Different methods of wheel alignment

[posplayr]

http://www.thegsresources.com/_forum...d.php?t=147705

Last post is my method but the rest is worth reding

String = a waste of time & effort
lazer = more accuate but much more difficult to do

tone

Tone,
I will have to respectfully disagree that it is a waste of time & effort to use a string. Clearly if it can be made to work to measure wheel alignment in the 1-2mm regime then it is worth the effort. I think it even better than that if done properly.

The sting method (and I use that term loosely because there are variations) is generally applied to a road ready bike except for the wheel alignment. It probably works just as well for checking frame alignment against the bare wheels alone.

So for the sake of discussion I will only contrast the string v.s. a laser for measuring straight lines as that is what will be used in whatever variation of alignment employed. Any method that can be conceived of for alignment will invariably project two straight line from either side of the rear wheel wheel to the front of the wheel. This is true for strings as well as lasers.

Of course in your description you said to get a straight edge that was really straight; but that begs the question how do you know the edge is straight. Well I confirmed the accuracy of my straight edge with a thin string. It was 1/16" at 6 foot. So one way or another your straight edge is predicated on some form of "at home" straightness measure.

So the question then becomes:

a.) how straight are the lines?
b.) how well can I position (with certainty those lines)?

For a.) everybody knows that a laser is light and is essentially a perfect coherent light source, but alas nothing is perfect and there is beam divergence. For a decent laser Beam divergence is typically 1 mrad so at 2 meters the beam is approximately 2mm is diameter. The question then is how well can that spot be located at with 1ft (one wheel) and at 7 ft (the other wheel)? Having tried this myself, trying to put a measure a laser at it's edge can be a little difficult so if you have a special fixture that is carefully factory aligned (probably with a string) then I would say that the real accuracy of being able to read a full spot is probably within a 0.25mm .

If you are sighting down a straight edge for example , it is difficult to tell when you are splitting the beam for true 1/2 and at best you are probably to a +/-1/8mRad accuracy which is +/-1/4mm at 6 foot.

In contrast how bad is the string? Well it depends allot on how you use it. The string will be quite straight and only suffer moderate catenary is you keep it thin and taught. If you use the string to measure horizontal distances then there is no error in the string as all of the catenery is in the vertical plane.

The real trick with use this string is how well (read accurately and consistently) it can be placed adjacent to a wheel or a tire . If you set the string up so it touches the wheel and then expect to site down the string to ensure it is straight, then you will likely be many mm off in your alignment and I would have to agree it is not going to be worth the effort. On the other hand if you position the string next to the wheel or tire and to make sure that the string is located against both left and right sides the same use the string strum technique.

We obviously want the string straight so that means the string can's be pressed against the wheel. It can however be very close. To insure it is not pressed against the wheel strum the line to ensure it will vibrate up and down, but not how long it continues to vibrate. Adjust the distance so that the fibers of the string cause the vibration to diminish consistently on both sides but still vibrate vertically[This is the main trick required to get accuracy with a string]. I used a very thick string that was approx 1mm in diameter (it is easy to use something much thinner down to 0.2mm). With the vibration method described, you can very easily determine position within +/-1/8 of the string diameter. Of course the hairyness of the string matters to some extent.

So for my string, it was 1mm and I was easily achieving measure positional accuracy to within +/-1/8 mm. At the other end you are typically using a caliper to measure offset between the wheel and the string once you have your strings properly strum positioned. I'm using a veneer caliper and a 1mm thick string; it is easy to achieve +/-1mm of accuracy there as well.

So my conclusion is that using a "considered" string approach, 1mm accuracy can easily be attained and that is all that is ever really required for either wheel or frame alignment. Infact, you would be hard pressed without specially machined and calibrated fixtures to even measure the straightness of a straight edge with a laser. I had both (laser(3 in fact) and string) and finally settled on measuring divergence from a string in the horizontal plane.

Jim

[posplayr]

I guess my question is is after my eyes bloodshot from reading this thread about how to check and verify or question ideal wheel alignment... is it worth it on a 25 year old street driven motorcycle that does not exibit any type of obvious ill handling, or unusuall tire wear behavior? In the past 6 motorcycles i've owned, not one of them did I ever suspect the need for a "chassis alignment" . Just my opinion, but if some of you are loosing sleep over + or - 1mm you shouldnt be screwing around with string and lasers, do it the RIGHT way and take your bike to a motorcycle specific chassis shop .

Contrary, race bikes, or a bike that tried to move a tree or guardrail, well that's a different story...

Most of these discussion come up in sport bike threads, and are primarily applied for GS's only when suspension mods are introduced. The issue of rear spacers lways comes up due to the various clerances issues. And it is a good idea to isure that the wheels are still in alignment. I dont think anybody is "worried about 1mm". The accuracy of alignment has been discussed in the thread Tone posted. The issue of what is good enough so I know to stop does come up.

While you have admitted to bloodshot eyes, you might have missed the point of at least part of this thread.That would be that using a string to check the wheel alignment can achieve +/-1mm accuracy which is all that any application would ever require. There is in fact no reason to go to a frame shop as you suggest. While you obviously don't care much about wheel alignment, there are several here that do so we are all huddle in this thread talking about just that. We perfer to not waste time and money going to an alignment shop.

[chef1366]

I line up them thar little liney thingys on the swangarm doo hickey.

[salty_monk]

Well... my swingarm doohickey seems pretty accurate against swingarm & tape measure, laser, straight edge. Now I just got to get the sprockets in tolerance...

[tone]

Tone,
I will have to respectfully disagree that it is a waste of time & effort to use a string. blah blah edited to save server space

Jim

Hi Jim, while i see your point that a string could be reasonably accurate if used carefully it is still a string hence bendy & easilly moved resulting in most cases with an inaccurate reading, as you point out there can be a variance with string as you could be measuring either side of it or moving it as stated above

With an accurate straight edge you will be measuring to the same point each time (EG the very edge) & there is much less likelyhood of accidently moving it

Fao my straight edge has a machined edge & has been checked for true on a surface plate hence i KNOW it really is a STRAIGHT edge

I have proven the reliability of my method by checking bikes i'd previously aligned on a jig I have also disproven the reliability of the string method in the same way

In summary...... string if you want it near enough, straight edge or jig if you want it right

Cheers tone

[cavehamster]

Wowey batman, I'm really impressed by how quickly posplayr can type an essay on the string method! Nicely done man!

Regardless, on any method you use, it takes some care to make sure your 'beams' be they light or string or metal bars are lined up coaxial down the frame and not being deflected by anything. If I might add one minor suggestion to any method, I would suggest as a basic sanity check that you measure the distance between the beams near the source, and again at the other end of the bike. If they are equal, all you have left to do is correct any parallax and you'll have a straight jig you can measure off of.

I found it a lot easier to measure off the front wheel and get that locked in so I could scoot the rear wheel around and not have to re-do the jig a lot, but getting setup to do this is a pain anyway.

Anyone have any links to what the pro jigs actually look like? I'd much rather see a few pictures than a ton of descriptions, just so I could look at it and see what I could be doing better.

Interesting discussion though.

[posplayr]

In summary...... string if you want it near enough, straight edge or jig if you want it right

Cheers tone

Although I'm not smart enough, a person so qualified could probably measure the speed of light with a peice of string and a stick of bubble gum, that is to say the accuracy and utility of the string is largely dependent on how it is used.

Perhaps the FSSM (Fuzzy String Strum Method) is not common knowledge , but as I described it is has sub mm accuracy.

[tone]

Anyone have any links to what the pro jigs actually look like

Thats another minefield mate there are a ton of different types of jigs out there & ideas or variations for hundreds more, a quick google should throw up more pics than you can handle

To help you understand a little better, there are 2 basic designs of jigs for 2 basic jobs although there are countless variations

#1 a frame building jig which can be fairly basic mainly consists of an ajustable post to hold he headstock, an accuately marked centre line to measure off, blocks & chocks for holding engine etc & guides for locating swingarm pivots & rear wheel spindle, A good example of a more advanced version of this type of jig would be a eurocustom jig

#2 a alignment or straightening jig which is similar to the above with all the above mentioned stuff & more but much stronger to allow the use of rams etc to straighten a bent frame eg the frame is not always held by the headstock & a pointer is installed there which is used to measure any misalignment before & after the frame is pulled, a good example of this would be a motorliner jig

If you want to build a straight frame #1 is the boy for the job & if you want to check or straighten a frame #2 is the kiddie, although there can be some crossover of usage, having used both i must say i'd hate to have to build a frame on a motorliner

hope it helps tone

[tone]

Although I'm not smart enough, a person so qualified could probably measure the speed of light with a peice of string and a stick of bubble gum, that is to say the accuracy and utility of the string is largely dependent on how it is used.

Hey Jim i think you are plenty smart mate but as you say the accuacy is dependant on how string is used, to my mind some people will get reasonable accuracy with this method but most wont so see no reason to remove one more variable

Leave me alone in the gaarage with a ball of string & i could maybe knit you a vest but i'm too clumsy to measure my wheel alignment with it

[Charlie G]

Fuzzy factor

Jim,

Nice write up on the various methods of alignment check. I used the string method a few years ago on my XT-350 Dual sport and it worked great. I was running about 8mm out. I used a "dental floss" like string that is used in construction for checking acoustical ceilings for straightness.

Charlie G

[posplayr]

Jim,

Nice write up on the various methods of alignment check. I used the string method a few years ago on my XT-350 Dual sport and it worked great. I was running about 8mm out. I used a "dental floss" like string that is used in construction for checking acoustical ceilings for straightness.

Charlie G

Thanks Charlie,
I was watching a show about the building techniques that the Egyptians are theorized to have used to build the Great Pyramids. I wonder how many Pyramids were build using Lasers? Does anybody think they used 1000 ft straight edges?

There was another story from ancient Greece I believe. IIRC, the people on an island were besieged and did not have any water on their side of the mountain. They needed to drill a hole through both side of a mountain so the water would flow through and still have them meet somewhere in the middle. Anybody think they used lasers? How about large T-squares? Think they understood error propagation?

These are all rhetorical questions as it is a matter of the user of the instruments (probably string and hoses) to make maximum utility by developing accurate measurement techniques with these simple tools.

Think about the first attempts to measure the speed of light, this has always amazed me. They did not have a laser, but they did understand light.

http://en.wikipedia.org/wiki/Speed_of_light

Earth-bound techniques
See also: Fizeau–Foucault apparatus

Diagram of the Fizeau apparatus


The first successful entirely earthbound measurement of the speed of light was carried out by Hippolyte Fizeau in 1849. Fizeau's experiment was conceptually similar to those proposed by Beeckman and Galileo. A beam of light was directed at a mirror 8 km away. On the way from the source to the mirror, the beam passed through a rotating cog wheel. At a certain rate of rotation, the beam could pass through one gap on the way out and another on the way back. But at slightly higher or lower rates, the beam would strike a tooth and not pass through the wheel. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, the speed of light could be calculated. Fizeau reported the speed of light as 313,000 km/s. Léon Foucault improved on Fizeau's method by replacing the cogwheel with a rotating mirror. Foucault's estimate, published in 1862, was 298,000 km/s.

[derwood]

... How about the 8 foot fluorescent light bulb (tube) method they're pretty straight, a couple of them work... good enough for canada anyways....
..for lining up the wheels on my cycle, not building pyramids or measuring the speed of light or nothing, ....it's not rocket surgery ....jeez

[salty_monk]

just don't break one... Good idea though.

I have just done mine with some Alumnium angle. I cut part of it down so it also clamps to the rear sprocket & can be used for sprocket alignment.

Dan

[posplayr]

... How about the 8 foot fluorescent light bulb (tube) method they're pretty straight, a couple of them work... good enough for canada anyways....
..for lining up the wheels on my cycle, not building pyramids or measuring the speed of light or nothing, ....it's not rocket surgery ....jeez

Yes I heard others mention the 8" florescent light bulb method. As I don't have one I can't do it for myself, but how straight are they?

Lacking a 20 ton slab of machined granite, you could use a sting to see how straight it is . Tape two fixed size blocks to either end of the tube. Run a string over the blocks from one end to the other. Put the string to ether the left or right side of the light bulb. Take a caliper along the tube to see if the distance is consistent. That is the definition of parallel and since the string is straight (in the horizontal plane) you can measure any deviations of the light bulb.

While this is not Rocket surgery, it is Pyramid Science

[posplayr]

just don't break one... Good idea though.

I have just done mine with some Aluminum angle. I cut part of it down so it also clamps to the rear sprocket & can be used for sprocket alignment.

Dan

same question Dan, how straight is your aluminum angle? The 1/8" stuff I bought at the local home improvement center curved about 1/4-1/2" in 6 foot. I straightened it by screwing it to some OBS and verified with the "little ruler from the Pyramids", (i.e. a piece of string).

My combo OBS angle straight edge is about 1/16" in 8 ft.