What Is Corner Balancing?
[AV] I will try my best to explain what corner balancing is and what it does to the car. I will tap into my knowledge in setting up karts, as well as basic race principles I have learned through the years. Anybody feel free to add or correct anything on this post.
Imagine a car as a four legged chair. In order for the chair to stand steadily, all four legs should be of equal length and as a consequence applying equal pressure on the floor. If one leg is longer, or shorter than the others, we have a chair that rocks, and is unstable.
By the same analogy, the suspension of the (race) car has to be adjusted so that each corner "applies" the same amount of force on the ground, relative to the diagonally-opposite corner, so that the car does not "rock." Scales are placed underneath each wheel/tire to measure the "weight" of each corner, and a "perfect" corner balance would have the sum of the weights of the right-front and left-rear corners equal the sum of the weights of the left-front and right-rear corners.
For example, we have a 200 lb. car, with the center of gravity positioned exactly at the middle of the car. An ideal situation would be that each corner (tire) would apply 50 lbs. of force.
50--| |--50 | | |200| (Looking at the car from above) |lbs| | | 50--| |--50
Corner balance is perfect at LF + RR = RF + LR = 100 lbs.
By the same token, if the CG is positioned a little towards the rear, as in the case of the NSX, we would have:
40--| |--40 | | | | |200| |lbs| 60--| |--60
Corner balance would still be ideal. The same applies if there was a driver (any good race car alignment shop worth their salt would put a ballast equal to the driver's weight in the driver's seat when corner balancing and aligning the suspension). In this example, say the driver weighs 10 pounds
44--| |--41 | | |10 | |200| |lbs| 64--| |--61
Corner balance is still ideal.
Say, for example, one corner is jacked up so it applies 10 lbs more...(refering back to our "perfect" example)
40--| |--60 | | |200| |lbs| | | 60--| |--40
Corner balance is off, with LF(40) + RR(40) = 80 and RF(60) + LR(60) = 120
It would have the same effect as having a leg on that chair a little too long, so the diagonally opposite corner would also apply more force on the ground, with lesser forces on the other two corners. The car, in effect, will "rock."
A car in this situation will have a very poor handling characteristic, and will handle differently when turned left and right. In contrast, a perfectly corner balanced car will handle the same when turning left and right, and will be maximizing tire contact area on all four corners, thus will have more grip all around.
Obviously, to be able to adjust the corner "weights" requires a suspension that has ride-height adjustability. Coil-over springs are mounted on adjustable (screw-type) perches that go up and down on the shock absorber. This allows you to adjust the ride height, as well as make fine tune adjustments to the "weight" of each corner on the road.
How Can I Corner Balance My Car?
[AV] If I may quote Andy W. on this subject, this is one of the best things you can do to improve the handling characteristics of your car. Now for my shameless plug...
Mark has installed a state of the "racing" art suspension, one with ball bearing joints and ultra lightweight double adjustable shocks. Truly a very high quality system, capable of winning the 24 hours of LeMans. I, too, was tempted to purchase this set when it first came out. However, I was dismayed to find out that since this product was introduced (just a few months ago), the price has nearly doubled (from $2600 to nearly $5000 !)
So, having not as deep a pocket as Mark <VBG>, while not planning on making my NSX a full-time WSC racer, as well as having to put aside some money for my kids' college education ;), I opted for a similar system, that has about 90% of the adjustability of the pro setup, at about 1/5th the price.
I started out with a set of Konis, the garden variety "yellow" Konis ($550.00, about $700 in NSXtra). Then I sent these to a company called Ground Control. They specialize in coil over conversions, as well as shock revalving, and other suspension fabrication. They modified the Konis to accept a threaded sleeve and an adjustable spring perch. Then they asked me what kind of driving I will be doing with the car, and supplied the (Eibach) coil over springs with the proper spring rates. These are the same type springs CompTech has in their pro kit. The springs are also the cheapest part of the whole system, so if you are into it, you can also experiment with different spring rates if you so desire. But I have found the supplied rates to be excellent. Cost of the conversion is $500.
So, for about $1,200, I have a suspension that is ride height adjustable, and corner balanced. I can also play around with the shock settings as it is very easy to get to (at the top of the shock tower). I have found the best settings to have the fronts set up a little bit stiffer than the rears. Very, very balanced handling, with lots of grip, and very little tendency now for oversteer.
The car is set up to run with R1s at the track, with quite a bit more camber front and rear (I'm not too concerned with tire wear, a lot of canyons out here, so I do a lot of turning ;) with 6mm of toe at the rear. HUGE difference. Plus it looks great.
I had my car corner-balanced and track aligned. Here are the specs (car is without
spare tire and engine cover, with a full tank of gas, and a 150 lb. driver):
The car is adjusted with a set of R1s for the track. I've been told that R1s have built in camber into their construction, so that it does not really require too much negative camber to be set into the suspension. An ideal tire actually for a dual purpose car, so that you don't have to dial in too much negative camber to wear out your street tires (although slightly increased tire wear than normal is to be expected) prematurely. Unlike the new Yokohama A-032R track tire, or even the Hoosiers which you have to dial in LOTS of negative camber to maximize their potential.
At first, I thought the car looked a little funny with the ride height level front to rear, with an increased gap between the front fender and the tire than on the rear. I was so used to the car having a nose down attitude. Overall the car is still lower than stock, though. But my initial impression while driving today through a local canyon is that it definitely handles a lot, lot better with more grip (and speed) into the corners. It is also more neutral, with much less of a tendency for the rear end to come around. I had the TCS off and it is much easier to go into a controlled four wheel drift than before. Almost go-cart like. I'm looking forward to the next track event to verify these impressions with a stopwatch.
One of the reasons the shop dialed in a higher front ride height in relation to the rear was to gain a little bit more suspension travel, as it appears that the front suspension has less travel to begin with than the rears, and is more susceptible to ride height changes than most performance cars (ie. Porshes). They also say high speed stability won't be affected noticably with this change. I have yet to prove this.
[HS] Alex gave a good explaination, but most don't understand the *real* issue: What is the proper starting point front-to-rear (side to side is obvious)? You must start by weighing several completely stock NSXs to get a baseline, otherwise you'd have too much weigh bias either to the front or the rear. I can tell you from experience setting up real race cars, that first day of set-up testing to get basic f/r ride heights is a pain in the ass and extremely time consuming.
All this *must* be done with the proper driver weight in the driver's seat.
[SF] My '96 NSX-T was almost exactly 60/40 rear to front and was about 15 lbs left side heavy with a driver. According to the owners manual, this is because the weight of the driver (me) is above the Nominal. With a Nominal Japanese Driver, I would guess that the car is almost perfectly balanced.
[DNG] I had my 92 NSX weighted by Bernie at Davis Acura today. With all the talk about loosing weight, I wanted to see, with all the stuff I took out/replaced, how much it actually weighs.
92 NSX 5 speed: NO spare tire, NO spare tire carrier, Black Panther 800 battery, RM sway bars (a bit heavier than stock), Headers, NO cats, RS*R exhaust (not the lightest exhaust available), 17/18 cast wheel combo (rear tires are (*heavy*), Air pump + jack, Mesh engine cover (a bit lighter than stock), 'Empty' gas tank (gas light was on so ~3 gal left). Total: 2867 lbs!! I think stock 92 NSX weighs 3010 lbs.
Here are the readings:
[AWN] The weights are different because the car's center-of-gravity is located slightly to the right and rear of the physical center of the car. Specifically, the center of gravity is located 0.3 inchesto the right of the car's front-to-rear centerline, and 59 inches behind the center of the front tires' contact patches.
[DNG] Now, with me weighing ~154 lbs after a full lunch, the car with driver reading is 3021 lbs:
Now, it so happens that with me in the car, the LR and RR are pretty much the same. Can't say much for the fronts.
[AWN] To shift weight to the right-front, you need to LOWER the left-front corner of the car. If you decide to buy adjustable spring perches so you can corner-balance your car, the ideal distribution (with your 154-pound body in the car) would be:
Your car's already balanced to within 1 or 2 percent of this ideal. If I were you, I wouldn't bother spending the money for adjustable perches.
[HS] I'm *very* impressed with these weight measurements (the ones with driver on-board. In my 25 years of racing it usually took weeks of work to get a car so well balanced. Try that with a 911 Turbo or a 355.
[JB] John asked if anyone had weighed their cars on the scale at Roebling Road. I did, and here are the data:
I have a '97 T. It had 2/3 of a tank of fuel when weighed. I had the spare, jack, air pump, and CD changer in the car when weighed (and my helmet in the passenger's seat). I have the Comptech muffler and restraint system (and full belts on both sides) installed. I also had Yoko A032Rs (225/50/16 and 255/40/17) mounted on a set of '95 OEM wheels on the car. I'll let someone else interpolate all this (the restraint system and tires increased factory weight whereas the CTech muffler reduced it, I presume), but these figures look pretty good compared to the curb weight of 3164 shown in my '97 spec sheet for a 6-speed NSX-T.
Any Other Related Information?
[AT} I just ran across a chart from Roger Kraus Racing which was given to customers of their software and suspension handling school. It depicts a scenario of a car's four tires in a right hand turn and the slip angles of all four tires in three handling states. These are neutral, understeer, and oversteer. The fourth example was a car brought back into neutral from an oversteering situation. Basically the slip angles of the tires for a neutral handling car are all the same. During understeer, the slip angle of the front tires is greater than the rear tires. On oversteer the slip angle is greater than the front.
Now in the fourth situation they give one example of how to correct for the oversteer situation by adding a 33% larger rear tires and wheels while leaving the fronts alone. The track width didn't have to be changed nor was anything else done to the suspension to achieve a neutral handling car. Finally at the bottom of the handout they make the following statements.
This seems to bear a lot of correlation to what is done with the NSX and in some respects to my car. With the stock 15"/16" setup on my 91, I've always felt the car had a real easy tendency to go into a snap oversteer situation. When I upgraded to the stock 16"/17" combination, I also increased the size of the rear tires up to 255x40x17 which is one size larger than the stock rear tire. Because of the larger size of the rear tire as compared to the fronts, (205'sx16"), my car tends to be much more neutral than in the past even with the newer Dali sway bars.
Just thought this was some useful information to share with the group. Take care.