When I first attended the Huntsville GP4,  I ran out of time and was only able to eyeball the wheel alignment.  As I later learned, it was off a country mile, never mind splitting 1/16″ or 1/8″ or 1/4″.  I needed a yardstick to measure how terribly off it was. 

Once I returned and started reworking my car I at last came to aligning the wheels.  I tried the chalk line approach but found that all a bit unreproducible.  Many would say, hey this is a cyclekart, not a precision racing machine, and they would be right.  But my car drove so horribly, I had to figure out why I was bouncing all about.  As it turned out, there were multiple contributing factors in addition to alignment, and it was only as I attacked all the variables that I was able to really stabilize my car to a point where I am personally satisfied.  I know there is most likely still room for improvement, but it runs clean and steady up to 40 mph now and I’m Ok with it for now.

Anyway, once I got past issues of correcting wheel balance, tire roundness, and the front suspension, all that was left was the wheel alignment.

LOCKING THE STEERING WHEEL
The very first thing needed was a way to center the wheels and lock the steering from turning to the left or right while I am making control arm length adjustments.  I initially used a ratchet strap but it was not what I wanted.  So then I simply took a piece of metal, drilled a hole in the middle and cut it to fit my steering linkage so it centered the wheels firmly.  Equally important to me was to ensure the positioning was always repeatable so I could make minute changes.  I learned through the process of designing this system that firmly locking the steering in a repeatable manner was important, otherwise you ended up chasing your tail.  The steel locking bar was one simple solution, there are probably a dozen ways to accomplish this.

LASERS
I’ve seen where accurate lasers can be had for real cheap now, meaning in the $20-$50 range and I thought it would be a fun experiment to see if there was a way to enhance the wheel alignment accuracy and also take less time in performing an alignment.

So I bought a unit off of Amazon for just under $30 and gave it a try.  The instructions were minimal, but it was easy to turn on, set on the ground and press the top button so it could self level.  One very nice feature of these lasers are the two lines they project; one horizontally, and a second vertically.  The vertical beam allows you to measure at any height along your wheel and not only at one point, how convenient!  It’s not restricted to a single point as in the really cheap pointer type lasers.

My initial attempts included clamping boards to the rear wheel tires and then setting the laser beam so it was parallel to the wheel.  I tried this method and saw some improvement as I was now getting closer to alignment by comparison to my eyeball method.  But I discovered after several tries, that it was not very reproducible.  Part of that lie in the fact that there exists some variation in the tires, clamping pressure, but mostly due to the fact I had no sure way of knowing if the laser was truly parallel to the wheel. 

So my next attempt was to use a piece of metal angle that was wide enough to lay the laser on it.  I cut the length so it only was a long as the diameter of the rim itself.  Now, I was able to clamp the angle to the rim only which I felt I had a more true surface to use as a reference.  But once again, I discovered after doing a drive test, that my measurements were not the same as I had set them before the test.  That’s when I had another revelation, my laser plastic housing was not square!  So even though I placed the laser nicely along the angle iron, it was sending an incorrect misaligned beam.  Who would have thought!  Furthermore, any worble in the rim would also introduce some degree of error.

OK, now it was time to get serious, off came the rear wheels so I could clamp the angle iron directly to the rear wheel hub.  Once the laser was placed on the angle piece, I used a small square to align the front of the laser so it was perfectly perpendicular to the wheel hub.  And whalla, my measurements were now greatly improved, but still not perfectly reproducible before and after a drive test.  It also still required a lot of timely setup.  I wanted something I could do quickly so I could make an adjustment and then test drive repeatedly until I found the right settings.  I needed a better way.

This brings me to my next step in the evolution.  I really didn’t like removing the rear wheels as per my last procedure, so I moved to the idea of building a magnetic attachment that directly adheres the laser assembly to the wheel hub.  What I came up with was a 90 degree bent piece of metal with the laser mounted on top and 4 sticky-back magnets facing outward on the bottom that aligned with the 4 wheel bolts.  The lasers conveniently come with a standard 1/4-20 camera screw hole to easily mount it to the bracket.  This feature was also important for calibrating the laser to the right angle from the wheel to make it perfectly parallel.

Using a square to attempt alignment of the laser proved iffy, so I decided to take an 8 foot length of 1.5″ square tubing I had in the shop.  I then clamped my laser bracket assembly to one end.  With the laser turned on, I measured the distance between the vertical beam and the edge of the steel tubing at the edge of the laser bracket.  Then with a ruler held against the steel tube at the opposite end, I adjusted the laser rotation until the front end measurement exactly matched and tightened the laser into place.  This gave me incredible precision now that exceeded the length in-between the front and rear wheels.  I only had to perform this calibration once, then lock the laser by tightening the 1/4-20 screw very firmly. 

That’s when I recognized that to keep with my lazy and fast approach, I wold need a second calibrated laser bracket assembly since the laser was pointed in the wrong direction when moving it to the other side.  Rather than saving about $30, I chose to buy a second laser and set of magnets, and calibrated it in the same manner.

With the steering lock and laser in place, I was easily able to adjust the steering arm within the width of the laser beam (I’m guessing about 1/32″).  I initially just measured the vertical beam at the wheel rim (aft and front) to set my toe-in.  And that worked very well, but it still wasn’t 100% correct.  According to a book entitled Kart Chassis Setup Technology that I had purchased, I read that the “Toe is the difference in distance between the front and rear measurements of the tires, measured in the center of the tread surface at spindle height!”  So that meant I was shorting my alignment by about 6″ in length.  I’ll leave it to the mathematicians to calculate the degree of error caused by not covering the added distance.

Well, since I’ve taken it this far, I might as well go the extra distance to make this as good as I can.  So I bent a 1/8″ steel piece to 90 degrees and welded a short piece of 1/2″ square tubing as seen in the accompanying pictures.  I made one to mount to the front of the tire and another for the rear.  Only one set was required as these easily transferred over to the other side.  The target was bent and shaved to length so it positioned the end of the bent steel directly over the mid point of the tire tread.

Using my metal steel ruler, I could position the ruler against the target edge at the tires center and measure where the laser intersected the ruler.  By taking readings from the front and rear targets, I could set the tow-in or toe out very precisely and repeatably.  By repeatable, I mean I could acquire the same measurement offset after my test drive. 

Using this last setup, I was able to perform a left and right alignment within about 10 minutes.  While it took me a considerable amount of trial and error, I feel the effort was well worth the result. 

Future improvements?  Yes, there is still room for improvement.  The target arrangement I devised is still a bit jenky; it requires a little care in getting it clamped securely and taking measurements as to not move it from its mid point.  I also want to take the time to figure out just how much error there is using the targets vs taking measurements from the rim itself.  If the error is very small, I might forego the targets and continue using the wheel rims.  

But for now, I got other projects to pursue so this one is put to rest for now.