iRacing GTP tuning series — 2, wing and springs

Hello there, it’s me again. How’s your Imola race last week? We were taken out by some trolls which basically removed us from the fight for podium.

Yep, that was (not on)me.

But anyway, let’s continue our topic: Since we knew that the core of setup is ride height management, it is only natural that springs and wings are the basic tools we need for managing that.

Basic theory

As modern racecars generate downforce(rather than lift), this following statement is universally true and should be true across all sim racing games:

— As speed increases, the ride height will reduce as the result of increased downforce applying to the car.

— The spring rate will decide how much the ride height drops: the stiffer the spring is, the less ride height it will drop.

So what implications to the handling? As we’ve established that the ride height affects the handling, we need to figure out how exactly the spring rate would affect it.

To make it easier and more specific, let’s imagine this scenario:

Say, the front end is fixed with a given combination of spring rate and static ride height(the ride height in the setup screen), what would happen to the REAR ride height with different combination of spring rate and static ride height?

Ride height vs speed graph

I’ve put up a graph with 3 different scenarios:

1. The baseline with standard static ride height and spring rate.
2. The stiff spring with the standard static ride height.
3. The soft spring with raised static ride height.

Generally speaking, with speed going up, there is a point that softer spring set’s rear ride height drops below other 2 sets. Same thing applies to the stiffer spring: it should stay relatively higher(than the baseline) over the whole speed range.

As you may have heard the word “rake”, which is the rear ride height — front ride height, and the general idea about how it affects handling: the more rake the car has, the more oversteer it is. And vise versa, the less the rake, the more understeer the car is.

So, the conclusion is pretty straightforward here:

1. With a stiffer spring, the car will have more oversteer over the whole speed range.
2. With a softer spring AND higher static ride height, the car could be more oversteery at low speed, but there is a speed threshold that the car becomes more understeery than the baseline set fromthat speed and above.
3. We could also utilize this in reverse: if you need a car that is more stable at low speed but more agile at high speed, a low static ride height + stiff spring combination would be the way to go with.

Practical approach

I’m trying to provide practical procedures on car setups and the theory at the same time with this series of blogs, so just bear with me if you are scared of “breaking the car with the setup”. But feel free to use your own approach if you are familiar with setups and want to verify the theory above.

Several clarifications first:

1. GTPs have 2 springs: one is mainly for ride height control, they call it Heave Spring in game. The other is mainly for body roll control, some cars use Torsion Bars, some cars use Roll Springs. To make it simple, we call both Roll Springs.
2. For ride height adjustments, you normally have 3 options: Perch on the Roll Springs(which can be different left to right), Perch on the Heave Spring, and the Pushrod offset that is also for ride height adjustments. I think the combination of these 3 “perches” would affect the suspension travel, or the bump stop travel, but since GTPs rarely bottom out, you could use any combination to achieve your target ride height, as long as they pass tech inspection in the setup screen.
3. Again, I have to stress that I’m setting the car “by the book”: using the iRacing setup notes as my target ride height. It is generally very balanced in terms of handling when the car is at that ride height, but if you have any secret knowledge on a better ride height target, feel free to use your own target.

OK, now we are all set, let’s start building a car setup.

Wings.

To start with, you will need to decide what sort of downforce level you would like to run on a specific track.

And an universal principle is: almost all real life IMSA(North America)tracks are using max wing / high downforce set, except Daytona (which would be low wing + long gear).

Moving to European tracks, same rules apply: unless you are running at Le Mans, a high downforce set with max wing would probably be competitive enough.

The reason behind is simple: the high downforce not only provides extra cornering speed, it also helps reducing brake distance a lot. Thus the benefits override the loss on straight line.

However, there are strategical choices of using 1–2 clicks lower wing than max on specific tracks, such as Monza or Spa: you will be caught up by others(who’s running highDF sets)in corners, but they would probably not be able to make any move even if they sit in the tow for a whole straight. This kind of choice really depends on your anticipation of your relative pace in your split, though: if you are going to be the mid pack with close fights, the relatively lower drag(from lower wing)may provide some overtaking opportunities. But if you are going to be the top of your split and leading the whole race, a high downforce might just be alright in terms of lap time and consistency.

Also, for target ride height vs wings, it seems that the ideal ride height(in setup notes)is suitable for max wing. With reduced wings, you might want to reduce your (rear)ride height accordingly: on average, a 0.5–2mm drop in rear ride height target should be applied to every 1 click less wing.

Springs and ride height.

Once you’ve made a choice on the wing setting, it’s time to set up the spring rates and ride height.

Another thing to clarify first:

Even though the purpose of Heave spring and Roll spring is to decouple the body roll control and ride height control, they do contribute to the ride height together. But different cars(chassis) may have different ratio of contribution to the ride height from Heave and Roll springs.

So, with a given ride height target, you may get that by using either stiffer Heave + softer Roll, or softer Heave + stiffer Roll. In general, stiffer Roll spring will provide a little bit aero benefit(better for high speed corners), whereas softer Roll spring will provide better mechanical grip(better for low speed corners). So it will be another choice to make.

With these concepts cleared, we could start setting the front first by doing some laps:

1. Always aim for the minimal static ride height at the front: a 30.0mm would be great, but a 30.1mm won’t make too much of difference.
2. For the spring rate, you will need telemetry tools(to check ride height)to make sure the front is not bottoming out at max speed.
3. Then we could look at the ride height in corner: for the fastest corner of the track, try to aim the average front ride height equal or slightly lower than the ideal ride height in the setup notes.
4. After getting both 2 and 3 sorted, we could keep the combination for now and revisit them later for fine corner entry adjustments: just remember, for better low speed performance, use softer Roll springs, for better high speed performance, use stiffer Roll springs. (And then use Heave springs to compensate for ride height.)

With the rear, you will need to consider following things while doing those laps:

1. Is the car understeer, oversteer at low speed corners, especially when it comes into the middle of the corner with a steady(and max)rotation rate?
2. Same question for high speed corners, is the car understeer or oversteer in high speed corners, at the steady cornering(middle corner)phase?
3. The low speed handling indicates a static ride height adjustment(oversteer = lower ride height, vise versa).
4. And the high speed handling indicates a spring rate adjustment(understeer = softer spring rate).
5. Try to aim the average rear ride height at the fastest corner of the track around the ideal ride height in setup notes.
6. The Roll spring at the rear will decide how much traction you could get coming out of a corner. Thus try to get to the point where you could put your foot down easily without excessive correction for oversteer.
7. The Heave spring is a powerful tool to keep the ride height high enough at speed(meaning to have enough rotation).

After tweaking the rear ride height and spring rate combination for several rounds(normally it takes 3–4 rounds of tweaks), you should get a car with proper mid-corner rotation in both high speed and low speed corners. Then we could go back to the front end and make tweaks on the combination of Roll Spring and Heave Spring to balance(or lean towards one side)the rotation between high speed and low speed corners.

Note that at this stage, we only worry about mid-corner rotation when the car is in a more stable stage of the corner. For entry and exit, we will use other tools to optimize for those.

This is a bit longer than I’d anticipated. But since the springs and ride height are the most important things in a car setup(actually, the car should be at least 80% done with the springs and ride height properly set), it probably should take this much to get them explained properly. Feel free to leave a comment if there is any point that is not clear or if you want to discuss anything in this blog.

If you find this useful, feel free to like, subscribe and share to whoever you think this may help.

Next time, we will have some discussions on dampers. Have fun and see you on track!