SoundGuyDave
This Space For Rent
- Joined
- Apr 9, 2007
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It's not really the easiest to explain, even though it's a pretty easy concept... Suffice it to say that if the cross-weights aren't pretty even, the left vs. right handling balance suffers. Understeer on right turns, oversteer on left, if you follow. Yes, you want your left-side weight as equal as possible to the right-side, and the front-weight as equal as possible to the rear, but the real key is in the cross-weight, and it's something you can seriously feel when its right!
Ahhh, but the devil is in the details! Google Smokey Yunick while you're at it, then put on his hat and start thinking about weight. Weight is the enemy, pure and simple. At 3441 you're actually already reasonably light for an S197 in full street trim but there are still places you can shave weight. I don't know the rule book, but you have to get creative with interpretation but stay legal to the letter. I helped a buddy build a race car, and working through the rules LINE BY LINE, we pulled as much weight out during the build as we possibly could, and came up almost 300lbs light. The scales said he was too light in the right rear, so instead of using the gucci aluminum mount for the cool suit cooler, we fabricated one out of 1/4" plate steel. This allowed us to put the weight where we wanted it, rather than having to run big lead ballast blocks in the specified location, which was less than ideal for the cross-weight. After testing, we wanted more rear-weight, so the ballast stack was reduced by an addition of a double-layer of dynamat under the entire trunk area for "interior noise control." There are a million tricks like that, but you have to start underweight to begin with. If you don't have a number to hit, but are required to have certain components in certain locations, you can still play... Need a stock-type battery? Take a scale and go shopping. I've found a certain "import" brand group 24F battery that was a full two pounds lighter than the typical Interstate replacement. Here is a place to get creative! I'm not advocating cheating, far from it, but if the rule book says "X," and you comply with it, that's hardly cheating. Just make sure you're reading what it says, and NOT what it means!This car is an autocross car though (well it's a daily driver that gets autocrossed), so no requirement for fire bottle, cool-suit or ballast. ST has no minimum weights just a crap ton of requirements stating what can be changed (and everything else is assumed not). I've autocrossed this car with the 50 miles to E spamming the information center on the dash without any fuel starvation issues hence why I wasn't afraid to have the corner weighting done at 1/8th of a tank where last year I spent most of my time autocrossing at for fuel. I generally fill up on the way home.
The good news is that the shop didn't lead me astray!
And no, your shop did NOT lead you astray, your numbers actually look killer. Like you, my cross-weights are within one lb, but I am way light in the rear compared to you! I really need to find some weight to ditch in the left-front...
Truth right there!@fun4me - I ran a full year + autocross with -1.7º camber and NO toe in the front but -0.16º toe out in the rear (thanks Ford!
California Special: Yes, final ride heights are completely dependent on the corner-weighting, but unless something is WAYYYY out of whack, you're only going to be looking at differences in the fractions-of-an-inch range, nothing visually obvious. Also note that to properly corner-weight the car, you need to be able to take the swaybars out of the equation. Adjustable endlinks up front, and some form of adjustment in the rear. In my case, there's enough room in the bolt-holes of the rear drop-links to take the preload off. There's no point in getting the cross-weight perfect, then adding 50lbs or so of front bar preload (25lb change to both front wheels), if you follow. The way that I approach it is to figure out where you want to be in terms of gross ride-height (factoring in suspension travel, spring rates, roll centers, handling balance, etc.), then scale the car. Proper corner-weighting is absolutely an iterative process. Test first to get the rough ride-height and spring package, THEN align, then scale, then aligh, then test, then align, then scale, then align... I think you get the picture. You may be surprised at how HIGH your final ride height winds up being! CG is important, but nowhere NEAR as much as roll-center and handling balance!
