Among the original SimplePlanes parts in desperate need of a facelift is the Resizable Wheel. It was introduced over nine years ago and has received relatively little change since then, besides the addition of a number of new visual styles.

Needless to say, improving the wheels has been a high priority for SimplePlanes 2, and we’re really excited to finally show off what we’ve been working on.

To start with, the model for the wheels is much more detailed. Look closely and you’ll see high definition rims, the brake rotor, and the brake caliper – all of which have their own paint trims. There’s also new skidmark and tire smoke visual effects, letting your craft leave a lasting impression everywhere it goes.

As far as customization goes, there’s the standard size and width options you already know and love, but we also went just a tiny bit overboard and now you have over 20 tire styles, over 20 rim styles, and a bunch of tread styles, all of which can be independently selected. You can also use a slider to adjust the offset of the rim, setting it deeper or shallower into the tire. All of these allow for an insane degree of personalization, letting you make your wheels look exactly the way you want them to.

But new visuals aren’t the only thing we did with the wheels. Come on, did you really think we’d leave the physics untouched? Because boy oh boy did we touch them.

The wheel physics have been totally redone, behaving in a much more realistic and fun way. They behave differently depending on the type of surface you’re on (roads, grass, sand, etc), you can drift in them, they have much better colliders, and so much more.

The new wheels use an elliptical grip model (shout out to @hpgbproductions for making a SimplePlanes 1 mod that does a similar thing two years ago!), which is a difficult concept to explain so if you’re interested you can check out this Wikipedia page. What it essentially means is the way the grip in your wheels works is significantly more dynamic and realistic than before, allowing each wheel to oversteer or understeer depending on a multitude of factors for much more interesting vehicle handling.

We’ve tweaked the default properties of the elliptical model to what we feel meets a nice middle ground for the needs of most players, but we’ve left those properties open in the craft XML for those of you who want to fine tune your craft’s handling in a more in-depth way.

---

Wheels are cool and all, but they don’t exist in a vacuum (unless your name is Apollo). In order to make a vehicle that drives smoothly and doesn’t violently break itself apart at the slightest bump, you need suspension.

You could make suspension in SimplePlanes 1 and many people have happily done so, but it required a fair bit of knowledge of the actual mechanics of real-life suspension and was generally not intuitive to a new player.

So in SimplePlanes 2, we’ve added a brand new procedural Double Wishbone Suspension part with a variety of tweakable properties. Now you can simply drag and drop some suspension onto your craft, tune it to your liking, slap a wheel on it, and go on your merry way!

Here’s a quick rundown of the suspension properties you can customize:

• Size & Extension
  
  
  
  • These are self explanatory. They affect the overall size of the part, as well as how far from the center of the craft it will extend.
  
  
• Length
  
  
  
  • This defines the suspension’s range of motion and how far off the ground the main body of your craft will be. A nimble racecar made for a track might prefer a shorter suspension that doesn’t travel much, but an offroader will want all the room it can get to navigate perilous terrain.
  
  
• Stiffness
  
  
  
  • This affects the strength of the spring according to how smooth of an experience you want. A softer spring will make for a more pleasant and stable ride on uneven ground, but may not give the desired responsiveness for a track-oriented car that a more firm spring would.
  
  
• Damper
  
  
  
  • Effects the suspension’s resistance to vibration. Low damper will make the suspension bouncier when absorbing bumps, and higher damper will keep the suspension steadier which will help plant your tires more firmly onto the road.
  
  
• Shock Position
  
  
  
  • A purely cosmetic property that affects how far forward or back the shock absorber is.
  
  

Tuning your vehicle’s suspension can be quite a fun process, with an endless variety of configurations depending on what you want – there is no singular “best” option, it’s all about what you want out of any given vehicle. So experiment!

While the double wishbone is the only suspension configuration currently in the game as of writing this, we also have plans to add straight axle suspension! Kevin has already made the model for it, it just needs to be brought to life on the programming side by Andrew.

Circling back to wheels for a moment, we’ve also added steering wheels to the game! You’ve got your traditional circular steering wheel, as well as the more rectangular type commonly seen in high-performance race cars. Just like the joysticks and yokes, they can be gripped by Chad for an added layer of interactivity to your craft.

To make operating the steering wheels more comfortable for Chad, there’s now a reclinable racing chair as well, perfect as a more grounded replacement for the aircraft-centric chairs currently available in the game. You can set it to recline anywhere from 0-90 degrees in the designer, and Chad will lean back along with it – maybe with some neck pain if you don’t adjust his head rotation.

---

For all the improvements you’ve seen us make to ground vehicles, there’s still one glaring issue left: engines.

In SP1, the Car Engine is incredibly barebones and hardly behaves the way it should, as it merely applies torque to a selected set of wheels and does little else. So let’s fix that.

Procedural Engine & Powertrain System

In SimplePlanes 2 we’re adding procedural engines and transmissions, along with several modular powertrain parts to make it all work. Let’s start with the engine.

The new procedural engine is highly customizable and has significantly more realistic behaviour, while staying simple to set up. Rotational inertia, torque curves, and angular velocity are all simulated now. This lets you really feel the way your engine responds to the variety of situations you put it in, especially with the new RPM gauge in the flight UI that appears when you’re in a car.

There are a few properties you can mess around with on the engine:

• Size

  • Raising this increases the engine’s horsepower and torque, but reduces its maximum RPM and increases its mass.

• Cylinders

  • Increasing the number of cylinders in the engine raises its horsepower and torque without reducing RPM, but makes the engine longer and heavier.

• Engine Tuning

  • With the Engine Tuning slider, you can tune the engine to produce more torque but less RPM, or vice-versa. More torque will improve your vehicle’s acceleration and make it better at carrying heavy loads, but the resulting loss in RPM will reduce your top speed which may not be desirable for a racecar.

Next, the transmission. A transmission allows you to optimize your engine’s output according to how fast you’re going, using a set of gears. The new Transmission part gives you a number of things to tinker with: you can choose between manual or automatic shifting, three different gear profiles preconfigured to be optimized for street, racing, and offroad performance, set the number of gears from 3-10, and you can tune it. Similar to the engine tuning, gear tuning allows you to choose whether to prioritize torque or top speed, allowing for further fine tuning beyond just the engine itself.

Now for some really cool stuff. In order to make the engine work, you use a combination of driveshafts, differentials, and transfer cases to link everything together.

Driveshafts build a path from your engine to other powertrain parts, and differentials and transfer cases allow you to split that output in multiple directions to make any drive configuration you can imagine.

This might sound complicated, but true to the game’s name (well, half of it anyway) we’ve made it quite simple. Just place a driveshaft at the end of your transmission, and the driveshaft will automatically shift and scale itself around to link to any parts you attach to it, allowing for creation of ground vehicles in a way that is both intuitive and educational.

While the whole powertrain system might sound like it’s just for ground vehicles, during development we realized how flexible it truly is – so not only will we be adding additional types of car engine, we’ll also accommodate use of the powertrain system for aircraft via propeller engines and turbines.

We've uploaded a video showing off the new powertrain system, check it out here: https://www.youtube.com/watch?v=F9HS7NEguvM

---

If you like what you're seeing, please consider wishlisting SimplePlanes 2 on Steam. If you'd like to see bits of these blogs early, consider joining our Discord Server!