A Lesson in Vibrations

In engineering school, we had a class called Intro to Vibrations.  In this class, we studied how real life systems will vibrate and how to predict and control them.  We had one very interesting group project that went from a 1 month project to an over-nighter in the space of 29 days.  It ended up being a 12-hour marathon for three mechanical engineering students and a 20-some page paper, all but 6 of which were calculation appendixes.

The problem went something like this: using a given simplified model of a car, supply spring rates and damping rates in order to make the car bounce (vertical vibration) at a rate between X and Y and pitch at a rate between U and W (two different given rates).  The idea is that a car is uncomfortable if the car bounces or pitches too slowly or rapidly when the car goes over a bump.  The car will be subjected to bumps modeled by a given sine curve.  Assume the weight distribution of the car is unknown.

In short, we select a car's springs and shocks based on comfort.  As complex as this was (36 man-hours plus were spent on this), it ignores the VAST, VAST majority of real automotive engineers' design goals (handling, stability, etc.).  That being said, this sort of thing is still important to automakers because cars should be comfortable.



Allow me to diverge for a minute to describe something that happened to me more than once.  The 2nd car that I drove in life was a 2005 Pontiac G6.  I admit, this was not a car I liked very much, its only redeeming factor being that if I drove it like a grandpa I could manage to get the gas mileage up around 36/46 (city/highway).  That and people seemed to think it was a nice car.

Anyway, here was a situation.  I'm driving down a curvy road through south Raleigh, very fun, often taken at or above the speed limit of 45 mph by most traffic despite the 35 mph suggested speed limit.  I was probably doing 48-50, nothing unusually fast.  While going over a certain rock or rumble in the road, my front tires gave up traction, my steering wheel went limp and the wheel snapped into the direction I was pushing it.  I, after my years and years of video game training, immediately straightened the wheel and braked until I was slow enough to complete the turn.  My decision was the correct one, though the unintuitive one, saving me from plowing into a tree (or five).



I got into this situation doing nothing wrong.  The suspension in the Pontiac just didn't like that particular series of waves or bumps in the road and the car lost traction.  My strong suspicion, having been through some of the basics of auto engineering, is that Pontiac didn't spend the engineering hours on this car to prevent this sort of thing.  I believe that many companies cut corners in any way that doesn't effect the bottom line, and they know that the last decision made before a purchase is related to the test drive.  The trouble is that test drives do not cover most driving circumstances, and in practice rarely include any driving that reveal the strength of the underlying car.  Instead, most test drivers focus on how comfortable and nice and rich a car is.  Therefore, the best way to sell a car to someone who is test driving it, is to make the car as smooth and comfortable and generally nice as possible.

This means that the most important thing to a suspension engineering team run by a company that wants to sell lots of cars is the extended version of my college project.  I don't mean to say that comfort is not important, but it's not what's most important.  What's most important is that the car safely and reliably gets you from A to B (in saying this I'm quoting every person who tells me "I don't need a race car, I just need something to get me from A to B").  Comfort and style are, at best, a close second.

I'm hoping my statement is already becoming clear here, but as I'm likely to ramble, I'll simplify the purpose of this blog entry to one statement (good luck to me).  Car companies often cheap out on engineering hours that do not lead to the sale of a vehicle and/or only spend time and money on making a car seem nice.

It's just something for you to think about.  The kinds of car companies that I and many other enthusiasts often support are companies that are willing to go the extra mile to make a car a better car.  Yeah, often we've got our heads stuck up our own butts about "true sports cars", but often we have a reason.  I love and support Mazda because they put a great chassis under their car, and I believe that this is more important than having sat-nav standard.