Updated: March 2022

If you've been directed here because your game is running out of RAM and started crashing, skip this intro and go straight to the RAM, pagefile and Loading Screen Mod sections below.

I've been updating this guide for almost 7 years - it contains everything I've found on making the game run faster.

The guide follows a logical progression: Launching the app -> loading a save -> in-game. It tackles the various issues at each stage with mods, hardware and system tuning. Don't just jump to the in-game section though, go through each step in sequence. For example, getting your page file set up (part of 'launching the app' stage) will improve loading performance and in-game performance. Likewise, the Loading Screen Mod (part of 'loading a save' stage) will help reduce strain on your graphics card and RAM, which in turn improves in-game performance.

When it was first developed, CO's team was small (just 5 developers). The game uses an old version of the Unity game engine which isn't "thread-safe" - that means it can't properly take advantage of modern hardware without rewriting the entire game for a modern game engine - buying faster hardware is not going to give you as much performance boost as you might expect.

As your city grows, potato computers will struggle to get above 20fps while gaming rigs will struggle to get above 40 fps. So you need to be prepared for that. That being said, we are now starting to see FPS Boosting mods which tackle key bottlenecks in the game code and potentially give big performance increases, but more on that later.

Updated: March 2022

This section no longer relevant due to paradox launcher being added in January 2020. Will update when there are more reliable ways of deleting it, but for now see this topic and this guide

When you first launch the app, there's a lot of communication with the Steam servers, especially if you have lots of workshop subscriptions.

Use `Control It` mod (a modern replacement for an older mod called `Less Steam`) to reduce network traffic, particularly for workshop assets:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2723628116
Use the `Skip Intro` mod to slightly reduce the time spent on the two intro screens that appear before the main menu is shown:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1665106193
Note: You can run the game in offline mode, but it disables all mods - and yes, there are ways to work around that limitation, however many mods rely on game APIs that are only available when they are treated as Workshop mods (which require online mode). If you use mods, it's best to run in the game online to ensure mods can identify each other.

On potato computers (very low spec), deleting unwanted save games weirdly makes app launch a little quicker and sometimes even gives slight performance increase while in-game. You can delete unwanted saves via: Main Menu > Content Manager > Savegames

Updated: February 2022

If you don't have enough RAM and page file, the game will lag and might even crash.

This game eats RAM like crazy, especially if you start adding DLC and workshop content. RAM usage peaks when loading and saving games. Assets (buildings, vehicles, roads, etc) eat much more RAM than mods.

The Steam store page for C:SL states the game will run in 4GB RAM - that's a joke. Even the vanilla game, with the content added by free updates, will struggle to run in 4GB. It will be a laggy mess.

• For the base game to run well, you need at least 8 GB RAM.
  
• If you start adding DLC and workshop, you ideally need 16 GB RAM or more.

If you don't have enough RAM the game has no choice but to start moving stuff out of RAM and in to the page file on disk. Disk (even super-fast NVMe M.2 SSD) is always significantly slower than RAM.

More RAM = less swapping to disk = faster performance.

Faster RAM is better, but only if your CPU can handle it. So check carefully before buying more RAM to make sure it's going to work well with your CPU.

AMD Ryzen users: B-Die finder[benzhaomin.github.io] + OC calculator[www.overclock.net] yw (:

ProTip: Use memtest86[www.memtest86.com] to check for faulty RAM. It is operating system independent and vastly superior to any mem testers that come with your operating system. Faulty RAM causes random problems (like broken textures) and crashes.

Note: This game will always use the page file, even if you have loads of RAM.

Anything that doesn't fit in RAM goes in to the page file (sometimes called "swap file"); if the page file isn't big enough to accommodate it, the game will crash. In addition, the game engine tries to push anything it isn't currently using in to the page file, and your operating system will do the same.

On Windows, it's critical that you set the page file size manually. The old version of Unity engine pushes stuff to page file in small chunks rather than one big chunk, and that caues lag during loading screen and can even cause crashes[support.microsoft.com].

Set the minimum size equal to 16384 MB or, if you have enough disk space, 32768 MB. The maximum size should be set to the same or more.

• Windows: See Windows 10 or Windows 7, 8 or 10[www.thewindowsclub.com].
  
• Linux: Try Zram[en.wikipedia.org] and zswap[wiki.archlinux.org], in that order. But do not use cryptswap as it causes problems (thanks @daniel.mantione and @flo for this info).
  
• Mac: Use Boot Camp to run Windows or Linux partition, then see above.

Tip: Check you have plenty of free disk space. If you run out of disk, it could cause the pagefile to shrink and will almost certainly lead to crashes (eg. if not enough room for log file or temporary data or save games, you get crashes)!

See also this guide by Snowfiltzer:

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2114415052

Updated: May 2020

The main performance bottleneck is the primary CPU core.

Most of the game runs in the "main thread" on the primary CPU core. It's a huge bottleneck and is mainly due to the old version of Unity game engine (as mentioned in Introduction section, it's not "thread-safe").

The faster your primary CPU core, the better the game will run:

• You ideally want 3.8GHz or faster for "gaming rig" performance.
  
• Intel CPUs generally have fast primary CPU cores, although AMD are starting to take the lead in many cases.
  
• If you use the computer for lots of other stuff, AMD CPUs are generally better value for money and beat Intel on almost everything.

Anti-virus apps sometimes put excessive strain on CPU, particularly Avira Antivirus.

The game works best on Windows, because it tends to get better driver updates (particularly for graphics card).

On Windows 10, use 'Balanced' or 'Performance' power profiles, even if you have AMD CPU; test to see which gives best results. See also: How to speed up Windows 10 (ignore stuff about mouse speed, that actually slows down C:SL).

On a Mac? Use Boot Camp[support.apple.com] to install a Windows partition and run the game on that. Sounds crazy, but it will be faster than the native Mac version of the game on OS X.

I've never played it on Linux, so can't help with that.

Updated: January 2020

Faster loads = biggest "quality of life" improvement

I cannot stress this enough: Out of every improvement I achieved, shrinking game loading times had by far the biggest impact on my enjoyment of the game - way more than increasing in-game fps (we'll get to that later, don't worry). I used to wait up to an hour for a save to load, now I wait less than 2 minutes. It means I can dip in to the game any time I want, rather than having to plan a session in advance.

There are four key stages which can be represented by the loading bar:

• 0-50%: Assets are laoded (vanilla first, then DLC, then workshop). Loading Screen Mod (see later) makes it hugely faster, having more assets makes it slower.
  
• 50%-95%: Asset textures get processed in to texture atlasses, and some mods start initialising. More RAM and faster CPU makes it faster, having more assets and mods makes it slower.
  
• 95%-100%: All of the AIs and game code initialises, and lots of mods do bulk processing. The progress bar and spinning circle will stall because this part of loading is so intense the screen can't update. A fast CPU and more RAM make it faster, grind mods make it hugely slower.
  
• In-game: Shortly after your city loads and appears on screen, lots of mods do their final stage of initialisation causing lots of lag and stuttering. Pausing the game on load helps them finish that work faster and helps clear any backlog of background processing tasks.

The next few sections of the guide focus on making the loading process much faster, but note that many of those things also improve in-game performance, particularly on potato computers.

Updated: January 2022

Reduce RAM and VRAM usage = faster loads and slightly faster gameplay.

Loading Screen Mod (LSM) is a "must have" mod regardless of your computer specs:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2731207699
It reduces strain on your RAM, page file, VRAM (graphic card RAM) and massively reduces load times, and often improves performance in-game too. It also has really good error handling features and can generate reports of broken assets.

Example (2500 assets and 110 mods):

• On my potato PC loading went from 50 minutes → 25 minutes
  
• On my new PC loading went from 10 minutes → 2 minutes
  
• I saved about 15 GB of RAM too!

If you're not using LSM, just turn everything off and go herd goats in the mountains or something.

Let's look at the main options (more are listed later):
⠀⠀
For hassle-free operation, both of these should be enabled (recommended).

However, if you want fastest possible load and minimum RAM usage, disable "Load enabled assets" but enable "Load used assets". This means only assets already used in the savegame will be loaded, but you will be limited to only those assets while building your city. More info.

Assets, particularly those in the workshop, have lots of duplicate textures, meshes and materials.

Enable the sharing options for those things and you'll save loads of RAM (often several gigabytes).

Note: Graphics cards with lots of VRAM (2GB or more ideally) can handle more textures (in other words, more assets) without relying on slower motherboard RAM. If you keep adding more and more assets, you will still eventually fill the VRAM and incure peformance issues.

This option, when enabled, instantly saves you 1.5 GB RAM or more.

These reports can help you track down missing assets, and also helps to find and remove bloated and broken workshop assets. We'll deal with that later.

Note: Creating reports slows the loading process a little so turn off reports if you're not using them.

This lets you turn off assets from the vanilla game and DLCs, and can save you huge amounts of RAM. See Prefab skipping guide for details of how to use the feature.

While loading, you'll see warnings about stuff that's missing. If, like me, you disabled a bunch of stuff, those warnings just clutter the screen and make it harder to spot other issues. To use this feature, load a saved game then go in to LSM mod options and click the button to open the file - then follow instructions at the top of the file.

If you are getting errors in your save games, enable these three options and then try loading your save. If it manages to load, create a new save with a new file name, then exit the game to desktop and then load it up again and it should work fine from that point onwards. See Safe Mode guide for more details.

If the options don't fix your save, then it's likely to be a broken mod or asset. See Finding Broken and Bloated Assets guide for dealing with that. There's also some useful stuff in the TM:PE troubleshooting guides[github.com] that might help.

Added: March 2022
Another mod that can help speed up the loading process is LOM - Load Order Mod.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2448824112
Just by installing the mod (and it's required dependencies - read the workshop page!) you'll get slightly faster load times due to it ensuring that Harmony mod (a depdendency for most mods these days) is loaded first.

But LOM also comes with a "Tool" app ( Windows only, unfortunately ) which lets you create per-city profiles to control which mods/assets are loaded, etc.

To learn more about the advanced features of LOM, see the wiki (link can be found on the mods' workshop page).

Updated: January 2022

The more you add, the slower the game becomes...

If you overburden your hardware with too many DLCs, mods and assets, the game will grind. But what sort of numbers are we talking about here? It's difficult to quantify, because no two DLCs, assets, mods or computers are alike - but here's a rough guide based on RAM (these values assume you are using Loading Screen Mod to help reduce RAM consumption):

• 8GB RAM: 100 assets, 5 mods, 1-2 DLCs
  
• 16GB RAM: 500 assets, 20 mods, 5-10 DLCs
  
• 32GB RAM: 2000 assets, 50 mods, 15 DLCs
  
• 64GB RAM: 4000 assets, 100 mods, All DLCs

Obviously, RAM is not the only factor but it's a good reference point. If you have powerful graphics card (with lots of VRAM) you can handle more assets. If you have powerful CPU, you can handle more mods. And, as mentioned later, a fast disk drive helps reduce lag in all aspects of the game.

Here's some guides that are useful if you're just starting out (if you know any others, let me know in comments):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1411897315
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1191748287
DLCs are official add-ons for the game. Depending on your hardware (particularly RAM and CPU), adding too many can impair performance and even cause crashes.

Radio stations don't cause any problems, as only one track plays at a time. But other DLCs can add huge numbers of assets (particularly content creator packs, and Green Cities).

Tip: You can disable purchased DLCs via Steam Library: Right-click the game in the library and choose "Properties...", then choose DLCs tab. But be careful - some workshop mods and assets rely upon DLCs and might break without them.

Content from Steam Workshop can be considered in three main categories:

• Maps & Map Themes: Only one of each is active per city. In terms of game performance, we can safely ignore these.
  
• Mods: These alter the game code (but can sometimes also include assets). You can have potentially hundreds of mods active per city.
  
• Assets (everything else): This is content such as buildings, roads, vehicles, etc. You can have potentially thousands of assets active per city.

Nothing will destroy game performance more than you subscribing to crazy numbers of mods and assets, so learn to deal with your subscription addiction!
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=449998850
Some general tips before clicking the Subscribe button:

• Are you really actually ever going to use this thing?
  
• Look at what other users are saying in the comments, and how the author responds to them.
  
• Author name is in yellow text, so easy to spot in comments - if the author is still around answering questions, that's a good sign.
  
• Good ratings and lots of subscribers is generally a good sign, but not always. There's lots of broken stuff which used to work years ago (hence subscribers and ratings) but no longer works with current version of the game.
  
• If there is a yellow "This item is incompatible with Cities: Skylines" banner across the top of a workshop page, DO NOT SUBSCRIBE (or, if you already did, unsubscribe it). It will literally break your game.

Each mod (generally speaking) adds more workload for your CPU.

The compatibility checker will help you find out if you have any problem mods (it lists any that are laggy, broken, etc):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2633433869
You can also check the list of broken and incompatible mods[docs.google.com] (the compatibility checker linked above contains most of that list). Someone tested 50 popular mods to see what effects they had on fps, here's the results.

Tip: You can sort mods alphabetically making them easier to work with using either the Sort Mod Settings mod.

There is a "zombie assemblies" bug in the game engine[github.com] which modders cannot fix: If you have more than one version of a mod subscribed, the game can't differentiate between them, even if you disabled the other versions. That causes weird problems, lag and crashes.

So, when using mods, always remember:

• If there are multiple versions of a mod, only ever use one version at a time.
  
• Completely unsubscribe mods you aren't using, don't just disable them.
  
• After making any changes to mod (updating, disabling, unsubscribing), exit the game to desktop to flush zombie assemblies from RAM

Each enabled asset adds extra load for your RAM and VRAM (Video RAM); even if you don't use it on the map it will still get loaded. And once it's on the map, it will put more strain on your GPU (graphics card).

When choosing assets, consider these things:

• Good asset authors often specify the number of triangles, texture sizes, etc., for their asset. If they've taken the time to optimise the asset, it's probably a good asset.
  
• TM:PE team maintains lists of known broken assets: Buildings[github.com], Vehicles[github.com], Props[github.com], Roads[github.com].

Removing broken and bloated assets will make the game more reliable and improve performance:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1846793796
Many workshop assets are acutally colleciotns of assets - a single subscription might contain a building and several props, or several variants of a network, etc. You can disable individual assets, even if they are part of a pack, via Main Menu > Content Manager > Assets screen.

This mod will help you browse and filter your asset list: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=814498849
By disabling assets you prevent their mesh (triangles) and texture getting loaded in to RAM (unless something else uses it). That will make loading faster and in some cases will improve visual quality of all other assets of the same type (by avoiding the need to rescale everything smaller to fit that extra texture in the texture atlas).

Updated: February 2020

Faster disk = faster loads, less lag during autosave and sometimes faster gameplay

The bulk of disk activity comes from loading the game and assets, saving your city, and the page file that we discussed earlier in the guide. If you run out of disk space, the game will crash.

NVMe M.2 SSD drives are currently the fastest choice, but are very expensive and they have limited lifetime (you'll need to replace them more often). They require a modern motherboard that has the M.2 slot, so you need to check if you have that before buying one. Note that some motherboard/processor combinations will reduce graphics performance (from x16 down to x4) if you install two or more M.2 drives, so always check your motherboard user guide first.

Tip: If you are using a Samsung NVMe drive, install Samsung Magician[www.samsung.com] to improve performance and update drivers.

If you can't afford or use M.2 drives, the next best alternative is an SSD drive. While still quite expensive, they are super reliable and still very fast.

If you can't afford SSD, then try and get a fast SATA drive. These used to be quite slow in the past, but recently they've improved a lot.

Most operating systems include some sort of disk optimisation tool, sometimes called a "defragmenter". It optimises data on your disk in such a way that it can be loaded faster, often prioritising the most frequently accessed files. There are also tools for cleaning up junk files which can save lots of disk space, allowing for larger page file and more workshop content.

On Windows 10, for example, you can use tools such as:

• Defragment and optimise drives[support.microsoft.com]
  
• Various disk cleanup tools[support.microsoft.com]

ProTip: Use Ultimate Boot CD[www.ultimatebootcd.com] to check disk for bad sectors (thanks to FireFlowerist[forum.paradoxplaza.com] for the tip).

ReadyBoost is a feature of Windows (Vista, 7, 8 and 10) primarily designed for potato computers. It can help overcome some issues assocaited with slow disk drives by caching stuff on faster disk drives. For more information, see Using ReadyBoost in Windows[www.winhelp.us] (Windows Vista, 7, 8 and 10).

tl;dr: AVOID RAM Cache!

RAM cache apps allow you to store regularly used files in RAM, which makes accessing them massively faster. However, anything that eats RAM is generally bad for this game. While you might get slightly faster loading times, literally everything else will be slower because the game will be starved of its much needed RAM.

As someone who regularly requests log files when tracking down bugs, the thought of this fills me with dread. However, I feel compelled to at least mention the fact you can turn off log file in case it helps anyone; it might save a few seconds on really old, slow computers.

To turn it off, add the following launch option:

Updated: January 2020

Test to see if your changes make a difference

This is probably what most people want form this guide. Before we can start improving performance, it's important to have a way to quantify it so you can check that changes you make are having an effect.

The most common way is to monitor "fps" (frames per second). The higher the fps value, the faster the game is running.

Steam has it's own fps display which can be accessed from main Steam settings > In-game section:



Alternatives include:

• Monitor It! mod - shows some fps and cpu stats in-game.
  
• Windows:
  
  • Nvidea GeForce Experience[www.nvidia.com] (either open the desktop app, or press Alt+Z while in-game, and then click the "gear" icon to show settings).
    
  • AMD Radeon software advisors[www.amd.com] (never used these, so if you know more let me know!)
    
  • MSI Afterburner[www.msi.com] (video: How to install and set up OSD)
    
  • FRAPS has an on-screen display feature[www.fraps.com] (note: Launch FRAPS after you launch the game, not before)
• Apple Mac:
  
  • Count It app[www.macgamerhq.com]
• Linux:
  
  • MangoHUD[github.com].

Obvious really, but if you have other apps running they will be consuming CPU and RAM resources. So close as may of them as possible. The improvement will be most noticeable on potato computers.

ProTip: You can use Autoruns[docs.microsoft.com] from Microsoft SysInternals to close down unwanted startup tasks.

Dedicate more system resources to the game:

• Windows 10: Type "Settings" in to the start bar and then choose "Gaming". In the sidebar click the "Game Mode" link and turn it on. See this guide for more info[www.windowscentral.com]
  
• Windows (all versions): Third party app, Razer Cortex Booster[www.razer.com] micromanages system resources to boost game performance. Also, Razer Cortex System Booster[www.razer.com] might be worht a look. There might be some privacy concerns with thrid party apps.

Updated: December 2021

Less CPU load = faster gameplay.

FPS Booster mods tackle specific bottlenecks in the game code.

A simple booster that improves performance of mouse position raycasting, giving 5-15% fps boost.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1938493221
A much more advanced FPS booster which includes the mini booster above but also significantly reduces UI rendering and font processing overheads. Read the description of the mod carefully, especially if you are on Linux or Mac.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2105755179
This mod includes an optimised tree rendering system which is faster than the vanilla game. Assuming you leave the tree limit slider in default position (ie. keep the original game limit for tree count), you'll gain some fps due to the faster tree rendering. Be sure to read the mod description page.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2527486462
This mod can double the speed of prop rendering - but read the workshop page carefully!
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2696146165
This mod has optimised versions of a whole bunch of prop-related mods (Additive Shader, Prop Snapping, Decal Prop Fix, Prop Precision, Prop Line Tool, Prop Resizing, Prop Painter...) which are listed on its workshop page. If you use any of those older mods, replacing them with the new Prop Anarchy mod will result in reduced city load times and less lag in-game.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2696146766
If you don't see any improvement to your framerate with FPS Booster mod(s) active, your graphics card is likely the main performance bottleneck of your system. If that's the case, reducing strain on your GPU becomes your primary goal...

Updated: January 2022

Faster graphics = faster rendering = faster gameplay

Fast modern GPUs (eg. anything above GTX 1060) won't usually improve framerate much, because CPU becomes the main bottleneck; but you will get nicer looking graphics, less lag on big resolutions, and be able to use graphics mods more easily.

"Integrated Graphics" (like Intel Iris) are not real graphics cards. They are designed for energy saving, not gaming. How do they work? They run on your CPU and use normal RAM. That's like a triple disaster for gaming. Not only will your graphics be weaker (and with less quality) but you just nerfed your CPU and RAM making everything else slower too!

On computers that have both integrated and dedicated graphics, particularly laptops but also some desktops, make sure you're using the dedicated graphics card:

• Windows - use Radeon Settings or Nvidia Control Panel[support.ubi.com]
  
• Windows - AMD: Set an application to use high performance graphics[www.amd.com]
  
• Apple Mac - use gfxCardStatus App[gfx.io] (free, open souce)
  
• Linux - I've never used linux, if you know how to switch graphics let me know!

See this guide for some tips on Intel graphics.

Graphics drivers are getting constant updates by manufacturers to fix bugs and improve performance, so keep updating them.

• Windows: Update direct from manufacturer website: NVIDIA[www.nvidia.com] (game ready driver recommended), AMD[www.amd.com]
  
• Macs: Mac driver updates are less frequent, often they come with operating system updates. However you can sometimes get updated drivers from NVIDIA or AMD websites. If you use Boot Camp to run the game under Windows, however, follow the guidance for Windows above.
  
• Linux: I've no idea how Linux handles graphics card updates - if you know please leave comment at bottom of guide and I'll update this section.

Graphics cards have a "Shader version" - it determines what features they provide. You can find what version you have in the game log file; search "Shader version" to find it (usually near top of file).

The game works best with shader version 50 or above.

If your graphics card has lower version, usually version 30, problems can occur - you'll see `d3dll` errors in the log, weird graphics glitches in-game, maybe even crashes. To fix, add the `-force-d3d9` Launch Option (or sometimes `-force-opengl` is better, particularly on older Macs).

Make sure your graphics card is running in high performance mode:

• Windows: Search for "Graphic Settings" in start bar, and under "Graphics Performance Settings" manually add Cities.exe as a 'Classic app', and set it to "High Performance".
  
• Apple Mac: From Apple menu, select "System Performance" then "Energy Saver" (the light bulb). Uncheck "Automatic Graphic Switching". (thanks LemonsterOG for this tip!)
  
• Linux: Not sure if there is such a feature on Linux - if there is, let me know.

Access these via Main Menu > Options > Graphics:

• Set a screen resolution that is natively supported by your graphics card (refer to your graphics card tech specs to find details). If your native resolutions aren't listed, fix that with More Aspect Ratios mod: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=561218257
  
• If the user interface looks blurry, fix that with UI Resolution mod: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2487213155
  
• Lower screen resolutions generally benefit older graphics cards
  
• Disable or reduce shadows - particularly effective on older graphics cards
  
• Disable film grain - most effective on old computers or weak graphics cards
  
• Reduce graphics quality settings - very effective on potato computers and/or weak graphics cards

Note: VSync can tank frame rate in some hardware configurations. Modern alternatives such as FreeSync (AMD GPUs) or G-Sync (Nvidia GPUs) are much better.

On old computers or weak graphics cards, turning off dynamic weather may give slight performance improvement.

GeForce Experience[www.nvidia.com] app recognises the game. You can see recommended settings for your specific NVIDIA-based graphics card and apply or customise them.

NVIDIA Control Panel app (usually accessed from '^' button in system tray) allows you to set additionaal app-specific settings under "Manage 3D settings".

The GTX 770 and older NVIDIA graphics cards are pretty weak and don't fully support DirectX 11. You can often improve reliability and performance on those cards with the `-force-d3d9` (force DirectX 9) Launch Option.

If using Zotac editions of NVIDIA cards, the "Zotac Firestorm" app has some tuning and OC functions.

If you have two NVIDIA cards, you can use the following settings to boost performance of the game (thanks to Shaowdane for this tip):

• Install Nvidia Inspector[www.guru3d.com]
  
• If you haven't used NVIDIA Inspector before, read this guide[wiki.step-project.com]
  
• Use these settings for your Cities:Skylines profile:
  
  • SLI Compatiblity Bits (DX1x): 0x202121F5
    
  • Nvidia Predefined # of GPUs to use on SLI for DX10: SLI_PREDEFINED_GPU_COUNT_DX10_FOUR
    
  • NVIDIA Predefined SLI mode on DX 10: SLI_PREDEFINED_MODE_DX10_FORCE_AFR2

Updated: December 2021

Reduce strain on GPU (Graphics) = faster gameplay

ULOD was developed to increase level of detail (more strain on GPU), however it lets you do the opposite too!
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1680642819
Try these settings:

• Tree LOD distance: 300m
  
• Prop LOD distance: 750m
  
• Decal prop fade distance: 750m
  
• Building LOD distance: Use game default
  
• Network LOD distance: 750m

The smaller the value, the faster the game will run. Play around to get your desired balance between graphics quality and performance.

While ULOD reduces complexity of stuff that is shown, Hide It mod allows you to completely remove stuff:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2513657277
The biggest gains come from hiding stuff that's very common, such as road-side props, billboards, etc. There's a huge long list of stuff - have a play with the settings to see what works best for you.

Hide It makes a load of other mods listed later in this guide somewhat obsolete. Normally I wouldn't recommend big "do it all" mods like Hide It, but it's just so much easier to use than having dozens of 'fix one thing' mods.

This mod reduces scene complexity (like shadows and props) whenever the camera moves, reducing lag while you move camera. There are some potential compatibility issues with other mods, so read the description carefully before subscribing.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2519929628

Updated: January 2022

Use the compatibility checker to detect if you have any laggy mods (the report will mention if they cause performance issues):

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2633433869

Updated: January 2020
If you spam your city with huge numbers of trees and props, that can cause huge fps drop.

This is particularly true if you are using lots of different tree and prop assets.

For example, if you only have 2 types of tree, that's only two tree textures that your graphics card needs to render the scene. However, if you have dozens or even hundreds of types of tree, then the texture for each one needs sending to your graphics card. That takes time, and if you fill its VRAM it will need to process the scene in multiple batches which takes even longer.

There are many occasions where I've gone crazy with Forest Brush, with like 50 types of tree and shrub, to create diverse foilage across entire mountain ranges. Big fps drop and I had to choose some specific types of tree and remove all of those form the map to revive the frame rate.

Tip: Forest Brush mod can sort items by triangles, etc., and hovering trees in its list shows details about thier complexity. When painting lots of trees, limit to just a few types of tree and minimise the use of any tree that's overly complex.

So try and limit how many tree and prop assets you use; the fewer the better. It's not so much how many times a tree or prop is used (that will still have an effect), but more importantly how many different types of them are used.

Updated: December 2021
If you have weak graphics card, getting rid of unwanted props can boost fps...

As mentioned earlier in the guide, Hide It is a great way to remove lots of clutter from the map and user interface.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2513657277

If there's a vanilla or DLC prop you never want to see anywhere, use the "Skip assets" feature of Loading Screen Mod. That way, it won't even get loaded in to RAM = faster loading time

Likewise, if there's a workshop prop you don't ever want to see, you can disable it - even if it's part of another workshop asset that you want to keep. Main Menu → Content Manager → Assets.. then find and disable the props you don't want; they won't even get loaded = faster loading time.

Roads have a load of props, and your map has a load of roads. People have actually taken time to comment saying this helped increase their fps. It's particularly effective on potato computers:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1117087491
Removes grass tufts and cliff boulders:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=547533304
Removes ferry route buoy props:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=949061920
Remove lots of ugly props from buildings to declutter residential and commercial zones:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=518456166
Remove pretty much any prop or tree from any building or even whole map (Increases game load time, but can boost in-game performance):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2197863850
Remember, always test! Use the fps counter stuff at top of guide - if something doesn't improve fps on your computer, ditch it.

Updated: January 2022
Limit amount of traffic or types of vehicles. Good for potato computers, and also useful for large cities where you're hitting vehicle, citizen and path unit limits...

These mods make game more realistic and also reduce amount of traffic which can gain you some extra fps, especially on potato computers.

Allows you to turn off dummy traffic (fake traffic that just drives in to the city and then out again):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1721492498
This balances your industry more, and greatly reduces the crazy traffic in farming district:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1562650024

You can prevent certain vehicles from spawning, which may help on older computers or weak graphics cards:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1548831935
Tip: Use Mesh Info (linked earlier in this guide) to identify bloaty vehicles and prevent them from spawning.

Removing seagulls (they're sort of traffic, right?) can gain you a few extra fps, especially in big cities and on potato computers. Also helps reduce strain on citizen limit:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=564141599
Removes animals; helps reduce CPU load and also less stuff to render for weak graphics cards. Also helps reduce strain on the citizen limit:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1706704781
Gets rid of dead people, freeing up space for the liviing. Reduces number of hearses on the road. Good for older computers:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=803074771
Even more drastic, get rid of death, garbage and crime:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=769744928

Updated: March 2020
These mods are useful for reducing load for older computers or weak graphics cards...

An extreme way to reduce GPU load is to render the world at a lower resolution (less than 100%) and then scale it up to fit the screen. The graphics will look awful, but it will greatly increase frame rate if your GPU is the bottleneck:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=812713438
Turning off tree movement may improve fps if your graphics card is weak:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1388613752
Turning off the clouds and fog can help with weak graphics cards. Although some users report this mod actually reduces fps so make sure you test what effect it has on your computer:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=523824395
Turning off problem notifications might help with weak graphics cards or older computers:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=917543381

Updated: March 2020
You can even speed up exiting the game to desktop with a mod!
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2037888659

Updated: January 2020

Performance tuned hardware is worth the effort

Windows users can use the free User Benchmark[www.userbenchmark.com] app to benchmark hadware components. It runs speed tests on each of your hardware components (CPU, RAM, Disk, Graphics, etc) and then compares them to results from thousands of other users around the world.

If any of your components are running slowly, compared to other users with the same component, it will tell you and then you can investigate why. Often you might need to update drivers (always get latest drivers from manufacturer website) or possibly tweak settings in your BIOS. For example, my memory was performing really slow (I forgot to set its speed in BIOS after replacing motherboard):


If your CPU or GPU overheat they will throttle down to a much slower clock speed, and everything will grind.

To prevent throttling, limit the frame rate (yes, I know, crazy, right?) with the "-limitfps" launch option.

Make sure your fans, fins and air filters aren't clogged with dust! I've had to vacuum dust out of my rig several times already to keep the cooling working at full capacity.

Liquid cooling is often the most effective, if you can afford it, but the liquid can corrode the cooler and clog it up. Do your research before investing time and money in liquid cooling!

Overclocking forces your hardware to run faster than it normally would, but there are risks involved: It can physically destroy your CPU, RAM and GPU.

Modern gaming motherboards often include automatic overclocking features that will do most of the scary stuff for you, but often you'll still need to read the internets and do some manual tweaking for god-tier results.

Overclocking the CPU will get much better results than overclocking the GPU.

Always speak to the internet before overclocking and make sure you have proper cooling in your rig. There's no point overclocking if that overheats your rig and causes throttling = it will be even slower than before you overclocked!

If you need help with hardware, a good place to start is r/pcmasterrace on Reddit.

Updated: September 2019

If you aren't an asset creator, skip this section.

Here's what CO had to say on asset creation:

引用自 CO_Dae：

The model size is not limited other than by Unity's limit of about 65000 vertices per mesh, but even approaching that is too much for single assets. To give some rough guidelines, the triangle count of the building models in the stock game ranges from less than 1000 triangles for the smallest and simplest buildings to about 5000 for large and complex buildings. A few exceptional buildings use up to 10-15k triangles. Vehicles typically have 500-1000 triangles, while trees vary from a few hundred for simple bushes to about 2000 for the more complex ones. Also note that a large number of props can also make the asset rendering slower, which is why there is a limit in the asset editor.

Please post details of your asset stats (triangles, texture sizes, etc) on your workshop pages so users don't need to guess what impact your asset will have on their game. Taking a screen shot of your asset stats shown by Mesh Info mod is a quick way to achieve that.

Please read LSM Guide for Asset Authors to learn how to optimise your assets for Loading Screen Mod. This makes a huge difference for end users, as it can save them huge amounts of RAM and greatly speed up game loading if the assets they use are optimised for resource sharing.

Also, please read the small guides at bottom of that LSM Guide. If your asset is throwing errors, users are likely to downvote it and unsubscribe it.

If you haven't already found it, head over to https://cslmodding.info which contains loads of excellent information and guides on asset creation.

Updated: December 2019

If you aren't developing mods, skip this section.

Make sure you're not using a debug version[github.com] of mono dll.

And check you don't have any DEBUG builds of mods installed. In particular, per-frame log file spamming can decimate frame rate.

The games' UI component system is slow, so please try and minimise the number of UI components you use. In particular, avoid anything that udpdates per frame (eg. `Update()` method).

If you want to speed up testing of your mod in-game, here are some suggestions:

• In LSM, disable "Load enabled assets" option, but keep the "Load used assets". This will greatly reduce loading time.
  
• See "Launching the App" section above to reduce app launch time.
  
• Bugfixing saves from users? See Tips for working with savegames[github.com].

If you can think of other useful things to add to this guide, or have any comments, let me know in the comments below.

If you found the guide useful, please consider supporting me on ko-fi[ko-fi.com].
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