Blue Juice

I posted a picture of my home made camber gauge on a thread last week and had a couple of positive comments and enquiry as to how I made it.





WARNING: these instructions contain metric. As a Brit; I am comfortable in imperial or metric, but for small accurate measurement of distance I prefer millimetres. Convert as you see fit…

The gauge works by sitting the “Wheel” edge against the bead of the wheel to be measured. The Plumb weight always sits vertically, so any angle that the wheel is at will be indicated by the string. Larger wheels are measured by moving the gauge to the front or rear until the gauge edge meets the wheel beads.
The gauge will always be vertically level as the string will not give good readings if it is lying on the gauge face or hanging too far away from it. Therefore accuracy and repeatability are almost guaranteed.





The gauge is physically a sheet of aluminium 300mm x 450mm (12” x 18”) and 3mm (1/8”) thick.
On my gauge; the side that will sit against the wheel is 12.5” to allow the gauge to work down to 13” wheels (as used on a modified GT hillclimb car I used to campaign).

Important details:

• The edge that sits on the wheel should be precisely 90deg to the bottom edge and both edges should be flat, with no imperfections. This will allow you to sit the gauge on your workshop floor and determine if there is a slope that should be accounted for in your measurement. I have a large engineer’s square for this.

• The Zero Degree Line must be parallel to the wheel edge
I also cut out a handle on the side away from the wheel to make using the gauge easier.


Markings
To make the markings you will need a scientific calculator that has a “TAN” (or tangent) function. This is a trigonometry function for finding angles or lengths of triangle sides.
Geometry Refresher 101:
On the attached worksheet there is a right angled triangle ABC with the right angle at B.
The line AC is the Hypotenuse (which we don't care about)
Angle X is what we are interested in
Line AB is “Adjacent” to our angle (this is known and constant)
Line BC is “Opposite” to our angle (this is what we need to calculate)
The tangent of an angle is equal to the length of the “Opposite” side divided by the length of the “Adjacent” side. Therefore Tan X = BC / AB







So, on the plate we will mark a line exactly 150mm from the wheel edge. This will be from the top of the gauge to the bottom. It should be approximately in the middle of the plate, but will very precisely be parallel to the wheel edge.
On my gauge, I came 50mm down from the top edge and made a mark. This is my point A, the pivot for the string.
I then measured exactly 350mm from point A and made a mark. This is my point B, where my horizontal line will be. This dimension (350mm) is important.
Now, because I was very accurate in making the bottom edge exactly perpendicular to the wheel, I can measure the distance from the bottom edge to point B and use that to very accurately make my horizontal line.


Calculations
The attachment shows a typical example (I wrote those sheets yesterday without measuring the actual gauge I have).
For the real gauge, I would start with 0.5 degrees and my AB line of 350mm.
So distance BC on my gauge equals;
Tan0.5 x 350 = 3.05mm

Measure this distance along the horizontal line from the centre point out (on both sides of the vertical line AB); this is point C. Now draw a line from point C towards point A.
For clarity, I did not continue the lines to point A.
Now recalculate for the rest of the degree marks;
Tan1 x 350 = 6.11mm
Tan1.5 x 350 = 9.17mm
Tan2 x 350 = 12.22mm, etc. etc…

REMEMBER, every distance calculated is from the original, vertical, centre, AB line along the horizontal line. Do NOT measure from point C to mark point D. Measure from point B for all degree distance calcs.
And mark each point on either side of the vertical line for positive and negative readings.


Final assembly
I used kite string and tied the M12 nut on about 15 years ago with great intentions of it being temporary.

Important detail

• The point that the string pivots from must be on the point A.

To achieve this I drilled a hole to the side of point A and installed a bolt with a spacer. I ensured that the side of the spacer was exactly on the point A. By doing this I can hang a piece of string over it and have the pivot point correct. Should I need to replace the string, I don’t have to disturb the bolt or spacer. They remain fixed and accurate.
The string is secured from a randomly positioned bolt to the side of the pivot bolt, and the string is coloured black with a permanent marker.






That’s it. I will answer any questions, but I don’t live online so apologies for any delayed replies.

cagotzmann

Any thoughts on getting the degrees down to 0.1 resolution. It looks like it would be difficult to break up the 0 - 1 degree into 10 segments where the distance is more than the width of the string.

Most alignments are in the range 0 - 0.5 anything above 1 can be seen visually and is very bad on the tires.

'75

That is a cool tool, great ingenuity!

20mercury

Interested in what Blue Juice thinks. IMHO, you could make the string longer which means the body of the gauge would need to be larger. However you would need to keep the part of the gauge that touches the wheel rim the same. Also. I would guess you need to check the floor for level too.

Pretty cool invention and thanks!!!

Luce

You don't need better than .25 degree resolution and you can easily make that out with his 1 deg marks. Add a hash mark half way if you want.

Nice job mate, and nice trig refresher for all. But for the effort/money, http://www.ebay.com/itm/Longacre-Rac...xWFayZ&vxp=mtr

It has magnets that stick it to the rotor.

grancuda

I use an old style angle finder & not really worried about too much accuracy. They do make these in a digital version for about $40.

Pop Chevy

This will work fine, however the car must be level. When I scale my race car, I level my scales 1st then do alin. This can be done with pads,plates or even floor tile.

Blue Juice

Cool, I didn't get bombed out of the water.

Cagotzmann, like any analogue gauge, the human eye is great at making comparisons.
Using this gauge I find that I can see where the string lies between two degree markings and make a jugement that will be accurate to about 0.25 degrees.
Considering the ever-changing camber and level of road surfaces, greater accuracy is unlikely to be of any practical value.
When I was younger and could afford to go racing I would do a couple of hot laps and then measure tyre temperature, looking for differences beteen the inner and outer edges which would indicate too much or too little static camber for that particular course, rather than relying on geometrical measurement only.


20Mercury, absolutely correct; the longer the string, the larger the distances between the degree markings, and easier to make more accurate readings.
There is nothing stopping the size of the main plate being taller, with the "wheel edge" staying where it is relative to the lower edge of the plate.

The reason for making the lower edge exactly perpendicular to the wheel edge, is to allow the gauge to be placed on the floor and any in-built workshop slope to be accounted for.


Luce, honestly I have to say that I made the original gauge in less time than it took to compile this thread, and because I had the aluminium plate in my "useful metal" stockpile (you all have one don't you? Next to the "nice bit of timber" pile), it didn't cost me a penny.

But each to their own, as with anything there are usually many right ways, and the one that you feel most comforable with is best.


Grancuda, a perfect example of another "right way". I have one of those for pinion angle recording, but my rally steel wheels prevent easy transfer to camber measurement.