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Ex-sunshine rider
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Discussion Starter · #1 ·
OK
So youv'e changed the swingarm for an aftermarket job. Bike is on blocks and a spirit level check in various places tells you that the bike is vertical. Now what's the best way to check dead centre of the rear wheel. I used a plumb bob from the centre of the middle hole where the rear fender bolts to beneath the pillion seat down to the centre of the tyre but Max has previously said that you cannot assume that the centre of the tyre is the centre of the wheel.
 

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Premium Member
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If I'm not mistaken I believe I saw a process in the Service Manual. The hogpro 280 swingarm came with all the spacers already sized. As far as I can tell it looks as if it's dead center.
 

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Ex-sunshine rider
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249 Posts
Discussion Starter · #3 ·
Hello V Ride

I understand what you are saying. I will check the service manual to see if there is anything there but assuming you wanted to check if the wheel is in the centre regardless of whatever spacers you have, releated to whatever swingarm, what's the best way. You have to decide what is the centre line of the bike and mark it somewhere.
 

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There are a couple of ways. One way I saw recently while cruising the paddock at the Moto GP races at Laguna Seca really excited me. It requires a long steel ruler marked off in millimeters. It is like a very long vernier calipers with a tapered flat the fits into the center of a hollow rear axle and a sliding flat that will fit into the swingarm pivot. The distance from the swingarm pivot center to the center of the rear axle is thus precisely measured, and the axle adjuster nuts may be turned to adjust the length on each side so they are identical. I had never seen this technique before and I wish I had had my camera to take pictures of the tool.
The way I have used in the past on my Sportsters is to support the bike with wood under the center stand so the bike is standing upright. You will need two concrete blocks, two C-clamps and a lot of string. I place the concrete blocks on either side of the front tire and in front of the tire. I clamp the C-Clamps to the center of each concrete block. The string must be more than twice as long as the bike. I tie one end of the string to one C-clamp. run it back to the rear tire, wrap it around the back of the rear tire once then run the string along the opposite side of the bike and pull it tight, then tie the loose end to the other C-clamp. Move the C-clamps and blocks so the string just touches both sidewalls of the rear tire, is tight and measure carefully to ensure they are parallel from front to rear. I use a ruler and measure the distance between the two strings at the rear tire and again in front of the front tire. The idea is to have both strings exactly parallel to each other and exactly as far apart as the rear tire is wide. The string will just touch the sidewall of the rear tire. When you have accomplished this, center the front tire between the two parallel strings exactly using a ruler to carefully measure the precise distance from the tire sidewall to each string at the front and back of the tire. By the way, I forgot to mention, the strings should be as high as possible above the ground without them touching any other bike part like a muffler bracket or radiator shroud. On a V-Rod they will probably be just under the frame, every bike is different but the same proceedure applies. The goal here is to adjust the rear tire in such a way that, with both strings parallel to each other, the front tire is exactly centered between these two strings. When this is accomplished the real wheel is perfectly aligned in the swingarm.
Now I will throw water on the who idea that the front and rear tire need to be centered. BMW builds bikes where the rear tire is offset to the side and does so deliberately. They build one drive line with a single sided swingarm and driveshaft that cannot be moved laterally in any way. The driveshaft must be aligned with the transmission output shaft. Then depending on the version will use different width wheels and tires at the rear, thus guaranteeing the centerline of the wide tire on a K-1100RS is offset to the left of the front tire while the narrow rear tire of the touring K-1100LT is closer to dead center with the front tire. Neither bike handles bad and indeed the off center rear tire of the RS is completely unnoticeable. It makes no difference at all.
 

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Ex-sunshine rider
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249 Posts
Discussion Starter · #5 ·
Hello Philthy

I understand the principle you describe. In my case I am going to "assume" that the front is OK and only concentrate on the back.

My bike is stripped down, on a lift and minus rear wheel, fuel tank, seat and rear fender. What I was thinking is that you could drop a plumbob from the centre of the top or outermost fender fixing hole down to the ground.

Use a spirit level across the frame where the fuel tank normally sits to make sure the frame is horizontal, shim as necessary to make it so.

Put a set square on the back of the frame where the fuel tank sits and move this to touch the plumbob string. Mark the position of the set square edge on the frame and tis can be assumed to be the centre of the frame.

Measure right and left on the frame from the mark and you should have equal distances. If not then I guess you could then use your string principle to decide the real centre.

Once the mind is confident that you believe the mark then it's just a measuring excercise from the inside of the swingarm, brake side, to the scribed mark and then install the wheel, without spacers, and move it towards the brake side swingarm until you measure the same distance from the swingarm to the centre of the wheel rim. In my case I have weld recluse wheels so it's easy.

When you have the wheel in position then you can use a vernier caliper to measure the spacers.

I think this is accurate enough and may work. I will be trying it out in about a month so I will let you know how I get on.

If anyone has an easier method let me know.
 
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