1 of 11 4/27/2005 10:06 AM The Pits racing realism for the PC! FAQ Search Memberlist Usergroups Profile You have no new messages Logout [ Jan Kohl ] Setup Development The Pits Forum Index -> Tutorials View previous topic :: View next topic Author Message Posted: Thu Mar 04, 2004 6:38 am Post subject: Setup Development I have done extensive reading and researching to better my setup development over the past few years, and my hopes are that some of the knowledge I have gained will help others as well. By no means am I perfect or do I have all the knowledge there is on any subject. In fact, I can only offer my translation of what knowledge was given to me. Please, if anyone reads something that they feel is completely wrong or backwards, please contact me (tmcarthur@email.com), not only so I can learn from it, but also that I can correct any mis-information I may have printed here. For best understanding, 99% of this information will be discussing the N2k3 "TA" physics specifically (using the most recent TPTCC mod). I am not a "hot-lapper". I can hot-lap, but my setup is not geared for that. I chose stability and control to get me through a race. A small piece of information that is not a common thing found in Simulated racing; The setup that I discuss in the following articles, is the setup I use for all road courses I race on. I literally copy-n-paste my setup from one track to another (with minor changes of course). This really helps me as I no longer have to learn, or re-learn, a track and a car. I know the car, I have raced it literally hundreds of times. I know how it feels, what it will do in nearly every situation, etc. Sometimes it may not be the "best" setup for a particular track, but it is stable to me and that is what matters more in a race that lasts longer then 1 single lap. Last edited by on Wed Sep 29, 2004 3:59 am, edited 3 times in total Posted: Thu Mar 04, 2004 7:01 am Post subject: Springs Springs: With the TA Physics, I have settled upon a set spring setup for all tracks. This is my chassis baseline, that I rarely change. Why not change it for each track? For the most part the springs are used for the main purpose to dictating ride height and body roll. In this artcile I will be discussing the 4 suspension springs. There are 2 additional springs mounted uner our sim-car, the anti-roll bars, but I will save that for another time. Lowering the chassis of a car and you need to run a higher rated spring to prevent it from bottoming out at high speeds due to aero down force or on bumpy surfaces. With N2k3 we do not get much freedom with ride height. The rear of our car is basically set in stone, unless we want to have one corner lower then the other, which for road racing, it is not advisable though there would be exceptions. Since we are unable to adjust the ride height of our car, we simply do not have to run extremely high spring rates. Lowering the spring rate will allow the chassis to compress at higher speeds when the aero forces are pushing down upon it. This gives us greater aero downforces as well as a lower center of gravity. Lower center of gravity equal less body roll, and since body roll is widely considered a bad thing in all forms of motor sport, we try to manage it as much as possible. Body roll can be helpful, if managed properly, but that is another
2 of 11 4/27/2005 10:06 AM article all together. Lateral body roll is what we try to prevent, Longitudal (front/rear) body roll is welcome in braking and acceleration. Opinions may differ of course. Stiffer springs do give a more responsive chassis. Don't mistake this as more grip though. Basically, the car reacts to our input quicker due to the springs hitting the weight threshold faster then a softer spring. This is great for very tight, twisty courses while in a very nimble car (ala Formula 1). Due to the heavy buckets we drive, nimble is not a reality, so even the tightest of turn sequences requires more grip then responsiveness as we cant get the car through the sequence fast enough to require responsivness. Make sense? Springs do also dictate the amount of grip allocated to each corner of the car. How? A stiffer spring is preloading that particular corner of the car greater then softer springs, effectively pushing the tire down into asphalt harder. The harder the tire is pushed into the ground, the more grip it has. I know what you are thinking, run as stiff as possible on all four corners, giving the most available grip all around. Yes, you could do that, but you will not have the highest available grip to the entire chassis, and would most likely have a very unbalanced and upredictable car. The springs need to compress and rebound or you may as well not have them at all. The tires need to follow the up's and down's of the track surface (and curbing). Bumpier surfaces require softer springs to allow teh suspension to more easily move up and down it's range to follow the roadway. Additionally, without suspension travel shocks cannot due their job of managing weight being shifted back and forth (again, another article all together). So, for this article I will use an example of a generic spring setup. In this example, we will work out a solution to adding more grip to the RF tire, in hopes to better a left-hand turn (be it an oval, or a road course). LF 700 RF 700 LF 300 RR 300 I am showing the car weight as 50/50 front/rear and 50/50 left/right. A 3000 lb. car with 750 lb on each corner is now our example. Each of the front tires carry 7/14th (or ½) of the weight spread between them. With what I stated above, about more preload euqaling more grip, the obvious conclusion is to add more spring rate to the right-front corner... to add more grip, right? If we were to add spring rate to the RF spring LF 700 RF 800 we would be adding preload to the right front tire, which will make it produce more cornering force in a left-hand turn. However, since changing spring rate doesn t change actual weight, adding to the right-front will take away preload from the left-front, (it has to come from some where) reducing the cornering force of the left-front tire. The spring change does not effect how much the front of the car weighs, it is still 1500 pounds, but it has altered how the weight is distributed. Now the left-front has 7/15th (slightly less then 1/2) of the weight distribution and the right-front has 8/15th (slightly more then 1/2). I am going to quote Mark Ortiz, a well known chassis consultant who has written many articles in print and on the Internet; When you concentrate the load on the outside tire, you lose more cornering power on the inside tire than you gain on the outside one. This is because grip from a tire increases with load, but at a DECREASING RATE. So what does that mean? Stiffer spring equals more grip, but not at a steady rate. So, at some point of adding additional spring rate you may only gain 1% grip to the RF while losing 10% to the LF, losing 9% of overall front grip. To complicate things further, the same effects happen to the rear of the car, but in reverse yes I m still talking about the fact that we only changed the RF spring: LF 700 RF 800 LF 300 RR 300 The spring rate has not been changed in the rear, but we have altered the percentage of weight of the right side of the chassis. In the original example, we had 7/10th (70%) on the right-front and 3/10th (30%) on the right-rear, it has been changed to 8/11th and 3/11th. While the left-rear still has 30% of the left-side weight, the right-rear now has less 30%, making for a complete reverse of what happened up front. I m not talking about weight, I m talking about preload of that weight. The right side has a wider gap of preload between the RF and the RR then the left side does, taking grip away from the RR.
3 of 11 4/27/2005 10:06 AM The net result of our example: RF +grip, LF grip, RR grip, LR +grip. We didn t add as much grip to the RF as we added grip to the LR huh? Remembering the quote from Mark Ortiz? We have lost overall front grip because of the outside tire not gaining as much grip as we lost from the inside tire. The reverse applies for the rear, with more preload going to the inside tire as opposed to the outside tire on the front so we added more rear grip then we lost. If we were racing on an oval, what did this spring change just do to our setup? In an attempt to give more grip, by adding spring preload, to the RF, we actually added more grip to the LR which would make the car understeer or push. What could we do to actually add some RF grip? Add some LF spring rate or even some RR. When I spent more time racing ovals then road courses, I would have my setup well before race day (of course). But, through the running of a race I would sometimes want to change how the car handles, maybe due to running up front, or behind another car. I am not able to change the actual spring during a pit stop, but I am still able o change the spring rate of any corner of the car. Do not forget, the tires are not just the utensil of adhesion, the sidewall is also a spring. Adding tire pressure to the LF in our example would be adding spring rate to that corner. Add 1 pound of tire pressure is like adding 25 lbs. of spring rate (estimated of course) and is easily felt on an oval. Hopefully I didn t confuse anyone. I try to stay out of exact figures and explaining all the math. I have let you in on the base line of my road course setups; Soft as possible without the car bottoming out or allowing too much lateral (side to side) body roll to maintain the camber angles I want in a turn. LF 650 RF 650 LF 250 RR 250 50% front/rear weight 50% left/right weight The above is my baseline for any road course I visit. Surely changes are made to suit each track and sometimes to suit one corner in particular, but rarely do I deviate from this stable platform. I am a firm believer of stability over all out speed. The above platform starts us out on the right foot with even weight to all four corners, easily manageable though the turns, and fantastic braking stability. (Added 3/11/04) I was testing last night for my Silverstone race in a few days. Trying to find an edge I started tinkering with my spring package that I hadn't altered in some time, (I do this some times and find some great information)... Through Replay Analyzer I was finding that in the hard braking zones, my front end would compress to the extent that my front camber would fall into the -4 degree range. This makes it very difficult to maximize front tire grip under braking. I wanted to stiffen up my chassis to limit the amount of camber change I was getting in these high speed corners and braking zones. I decided to simply double my springs on all 4 corners... LF 1300 RF 1300 LF 500 RR 500...with the assumtion that as long as I changed all 4 springs by the same multiplier (X2) then the handeling characteristics of the car will/should not change. I was pleased with the results, as I continued to turn the same general lap times. This change did get rid of *some* of the excessive camber change in braking, but not as much as I thought it should. It also increased my tire temps to an alarming 240+! Afterwards, I did decide to stick with my soft chassis as it is too late to "get to know a new car" with only 2 days before the race. Still, a nice piece of information that I thought I would share. Last edited by on Thu Mar 11, 2004 4:48 pm, edited 1 time in total Posted: Thu Mar 11, 2004 4:37 pm Post subject: Gearing & Horsepower Gearing & Horsepower At 70-clear weather, our TA type cars produce peak horsepower of 625 (Actually I don t much agree with the whole concept of horsepower, but for simplicity I will use this term), at 7500 rpm. Cloudy weather conditions increases out produced power by roughly 15%, a lot of additional power for your setup to handle. Still, let us
4 of 11 4/27/2005 10:06 AM just discuss the standard 70-clear power and how to best utilize that power to your advantage. Figures to show the power band of our motor: RPM...HP...+/- 6200...563...-62 6500...587...-38 6800...605...-20 7000...614...-9 7100...619...-6 7200...621...-4 7500...625...0 7700...623...-2 7800...619...-6 What we want for maximum power to the ground at all times is keep the engine running in its optimal power range... the range of RPMs we will run our motor. Of course this is going to be centered on our peak power RPM of 7500. Reviewing the numbers above, we can keep our engine output by keeping the engine in the 7200 to 7700 RPM range. Not an easy task considering we have to slow for corners and that we begin over revving the motor above 7500 RPM. It is up to the driver, that is you, to know when to over rev and when not to. Eventually we will have to shift gears and this is where most run into problems as the gear change drops the RPM too far below the power band. This was a very large problem in the 4-speed gearbox which we had in our stock-cars, but with our cool 6-speeds we can keep it in the power band with appropriate gearing. Setting up the gearbox so an up-shift will drop the RPM to 7000 will drop 9 more horsepower then if we kept the engine at 7200, which is only 4 horsepower below our peak. Allowing the motor to drop below 7000 becomes a greater drop in power, losing 10% of power at 6200 RPM. There are times where allowing the RPM to drop into the 6000 range is helpful. When in a corner that requires very low speeds, the rpm would likely drop well below the 6000 range. Exiting that corner you have a choice of 1st gear in the power range, or 2nd gear well below the power range. An up-shift takes nearly 2-tenths of a second, and you will most likely rev through the power range very quickly in 1st gear requiring a gear change, and likely at a very bad time (car has not stabilized weight). Additional acceleration can be found in using less overall horsepower (less revs in 2nd gear) for a small amount of time and not have to spend the 2-tenths off the throttle for a gear change. On the opposite side of the spectrum is the long straights where you want to keep maximum power every millisecond. Horsepower is a simple calculation of torque multiplied by RPM. What really pushes the car down the road is this torque, actually it is the torque of the rear tires pushing against the asphalt which in turn pushes back launching the car forward (since the car can t launch the asphalt backwards Newton s Law). The engine torque will always remain the same between all gears. Yet, the rear-wheel torque will change with gearing. Remember your old 10-speed bicycle in the garage yea the one covered in dust? Go dust it off and do this; Put it in first gear and pedal away as fast as you can Bam! You shoot off right? Now place it in the 10th gear and try again ugh! Much slower right? The engine (your legs) are producing the same amount of torque no matter what gear you are in, but the gearing has changed the amount of torque being delivered to the rear tire. Moving along With that said, some more numbers. (Basically it is peak power times the gear ratio = the wheel output against the asphalt = the asphalt forces against the wheel), but for this I will stay with horsepower, though it is over-simplifying it gets the point across: Gr...HP...Ratio...@Wheel 1...625...7.467...4667 2...625...5.639...3524 3...625...4.813...3008 4...625...4.148...2592 5...625...3.652...2282 6...625...3.360...2100 We are nearing the end of our long straight at 7700 rpm in 5th gear producing 623 engine-power, 2275 @wheel (623*3.652) and shift to 6th gear. This in turn drops the engine RPM to 7200 rpm, producing 621 engine-power ah, but only 2086 @wheel (621*3.360).
5 of 11 4/27/2005 10:06 AM This is not to discourage the use of 6th gear by any means. You will be in need of all gears to keep your engine RPM in the highest power range through all the gears. You will need to shift to 6th gear, it again comes down to you, the driver to find that sweet spot over revving for maximum power before making the up shift to a less powerful gear. And of course, there has to be exceptions to what I just said above: I have found there to be occasions where *not* using all 6 gears and falling out of the power range, is less time per lap then staying in the power range (cough, cough Longbeach). Reducing the number of up shifts by 5 per lap and you just gained 1 second of off throttle time. You may give some of the time back as you will not be delivering maximum power, but again, that is up to the driver to decide. Lastly, I would like to make one last comment in regards to gearing. Try to set your gearing up so that you are in that maximum power range at track out, not when you are still tracking out. Posted: Sun Mar 14, 2004 8:41 pm Post subject: Camber and Anti-roll bars Camber and the Anti-Roll bar For the most part I feel that just about anyone realizes that what camber does with our suspension, but I will give a quick explanation as best I can; Negative camber leans the top of the wheel in further then the bottom putting them at an angle when the car is static. Something like this (if you were looking at the car from the nose at ground level).. /----------\. Positive camber leans the top of the wheel out. \----------/. When under heavy cornering forces, the weight of the car will shift heavily to the outside tire, compressing that spring and leaning the entire chassis of the car to non-parallel in comparison to the track surface. The outside wheel begins to lose (adding positive camber) its static camber due to the chassis rolling and the wheel tucking up into the wheel-well as the spring compresses. When our wheels are cambered, negative or positive, we are reducing the contact patch of the tire to the track surface. If we can set up the static camber so that the contact patch is at it s largest during the corner, then we are maximizing the grip of that tire when it is needed to most. The largest contact patch can be found when the tire is exactly perpendicular to the track surface. If you do not use the Replay Analyzer it is near impossible to determine if your camber is a 0 degrees during the corner. If you are serious about setting up your sim-car, then I would recommend purchasing the Replay Analyzer. The idea is to have as much static negative camber built into the setup so that when you are in mid corner that the camber is near 0 degrees, (if you take out the whole equation of camber thrust, which it seems Papyrus has). Too little static camber and the outside wheel will go into positive camber, producing under steer at a point that is less then desirable. Too much static camber and the tire will not have the maximum contact patch and again bring upon under steer. What about the inside tire? Ah, something I wish N2k3 handled better is the camber change of the inside tire. Ideally, this wheel would go into slight positive camber in the turn, while the outside tire is at slight negative or 0 degrees. I have not found this to be the case so I end up focusing on the outside tire. NOTE: Under braking, both front wheels will go into massive negative camber, reducing braking efficiency of both front tires. Rear camber is not very adjustable, either -1.8, 0, or +1.8. Either of the 1.8 settings it too much camber as you will never get the tires at or even near 0 degrees with that much camber. Some argue that they get more grip by going to a 0 degree setting to the rear camber. I have used both, and have settled upon 0 degrees myself with a few exceptions on tracks that have highly banked turns (Riverside, Bullrun) where I will give the outside rear tire negative camber and/or the inside rear positive camber. In either case, the rear camber will fluctuate only +/-.5 degrees of camber no matter what setting you start with. Springs and Anti-roll bars (aka, sway-bar) both work to prevent or manage camber change under load. Springs are the simplest form. Increase the spring resistance and the weight of the car under load will not
6 of 11 4/27/2005 10:06 AM compress the spring as much, lessening the camber change under load. Still, I would not recommend changing spring settings without changing all 4 by the same multiple. The other set of springs that are there solely for the purpose of preventing chassis roll which in turn prevents unwanted camber changes, are the anti-roll bars. In reality, when the outside wheel is pushed up into the wheel well, the Anti-roll bar will try to lift the inside wheel into the wheel well as well, in effect trying to lift the inside wheel off the ground. (Credit to Goy Larsen for the correct wording of the previous sentence) The larger diameter bar, the less overall grip those two tires are getting. With that said, in N2k3, anti-roll bars are used more to balance the front and rear grip levels of the car. Smaller diameter anti-roll bar will give more grip then a larger diameter, but it will still allow a larger camber change when the weight is on the outside tire. It is not uncommon for me to completely remove the anti-roll bar from the rear, especially under cloudy conditions where rear grip is in such need. Your spring package will be a big player in this as well. Stiffer springs will not require as much static camber or as stiff anti-roll bars. Still, even with that knowledge I have still preferred my soft spring package, along with a soft anti-roll bar package with my standard -1.2 to -1.8 camber settings. These settings, Camber and Anti-roll, are something that we have to just practice with to find the best combination. It all comes down to practicing and testing numerous settings until you find what you are comfortable with, but if you are looking for a starting point, try -1.5 degrees on both front wheels and 0 degrees on both rear. Make small adjustments back and forth with the knowledge that the outside tire will most likely need more negative camber then the inside wheel. If increasing the outside tire s negative camber is not helping, try reducing the inside tire s negative camber. If you would like a great read regarding anti-roll bars, check out http://www.grmotorsports.com/swaybars.html Posted: Fri Apr 02, 2004 5:09 pm Post subject: Aerodynamics, Wheel Force, & Springs (revisited) Aerodynamics, Wheel Force, & Springs (revisited) First I wanted to revisit springs as I didn t feel comfortable with my previous article. I will make it quick (I hope). Springs will not alter the weight that is being shifted back and forth or side to side in a corner. They will however add or reduce preload (there is that word again) of that weight on the tire. The greater the preload, the greater the grip that tire, but also the faster that tire will exceed it s available grip and begin to slip. Hence the reasons why we hear that a softer spring package is more grip then a firm spring package. More on this as we discuss Wheel Force. Before I get into wheel forces, I wanted to bring up aerodynamics. Though our stock cars and TA-type cars are not known for their ungodly amounts of aero forces, they do have some. While testing for a league race recently I began looking at the differences of a 70 degree rear wing compared to a 45 degree rear wing. The track had this very long straight and I wanted to maximize my speed down this straight, but did not want to loose a great deal through the remainder of the course. What I found was that front down force does not increase a great deal with additional grill-tape, but rear down force does change with the spoiler, as it should. Speed..45*..70* 150 9%.22% 175.35% 47% Basically, at 175 MPH with a 70 degree rear spoiler, the rear tires are being pushed down by the 750lbs on each corner of the 50/50/50/50 car I explained in my first article along with an additional 47% of weight due to aero down force. This brings the weight of the either rear corner to roughly 1100lbs, 12% more then with a 45 degree spoiler. Though that doesn t sound like much, consider this: In other testing I had found that the tires in the Road Racing physics can handle about 2g of lateral force before they have a complete grip failure (this is true under braking as well). The amount of grip is determined by how much force is pushing the tire into the racing surface. Weight (including weight generated by aero down force) equals the grip budget. If the corner of our car weighs 750lb, and that tire can handle 2g of lateral force, this means that this specific tire bas a budget of up to 1500lb of lateral force before complete
7 of 11 4/27/2005 10:06 AM loss of grip. Now, include aero forces of 175MPH with a 70* spoiler and that tire could take up to 2200lb of lateral force before loss of grip. Same equation at the same speed but with a 45* spoiler equals about 1900lb of lateral force. As the above figures show, it takes very high speeds to produce the aero forces needed to increase the cornering ability of the tires. At 150 MPH the added aero down force of a 45* spoiler is near nothing in comparison to a 70* spoiler. And at what speed do we take most of the turns on a road course? Well below 150 MPH. At a track like Spa where speeds stay in excess of 170 MPH in nearly all corners, reducing the spoiler will reduce rear grip, but due to the high speeds, aero forces are not all that much less then with full spoiler and the added MPH through-out the entire track is worth the loss of cornering speed. Also noted while testing (specifically at Spa in fact) was that with the constant 200+ MPH speeds, my baseline softy setup could not handle the aero forces pushing down on the car. At 200MPH I was producing enough frontal aero forces to effectively make the nose of my car weight over 2200lb (1100 per tire in a straight line). Yes, this is a lot of grip available, but the problem I was having was that 1100lb was crushing my 600-650lb rate springs giving me over 4 degrees negative camber, which is not good for grip in a corner. In turn I had to both, raise my spring rate *and* bring my static camber to a positive number. This allowed the aero forces to crunch the springs into giving the suspension slight-negative camber at high speeds for all those high speed corners. The stop-watches spoke out loudly with all the time cut off the laps. Above, I said, The amount of grip is determined by how much force is pushing the tire into the racing surface. This is true and is what I will define as Wheel-Force, the force in which the tire is being pushed to the asphalt. This simplified number is what dictates how much lateral forces that wheel can take before loss of grip. Of course, the outside wheels are going to take the brunt of the weight as the car rolls. What I became concerned about in some testing in the previous weeks (and spoke about in discussions regarding my last article @ http://www.tptcc.com/board/viewtopic.php?t=3277&start=15 ) was the inside wheel s wheel-force while maneuvering though a 2g corner was reaching a critical point of zero (lifting off the ground). This is where I bring up that spring preload again. With my baseline setup I was giving the outside wheel a work-out with a full 2g s of force, maximum it can take. But the inside wheel was nearing lifting off the ground. Preloading the inside wheels with more spring rate would effectively increase how hard the inside wheels are being pressed to the asphalt, planting it better, and giving it a larger budget of grip to play with. (When the inside wheel is only getting 100lb of wheel-force due to cornering, it begins to lose grip at only 200lb of lateral force, get it?) By raising the spring rate of that inside wheel it is being pressed into the asphalt harder giving more wheel-force, giving more overall grip between the two tires. Of course, in road racing you have to think of left and right hand turns so setting up for one direction will reduce ability in the other. Keep in mind also, that springs with a higher spring rate prevents the car from rolling and the suspension from traveling up and down. There is good and bad to that, but one thing I want to bring up is that spring travel is necessary for the shocks to do their job of managing that suspension travel. Without the travel, the shocks can not work effectively and a loss of grip is in order. Shocks are the next article, now that I brought them up again. Posted: Wed Sep 29, 2004 3:54 am Post subject: Shocks Shocks I promised to discuss shocks next and it is what I will attempt to do. I must first admit my lack of complete understanding of shocks, and then to top it off I have spent months trying to find a way to simply the understanding I do have to easily communicate via this thread and failed to do so; First, lets get some terminology clarified: I will refer to our car s shock absorber as Shocks I will refer to the downward stroke of the shock as compression I will refer to the upward stroke of the shock as rebound We can all argue the true names for each, but I would like to stay consistent with our setup menu in NR2K3. I was standing outside my house over this past weekend and opened the hatch of the Jeep Cherokee to sit and have a cigarette. The hatch opens upward, and two small shocks prevent the door from swinging up very fast. I'm sure this is to prevent me from biting my tongue off when the hatch slams into the bottom of my chin if it were allowed to open at the rate the springs want to push the door up/open. I then closed the hatch and noticed it was fairly easy to do so, with little resistance at all. I spent then next 5 minutes opening and closing this hatch (I never did get to smoke, and got odd looks from the neighbors) and finally decided to write this
8 of 11 4/27/2005 10:06 AM article. When I was opening the hatch, the shock s rebound was valved stiffly, which prevents the oils inside the shock from traveling past the valve very easily, which in turn allows the shock to travel upward. The rebound forced the hatch to open slowly because of the resistance against the forces of the springs that was pushing the hatch open. When I want to close the hatch, the shock s compression valving was light which allowed the door to quickly close using only the weight of the hatch as the spring mechanism. I tried for months to simplify this but I cannot find a way. Shocks are not simple, and their description cannot be simplified. My standard definition is this; Shocks dampen (via the hydraulic fluids within the shocks being forced past small valves within the shock itself) the springs natural compressing and unloading by offering resistance against those natural forces. Shocks do not prevent or absorb shock, why they became known as this baffles me much like why Coolant has nothing to do with cooling a motor (It is Anti-Freeze and/or Boiling point increaser, not a coolant!) NOTE: When a spring is fully compressed is when that wheel has maximum weight being translated through the suspension, tire, and to the ground. That weight, to an extent, equals grip until it exceeds the lateral limitation of the tire itself. How quickly or slowly that spring is allowed to fully compress is the job of the shock The easiest way to begin to understand shocks is in a straight line. Under braking the car is mostly in a straight line and the weight will shift from the rear of the car to the front. The front springs will compress while the rear springs will un-compress or rebound. The shocks follow suit and will compress (front) and rebound (rear). The faster the front springs are allowed to compress fully, the faster the front tires will have maximum grip from the weight of the car pushing the tires into the track surface. A softer compression setting will give the least amount of resistance to the springs natural tendency to compress, offering the maximum grip very quickly once the brakes are applied. The shock s compression setting in the rear will have no determination on what happens just yet, but the rebound still will. A stiff rebound setting will not allow the rear springs do un-compress very quickly. Since the spring is not allowed to rebound quickly, the rear tires will be somewhat lifted off the ground (exaggerated of course) until the springs are allowed to un-compress. Softer rebound setting in the rear will allow the tires to stay better connected with the road and offer more grip. Under straight-line acceleration the complete opposite is true; with the rear shocks compressing and the front shocks going into rebound, and the reason you see very light compression settings in the rear and heavy rebound settings up front on drag racing cars to maximize the grip to the rear tires as quickly as possible. Diagonal shocks Imagine in your head the right-front suspension of your simulated racecar as we go barreling into turn 1 at say any oval like Rockingham (braking and turning). As the driver lifts off the throttle and applies brakes the weight of the car is being shifted from the rear of the car to the front. Added to this is a left to right shift as you begin to turn in to the corner. The right-front spring will compress under the added weight, and the shock will do the same compress. A low compression setting will allow that spring to compress quickly, giving that tire it s full available share of grip very quickly. A higher compression setting will force the spring to compress slower, meaning the weight of the car will not transfer as quickly and maximum grip will still be there, just slightly later in the entry of the turn. The spring will fully compress no matter what the shock s compression setting is, but WHEN and HOW it does is the job of the shocks. The exact opposite is happening to the left-rear of the car; the left-rear is losing weight both from braking and turning so that spring and shock are rebounding (coming out of compression). How quickly that suspension is allowed to rebound dictates the grip for that wheel. If the shock is set to a low rebound setting then the spring will be allowed to easily un-compress. If set to a higher rebound, the spring will not be allowed to rebound as quickly. Which offers more grip to the left-rear wheel? A softer rebound setting as a stiffer setting would keep the spring from un-compressing which would make the wheel to lift off the ground, offering less weight/grip to that wheel. As the car approaches the middle of the corner, the springs are already at full compression and/or rebound, and the shocks would be as well. Shocks do not play a large roll in the handling of the car once this has occurred, as shocks need to be in-travel (either up or down) to offer any form of resistance to the springs. As we pass the point in which the car is at a settled state in the middle of the turn, the drive begins to apply throttle for maximum exit speed. Applying the throttle will shift weight to the rear of the car, and as we easy out of the steering the weight will begin shifting back towards the left, though will never reach it s 50/50 spilt with the right-rear until the car has reached the next straight. So with the weight transitioning to the rear, and
9 of 11 4/27/2005 10:06 AM still predominately to the right side of the car, we will look at the right-rear spring and shock: Just as we apply throttle the right-rear shock begins to go into more compression, though would already be near it maximum compression. Since we can t force this spring/shock to compress even further, steps can be taken from the other rear tire (left-rear). Altering how that spring deals with the weight changes (via shocks) will increase or decrease rear overall grip just as the changes on the right-front would under braking. There are hundreds of variables in shocks, though there are only 4 on the car. Changing one will alter the other 3 as well; One adjustment to the right-front rebound will alter how the weight is shifted to the left-front wheel (Lateral weight transfer on straights and even mid-turn or quick succession turns like chicanes), the left-rear (diagonal weight transfer in corners while braking or accelerating), and the right-rear (Longitude weight transfer under braking and acceleration.) NOTE: Keep in mind that stiffer springs usually require softer shocks as the springs will give resistance against themselves already. The same applies in reverse, where softer springs would require stiffer shocks. Take the Rockingham Oval example (above) and we can troubleshoot a common handling problem: Car is tight upon turn entry The car has a balance issue between the front and rear while under braking and turning. We can resolve this in many ways, but let s do it with just the shocks. We either need to reduce the rear grip or increase the front grip to loosen the car up WHILE in the turn-in phase of the corner. Remember, in the turn-in phase the car is braking and turning left, so the right-front is compressing and the left rear is rebounding. So one solution would be to get the right-front to it s maximum grip quicker by reducing the shock compression. If you already have a very low compression setting on your right front, you still have an option of increasing the left-rear rebound setting to take more weight off that wheel during the turn-in phase, effectively loosening the car up until you reach mid-turn where the suspension is no longer in a rebound state. Below, I made up a little cheat-sheet. It covers the basics only. There is a lot more that can be done with spring and shock combinations and the only way to get to know it all is to experiment with it. Best done at a small track with many similar turns (I recommend Limerock_Twist as you will get the chance to see how a minor shock change will make these differences). Sometimes it just comes down to driver comfort, and there is nothing wrong with that. One thing I want to mention regarding the cheat-sheet since it conflicts with my first article regarding springs; When using springs to correct a tight or loose condition like in the Rockingham example above, if you are unable to reduce the right-front spring any further (reached limit or bottoming out) then you can accomplish the same thing by increasing the left-front spring. You are just changing how the spring is preloaded between those wheels and either adjustment would accomplish the same thing.
10 of 11 4/27/2005 10:06 AM If you're not opposite lock, you're not going fast enough! This sig on hold pending talks with First-Racing.net Setup Development Articles
11 of 11 4/27/2005 10:06 AM Last edited by on Wed Sep 29, 2004 4:16 am, edited 2 times in total Posted: Wed Sep 29, 2004 3:55 am Post subject: I have mirrored all of these articles on my site's board Feel free to drop by any time you like, any future artciles will be posted there. If you're not opposite lock, you're not going fast enough! This sig on hold pending talks with First-Racing.net Setup Development Articles Display posts from previous: All Posts 6 Oldest First 6 Go The Pits Forum Index -> Tutorials All times are GMT Page 1 of 1 Watch this topic for replies Jump to: Tutorials 6 Go You can post new topics in this forum You can reply to topics in this forum You can edit your posts in this forum You can delete your posts in this forum You can vote in polls in this forum You can moderate this forum Go to Administration Panel Powered by phpbb 2.0.13 2001, 2002 phpbb Group