Nascar 4 Setup Question (springs)

I am really trying to understand the basic of Nascar 4 car 'set up' in order to develop my own for each race track. I have read the main setup guides on the net, but there are two matters that I just can not understand; a) I read in one guide that a stiffer spring means more weight is applied to that wheel. Surely though a weaker spring would have less resistance and so allow more weight to be transferred to the particular wheel? b) if the LF wheel has softer springs that the RF, how will the car react and why? Any help will be really appreciated. From one very confused soul. PJ

"Paul Jager" <[email hidden]> wrote in message news:iGj%6.2212$[email hidden]... > I am really trying to understand the basic of Nascar 4 car 'set up' inorder > to develop my own for each race track. I have read the main setup guideson > the net, but there are two matters that I just can not understand; > > a) I read in one guide that a stiffer spring means more weight is appliedto > that wheel. Surely though a weaker spring would have less resistance andso > allow more weight to be transferred to the particular wheel? The weight will tranfser quicker on harder springs so it will use the tyre harder than softer springs > > b) if the LF wheel has softer springs that the RF, how will the car react > and why? It will help the car turn in under braking or deceleration probably because it will transfer the weight to the rf quicker thus helping the car turn in.

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> > Any help will be really appreciated. > > From one very confused soul. > > PJ >

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I think I can explain it. The total amount of weight that gets transferred to the outside wheels in a turn is totally a function of the car's geometry and has nothing to do with spring rates. What spring changes do is change the distribution of that weight from front to rear. When you put a lateral force on a car, it attempts to roll due to the fact that the CG is above ground. If the chassis has sufficient torsional stiffness (which race cars generally due) it will attempt to roll the same amount front and rear. If the front has more roll stiffness than the rear (either through stiffer springs or bigger anti-roll bar, or dynamically through stiffer shocks) then it will resist that rolling motion more than the rear, consequently transferring more weight from the inside to outside tire than at the rear. It's actually a little more complicated than that, due to the fact that the roll axis isn't usually parallel to the ground, and the fact that suspension deflection can change the height of the CG, but that should be a good enough explanation to get you started. HTH, Hal "Paul Jager" <[email hidden]> wrote in message news:iGj%6.2212$[email hidden]... > I am really trying to understand the basic of Nascar 4 car 'set up' inorder > to develop my own for each race track. I have read the main setupguides on > the net, but there are two matters that I just can not understand; > > a) I read in one guide that a stiffer spring means more weight isapplied to > that wheel. Surely though a weaker spring would have less resistanceand so > allow more weight to be transferred to the particular wheel? > > b) if the LF wheel has softer springs that the RF, how will the carreact

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> and why? > > Any help will be really appreciated. > > From one very confused soul. > > PJ > > > >

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>I am really trying to understand the basic of Nascar 4 car 'set up' in order >to develop my own for each race track. I have read the main setup guides on >the net, but there are two matters that I just can not understand; > >a) I read in one guide that a stiffer spring means more weight is applied to >that wheel. Surely though a weaker spring would have less resistance and so >allow more weight to be transferred to the particular wheel?

Hi Paul, One way to think of it is like this: When a car is in a "steady state" turn, meaning the car is following a constant curve without speeding up or slowing down, and you've got the steering wheel in one position, the car wants to roll to one side. If it's turning left, it rolls to the right (you know this already). The springs on the right side are being compressed, which does two things: It pushes the wheels down harder into the ground, and it pushes up on the right side of the car, preventing it from rolling any further. The opposite is happening on the left side. The springs are extending, so they aren't pushing down on the left wheels as hard as they were before, and they aren't pushing the left side of the car upwards (rolling it) as much. Eventually, the car sets itself at a constant roll angle. If the car rolled 2 degrees while turning through the corner, the springs on the right side might compress 1 inch. (They probably compress more than this, but just for example) A spring rate of 300 lbs per inch means that if a spring is compressed one inch, there will be 300 lbs of force pushing up on one corner of the car, and also pushing down 300 lbs on the tire. Make sense? If we doubled the spring rate on the right front tire to 300 lbs and assumed the body still rolled about 2 degrees in the corner as before, still giving 1 inch of spring compression, there will now be 600 lbs of force pushing down on the tire, instead of 300 like before. There's now more "weight transfer" at that wheel. In reality, increasing the spring rate will cause the body to roll a little less than 2 degrees now, so you wouldn't quite get the full 600 lbs of force pushing down instead of 300, but you'd still wind up with more than 300 lbs of force. Anyway, the total force at all four tires is going to equal the weight of the car (if we ignore the aerodynamic downforce.) This means the force is going to be less at another wheel because of this. I'm not sure how much you care for the mathematics behind this stuff, but here's a simplistic example of how you might estimate the force pushing down on each wheel (wheel load) if you know how much the body is rolled in a corner. Studying this may help you understand better what is happening when you change spring settings in Nascar 4. ------- We could have four springs, RF (right front), RR (right rear), LR (left rear), and LF(left front). The spring rates might be: RF = 300 lbs/inch RR = 300 lbs/inch LR = 300 lbs/inch LF = 300 lbs/inch If our car rolls 3 degrees to the right in the corner, which might cause 2 inches of spring compression/extension, we could estimate out how much weight transfer there is at each wheel. For note, the * sign means times, or multiplication. Weight transfer at right front (RF): 2 inches * 300 lbs = 600 lbs Weight transfer at right rear (RR): 2 inches * 300 lbs = 600 lbs Since the car is rolling to the right, the springs on the left side are being extended rather than compressed, so they're not pushing as hard as they were before. We can show this by multiplying by -2 inches instead of +2 inches. Weight transfer at left front (LF): -2 inches * 300 lbs = -600 lbs Weight transfer at left rear (LR): -2 inches * 300 lbs = -600 lbs As we can see, all four wheels here have changed they're "load" by 600 lbs. The left side by -600 and the right side by +600. From a birds eye view of the car, it might look like this: -600 600 -600 600 -------- If we wanted to stiffen up the right and left front, we could do it again: The spring rates might be: RF = 400 lbs/inch *< This is a stiffer right front spring RR = 300 lbs/inch LR = 300 lbs/inch LF = 400 lbs/inch *< This is a stiffer left front spring If our car still rolls 3 degrees to the right in the corner, causing 2 inches of spring compression/extension as before, we could estimate out how much weight transfer there is at each wheel with the stiffer front end. Weight transfer at right front (RF): 2 inches * 400 lbs = 800 lbs <--stiffer spring Weight transfer at right rear (RR): 2 inches * 300 lbs = 600 lbs Since the car is rolling to the right, the springs on the left side are being extended rather than compressed, so they're not pushing as hard as they were before. We can show this by multiplying by -2 inches instead of +2 inches as before Weight transfer at left front (LF): -2 inches * 400 lbs = -800 lbs <--stiffer spring Weight transfer at left rear (LR): -2 inches * 300 lbs = -600 lbs So now the weight transfer situation looks like this (birds eye view of car): -800 800 -600 600 Notice here that there is more weight transfer at the front than at the rear. In reality, if you totaled the numbers from the first set of four (with equal spring rates) and this set of four, they should end up at the same number. They don't here, because in the real car the roll angle would be smaller with the stiffer front end. But still, you can see that there will now be more weight transfer at the front of the car than at the rear. What does this mean? Because of a factor called "load sensitivity" in tires, the total force at the front end of the car will now be less than what's available at the rear, so the car will tend to go more straight (understeer) with the stiffer front end. If you'd like to see a little more math explaining why this happens, let me know. Off the top of my head, I'm not sure what would happen if you stiffened up the front right and softened the left front. Whoops, you're posting from UK, I should have used metric!! Sorry! Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

Does this happen at all speeds, or only when the front tires are at/near the cornering limit? [email hidden] (J. Todd Wasson) wrote in message news:<[email hidden]>... > the car will tend to go more straight (understeer) with the stiffer front > end.

>Does this happen at all speeds, or only when the front tires are >at/near the cornering limit? > > Theoretically, it should happen at all speeds. You might need to turn the wheel just a little further to follow the same corner when under the cornering limit. There are a lot of other factors though too, this is just isolating a couple things and their basic effects. For example, I'm writing a thing (not as pretty as N4) that does vehicle physics and am learning a lot this way. One thing I've noticed is that changing spring rates has a huge effect on suspension travel, which effects camber with body roll and pitch, something that I didn't mention in the other post. The camber change effect could easily undo the "load sensitivity induced understeer" I was talking about before. So to further confuse the issues :-)... this all depends partly on whether or not N4 models proper wheel movement. If it does, the arm lengths and mounting positions will really throw a lot more into the equation. But if this could be ignored, than yes, stiffening the front end should cause a bit more understeer (at least in my mind) at all speeds, not just at the cornerning limit. I don't know if that helped! :-) Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com