Will Power - Long Beach Grand Prix 2009
Jonathan Stewart posted an excellent guide on the iRacing forum. It’s posted below with permission.

For each setting I will show you normal ranges that I have been using so far this build. I am not at all saying you shouldn’t try values outside that range, but it will give you an idea of what has been working well for me. However, there are some settings where I would recommend not going outside my suggested range. One example is the front wicker, I have not found one situation were increasing it from the minimum value was beneficial.

Tire Pressures
There are some areas of the setup that I simply don’t change very much, and this is one of them. Tire pressures confuse me somewhat in iRacing, and I pretty much run whatever I see the majority of other people run. It seems that the optimum pressures are a bit lower than what you would expect them to be, and often the tire temperatures will be coldest in the middle as a result. For the most part I ignore the pressures because there simply doesn’t seem to be much potential to decrease my lap times by adjusting them, especially compared to other settings.

Normal Ranges:
Front: 18-20 psi (117-138 kPa)
Rear: 16-18 psi (110-124 kPa)

Front Aero
Wing Angle: This will significantly affect the balance of the car in high speed turns, and not as much in the slower ones. For me it is completely dependent on how much rear wing you have, as well as your ride height at speed. Therefore I determine those things first, and then adjust the front wing to balance the car. If I am changing the rear wing for whatever reason, I note the percentage of front downforce in the calculator before I change it, and then adjust the front wing afterwards to get the percentage as close as possible to where it was. This usually gets the car close to where I want it, but I may have to add or remove a couple clicks of front wing after driving the car.

Wicker Height: I could explain various things about the wicker, but it’s a lot easier and more practical to simply say leave this at the minimum value at all road courses you go to.

Wicker Span: Cannot be adjusted on road courses.

Normal Ranges:
Wing Angle: N/A. Do not be afraid to use any value as long as it balances the car at high speed.
Wicker Height: 0.125″ (Always)
Wicker Span: 3/3 (Can’t be changed)

Underside Aero
Horizontal Wicker Height: Increasing this adds rear downforce. I always leave this at the maximum value at high downforce tracks, and have only slightly experimented with reducing it some at Road America to gain top speed. If you click through all the values you will notice that the percentage of downforce added for one click becomes less as the height is increased. This tells me it becomes less and less efficient the more you use. It may be worth trying out a value as low as 2.0″ at low downforce tracks, but the potential gains are likely insignificant.

Horizontal Wicker Span: Also adds rear downforce. Just like the wicker height, increasing this value produces more downforce, but less efficiently. Going from 2/3 to 3/3 increases the rear downforce by a very small amount. For this reason I tend to use 2/3 at low downforce tracks because I simply can’t notice the difference when driving the car. Everywhere else I always leave it at 3/3.

Side Wicker Height: This is similar to the horizontal wicker but if you reduce it from maximum you will notice that it actually increases the rear downforce going from 3.0″ down to to 2.5″. Reducing it from there it will decrease the rear downforce just as the horizontal wicker does. This leads me to believe it’s becoming very inefficient at the highest values and it is possible that it is reducing the overall downforce while increasing drag. I tend to use 2.5″ at high downforce tracks and have went as low as 2.0″ at low downforce ones.

Normal Ranges:
Horizontal Wicker Height: 2.75″ – 3.0″
Horizontal Wicker Span: 2/3 – 3/3
Side Wicker Height: 2.0″ – 2.5″

Rear Aero
Wing Angle: For each 0.1 degree of rear wing added, it will affect the car much less than 0.1 degree of front wing added. I most often run this at either the maximum value or minimum value depending on the track. I usually don’t try values in between these, however there are no clear disadvantages to doing so, and it may be faster overall depending on the track. I really haven’t tested it enough. All you have to do is change the front wing to maintain the same percentage of front downforce and you are all set to try any rear wing setting.

Wicker Height: I never use this unless I want more downforce overall and already have the wing angle at maximum. Once you go past 0.5″ you begin reducing rear downforce so there is never any reason to go above that value. I usually stay below 0.375″ myself because I am scared to add too much drag.

Ramps and Extensions: To be honest I know almost nothing about these. I tend to run All ON at high downforce tracks and Sidepod extensions OFF on low downforce tracks. Not sure if that’s the best way to use these settings, but I am pretty sure you won’t gain very much time by playing with this stuff.

Normal Ranges:
Wing Angle: 49.0 deg – 71.0 deg (The entire range)
Wicker Height: 0″ – 0.5″
Wicker Span: All ON or Sidepod extensions OFF

ARB Diameter: I’m not sure why they call this ARB Diameter, since you can only change the material and both are 40mm in diameter. Using an ARB will make the car understeer. Titanium is about half as stiff as the Iron ARB so the Iron one will add more understeer. I never run ARBs and I tend to stick with adding more front spring as an alternative, but that doesn’t mean you shouldn’t try using them as some guys seem to run well with them, and I have raced a few times with one. I prefer the feeling that no ARB gives though. One thing to note about ARBs is that if you add one it will lift the inside tire up more when you turn in, so if you are having troubles locking up the inside brake you don’t want to run a front ARB.

ARB Arms: A higher value simply makes the ARB stiffer. This is especially useful if you find that your car’s handling changes as a race goes on since you can adjust it in the car, but you need to run an ARB to do so. I never have major problems with the balance of the car changing so I still don’t have any real reasons to run an ARB.

ARB Preload: I really am not sure about what exactly you use this for. Of course, by never running an ARB this isn’t a problem for me, lol.

Toe In: Using toe out (negative value) will help the car turn in, and using toe in should make it a bit more stable on entry or under braking. I tend to like a bit of toe in for the new build because my setups are a bit unstable on entry usually.

Steering Ratio: This only changes how far you have to turn the wheel, and it’s completely up to you what you run. Lower values make the steering more sensitive.

Front Brake Bias: If you are having trouble locking your front tires then you will want to lower this percentage. If you want to rotate the car more on entries then reducing this will also help with that. If you are running a low enough value you may need to add throttle under braking to keep the car stable. I am running much higher values with the new build, I used to run 47% at Watkins Glen and I am now at 53%.

Normal Ranges:
ARB Diameter: None
ARB Arms: 1 (This value makes no difference if you have no ARB)
ARB Preload: 0.0 ft-lbs
Toe In: -1 deg – +1 deg
Steering Ratio: 11.8
Front Brake Bias: 52-57%

Front Corners
Ride Height (Pullrod Length): When adjusting this value you always need to keep in mind what springs you are running. This is a static value and it will lower as your speed increases due to downforce. If you are bottoming out and would like to prevent it, you can either raise this up, increase the front springs, or do both. So far it seems like we want to run the front quite low, and I have been using values as low as 0.75″ and as high as 1.1″, but I haven’t had much luck with the higher ride heights. The front ride height relative to the rear ride height is extremely important. This is called rake, you can increase rake by either lowering the front or raising the rear. There is a certain amount of rake that is best for downforce and a certain amount that is best for low drag, but I really have no idea how much rake is best for either. Increasing rake will increase the front downforce and decrease the rear, and you will easily feel this effect in high speed turns. Another thing to note about rake (however it may not be significant) is that by increasing rake, you also increase the effective angle of both the front and rear wings, since the angle of the whole car is increased. For this reason I like to run more rake at high downforce tracks so that the rear wing can provide more downforce, and then the front can just be adjusted to whatever is safe.

Spring Rate: Increasing this will reduce the front grip, and add understeer. It will do this in slow speed turns, but also in high speed turns, and even more so if you do not adjust your front ride height back down after increasing the springs. This is due to the decreased rake from the increased front height. I tend to adjust my springs to make it handle well in the slow speed turns first, adjust the ride height next, and then finally change the wings to make the car work well in high speed turns while maintaining a good balance in the slow stuff.

Bump/Rebound Stiffness: There is a lot that can be said about these settings, but it’s very simple if you just leave them at 0 at all times like everyone seems to do. I’m not sure if it’s the fastest way to run the car but it seems as though lots of cars in iRacing like soft dampers. I hope someday this will change, but for now it makes setting up the car that much easier.

Camber: I’ve always had a hard time determining what the optimum camber angles are in sims so I’m not really sure what to say here. Other than in general, more negative camber means more grip. You can use the inner and outer tire temperatures to see if your camber is at an extreme value, in which case you may want to change it. Too much camber will overheat the inside of the tire and not use the outside enough.

Castor: More castor will increase the force feedback that you feel. If you increase the castor then for a given amount of steering wheel rotation you will have a higher camber change in the front wheels. This should make the car turn in better, and I’ve been running less castor in the new build because of how much more oversteery it is. I used to run maximum a lot in the old build, but I’ve reduced 5t some and it seems to work okay.

Normal Ranges:
Ride Height: 0.75″ – 1.1″ (Remember these are static, so note my spring settings also)
Spring Rate: 1000 lbs/in – 1600 lbs/in
Bump/Rebound Stiffness: 0
Camber: -2.3 deg – -2.7 deg
Castor: 8.5 deg – 10.0 deg

Rear Corners
Ride Height (Pushrod Length): Everything about the front ride height and rake applies here, except the rear will rarely bottom out unless you have some extreme pushrod lengths/rear spring settings. As far as I know you always want the rear to be higher than the front.

Spring Rate: Again this is the same as the front springs but of course they affect the rear of the car. The rear springs are usually quite a bit softer than the front springs, for two main reasons. First, to increase the rear grip when exiting slow speed turns, and secondly the rake angle will reduce as speed increases. This will help decrease the drag, because the rear will travel more than the front, which has stiffer springs.

Bump/Rebound Stiffness: Leave these at zero just like the fronts.

Camber: This is the same as the front, except less camber is usually used on the rear tires. Using less camber will help add rear grip for slow speed exits where the car is not turning much. More camber will help in the rest of the turn.

Toe In: If you want to crash your car in the first turn you drive into, add toe out. If you’re like me and you want more stable exits, then you would probably want to add toe in.

Normal Ranges:
Ride Height: 1.6″ – 2.1″ (Remember these are static, so note my spring settings also)
Spring Rate: 750 lbs/in – 1100 lbs/in
Bump/Rebound Stiffness: 0
Camber:-0.8 deg – -1.2 deg
Toe In:0″ – +2″

Fuel: Fuel is weight and weight is bad for everything. You may need a bit extra fuel if you use lots of throttle under braking, so that is one thing to be aware of. As the fuel burns off in the race it will raise the rear of the car more than the front. This may make your car oversteer a bit more later in a long run, but I’ve not had any major difficulties with this. If you want you can set up your car to understeer more initially, and it will slightly improve as the run goes on.

ARB Diameter: This is the same as the front ARB, except you actually change the diameter rather than the material. I don’t think I’ve ever drove through one turn with a rear ARB and I don’t feel like I need to try one anytime soon. I have heard of a few people running one and it certainly won’t ruin your lap times, it just makes me less comfortable in the car so I avoid them.

ARB Arms: Again, higher value means stiffer ARB and less grip.

ARB Preload: I need someone else to explain the purpose of this to me, lol.

Weight Jacker: For ovals only.

Normal Ranges:
Fuel: 2.9 – 22.0 gal (Yes this is pretty redundant, but in some slower cars you never run a full tank)
ARB Diameter: None
ARB Arms: 1
ARB Preload: 0.0 ft-lbs
Weight Jacker: 0 (Always!)

Drop Gears: Drop gears A and B are multiplied (or something like that) together to make the final drive ratio. All you really need to know is that this changes the ratio of all six gears. So for instance if you have your first gear set to the highest value but want it to be even shorter, you will need to use these gears. These can also be used to make fine adjustments to get ratios in between what ratios you can select for each individual gear. Again, this is useful for adjusting the first gear because there are only four ratios for it and they are relatively far apart.

Other Gears: Higher value means shorter gear so you have better acceleration but lower top speed for that gear. I tend to set these so the engine responds quickly in the turns with the longest straightaways after them. For example if you have two turns that have different apex speeds but both are run in gear 2, you would want to optimize your gear 2 around the turn with the longest straight after it. This may not apply to gear 5 and 6 because they may only be used on the straights. Generally I try to make the lower gears farther apart and the higher gears closer together. This is because you want more power at higher speeds to in order to maximize top speed, so you can achieve this by keeping the engine at a higher rpm at high speeds.

Clutch Plates: More clutch plates means more locking. This will usually increase understeer when you are off the gas as well as on the gas, however the rear of the car will break loose more suddenly if you apply too much gas. I always run minimum because the car understeers on the throttle for me and I don’t want it to understeer anymore and I certainly don’t want to make it any harder to catch a slide from too much throttle.

Preload: Adding preload will increase how much the differential locks when you transition from straightway to turning, or from turning back to going straight. Again I run this at minimum for basically the same reason the clutch plates are minimum.

Ramp Angles: For some reason, I am slightly confused about this part. The numbers are for adjusting the power and coast ramp angles, with power being the first one and coast the second. A 45 degree angle will lock less than a 60 degree angle, and I THINK this is true for both power and coast. From reading posts here I have confused myself and have got the idea from somewhere that the ramp angles may be opposite for power and coast. That is, 45 would lock less for one and more for the other, compared to 60. I am quite certain that 45 locks less for power however, and because of this I usually like driving with 45/45. I would like some clarification about this adjustment from someone who knows for sure.

Normal Ranges:
Clutch Plates: 1
Preload: 0 lbs
Ramp Angles: 45/45