Most enthusiasts are aware that lowering a car's center of gravity is good for handling and indeed, grip.
It's easy to see the real world implications as well when we think about how a tall SUV handles versus a very low Ferrari or Corvette.
Where the Center of Gravity Is
The car's center of gravity has both a horizontal (x, y) and vertical (z) location and actually refers to a single point where if suspended, the car would balance perfectly (at least in theory).
So vertically, we already know that the lower the center of gravity - the better. What about horizontally? Well, again, take a look at super cars - the closer weight is to the center of the vehicle the better. This is why super cars are typically mid-engine, so the heaviest part of the car (the engine/transmission) is closer to the middle of the vehicle.
The center of gravity in most cars is roughly at the top of the front bumper in terms of height (just a very rough estimate). The (x,y) coordinate of the center of gravity is much more variable, the Y being affected by the car's front and rear weight distribution. So in most cases, the CoG is at bumper height, somewhere in front of the midline of the car as you look at it from the side of the car. As you look from the front of the car, it is going to be either in the driver or the passenger's lap as most cars are slightly heavier on one side or the other.
Improving Center of Gravity - Vertically
Lowering a car is one way to improve the vertical center of gravity. This will offer increased stability, lessen the risk of roll over in extreme situations, and in most cases increase lateral grip (or the "g" handling figures on the skid pad). There are practical limits on how low you can go due to road imperfections and so on. There are also limits on how low you can go on a factory suspension without actually hurting handling. Usually around an inch of lowering is the farthest you can go without serious changes to your suspension geometry... but more on that in another article.
Vertical CoG can be improved by removing weight or choosing not to locate weight high in the vehicle. You can also get a CoG advantage from choosing a vehicle without a sunroof. Sunroofs in modern cars are around 25-30lbs, but in older vehicles they were sometimes 40-60lbs. In any case, take note that BMW thought it worth the exceptional expense to use a carbon fiber roof on many of their M vehicles. A few pounds on the roof of a vehicle can make a significant difference on the track, and 10-15 lbs can make a noticeable difference even on mountain roads.Having removed the sunroof on a car before, I can say that removal is not ideal (reasonably expensive) and you'll be better off to start with a car without a sunroof if possible.
Improving Horizontal CoG
Improving the horizontal CoG (center of gravity) is done by strategically mounting and moving items in the car that have significant weight towards the center of the car. This is much more difficult to do, but is a good thing to keep in mind when doing modifications.
Some ways to improve horizontal CoG include utilizing lightweight body panels. The further from the CoG, the more the weight of tha panel matters. Other ways are relocating the battery rearward to the trunk (but close to the rear seats), or to the rear of the engine bay where possible. If you're mounting racing seats, you may want to choose mounts that sit low to the floor (assuming you can still sit comfortably at that height) and that move the seat slightly in-board towards the center of the car. This is often done by race teams for CoG advantage as well as to give more room for side-impact bars in a roll cage.
Strategically Improving CoG
You do not need to do serious surgery on your car to lower CoG though. Keeping CoG in mind as you do all of your modifications can add up to a serious improvement in weight distribution and CoG height/location.
Mounting the battery as low in the vehicle as possible is one way to improve CoG. When I fitted an Optima Red Top to project Lexus, the battery itself was not much lighter than the factory battery. However, it was significantly shorter. This means that while it weighed the same, the distribution of that weight was lower than with the original battery. Because the factory battery was wider, I was also able to move the new battery a little closer to the center of the car without any modification. Eventually, it MAY be moved to the trunk to further improve its location. By itself, a very minor change in weight in terms of the car, however, moving several components and being mindful eventually adds up. The battery is one of the heaviest components in a typical car that can be moved easily. In the case of our IS300, the battery is about 1% of the vehicle's weight which is enough to be significant.
The TRD front seats fitted in project Lexus are another place where weight was moved in a favorable way. The seats are lighter than factory, but they are by no means super feather weight. However, the rails they are attached to move the seats inboard an inch or two and the seats themselves are several inches shorter than the original seats. Even if these seats weighed the same as factory, they concentrate the weight lower and more inboard than the factory seats and thus would give an improvement in weight distribution regardless. As an added bonus, they do weigh less and they are in the front half of the car, so they help even out the front/rear weight distribution of the car somewhat. Most of the weight in these seats is also in the seat rails, the lowest point of the seat/rail assembly whereas the factory seats have their weight distributed more evenly.
Other examples of component placement might be in placing stereo components. If you're going to install a stereo system, try to locate the amp and subwoofers as close to midship as possible. Most people do this any way as it makes the most sense, but now you have a specific reason to do so. If possible, consider mounting amplifiers under the driver and passenger seats. Avoid adding significant weight to the rear trunk or either side of the trunk.
One unexpected way that I lowered the IS300s center of gravity as well was by fitting the TRD under braces to the car. These braces are about 13lbs (between the two of them) heavier than the factory braces they replace. Without getting into the details of those braces, this effectively lowered the center of gravity because of where they are - the lowest part of the car.
The main point I'm trying to make is, you need to be aware that when you remove something, install something or move something that you are changing the dynamics of your car. Use this information to your advantage and make sure changes you're making are pushing your car further and further towards ideal rather than further away.
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