Swing arm location

[docc]

My Sport sure seemed to track better after aligning the swingarm. I'm sure I got it closer than the factory.

 

A couple mm is no big deal , I'm sure. But when it's a couple mm on the swingarm, a couple cm in ride height, a couple psi here, a couple mV there, 4 or 5 mmHg between the throttle bodies it all adds up to a bike that's merely decent and one that is magic.

[Guest Nigelstephens]

Yes definately any small improvements mount up.

OK I agree that it is worth doing but how does one get the accuracy to less than 2mm difference in wheel alignment when the laser sight is resting against the tyre?

 

The only way to get the accuracy required is to use a tool that rests on the rims, assuming they are not buckled. Resting on the tyre on both sides assumes that the tyre wall is smooth and is set on the rim accurately. This in itself is not done to high precision as the tyre positions its self when being inflated.

 

How does the string method work?

[mike wilson]

Yes definately any small improvements mount up.

OK I agree that it is worth doing but how does one get the accuracy to less than 2mm difference in wheel alignment when the laser sight is resting against the tyre?

 

The only way to get the accuracy required is to use a tool that rests on the rims, assuming they are not buckled. Resting on the tyre on both sides assumes that the tyre wall is smooth and is set on the rim accurately. This in itself is not done to high precision as the tyre positions its self when being inflated.

 

How does the string method work?

 

The string method works very badly, especially if your tyres are of different widths..... It's just using a piece of string, looped round one tyre and brought back to the other one and seeing if there is parallelism of the wheels by viewing along the string.

 

If I had 2mm runout on a modern tyre, I would not be happy. Don't forget that the outside of rims has no engineering for accuracy, so it could happily be all over the shop as long as it does not affect balance.

[Guest Nigelstephens]

If the laser is shining on to a target 1 meter away and the laser is 10cm in width it takes only 10/100 *2mm = 0.2 mm difference at the tyre to make 2mm difference on the target.

Quite possible.

[docc]

Your lazer beam spreads to 10 cm (that's 4 inches) in a meter? The one I used was mounted in a 12" level and spread to maybe 3 or 4 millimeters next to the front tire which is a distance of around 1300mm.

 

Certainly any variance in the mounting surface would magnify the error. Better stop using those Cheng Shin seconds on the Guzzi . . .

[Guest Nigelstephens]

Sorry I meant the laser base width in contact with the tyre not the difusion of beam.

[Guest ratchethack]

Your lazer beam spreads to 10 cm (that's 4 inches) in a meter? The one I used was mounted in a 12" level and spread to maybe 3 or 4 millimeters next to the front tire which is a distance of around 1300mm.

?? EH? ??

 

Lasers not aligned and beams spreading? I don't know wot kinds of lasers are out there, I'm sure the quality varies as it does with everything else. The one I picked up at Home Depot is a Lazerpro CL2062, about $20 USD as I recall. It will project a dot 1500 feet and claims an accuracy of better than .2 inch at 30 feet. As mentioned previously, its lateral accuracy is dead on at 15 feet when tested on my bench.

 

I've got 2 different laser pointers in 2 different handguns. Of course, they're built, calibrated, and tested to much higher tolerances, but the dots they each project on a target look to be the identical size at the same distance as the one on the laser level.

 

I don't have any perceptible lateral runout in either my wheels or tires on the Guzzi. Like Mike said, if I had a 2 mm runout in either, I wouldn't be too pleased. In this case, it wouldn't be possible to trust the laser, the string, or the flourescent light tube method, either.

 

FWIW, the broad, flat side of the laser level drawn up equally "snug" against the tire on each side by its own weight suspended by the loop as described in my procedure gives a consistent, accurate read. Without an indication of excessive lateral runout, IMHO, the ability to repeat results with consistency is pretty good validation of high enough accuracy for our purposes here.

 

I tried to think of a way to do an accurate alignment with bent wheels and/or wonky Cheng Shin tires by using the old car alignment trick of scribing chalk marks on the circumference of the tires and using a straightedge as a reference. I'm sure it's possible, but I sprained my brain before I could come up with anything. In my case, I figure best not run wonky tires, and have a mildly bent wheel straightened by a Pro, anyway. Then you've got 3 methods that I know of to choose from, all work better than setting stub axles equal, IMHO, each has advantages and trade-off limitations.

 

BAA, TJM, & YMMV

[Guest Nigelstephens]

Thanks Rachet.

The point I was making that an irregularity at the wheel is magnified 10 to 15 times by the time the beam hits the target. This simply becasue of the laser housing width over the projected length causes this magnification.

 

I can quite easily imagine an irregularity on the outside edge of the tyre amount to 0.1 mm. This would give 1 - 1.5 mm difference in the measurement. However, if you have had repeated results that are similar then the laser technique may still have some merit.

[Guest ratchethack]

Thanks Rachet.

Por nada, mi compadre.

The point I was making that an irregularity at the wheel is magnified 10 to 15 times by the time the beam hits the target. This simply becasue of the laser housing width over the projected length causes this magnification.

I understand completely and have always recognized the point about irregular tire and/or wheel shape potentially throwing off alignment setting, Nige. Not sure at all how a magnification of 10-15X could occur the way I've done it, however? Truth be told, I've never had wheels and tires far enough out o' true for it to've been much of a consideration (except on dirt bikes, where a small amount of lateral runout is "normal") -- whether using string, light tube, or laser.

 

Not sure I understand your concern over laser housing width. The width of the laser is exactly the same on each side and of no concern, as it cancels out. The way I've used my laser, the contact between tire and laser level is equal and identical at front and back ends of the laser level by virtue of it being hung and supported at its center. Contact between laser and tire is also equal and identical side to side, due to consistent weight and "mirror image" placement against the tire on each side.

I can quite easily imagine an irregularity on the outside edge of the tyre amount to 0.1 mm. This would give 1 - 1.5 mm difference in the measurement. However, if you have had repeated results that are similar then the laser technique may still have some merit.

Yes, I can (and have) easily imagined such irregularites also, my friend. None detected yet in repeat checking -- even with different tires mounted, one check to the next.

 

I reckon wot it comes down to is this: Using the tires for alignment does have some potential for introducing inaccuracies, though assuming wheels are true, modern tires make this a very small concern.

 

Wot are the alternatives?

 

Best pick one method of alignment (all subject to the same potential compromises up front, easily found by checking runout), or skip it altogether.

 

The proof is in the puddin', as they say.