Project SC300 Road Racer: Part 31 – ECM(easure all the things!)
Silver ASUS Republic of Gamers laptop sitting on a cardboard box
The CMM doesn’t have a display on it, so you need a computer to interface with it to take the measurements.

Fortunately for you, another thing included in your rental is a high-powered laptop preinstalled with the software you need for the task. In my case, the computer came with a USB dongle specifically for the portable CMM arm manufacturer’s measurement software. If you were using a 3D scanner, you might use a different piece of software and get a different USB dongle. If you were trying to validate that a CNC-manufactured component was within the promised manufacturing tolerances, you might use yet a different software program (and a different dongle). No matter what the measurement task, ECM has you covered.

Almost ready!


race car sitting on hub stands on top of scale pads and scale levelers
Getting the car into a situation where it can be measured comes next.

You may remember this equipment from our DIY alignment article, where we performed our corner weighting and alignment using the CSM hubstands and the Intercomp scales and scale levelers. The hub stands make the measuring we’re about to do much more straightforward because they allow easy access to all of the suspension points without obstruction from the wheel and tire. It’s also easy to locate and measure the brakes, as well.

Don’t forget that the steering pick-up (tie rod attachment to the front knuckle) and rack stroke will need to be measured. This is how the sim can evaluate the steering force and how much the wheel being turned moves the front hubs, which moves the tires, and etc.

The vehicle must be at its static ride height and at the desired alignment before beginning the measurements. The static ride height impacts the suspension point locations, affecting the static alignment, and all of that alters the suspension dynamics — these are all inter-related. I didn’t think about this until after taking all of my measurements and sending the equipment back. Oops! So, things will end up being off by some amount on top of everything else that is making things slightly off.

There are other reasons that I’ll go into why my measurements were not ideal. But it’s not the fault of the equipment – it’s the fault of the operator and the set-up.

Time to measure? No, not quite. It’s time to measure to measure.



really long ruler, chalk line, tape measure, calipers, masking and painters tape, markers, level, and plumb bob laying on concrete garage floor
Here’s a set of simple tools that you’ll need to perform the measurements you need to take the measurements.

This will make sense, I promise.

A plumb bob is used to transfer a location on the vehicle onto the ground to be marked. A chalk line can be used to mark long lines along the floor to help establish planes. Tape and markers are used to mark the floor for repeatable references. You also want a large square (not pictured).


permanent marker with a string taped to it
In a pinch, you can use something pointy hanging on a string to act as a MacGyver‘d plumb bob.

But a real plumb bob is less than the cost of lunch in most cities. So buy a real one, you cheapskate.


  1. There’s places that will do tire testing and it’s… expensive but if you keep the test matrix down, in the 4-figures level. Would be interesting to add that to the mix. I’m figuring that most of the time in sims it’s not that the tire model itself has issues, just that it’s filled with variables that people are guessing at.

    1. The most important thing is that the driver understands how the tire develops grip, and how to keep it at the proper temp. You can collect as much data as you want, but if the driver doesn’t understand that data, it is worthless. The pneumatic tire has been around for over a hundred years and there’s only one book written about it? Sad.

      This is a must read for anybody serious about racing:

  2. Very interesting, great work Erik! I had no idea this type of equipment could be rented and used by near mortals.

    The wheels are turning on other ways this type of equipment could be used.

    1. Calspan does – if you are willing to be flexible on schedule and don’t get too complicated it helps hold the cost down, and the gent I was talking to was willing to deal with it as a smaller project.

  3. Yeah, I really like this article. I wrote my own code in MATLAB in college using Dixon’s equations and precise measurements (by hand) of the EG6 Civic suspension. I had so many parts lying around, it was pretty much a no brainer. You can learn how to avoid so many mistakes through simulation. While I did some minor modifications using a LCON traction bar which allowed me to remove the rear half of the LCA, and drop 8lbs of unsprung weight, I also gained enormous appreciation for Honda suspension engineers. The stock bump steer curve could not actually be improved upon without new spindles. Simulation proved to me that some things are better left alone.

    This is a great book, BTW. It is the ‘Bible’ for suspension engineers.

    1. Thanks, Joe! That looks like a real textbook there. Probably well over my head. As you’ve learned some things are best left alone, I have learned that for some things I should probably outsource. Suspension engineering is one of those things. I’m fortunate to have folks like Figs Engineering, Mike Kojima, and Rob Lindsey (Morlind Engineering) available to me!

Leave a Reply

Your email address will not be published. Required fields are marked *