front wheel rim offset on a 850 mk 2a Commando #74780
05/17/08 9:48 pm
05/17/08 9:48 pm
Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
J
John Healy Offline
BritBike Forum member
John Healy  Offline
BritBike Forum member
J

Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
Actually Ludwig, many thousands of these were done by the factory, and if you examine most automobile wire wheels of the era you will see a similar problem. One set of spokes near vertical.

The Triumph rear disc wheel is laced in a similar manner with one set of spokes nearly vertical, and is certainly strong enough if you use the late spokes and nipples (early T140 disc rear wheels used too small a spoke and nipple and spokes failed).

While you have to know, or learn, what you doing it is not that difficult wheel to do. It takes us no longer to lace, true and tension a Norton disc wheel than any other of the ones we do.

The key to doing these wheels is the amount of initial extra offset (this varies with the spokes being used) which allows you to tighten the off disc side spokes and not pull the rim past the proper offset.

While i encourage you, and find it interesting that you created your own solution, if you are faced with lacing and truing the original set-up it is nice to understand what the task intales... or should I just keep my mouth shut!
john


Re: Front wheel rim offset on a 850 mk 2a Commando #74781
05/18/08 4:39 am
05/18/08 4:39 am
Joined: Aug 2006
Posts: 730
Dordogne, SW France
johnnyrvf Offline OP
BritBike Forum member
johnnyrvf  Offline OP
BritBike Forum member

Joined: Aug 2006
Posts: 730
Dordogne, SW France
Hi All, thanks for the replies...... The person who laced the wheel is in his twenties, French and does'nt speak any English, his Father had a friend when he lived in Paris who had an old Norton and from what he was telling me he won't be surprised by this, how I explain all this in French is going to be a challenge, but I'll persevere! Johnny. :bigt:


What d'ya mean it won't rev to 10?
1965 BSA A65D Lightning Rocket
1976 K*w*s*ki Z900.
1978 Triumph Bonn3ville (930 T160 Powered T140)
1988 H*nd* RC30
1990 Moto Guzzi California 3
1993 Y*m*h* TDM 850
Re: Front wheel rim offset on a 850 mk 2a Commando #74782
05/18/08 9:17 am
05/18/08 9:17 am
Joined: Sep 2002
Posts: 554
belgium
ludwig Offline
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ludwig  Offline
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Joined: Sep 2002
Posts: 554
belgium
Quote
.. or should I just keep my mouth shut!
john
But of course not , John !
For museum or show purposes it is important to know how things where done at the factory ,
and from a financial point of view , absolute originality is definetely the way to go .
But if you want safety , perfomance, ease of maintenance and reliabitity , than there is more than one part of a Norton that can benefit from some "re-engineering " ( to put it politely ).
The extreme offset of that hub is simply not nessecary .the spokes clear the caliper by about a mile . Personally , I am more inclined to correct engeneering mistakes from the past than repeating them . If the factory had done the same , they might still be in buisiness .

Re: Front wheel rim offset on a 850 mk 2a Commando #74783
05/18/08 9:52 am
05/18/08 9:52 am
Joined: Aug 2006
Posts: 730
Dordogne, SW France
johnnyrvf Offline OP
BritBike Forum member
johnnyrvf  Offline OP
BritBike Forum member

Joined: Aug 2006
Posts: 730
Dordogne, SW France
Hi Ludwig..... Ain't THAT the truth! confused :rolleyes: mad Johnny.


What d'ya mean it won't rev to 10?
1965 BSA A65D Lightning Rocket
1976 K*w*s*ki Z900.
1978 Triumph Bonn3ville (930 T160 Powered T140)
1988 H*nd* RC30
1990 Moto Guzzi California 3
1993 Y*m*h* TDM 850
Re: Front wheel rim offset on a 850 mk 2a Commando #74784
05/18/08 7:40 pm
05/18/08 7:40 pm
Joined: Sep 2002
Posts: 554
belgium
ludwig Offline
BritBike Forum member
ludwig  Offline
BritBike Forum member

Joined: Sep 2002
Posts: 554
belgium
Quote
..not pull the rim past the proper offset.
OK John , but this is a static situation . What about the extra pull generated under hard braking ( asuming you have a decent front brake ) ? The ( few) times I had a factory laced motocross wheel in my hands , I have allways been surprised how tight the spokes where . The tension on the LH spokes on a disc braked Commando is nowhere near 0.5 kgm .I 'll readily admit that Iam not shure about this ,but I can't help but think that under heavy braking , the rim moves further to the left , when these 10 "loose" spokes come under tension . Many Commando owners complain about drifting and pulling to the left . Is there no relation with this hub offset ?

Re: Front wheel rim offset on a 850 mk 2a Commando #74785
05/18/08 9:33 pm
05/18/08 9:33 pm
Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
J
John Healy Offline
BritBike Forum member
John Healy  Offline
BritBike Forum member
J

Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
Ludwig: If you were really worried about correcting engineering mistakes would you be riding a Commando in the first place? Well it should keep you busy.

I guess I should shut up and go back to the Triumph Forum... wink wink

It's a joke Ludwig... just a joke!
John



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