"If your car is really tight or really loose during hot laps, you have to take a look at the things that are going to make the biggest difference. section). All of these factors play a huge part in what each corner of the car will weigh. The first spreadsheet below is what I started with. , = change needed to get to target weight, Cross Weight = 35 psi hot tire pressure target . To keep it clear in my head, I think of the car as a four-legged table sitting on a mattress. If you don't want to change your ride height then a more balanced approach would No, not as in the law, but in being legal in tech. It changed the wheel weights by 10 pounds at each wheel: I finally went too far when I took two turns off the Right Front (went This will pitch the vehicle's. To find LR weight: you raise the rear of the car 10 inches or more and re-weigh it. Understanding corner weights. Motor: 550 or 540 motors only. Since each side at each end will usually have different rate springs, the amount we change the spring height adjusters will differ side to side. Then if it's for a particular road course, you will find several seconds optimizing for select turns and throwing any of the above methods out the window A friend's Chump Car found 2 sec at VIR making it turn right better than left. I used a laser level to project a horizontal Raising the rear end will also provide a little more on-power grip by keeping more weight directly above the rear tires during acceleration. the sway bars because they fail so often and the bars only added a couple of Oval shocks set to same length left to right (front to rear will be different). The tiles I Check your tire pressure and bump it up to the hot pressure Shock Position Or maybe I read the post wrong. Struts and trailing arms generally arent great in this case as they have a lot of inherent bind. This is my 2001 S2000 with 1/2 tank gas, 216 For our example we use: LF 200, RF 250 - 250 200 = 1.25 multiplier for the front. I had the same question. If the car feels loose throughout the corner, lower both track bars evenly. Take care that the car does not accidently slide off the scale pads. Ah, OK, thanks for the clarification. Hub stands are a great idea just for ease of access, but removing friction is an added benefit. The advantage to wedge is that the left rear tire carries more load, so the car drives off the turns better. The process is so basic to the setup of the car. Adjusting the corner weights is how we establish the crossweight percent, or what is often referred to as the amount of bite, left rear weight, or wedge. The coiloversare typically mounted parallel to the centerline above the driver footwell. And don't ever believe the track scales. Adjust the cross weight for more extreme conditions or different circumstances. Recheck air pressure often to assure ride heights stay consistent. The total weight will ALWAYS be correct unless you can find some way to suspend gravity, if you can let me know. I just back all of the damping off totally. A jumbo ziploc bag prevents lube from escaping when not in use. So, deviating from those numbers will mean you have a design other than what was intended for the car. 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. I started out with the KW spring perches set exactly the same weights: Corner Weight Calculator if In order for the table to stand steady, all four legs should be of equal length, and as a consequence each will apply equal pressure on the floor. Right Front tires. pounds of preload to the scale weights. Choose your ride heights before you measure and/or redesign your front geometry and then maintain those chosen ride heights. Picture the following: Your car is really fast in right-hand turns, but understeers in left turns. Don't be in a hurry to set ride Now with the steering straight ahead and both hands on the steering have your buddy record the . I've read all the info before, in various places, but it's good to have a refresher. Positive Caster is created when the caster line lands forward of the contact patch. LF and RR (extend coil over), remove preload to RF and LR (shorten the coil If you have uneven mass on your wheels then your tyres will all have different levels of grip which can lead to an unpredictable car on circuit and make it corner faster in one direction than the other. Plan to win in a repeatable fashion. Thinking about this a little, the weight measured by the scales is the sum of the force of gravity acting on the car's mass, and the force of the springs pressing downward. Calculate the rear weight bias by adding the rear weight (LR and RR) of the chassis and dividing it by the total weight of the chassis (LF + RF + LR + RR). The outer rear tire drives "around" the outer front tire, allowing the chassis to efficiently turn into the corner because the rear tire Beyond that, if your bushingsand other parts bind on the scales then they're also going to bind out on the road, so who cares? Also you will obviously want to have some way to ensure all your scale pads are level with each other. I usually mark an even inch and write that inch number on the tape. The car literally registered several hundred pounds less that what the weight finally settled at after I jumped up and down on the door sills for several minutes. intentionally favor a turn direction. Guess I have to try it. The car should be at minimum weight, using ballast as needed to make the proper weight. My starting cross weight was 50.6%, I was off 7lbs surface. Useful fabrication tips for just about any project, A crash course in 3D printing | Making Stuff: Part 2, How to make the move to an aftermarket ECU, 10 Must-Have Tools for a Scratch-Built Car, Fitting tires and wheels when an off-the-shelf option isnt listed. If most of the important turns on your Now that we understand why we need to maintain a set ride height, let's go through an example of how to set ride height. Setting static weight distribution and adjusting cross-weight percentage is one way to assure good handling. However, if you have to apply opposite lock steering (turning the steering wheel to the right) and you drive the car throughout the corner balancing it with the throttle . you run on the track. But this doesn't explain why the Vette's readings came in so well, while I had to jump up and down on my door sills quite a bit before my car's weight stabilized at its expected value. Moving or removing weight is one Replacing a heavy battery with a light weight one allowed me to get close . Using dead struts and lots of bearings will help. retract the right rear tire which puts more weight on the Left Rear and It is important that you complete the corner weighting process before doing an alignment. I use 2x6 wood planks as ramps to drive the car onto Hot Rod. You can 2) Stagger: Stagger is how much bigger the right side tires are compared to the left side tires. These are your target weights which will yield a 50% Cross Weight: Left Front = after this adjustment we still need to add 39lbs to the Left Front and If you align your car prior to doing the corner weights, it will be necessary to verify the alignment again after the corner weighting is completed. This adds pressure to that end of the car just like putting the paper wedge underneath the table leg. decided to try 5 turns total of spring perch movement to balance the car. Caster creates stability as the geometry . If you want to lower the ride height then retract both RF and Funny. This keeps the ride heights as close to ideal as possible. Always try to start with the track bars first. Record each spring rate. I've spent an hour this afternoon trying to do corner weights "on the cheap" using our IKEA kitchen scale (cost - 15.99 a few years ago) and three wooden blocks cut to the same height as the scale (38mm). does not change when a driver is added. You can make this adjustment in several ways: If you don't want to change the ride height of the car then The new existing ride heights are LF 3.6875, RF 4.8125, LR 4.1875, RR 5.3125. (I suppose cooking oil, motor oil, KY, or Astro-Glide would also work). Thanks; what you say makes sense, of course, but repeatability is always going to difficult unless you can get rid of most of the bind, right? Delta which is simply the difference between the two diagonal tire weights. You can also use this online calculator to compute your corner For road racing and autocrossing, the ideal left weight percentage is 50 percent. Left Rear tire is carrying more weight so it will get more traction and With my KWV3 shocks I had to remove the wheel to adjust the scales are connected properly--you can really screw up your suspension settings After these items are completed, it is necessary to corner weight the car. then leave them connected. February 2017 -Suspension design process. need to roll the car back and forth a few inches several times, being careful If you moved only one point, then the problems begin. Corner_Balance.zip Excel spreadsheet. 19. In any case, only make one spring change at a time and re-establish the ride height at that corner, then change the other spring(s). It varies with weight removal, added. Some racers like to take matters into their own hands-and that's OK. To favor right turns, put more weight on the 2 When you make a spring change, bring that corner back to the measured distance from the wheel rim to the fender mark by adjusting the spring height. looking forward to getting it back! used cheap linoleum tiles (49 cents each at Home Depot) to shim two of my scales Improper weight distribution in your race car - strip burner, autocrosser, circle tracker, etc. "Many racers are running stacked springs (pictured), or dual-rate springs, or soft, long-travel . If you think you need to make crossweight changes, remember the amount of change per adjuster number, in our case it was 7/8 turns per percent of crossweight at the right sides (left sides again are times the multiplier), and make even percent changes, such as a half percent or whole percent. Doing the multiplication to square that number, we get 1.1056. Grassroots Motorsports Understanding Corner Weights They are not too suitable for racing and oval dirt cars. The intent of the track scales is to determine a car's total weight to meet minimum weight rules and left side percent (or right side weight) to meet a side weight rule. Since I went to 800 front and 700lb rear springs over the winter I Just to confirm the theory I checked the corner weights with These weights are in ready to race form (including driver on board). You will never find a perfectly level spot at the track, so don't waste time looking, unless you can set up your scale pads and set up ramps level. 1) Tweak: Tweak is the amount of weight on the LR as opposed to the RR. If you go to a tuning shop that provides this service, estimate that it will cost you $90 $150 to have them corner weight the car for you. It was a good car. The only way to change the static weight distribution percentages is to physically move weight around in the car. 3. . racers only turn left we can balance the car for better grip in left There are many ways to corner balance a car. For ovals we want a Toe inn a 1/4 inch. The other two corners will lose weight. You've mentioned "dead struts" a couple of times - what do you mean by that? McMaster-Carr adjustable end links My car has solid/spherical bushings everywhere, so there should be very little bind from them. "Springs and chassis components can be adjusted to push down on one rear wheel," Bickel said. Take the total weight of the car in the configuration you decide on, with driver or without, and to find the corners, do the following: TVW = Total Vehicle Weight = 2,800, LSP = left side weight percent = 0.54, FWP = front weight percent = 0.51, CWP = Crossweight percent = 0.52. close to where I wanted it. the scales and zero them with no weight on them. If a setup sheet read as "30 pounds of bite", there would be 30 pounds more weight on the left-rear than the right-rear. Check your tire pressure and bump it up to the hot pressure The SRM will determine the relative changes to the spring height adjusters for weight changes. Still, it is a worthwhile goal to strive for 50 percent left-side weight. I dropped my integra off at edge to have this done today. from +1 overall to -1): I put + 3/4 of a turn back on the Right Front and ended up Then just leave them attached. I dont get this. I didn't hunt for that missing 1 %. We delve deeper into race suspension tuning basics here. Astrut with its innards removed? In our example, move the LR and RR corners down by 0.4375-inch. Once you get the car up on the scales you'll When that time arrives, you walk across the racing surface, into the dirt oval's imperfectly defined center, and meet your instructor. Lay the bag flat onto the scale pad, partially open to vent, lower the car into the bag. This makes the cornering force balanced from left to right and offers the best performance overall. The CG height Then measure from the lower wheel rim edge up to a spot on the fender on a piece of masking tape. What you're saying makes sense, but I can't explain why it took so long for my car to settle into its final weight reading. Cross-weight percentage compares the diagonal weight totals to the car's total weight. of the scale to take a reading. Corner balancing, sometimes referred to as "corner weighting," All 4 scales must be within 1/8 of an inch. Examine a modern push/pull rod suspension, particularly if it uses a crank link to transformthe started with the Left Front because I wanted to raise the ride height of the car Small angles can throw off your readings significantly. I lowered the right front spring perch 1 full turn (equates to The suspension of the racecar uses the same general theory and needs to be adjusted so that the car is stable. will help with those turns. camber angle of the wheels (-3.5 front, -3 rear). if you have any of the scales connected improperly (i.e. Let's explore some ways to do this in an orderly and sensible way. 9. Here's the car with the same settings but empty: I took the newly corner balanced S2000 to a Summit Point Raceway Friday at 4m.net - The Most Opinionated Racing Message Board In The Universe. In our example, the front average is 4.25 and the rear is 4.75. The weight transfer process occurs regardless of the spring rates at each corner of the car. There is work involved in going fast for the full race and racing other racers clean. I needed 3 linoleum tiles (0.045" thick A 50% Cross Weight will yield a balanced handling car, one The following weights are with the front Comptech adjustable 14. So, ride heights in the front are more critical for maintaining camber angles. calipers. Crossweight is calculated by adding the RF and LR weights and then dividing that sum by the total weight. At the rear, your rear control link angles are critical to maintaining rear alignment and determining rear steer angles and/or reducing rear steer altogether. Similarly, dirt oval cars often represent crossweight as "bite", or weight on the left-rear tire relative to the right-rear tire. Take the total weight of the car in the configuration you decide on, with driver or without, and to find the corners, do the following: TVW = Total Vehicle Weight = 2,800, LSP = left side. Exhaust/Headers, Limited Slip Differentials and Fuel Injectors, Engine Dyno Tuning, Racing Wheels and Air Dam/Splitters, The Costs of Racing Personal Safety Equipment & the Racecar, Brake Pads, Fluid Routine Maintenance Timeline, Dealing with Cosmetic Bodywork: Painting the Racecar Interior. few inches several times on the scales before each reading though just for good Adjustable end links are more Wedge is a term used in the Or use an automotive tuning shop. The vanilla neon setup would be SDK suspension (stock ACR, look at neon.org and figure out what you have) with 3.5 deg front camber, 1 to 1.5 rear, zero to 1/8" in toe front and rear. this excellent article: Right Front = It is best to get 50 percent left-side weight when possible. Example: RF = 643, LR = 751, so, (643 + 751) 2,800 = 0.498, or 49.8 percent. The car is built on a jig for a particular ride height layout. The crossweight percent will have changed to, say 55.4 percent. Rolling the car onto the scales from a small ramp that's the same thickness as the scales seems like a better option, but does it truly remove all the bind? Delta is equal to (Right lot of force to the suspension. One of the problems with cross-weight is that it will change the handling balance from a left to a right turn. You can change ride heights later on, but remember that your front moment center geometry will change and your rear geometry will also change, including link angles and pinion and third link angles, as well as rear alignment in some cases. When you adjust your coil overs suspension). I'm not saying you get what you pay for with race scales but there is a reason I went with longacre. Bite tells us how much we you don't use Microsoft Excel. Disconnect the sway bar. This obviously means that decreasing cross weight or left side weight scales. Leebo's Corner. [ 1] In circle track racing, the use of the term "crossweight" gives us an indication of the weight distribution on the four tires. I used a laser level to project a horizontal be appropriate such as making small adjustments to all 4 wheels--add preload to 1. We run an extremely high banked 1/5 mile clay oval in Alabama that is always wet and low bite. Right Front tires. more traction or bite in left turns. Taking the time and making the effort always pay dividends. To find LF weight: turn to the RF simply to raise the ride height of the front of the car. Classic Truck. So, we are not reinventing the wheel here, just refining the process. Once you get the car up on the scales you'll To find RF weight: which is simply the difference between the two diagonal tire weights. Corner weighting your car is To keep things clear I call this added LR/RF weight Wedge and measured between the outside bottom rim edge is 67.75" front and 69.875" turns. I saved a copy of the spreadsheet for each Conversely, if the car feels tight throughout the corner, raise both track bars. 3) Reverse stagger: The opposite of stagger when your left side tires are . You need a nice, flat and level surface for the scales. Adjust the front up by 0.0625-inch and the rear down by 0.4375-inch. springs to put more weight on the left rear (and right front) tires and - can make your car dive like a dump truck or a block of wood on ice. car for a week to let the suspension settle: I decided to disconnect the front and rear sway bars to see what It seems to me that if there's bind in the suspension that's preventing all the force of the springs to come into play, the weight read by the scales will be less than the correct value. I lowered the left rear spring perch 1 1/4 turn and put it on The left weight percentage is found by adding the LF weight to the LR weight and dividing the sum by the total weight. Wheel offsets can make a huge difference in fine tuning the chassis which will allow the driver to find a good racing line on the track. much Wedge Delta and make the handling worse. Even if you pay someone a small amount of money for their help, it will be far better than buying the scales yourself. cars through the corners and thats where there eating me up. One of the keys to obtaining a good setup is using the correct procedure to weigh your race car.
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