Sunday, February 26, 2012

Motorcycle Wheel Alignment

This post has been updated and the new and improved version is here: New Motorcycle Wheel Alignment Post

I just aligned the wheels on a new old motorcycle I just acquired. This is one of those activities that is an arcane procedure.
I dug up an old post I made to the ducati mailing list in the mid 1990's about this.

The "Thread Method"
I've always aligned my wheels the way I saw Rich Oliver do it on his TZ250 years ago. I think this way is standard "racer" practice. Put bike on service stand. Take about 15 feet of string (elastic thread works best!). Tape center of string to back of the rear wheel about 4" off the ground. Bring the ends of the string to the front of the bike. Tie the ends of the string to some movable objects (I use a pair of jack stands), at the same height (4"). The idea is to set the strings so they are parallel and "just" in contact to the front edge rear tire by moving the jack stands. With the strings taped to the back of the rear tire, and "just" touching the front edge of the rear tire, they should make two parallel lines that run forward, passing along either side of the front tire. Now the alignment of the front and rear wheels can be easily observed by examining the clearance of the front wheel and the string on either side. Adjust the chain adjuster appropriately if necessary, and then recheck. It's a pain to do the first time, but then it gets easy. Use the thinnest, elastic thread you can find. Also, try rotating the rear wheel to several points to make sure you aren't just adjusting for uneven tire manufacture. And make sure the thread isn't on some bump of "mold seam" rubber or in a tread at the edge of the tire. This would screw up everything. Obviously, this method ignores how the chain and sprockets are aligned, and focuses on how the wheels and tires are aligned. I can imagine that having the sprockets and wheels aligned simultaneously may not be possible, and I'd rather have the wheels lined up. When using this procedure on my '92 750SS, a quarter turn of one of the chain adjusters is quite significant. When complete, the adjusters appear to be at even marks at either side of the bike, indicating adequate manufacturing. However, a quarter turns seams to effect the alignment significantly, but is just about invisible in relation to the adjuster marks.

The "ProAligner"
There is a relatively new gizmo available to help riders to align there wheels, its called the ProAligner. What I quickly found, is that I had trouble using the ProAligner on my oldest vintage bikes. The tires are very narrow (2.50" or 2.75"  by 19) and have the same size front and rear. One might say that you could in theory just sight down the tires even without the ProAligner, but I have trouble with that. I ended up doing those old bikes with my old and reliable thread method.

Today, I aligned the wheels on my newly aquired 1981 GPz 550. It came to me with the tires visibly way out of alignment. Investigation showed that the plastic chain guard had warped so it hit the tire, and some previous owner had "fixed" this problem by tweaking the chain adjusters until the tire was clear of the guard!
The GPz has a 3.25 x 19 front and a 3.75 x 19 rear. I quickly tried out the Proaligner and saw how it would work, but this time had a bit of trouble with my vision sighting down the tires. It occured to me that the bigger the difference in tire size, the easier the aligner would be to use. Frankly, I again went back to my old thread method.  Having done it that way for 30 years, I'm just very comfortable with that. After getting the wheels spot on with the thread, I pulled the ProAligner back out and tried it again. Lo and behold, the ProAligner also showed the wheels perfectly aligned.
(A note here, with the wheels aligned, I note that the hash marks on the chain adjusters are not even on both sides. This is typical, especially on older bikes. That's why some of us don't trust the chain adjuster marks.)

My thoughts? The ProAligner is a great gadget, especially for those with laser vision, no experience with thread, and tires that differ significantly in size from front to rear. Its certainly easy to see when the tires are way out of alignment. But if the tires are similar in size, it is delicate, and requires a really sharp eyeball to tell the small differences between each side of the tire. The ProAligner web site claims accuracy to "less than 0.1 inch (2.5mm)". That's possible, but, well I'd have trouble getting it that close. It's not just about being able to sight down the ires, you also have to adjust your focus from the front tire to the rear tire, and not move when you do that. I'd say getting to within 5mm or 3/16" would be pretty do-able with good vision.

For me, an engineer and long time rider and thread aligner, I don't see the ProAligner as much more (or any more) accurate than the thread method. But I don't think it's any less accurate either! With the thread, you really have to be very careful to get it to just touch/miss the front edge of the rear tire and to not "bend" the thread. With the Pro Aligner, you have to sight down the tire just right, adjust your focus carefully, and really see the hash marks.

I think if the tires (front and rear) are close to the same in size, or if I want to align the tires very, very close to perfect, the thread works better for me.

But, I'd say, that if you are double checking an alignment that was already done (assuming differing front and rear tire sizes) the ProAligner is quicker and easier. I'd also say, that if the tires are way out of alignment, the ProAligner would be quicker to get the wheels somewhat aligned, as there is no hassle with thread.

And if you have sharp vision, and no experience with the thread, the ProAligner might be the way to go. If you can "see" it, it's pretty foolproof. The thread system takes some time to learn. Then again, if you have trouble with it, don't hesitate to try the thread method.


No comments:

Post a Comment