As Spring blooms, a boy's thoughts naturally turn to, er, cars. Sorry, dear.

It's so nice to be driving with the top down again. Soon, we'll be back hurrying around racetracks having fun. I started thinking about this today as I drove back from lunch. And, of course, as soon as I start thinking about (real) driving, I start thinking about the fiddling I need/want to do on my car.

Of the short list of things I want to get done before my first track day, the thing I really want to make sure I get done is a good corner-balancing of the car.

"What's corner-balancing?," you say? Glad you asked, because it's kind of cool and absolutely helps your car handle better.

Here's how to do it:

A corner-balancing primer

Corner-balancing, in simple terms, is adjusting the car so there's an equal amount of weight on all four tires. In real life, of course, it's not quite that simple, but I'll get to that in a minute.

To do it, you need four scales (one for each tire--there are scales made specifically for this. Look for a racing shop near you and see if you can rent a set for an hour or two) and some way to adjust your suspension. Ah. That's the tricky bit. There are several ways:

1. Coil-overs. A lot of the performance-modified cars these days include adjustable coil-over suspensions. Unfortunately, very few vehicles come from the factory that way. If you're not driving a Lotus Elise or Porsche GT3, chances are your car didn't come stock with them. Mine, for instance, are aftermarket.

These are the easiest to adjust since there is a threaded collar on the outside of the shock absorber housing which holds the lower spring perch for each corner of the vehicle. Turn the spring perch and it raises or lowers the suspension.

Coil-overs make corner-balancing really easy.

2. Torsion-bar adjusters. Early Porsches used torsion-bars instead of coil springs. I won't go into the technology here but the front torsion bars had little adjusters you could turn to change the ride height of the front of the car. You could change it at the back, too, though that was a little bit more work (but not a lot). If you need more information, write me.

3. Spacers. Ugh. If you don't have an adjustable suspension, it's technically possible to adjust the ride height by inserting spacers beneath the coil springs. However, without a great (which is to say powered) spring compressor, this is such slow and miserable work that you'll want to ignore it altogether.

OK, so. One way or another you've got a way adjust your suspension height. I'm not talking big adjustments (hopefully), but if you can't adjust it, you can't corner-balance. Sorry. The first thing to do is get your car on the scales, preferably in the mode you expect be driving it which is to say with you behind the wheel and probably half a tank of gas.

Get a friend to read the weights on all the scales and write them down so you know which weight is where. You should end up with something like this:

Now, the trick here is to figure out what the weights should be. Ideally, every tire would carry the same amount of weight ((575 + 605 + 750 + 632)/4 = 640.5), but that's not possible so you have to figure out the best that is possible. Here's how:

First, add up the two front tires' weights to get the weight of the front of the car (575 + 605 = 1,180 lbs in my example). Next, do the same thing for the rear (1,382), the left side (1,325) and the right side (1,237).

The thing to understand here is that whatever weights you come up with for each of these calculations (for your car), those are the numbers. Unless you start moving parts around inside the vehicle (like, for instance, moving the battery to the trunk), the relative numbers won't change, regardless of what adjustments you make to the suspension.

Ah, but there's a loophole:

You can't change the total weight on the front or left or right or rear, but the distribution of weight between the two tires that comprise each of those measurements can be changed. That's what we're here to do.

Next, figure out what percentage each side of the car's weight is of the entire vehicle's weight. In my example, the left side is 1,325 / 2,562 = 51.72%; the right side comes out to 48.28%.

Almost there. Now, if the front of the car weighs 1,180 lbs and the left side is 51.72% of the car's weight, the front left tire's share of the car's weight should be 1,180 x .5172 = 610.3 lbs. Using the same logic, compute the values for the three other tires and you should come up with this:

Comparing this to the actual figures you find the weights need adjusted as follows:

It's coincidental that the same numbers are at both ends of the car in this example (you won't always see this) but the diagonal arrangement of the pluses and minuses is ALWAYS there. That's how it works. If there's too much weight in one corner there's also too much weight in the opposite corner. In fact, that's the whole basis of corner-balancing.

Think of it like this: If you put a jack under the right rear tire of your car and lifted it high enough, eventually all of the weight of the car would be distributed between the right rear and front left tires as the other two tires would be off the ground. As you started letting the car down and the other two tires started to touch the ground, some of the weight of the car would start to be transferred onto them until, eventually, you were all the way to the ground and the weight was more or less evenly distributed.

At a much more subtle level, you can do pretty much the same thing by adjusting the ride height at one or more corners of the car. For instance, lowering the right rear corner of the car a touch will make it AND the opposite corner (the front left) press on the ground a little less. As they press a little less, the other two tires (back left and front right) will have to pick up the slack because, after all, the car still weighs the same amount and all of that weight has to be supported. So, by lowering the right rear you simultaneously reduce the weight on the right rear and front left while increasing the weight on the opposite two corners.

With a few go-arounds of adjusting and weighing, you can dial in the balance until each tire is carrying its appropriate amount of weight. Unless you have weird ride-height issues (or a bent frame), or started out grossly out of adjustment, you can usually get the car balanced by adjusting just one of the corners, but sometimes you have to do two.

While it may seem like a lot of trouble (heck, if your suspension isn't adjustable it IS a lot of trouble), there's a payoff in improved handling both at the track and on the road. Give it a try (if you can).

1. Phil02/03/2007 01:12:04 AM
Homepage: http://www.dpeweb.com

Nice post on corner balancing! Just for clarification though, in the following paragraph note the change in bold; I believe it is correct and makes sense, though it is late at night so I could be mistaken:

"For instance, lowering the right rear corner of the car a touch (in the above example) will make it AND the opposite corner (the front left) press on the ground a little less. As they press a little less, the other two (back left and front right) will have to pick up the slack (the car doesn't weigh any less), gaining a little weight on the two that are too low.

2. Scott Good02/03/2007 11:42:26 AM
Homepage: http://www.scottgood.com

Phil,

You're absolutely right...change made to the original copy.

Thanks!

Scott

3. tony05/12/2007 04:23:41 PM

think i understand but can you tell me on my race car i only go round one way on a 1/4 mile oval ,we travel clock wise what sort of set up would be the best for me thanks tony.

4. Scott Good05/14/2007 11:09:57 AM
Homepage: http://www.scottgood.com

Hi Tony,

A quarter mile track that runs clockwise? I've never heard of an oval that wasn't counter-clockwise. In any case (and even if you meant counter-clockwise), oval track set-ups are very different from those we use for road racing.

I have not spent much time looking into what you need to do to corner balance properly for ovals but I know they often use a staggered weight set-up. In other words, where we (road racers, who need to turn both left and right) want our weight as evenly balanced as possible, the roundy-rounders, as I understand it, may add more diagonal weighting to get the car to handle better in that always-turning-the-same-way situation.

Also, and I'm sure you know this, you should have positive camber on the inside wheels and negative camber on the outside ones. In road racing (and street cars, for that matter) we use negative camber (where the tops are leaned in) on all tires so the outside tires sit more squarely on the ground once the car is leaning into a turn. This compromises the inside tire's contact patch but since it carries a lot less weight during the turn, that's the trade-off you make for best overall speed in turns of both directions.

With only left (or right) turns, you can lean all the tires the same way so they all make the best possible contact with the track in the middle of the turns. You can play around with this but the only way to really know the right setup is to use a probe-type pyrometer and measure tire temperatures across the treads of all four tires.

I can tell you from my one experience driving a stock car that once your car is properly set up for an oval track's corners you will find it hard to drive down the straights as it will want to be turning. It's strange at first but then you get to a turn and everything feels great and, let's face it, the race is pretty much won or lost in the turns because the straights are all about the motor which can only do whatever it can do. Every mph you can add to your exit speed from the turn is an mph you're ahead for the entire straight.

I'm not sure where to tell you to go to find specific oval track setup information but you've gotta think it's out there somewhere.

Good luck!

Scott