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front wheel offset on disk brake commandos

Classic Norton Commando Motorcycles.

front wheel offset on disk brake commandos

Postby manxman » Sun Jun 21, 2015 9:48 am

I'm a newby, so apologise if this has been covered. I read the "Crooked Norton" thread and thought I'd add my $.02

When I first got my '72 Commando barn bike running, I aligned the rear wheel with string, then "road tuned" it with hands-off coasting in 4th gear. I tweaked the rear adjusters until all tendency to side drift disappeared. This is the way I've always set alignment. Trouble was, with the bike coasting straight, it had a slight lean to one side. Never had a bike that did that. Then I noticed it handled slightly differently in right verses left corners. Not a huge difference, but it was real. It would drop into right hand corners, eager as a puppy, but had to be asked politely to go left.

When I checked the front wheel, the rim was offset 1/4" to the left. To my mind, there is no way a bike can be aligned if the front wheel is offset from the steering stem axis. Sure, you can get the 2 wheels to point in the same direction (by turning the back wheel with the adjusters so it no longer aligns with the steering stem either) and the bike will pass the "string test". But now neither wheel is aligned to the frame.

I went to a British bike meet and checked every Norton. 90% of the right-sided-disk Nortons were offset 1/4" to the left. Stick a finger on each side of the rim to gauge the distance to the fork slider. You don't need a micrometer.... this is not subtle.

I had the rim replaced (rusted from 17 years in a barn) and told the bike shop I wanted the offset removed. They assured me they would do it right and would lace my new rim exactly to factory specs. They had a brand new laced wheel straight from Andover they could compare it with, just to be sure.

The new wheel had the same 1/4" offset and the bike handled the same. I had them adjust the spokes until the wheel was centred. Now the bike tracks straight and handles the same right/left.

My theory: When Norton adopted that hulking huge Lockheed caliper, they had to get the spokes out of the way. That's why the hub is asymmetric and the "cone angle" of the right side spokes is flatter than the left side. The "cone angle" of the spokes determines the tension on the spokes under wheel side load. Flatter cone, higher load. (It's a trigonometry thing). That's why Norton uses thicker spokes on the right side than the left. I think some engineer got the willies and offset the rim to the left to increase the cone angle and reduce the spoke tension.

As a result, the world has crooked Nortons. I know it sounds ridiculous that Norton would deliberately mis-engineer the bike. But they do have a history of bad engineering. Look at that disk brake! It is the worst brake ever installed on a motorbike!

So, for anyone interested in a straight Norton, align your front wheel with the forks before aligning the back wheel with the front. Then both wheels will be aligned with the steering stem, instead of neither.

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Re: front wheel offset on disk brake commandos

Postby Beach » Sun Jun 21, 2015 10:37 am

HUH......mine was laced exactly the way Old Britt says, which is exactly how the factory suggests and it handles great.. Not quite sure where you got the 1/4" offset from but do know when lacing there is a huge offset built into wheel to center it....
Bill

1974 850 Commando
1967 Atlas
1966 Atlas
1948 Panhead
1966 BSA Lightning
1965 BSA Lightning Rocket
1971 Honda CB350
1967 Honda Dream
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Re: front wheel offset on disk brake commandos

Postby dynodave » Sun Jun 21, 2015 11:36 am

Sounds like you're in England...brought it to your shop and they had an Andover wheel? When was the last time Norton actually laced a rim? 1975?
Three original commando wheels here, measured. rim to fender mount on the fork is about 1.10"disc side, otherside 1.20"...so offset .10". I get the same offset results measuring from the fork tubes to the center of the tire.
Worst one was .2 offset. None as much as 1/4".
I don't "have" wheels built, I build them myself and have been for 20 years... Norton, BSA and Triumph.
My theory on residual offset is the brake side has the straightest spokes (3.6 & .84 degrees) and has the least side thrust from the spokes and offset will always error to the nondisc side (14 & 11.25 degrees spokes).
I can say my wheels run awfully close to centering in the forks. Because I make them that way. :mrgreen:

Not Commando wheel: dial indicators removed to protect the innocent...
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Re: front wheel offset on disk brake commandos

Postby L.A.B. » Sun Jun 21, 2015 12:36 pm

dynodave wrote: Sounds like you're in England...brought it to your shop and they had an Andover wheel?


I don't think he is?

dynodave wrote:Three original commando wheels here, measured. rim to fender mount on the fork is about 1.10"disc side, otherside 1.20"...so offset .10".


The offset in this instance is 0.05" as the rim would need to be moved by 0.05" to centralise it (both clearances then being equal [1.15"]).
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Re: front wheel offset on disk brake commandos

Postby Danno » Sun Jun 21, 2015 3:32 pm

I remember seeing a diagram years ago that showed Commando wheels BOTH offset 1/4" with respect to the centerline of the frame. On the rear, this could be accomplished several ways; wheel spoked off center, different spacing from one side to the other, engine cradle offset. In the front, either the wheel would have to be spoked offset or the triples would have to be offset in relationship to the steering stem. The former seems more likely than the latter. Although the wheel could be spaced differently side-to-side, at least on disc brake models, the ability to switch sides with the rotor and caliper would really weird this out. Everyone here has looked at their back tire and wondered why the hell it looks so kawhopperjawed.

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Re: front wheel offset on disk brake commandos

Postby Rohan » Sun Jun 21, 2015 6:11 pm

I've got a disk front wheel here, taken off a bike in the 1970s (factory lacing ?), and without measuring anything,
but eyeballing it, I'd say the rim was offset from centred on the flanges on the hub by about 1/4 ".
Necessary to clear the disk.
??

The rim and tire should be centred in the forks, and with the steering column, with this lacing.

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Re: front wheel offset on disk brake commandos

Postby dave M » Sun Jun 21, 2015 6:25 pm

I agree the rim should be centred in the forks, I also build my wn wheels and do the final adjustment with the wheel mounted in the forks but without the tyre fitted.

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Re: front wheel offset on disk brake commandos

Postby manxman » Tue Jun 23, 2015 6:36 pm

If you pop the rubber bung out of the top of the steering stem, you have a clear shot down the centre of the stem, a 19/32" hole I believe. Next time I check the wheel alignment I'll poke a rod down there, or even just put a plug at top and bottom with a central hole to sight down. If the steering axis lines up with the centre groove on my TT110's that's good enough for me.

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Re: front wheel offset on disk brake commandos

Postby gortnipper » Tue Jun 23, 2015 8:10 pm

manxman wrote:If you pop the rubber bung out of the top of the steering stem, you have a clear shot down the centre of the stem, a 19/32" hole I believe. Next time I check the wheel alignment I'll poke a rod down there, or even just put a plug at top and bottom with a central hole to sight down. If the steering axis lines up with the centre groove on my TT110's that's good enough for me.

Manxman


Good idea. A 15mm rod would work a treat.
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Re: front wheel offset on disk brake commandos

Postby Mr. Rick » Sun Mar 05, 2017 10:06 pm

Pulling up this older thread, cause I'm struggling a little in my efforts to get the rim centered.
Thanks to Manxman's idea (which does not require tire removal, a big plus), I got some #0 rubber stoppers with a hole in the center, and a pc of 1/8 steel rod. Pulled the plug over the steering stem, put the stoppers top and bottom, poked the rod through, and expect to be pointing at the center of the steering axis.

Regarding the rim-to-fork centering: With the fender removed, I measure about 0.21 inches more clearance on the disc side than on the left. This wd indicate a remedy involving pulling the rim to the right with the spoke wrench.

So here's the rub: the pointer is already almost exactly in the center. If I pull the rim over 1/10" to the right, it won't be centered on the steering axis anymore.

Question 1: Can you imagine a condition which might explain this?

Question 2: Just how accurately made are the lower yokes? Over the 8 inches of exposed fork leg, I find the legs converging toward the bottom by about .070". Extrapolating over the entire 30" leg, we wd see the bottom closed up about 1/4" at the axle, which wd explain why I have no "gap" between the left-side dustcover and the slider.

I shd also say that everything comes apart and goes back together smoothly. I don't have to pry on things or bash the axle in or anything like that.

Question 3: who has come up with a better idea for putting the headlamp ears back in place? Those ridiculous tiny o-rings get mashed, fall out, just a general PIA dealing with them. I had to use them at the top because the recess in the top yoke is so shallow, but trying to use them for the bottom yoke is frustrating to say the least. I wish I cd find some ears sorta like the ones used on the Goldstar, but which wd clamp to the stanchions. I love the look:
https://en.wikipedia.org/wiki/BSA_Gold_ ... RCYCLE.jpg
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Re: front wheel offset on disk brake commandos

Postby Deets55 » Mon Mar 06, 2017 6:28 am

Mr. Rick,
Did you measure from the fork tube or slider? If you used the slider there could be a difference in machining you are dealing with. One of the better ideas I have seen on this forum is one member leveled the bike on the center stand. The leveled a steel rule between the fork tube and then used a square to locate the rim center. But the tire needed to be removed.
Something else you might want to consider. If you adjust the rim with the tire in place you do not know if the ends of the spokes you are tightening are protruding into the rim band or tube until it's too late.
A .250" difference in overall measurement is only requires moving the rim .125". In your case you are looking at less than a 1/8" of an inch. That does not really seem like much to me, but to someone else that may seem like a lot.
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Re: front wheel offset on disk brake commandos

Postby Mr. Rick » Mon Mar 06, 2017 11:34 am

Thanks, Pete.
Yes, I am measuring at the slider, cause that's where the rim is. How else wd we do it? Or do you mean that I shd remove the sliders, so I can measure to the fork tube itself?
I've been using the tire to see center because it's easy to find. At some point the tire will have to come off anyway, as you say, to check for spokes poking out, so I'll get to check the rim center, too.
My suspicion is that the lower yoke is not bored exactly in line with the upper yoke, and is sending the left tube down at a very slight angle toward the right side. I'm probably worrying too much about too little, as usual..
As a point of interest: Which part of the bike was used to get the bike level? Frame tubes under the seat, maybe?
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Re: front wheel offset on disk brake commandos

Postby Deets55 » Mon Mar 06, 2017 11:58 am

Mr. Rick wrote:Thanks, Pete.
Yes, I am measuring at the slider, cause that's where the rim is. How else wd we do it? Or do you mean that I shd remove the sliders, so I can measure to the fork tube itself?
I've been using the tire to see center because it's easy to find. At some point the tire will have to come off anyway, as you say, to check for spokes poking out, so I'll get to check the rim center, too.
My suspicion is that the lower yoke is not bored exactly in line with the upper yoke, and is sending the left tube down at a very slight angle toward the right side. I'm probably worrying too much about too little, as usual..
As a point of interest: Which part of the bike was used to get the bike level? Frame tubes under the seat, maybe?


I would put a level on the exposed fork tube and see how they compare w/ each other. Use wood shims under the center stand to get them vertical. In the original post I saw I think the owner clamped either a level or a steel rule across the fork tubes, found that center and used a small square down to the rim. IMHO there are so many other variables that come into play that if you are with in an 1/8" now you should be good. Just make sure you are true and balanced correctly. I sometime wonder if the tires themselves are that accurate. It is probably more important to get the rear rim on the bikes center line and axel square to that CL than the front tire being slightly off. All this is just my opinion, using the KISS method. I actually centered mine off the fork sliders like you are doing it now and then checked it using a laser. All I know is I can take my hands off my bars at any speed and any condition and the bike travels straight and w/o weaves. Barring any major bumps or pot holes.
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Re: front wheel offset on disk brake commandos

Postby o0norton0o » Mon Mar 06, 2017 12:03 pm

I wouldn't put too much faith in rubber stoppers and 1/8th" rod for projecting the fork center accurately.

All the front end components have to be correct for all the measurements to "jive". If your yokes are slightly misaligned or your fork tubes aren't perfectly straight, then your 1/8" rod method to project pivot center (even if it's accurate) won't give you a point that measures out as centered between the fork tubes...

SO,..... IF you're NOT going to take your fork tubes off and check them for perfect straightness, and you're NOT going to reassemble the yokes and fork tubes in a jig to keep the yokes aligned, then you're starting your measurement process assuming that the yokes are aligned and fork tubes are straight, IF that's the case, then why not just use the measurement beween the fork tubes to each side of the rim to center the rim???

As far as you measuring some amount of taper in the fork tubes between the yokes, perhaps you are measuring the taper in the top of the fork tube so it fits into the upper yoke. If you measure the fork tube distance just below the lower yoke, it should be the same as the measurement as it measures just above the sliders. That's the only way the sliders could move over the fork tubes without binding, without having some sort of an accomodation to allow the axle distance to change when the sliders move...

As far as spacing goes, the axle only bolts up on the disk side. The other side of the axle floats UNTIL you secure the pinch bolt. This allows the axle distance to be secured in a position where the sliders are in their "most" parallel location, which cuts down on friction between slider and fork tube and therefore wear as well... This is why you set up your front end and pump the forks while you hold the brake before you tighten the pinch bolt... (working the forks and sliders with the pinch bolt loose allows them to seek their best alignment, then you tighten the pinch bolt)

Ever since I've owned my bike, it had an aftermarket headlight support, rather than the factory parts. It never bothered me. They are still available if you want to use a set. I've seen them on a lot of british twins of that era.

mine looked like a chrome version of these:
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Re: front wheel offset on disk brake commandos

Postby bucksfizz » Mon Mar 06, 2017 12:37 pm

I'm restoring a bitsa ('74 Mk2 engine and swinging arm in a '75 Mk3 frame), and I was going to start a separate thread entitled: why is my rear wheel offset to the left?
Here's what it looks like:

Image

Perhaps the answer is that the front wheel is similarly offset in the front fork.
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