Welcome Guest!!!

Thank you for visiting the GM Kappa Performance Forum. This forum is the only performance oriented forum for all GM Kappa Platform Enthusiasts.  We hope you will join and share your experiences.  Becoming a member is FREE! If you want to advertise on this forum, email KappaPerformance at yahoo.com.


Registration required to view the forum attachments. Below is a sample of the current top 25 topics.
Supporting Membership has many advantages.


More information on becoming a supporting member or vendor can be found on the sub forum; Site Help and Suggestions; thread - Supporting Members and Vendors.

Author Topic: Corner weighting  (Read 3637 times)

0 Members and 1 Guest are viewing this topic.

lil goat

  • Guest
Corner weighting
« on: May 06, 2009, 09:06:43 AM »
I put this in the DDM supporting vendor section because it is Dave that has started my education on this topic, they will be installing my HKS coilovers at the MD. Mod meet and will be doing corner weighting as part of my install, they can do this on any car, but it is easier to setup with adjustable coilovers. They will actually weigh the car at the 4 corners with me in it and half a tank of gas and then make adjustments. I am very interested to see how our cars weigh in from the factory. This is not an easy procedure and it would seem it is a commonly overlooked issue to improve a cars handling. DDM has the equipment to do this at there shop, and will be bringing it to the Mod meet. There is a charge for this but if anyone wants it done they can schedule it with Dave at the meet or in the shop.

Here is a link to an article from Grassroots Magazine that explains what corner weighting is all about.
http://grassrootsmotorsports.com/articles/understanding-corner-weights/


(by the way I did cross post this on the "other" forum for those less informed that are not members here)
Understanding Corner Weights

    Cross-weight percentage compares the diagonal weight totals to the car’s total weight. To calculate cross-weight percentage, add the RF weight to the LR weight and divide the sum by the total weight of the car.

One of the most important aspects of car setup is the static weight distribution and the cross-weight percentage. Why? Picture the following:

Your car is really fast in right-hand turns, but understeers in left turns. If you get the car neutral in left turns, it oversteers in right turns. The situation is frustrating. You’ve tried springs, shocks, different bars, neutralizing the anti-roll bar, and nothing seems to work. Even on a track with mostly right-hand turns, the problem in the left-hand turns cost a lot of time.

While several different setup parameters could have caused this situation, a likely cause is excessive cross-weight.
Static Weight Distribution

Static weight distribution is the weight resting on each tire contact patch with the car at rest, exactly the way it will be raced. This means the driver should be in the car, all fluids topped up, and the fuel load should be such that the car makes your minimum weight rule at the designated time-usually after a race. The car should be at minimum weight, using ballast as needed to make the proper weight.

When working with static weight distribution, we use two percentages to analyze the car’s corner weights: Left weight percentage and rear weight percentage. These tell us all we need to know about the setup relative to the weight distribution. The left weight percentage is found by adding the LF weight to the LR weight and dividing the sum by the total weight.

The rear weight percentage is found in a similar manner: Add the LR and the RR weight together and divide the sum by the total weight. Many electronic scales will perform the calculations for you.

For road racing and autocrossing, the ideal left weight percentage is 50 percent. This makes the cornering force balanced from left to right and offers the best performance overall. However, many cars cannot make the 50 percent left-side weight percentage due to driver offset. Still, it is a worthwhile goal to strive for 50 percent left-side weight.

Rear weight percentage for road racing and autocrossing is less definite. The more power a car has, the more that static weight over the drive wheels helps acceleration off the corners. Additionally, it is much more difficult to change rear percentage much, since rear weight is mostly a design function. It still pays to be thoughtful about weight placement fore and aft in your car.

The only way to change the static weight distribution percentages is to physically move weight around in the car. Jacking weight will not alter the left side or the rear percentages.
Cross-weight Percentage

Cross-weight percentage compares the diagonal weight totals to the car’s total weight. To calculate cross-weight percentage, add the RF weight to the LR weight and divide the sum by the total weight of the car. Cross-weight is also called wedge: If the percentage is over 50 percent, the car has wedge; if below 50 percent, the car has reverse wedge.

More wedge means that the car will likely understeer more in a left turn. The advantage to wedge is that the left rear tire carries more load, so the car drives off the turns better. But in a right turn, the opposite occurs and the handling is worse. In almost all cases, the loss of cornering performance in one direction is greater than the gain in the other direction.

On oval track cars, cross-weight is usually used in conjunction with stagger (where the right rear tire is larger in circumference than the left rear tire) to balance handling. More stagger usually loosens the handling in left turns, so more cross-weight is used to tighten it up. But stagger is not a good idea on a road course or autocross either, where the ideal is 50-percent cross-weight and no stagger.

One of the problems with cross-weight is that it will change the handling balance from a left to a right turn. This can make maneuvering in traffic difficult, even dangerous. On a road course, the cross-weight percentage should be very close to 50 percent, within a half-degree either way, to keep the handling balance similar in a right-hand turn compared to a left-hand turn. In the example at the beginning of the article, this was the problem: a cross-weight percentage that was less than 50 percent, and probably off by at least two percent.

One of the keys to obtaining a good setup is using the correct procedure to weigh your race car.
How to Weigh Your Race Car

Here are some points to remember when weighing your race car:

    * Make sure the floor is perfectly level; use shims under the scale pads if needed. Small angles can throw off your readings significantly.
    * Set tire pressures first.
    * Check stagger at each tire, even if using radials.
    * Put the driver weight in the car, preferably the driver.
    * Use a load of fuel for where you you want the car balanced, either at the start of the race, the end of the race or an average between the two.
    * Disconnect the shocks, when possible, and the anti-roll bars.
    * Use blocks the same height as your scale pads to move the car off the scales to make adjustments.
    * Bounce the car at each corner to free the suspension from any bind, then roll the car onto the scales.
    * Make sure the tires are centered on the scales.
    * Recheck air pressure often to assure ride heights stay consistent.

Setting Static Weight Distribution:

    * Check static weight before working on cross-weight.
    * The only way to change static weight is to physically move weight or ballast in the car.
    * To increase left-side weight, move weight as far to the left as possible.
    * To increase rear weight, move weight as far back as possible.
    * Move ballast first, since it’s easier. Then move components like the battery or fuel cell.
    * It is best to get 50 percent left-side weight when possible.
    * Get the rear percentage as close to the manufacturer’s specs as possible.

Setting Cross-weight:

    * Once static weight percentages are set, work on cross-weight percentages.
    * You cannot change the left or rear percentages by jacking weight around in the car, although this will change cross-weight.
    * Changing the ride height at any corner will change the cross-weight percentage.
    * If you raise the ride height at a given corner (put a turn in or add a round of wedge), the weight on that corner will increase, as will the weight on the diagonally opposite corner. The other two corners will lose weight.
    * If you lower the ride height at a given corner, that corner will lose weight as will the diagonally opposite corner. The other two corners will gain weight. This will not change the left-side or rear weight percentages.
    * To add weight to a given corner, raise the ride height at that corner or lower the ride height at an adjacent corner. For example, if your initial setup is 52 percent cross-weight, and you want 50 percent cross-weight, lowering the right front or left rear corner will decrease cross-weight percentage. You could also raise the left front or right rear ride heights to do the same thing.
    * It is best to make small changes at each corner, instead of a big change at one corner. This keeps the ride heights as close to ideal as possible. In the above example, to go from 52 percent to 50 percent cross-weight, try lowering the right front and the left rear one-half turn on the weight jack bolt or spring perch while raising the left front and right rear the same amount.
    * Always record the cross-weights and ride heights for reference at the race track in case changes are needed.
    * Measure control arm angles after each change. The angles are another way to set the suspension for the desired ride height and cross-weight percentage.
    * The distance from the ground to an inner suspension arm pivot point will also accomplish the above goal.
    * Remember that changes in stagger, tire pressures and springs will change the ride height and alter the cross-weight percentage.

Change at the Track:

    * Make small changes at the track, and make only one change at a time.
    * If the car understeers or oversteers in only one direction, check the cross-weight percentage.

One of the most important aspects of racing is having a good handling balance. Setting static weight distribution and adjusting cross-weight percentage is one way to assure good handling. Taking the time and making the effort always pay dividends.
« Last Edit: May 06, 2009, 12:25:26 PM by lil goat »

Offline Critterman

  • Retired, thank you very much
  • Premium Member
  • General Manager
  • *
  • Posts: 13571
  • Karma: +17/-58
  • Baltimore/Washington Corridor
Re: Corner weighting
« Reply #1 on: May 06, 2009, 01:10:27 PM »
And to think he is going to do all of that for 100 bucks.  A good buy
GONE: (but not forgotten) 2006 Cool named BIXABEL (BISH-AH-BEL) Mayan for "Good Roads"

DDM
StageIII intercooled Supercharger, Wisco ceramic coated pistons, Carrillo rods, superTech valves and Springs
Ported and polished head
Exedy Stage II Clutch
big brake kit, slotted/drilled Rotors w/Porterfield pads & blue juice
Backbone, Probeam, Cross Strut Brace
Underhood, trunk, & door Lights
ZOK suspension

JPM
Center console, door inserts, & dash
Seat bolster & lumbar support

Focuztech Tri-Y Header & hi-flow cat
Solo Performance SQR-2
Norm's Rear facia
Heated Seats
Black Cat inserts

Offline 2kwk4u

  • not really THAT quick
  • Premium Member
  • Gearhead
  • *
  • Posts: 1466
  • Karma: +8/-4
  • Location: Frederick, Maryland
    • '06 Solstice bits and pieces photo gallery
Re: Corner weighting
« Reply #2 on: May 06, 2009, 01:31:29 PM »
Great article!  Thanks for posting it, LG.

lil goat

  • Guest
Re: Corner weighting
« Reply #3 on: May 06, 2009, 01:36:08 PM »
And to think he is going to do all of that for 100 bucks.  A good buy
You are getting a better deal than I am if that's what they told you, I was told $150 and I had to make them breakfast AND lunch!

I guess I sort of knew what corner weighting was, as you have to do shock weighting when you set up a bike, but I had never really thought about it in that much depth. I REALLY wonder how are cars are stock, not sure how Dave and the boys will adjust the weighting this should be very cool to watch.

Offline 2kwk4u

  • not really THAT quick
  • Premium Member
  • Gearhead
  • *
  • Posts: 1466
  • Karma: +8/-4
  • Location: Frederick, Maryland
    • '06 Solstice bits and pieces photo gallery
Re: Corner weighting
« Reply #4 on: May 06, 2009, 01:57:56 PM »
With coilovers, from the way the article is written, the corner weighting sounds relatively easy.  Think of it like stuffing a coaster under the short leg of a table to keep the table from rocking.  The weight distribution (f/r and l/r) seems like the trickier part.  For a street car (without having to worry about ballast and so forth) we're talking about moving the battery to the trunk (as far to the rear and right as possible) and things like that.  Probably wouldn't hurt to have a 100 lb driver, either :lol:

Offline Critterman

  • Retired, thank you very much
  • Premium Member
  • General Manager
  • *
  • Posts: 13571
  • Karma: +17/-58
  • Baltimore/Washington Corridor
Re: Corner weighting
« Reply #5 on: May 06, 2009, 03:28:43 PM »
  Probably wouldn't hurt to have a 100 lb driver, either :lol:

That leaves goat and I out :(
GONE: (but not forgotten) 2006 Cool named BIXABEL (BISH-AH-BEL) Mayan for "Good Roads"

DDM
StageIII intercooled Supercharger, Wisco ceramic coated pistons, Carrillo rods, superTech valves and Springs
Ported and polished head
Exedy Stage II Clutch
big brake kit, slotted/drilled Rotors w/Porterfield pads & blue juice
Backbone, Probeam, Cross Strut Brace
Underhood, trunk, & door Lights
ZOK suspension

JPM
Center console, door inserts, & dash
Seat bolster & lumbar support

Focuztech Tri-Y Header & hi-flow cat
Solo Performance SQR-2
Norm's Rear facia
Heated Seats
Black Cat inserts

Offline 2kwk4u

  • not really THAT quick
  • Premium Member
  • Gearhead
  • *
  • Posts: 1466
  • Karma: +8/-4
  • Location: Frederick, Maryland
    • '06 Solstice bits and pieces photo gallery
Re: Corner weighting
« Reply #6 on: May 06, 2009, 03:38:36 PM »
That leaves goat and I out :(

as it does most of the rest of us.  Maybe a 200+ pound passenger then :)

Offline shabby

  • Master Tech
  • ***
  • Posts: 483
  • Karma: +0/-0
Re: Corner weighting
« Reply #7 on: May 06, 2009, 05:03:15 PM »
Corner weighing is nice but only if your competing in autocross/road racing since that's the only place where you're going to notice a difference. I was thinking of getting this done but i doubt i'm going to notice the difference let alone take full advantage of it, this is basically the last thing you do on a well prepped car. I would rather opt for a more aggressive alignment, you'll notice that instantly.

Ben L

  • Guest
Re: Corner weighting
« Reply #8 on: May 06, 2009, 06:24:45 PM »
IMHO, $150 is a good deal for precise digital corner weighting with the driver there in the seat, which is how it should be done.   

I can tell you from experience, its not so easy.  A friend and I did it on my Factory Five roadster with a set of borrowed digital scales, and it took the best part of half a day.  You have to split the differences front to back and side to side, and watch/adjust the alignment before everything is set, which takes several cycles.

We did have some beers, though. 

Dialing in the left/right cross weight showed me just how fat I am, too.  So its kind of enlightening in not a good way.

Goat, you won't regret either going to coilovers or corner weighting.  I thought having the car weighted and balanced improved handling and neutrality noticeably.

If you've sprung for coilovers, why not use all the adjustability you have and get it set up right, to fit your personal body mass like a glove? 

If I wasn't autoxing on Mod Meet day, and I wasn't too embarrassed to ask DDM to install the BC coilovers I got from someone else, I'd jump on this opportunity in a minute. 

Its definitely a must-do step for the Daytona Coupe . . .

lil goat

  • Guest
Re: Corner weighting
« Reply #9 on: May 06, 2009, 09:19:10 PM »
I think only the weighing will tell the story, if the factory set up is way off as I expect it may prove to be very noticeable, it sure won't hurt. I don't autoX yet but hopefully will be doing road courses at Summit Point soon, I have an instructor friend just have to add a petty bar to make sure I can get on the track, got that lined up too just time and money. I already have the Z0K alignment and this seems to be the logical thing to do while I can so easily, and having it done by someone I trust doesn't hurt at all. I expect to be a doing autoX next summer been doing some weight adjustments on the driver, down almost 70 lbs only 50 to go, I look forward to having to do the corner weighting again due to driver weight adjustment.

Offline Bigblau

  • Tech
  • **
  • Posts: 31
  • Karma: +0/-0
Re: Corner weighting
« Reply #10 on: May 19, 2009, 05:20:08 AM »
Actually the factory isn't too far off.  But adjustable coilovers are the way to go if you know what your doing and have the time to do it.  Just don't forget, you'll have to readjust your alignment after your done jacking everything.  You'll probably also need to makeup some adjustable roll-bar links ...otherwise the preload from the roll bar will mess it all up when you hook it up.
« Last Edit: May 19, 2009, 07:33:29 PM by Bigblau »

Offline snaponbob

  • Gearhead
  • ****
  • Posts: 3655
  • Karma: +0/-0
  • Location: Lee's Summit, Mo.
Re: Corner weighting
« Reply #11 on: May 19, 2009, 08:39:32 AM »
After I installed my spring adjusters and heavy springs I made some adjustments at home just to have the car sitting as "square" as possible. Mainly I made sure that dimensionally the measurements of where the spring bases were was first followed by making sure the ride heights were equal side to side. Then I threw my spare set of wheels and tires in the drivers seat to equal my weight. Doing a bit of very sophisticated computer modeling (fresh cup of coffee, $12 calculator, note pad, and head scratching) using spring rates and spring compression with the car on the ground I estimated that I needed to raise the left side about 3 turns on the left side adjusters. That DID work for the static ride height with 200# in the driver's seat. From there I went to the shop that had the KC regions scales. I would like to brag about how WELL this was all done, but frankly I think I was just damn lucky. Naturally, the left side is a bit heavier than the right, but the weights were dead on balanced to the point where the shop owner said HE would not touch the car and walked off. I didn't write down anything, but deviations were under 2 pounds from where they should have been. One could only hope that they drove so well that this little bit of "error" could be felt!!! The numbers that REALLY blew me away was the f/r balance @ 51.8F/48.2R.

The one part of the explanation that Goat provided is understanding the L/R balance. Without actually moving weight in the car the static L/R is whatever it is before one starts adjusting the corners, but after the corners are adjusted the L/R totals will still be the same as before corner weight jacking was done. 
Bob Buxbaum
snaponbob AT comcast DOT net
2007 Redline, Revalved Konis, Crazy alignment
FE3 front and Z0K rear bars, owner installed pwr lock buttons
catless downpipe, SP custom exhaustWester's tune
racing springs and adjustable perches
DDM ProBeam & Tower brace, CCW 18x11 wheels for racing

 

Powered by EzPortal