Front Hub Offset?

I just laced up new 19" WM2 Excel rims for my '74 850 Commando. I used new stainless spokes from Buchanan's. I'm concerned that I don't have the correct offset for the brake rotor. Can someone on the forum with this setup please provide me with a measurement for the distance from the outside of edge of the rim to the outside of the brake rotor? I currently have a measurement of 1 5/8" (42 mm) and fear that may be too great.

Thanks,

Jim

I got 1 5/16" on a bone stock 72 750 steel dunlop rim. If you look across the rim edges from a distance the actual hub outside surfaces are pretty equal on each side. This means the side with the spoke holes on the outside edge sticks out whereas the opposite side with the build up for the disc also sticks out the same but the spoke mount ridge is inside the edge of the rim. Basically the outside edges of the hub are equi-distant from the edge of the rim.

Jim, if the bike is assembled, measure the distance between the rim and the fork on each side with a calipers. The offset should be that which allows the rim to be centred in the forks, i.e. the measurements on each side should be the same.

That would be why they were able to spin it around from 73 to 74 so the caliper was on the left in front of the fork leg. It had to be centered.

I have a new set of 73 wheels I just got back from Buchanans with Excel WM3's. When I get home I will measure mine if you want. My rim size is differant so you will need to take that into consideration. Personaly I would call Buchanans & ask them. They are very nice people to meet or talk to and given you bought spokes from them I'm sure they would be glad to advise you.

gtsun said:

Personaly I would call Buchanans & ask them. They are very nice people to meet or talk to and given you bought spokes from them I'm sure they would be glad to advise you.

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Wisely spoken

Thanks for the replies. I'm still working on resolving this question. I called Buchanan's (twice) and didn't get an answer that I understand either time. My first call was answered by the receptionist who consulted with someone off the line and came and told me that the offset was. "...1-13/16" from the hub center to the disc mount." I asked what the measurement was from the ouside of the disc rotor to the line across the edges of the rim and she just repeated the above statement. I tried to apply that information to my rim and was stumped so I called again, this time speaking to someone I think was a technician. He told me that the 1-13/16" measurement was, "... from the center of the rim to the disc mount." I am obviously missing something here - can someone explain where that measurement applies? I sure couldn't figure it out. It looks like that number should be closer to 1-3/16. Old Britts' write up on wheel lacing says the offset is 1.4" om WM3 rims. I have WM2 Excel rims and the bike is not together. The 1-5/16" number previously provided sounds about right (thanks!). If someone has Excel WM2 rims mounted up I sure would appreciate a confirming measurement from the outside edge of the rotor disc to the line across the edges of the rim.

Jim

Jim, I understand why you want a precise dimension for the offset. Did you build the wheel yourself? I kinda got that from your first post. Regardless of what Buchanans say, and regardless of rim size, you would still have to stick the wheel into the forks, nip everything up, check that the rim is centred in the forks, and adjust the spokes if you have to. I feel that this is the most important thing, since it provides a datum to enable the rear wheel to be aligned, which is awkward enough to do on a Commando but vital for good handling. Even if your bike is apart, you can still put the forks into the triple trees, stick the wheel in and do the job on the bench. If the front end is completely dismantled, it might be better to wait till you can re-assemble it and then measure and adjust, as necessary.

Like you, I rebuilt the front wheel myself and I did as I suggested above.

How does this sound to you?

Dave

Jim, I'm sorry I got busy & forgot to measure mine last night. If someone with a WM2 rim hasn't done it for by the time I get home today I will measure my Excel WM3 & we will figure out the diferance. I must say you guy's must like a chalenge. I have laced bicycle rims but wouldn't try this. I've watched my friend who owns a Indian restoration shop rebuild wheels on his custom truing stand. He has dial gages for checking all directions & it's a learned art to do. One BIG bit of advice I learned from him. Always cover the threaded spoke ends with tape or something. They are razor sharp & will scratch your rim. He uses little plastic nut caps you can by at any good hardwere store. If you don't you will have tiny little scratches on your new rim from where they lightly grazed them finding the holes during assembly. My friend got cocky lately, thought he was more carefull after all the years but had to disassemble & re powder coat a rim when the little scatches showed in the day light. I should be able to get you the measurment by 5:00 pm Caifornia time. Glenn

As daveh already recommended, simply fit the wheel assembly into the forks and check if the rim is centrally postioned between the fork legs.

If the rim is off-centre to either one side or the other, then re-adjust the rim until it is in the middle of the forks.

It really is as simple as that!

Here are some shots of my Borrani WM2 rim and a Norton hub. I noted what I think Buchanan meant but the bottom line is - the outer surfaces of the hub should be equi-distant from the center of the rim. As Dave said instal the wheel in the forks and do the final fine tuning there.

I think I finally get it. Thanks to all for the patience and assistance!

Jim

No problem, disc brakes are a lot less forgiving than drum brake hubs.

RennieK said:

Here are some shots of my Borrani WM2 rim and a Norton hub.

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Rennie,

I'm guessing you have a 19" rim, but you wouldn't believe what people are asking for 18" Borrani 4777 rims these days....
One on fleabay recently ...asking price £1500 :shock:

Apologies for drifting off-topic

Yes it's a 19" Maybe I can cut an inch out and re-weld it for that kind of money. That is an unbelievable price!