Make your own corner balance scales? - Page 2

diverdan · diverdan's Garage

John Ruggles makes a great package available for about $400 for a complete set of scales. Highly recommended by people like Caroll Smith. They are so simple and accurate. While you could make your own, why bother at $400.00 U.S.? Search for "Ruggles scales."

Diverdan

diverdan · diverdan's Garage

Being the cheap #*@!ard that I am I do it on a mathematical basis. First I find the midpoint on the steering crossmember. Then I put a 2x4 under the full length of the crossmember. Then I take a floor jack with my 3/4 inch extention bar on top and and align it with the center of the crossmember and jack the front wheels just off the ground. At this point I measure the rear fenders to the ground and check the torsion arm deflection. Then I decide the ride height that I want and do the math to adjust the rear torsion bars.

After the rear torsion bars have been adjusted and checked as in the above, I slowly lower the front back down until the front wheels just touch the ground. At this point the distance to between the front torsion bar adjustment screw and the housing needs to be checked. Once they are equal you are in the ballpark.

jester911 · jester911's Garage

So how do you account for drivers weight or do you?

randywebb · 04-29-2007, 11:02 AM

The Ruggles "scales" are not, in fact, scales. They are lever arms that you fit to YOUR scale. This means that the repeatability of the scale used is an issue in the accuracy of the measurement -- among other things. Maybe they usually give a good approximation - I dunno.

DiverDan's idea doesn't seem like corner balancing to me.

It would be nice to have something cheap that works, but my plan is to let a good pro racing shop do it, and then not modify the car too much or else get it done again after any major wt. mods.

911pcars · 04-29-2007, 12:13 PM

diverdan's method will verify that rear wheel heights don't affect the front wheel heights (and vice versa). That in itself will get you closer than any other DIY method w/o scales.

The Deco weight checker from Speedway Motors is a relatively low cost, off-the-shelf scale - around $160.00. Probably not as accurate as dedicated individual chassis balancing scales, but maybe more accurate than a set of typical bathroom scales, digital or analog.

Sherwood

dad911 · 04-29-2007, 01:41 PM

I bought scales. Like any quality tool, I figure they are still worth 75% of what I paid, so if I ever decide to sell them, my net loss will be less than most of the solutions presented above.

Todd Simpson · 04-29-2007, 01:45 PM

+1 on the wheel load checker.

It is *so* nice not to have to write those corner balance checks anymore.

duke3282 · 04-29-2007, 05:10 PM

Building your own seems like an interesting idea. I think one could be rigged up for a pretty reasonable price. Check out these piezoresistive force sensors.

http://www.tekscan.com/flexiforce/flexiforce.html

The 1000lb sensors is 100.00 for a pack of 8 or 60 for a pack of 4. The only downside is they only have an accuracy of +- 2.5%. I dont know what is requred but you could probably calibrate before each usage to try and minimize the error as much as possible. You could fairly easily use the A/D on a microcontroller to read the voltage output. I have used PIC's in the past, you can get programmers pretty cheap and there are c compilers available. Probably the cheapest solution is to use a picaxe which can be programmed from your serial port but you can only use BASIC (which I am not as familiar with). After that it would be easy to output to a LCD or just use hyperterminal on a laptop. If you wanted to get fancy you could write a vb or labview program to read in the serial data from the microcontroller. If the flexiforce sensors will work, I think that all the electronics could be done for under $100 pretty easily. Next you would just need to rig up some pads which you could park on. Probabaly not too expensive either. I bet total, it could be built for around 200. If anyone is interested in moving forward with this I would be happy to help.

Hugh R · 04-29-2007, 07:04 PM

I think you guys are being too smart. Correct me if I'm wrong, but you know the weight of the car so if you put a clean sheet of paper under each tire and then take the paper out and measure the total surface area of the marks they leave and divide vehicle weight by the total square inches you'd get pounds/sq. inch. Then allocating the sq. inches out to each piece of paper you'd have and idea how much weight is on each tire. Remember, at a given psi of pressure in a tire, the contact surface area of the tire is going to be the same regardless of width of tire or profile of tire. In other words, a 225/50VR16 tire has the same surface area in contact with the road as a 205/55VR16, IF the psi in the tire is the same; just a different profile the 225 rear tire has a wider, but thin front-to-rear contact area than a 205, its profile is narrower, but thicker front-to-rear.

I know a lot of guys think a big fattie tire puts more rubber on the road, but it doesn't, when psi is unchanged. If you have 900 pound pushing on the axle, and 30 pounds per square inch pushing back, then the surface area in contact with the road is 30 sq. inches everytime, regardless how wide the tire.