What the hell is PTMu? – short history of the mod

PTMu (Polish Tyre Mod for Shift 2 Unleashed) is a complete tyre physics overhaul for Shift 2 game aimed to convert this title into simulation. If you ask ‘how do you want to turn NFS into a sim?’ the answer is quite simple but the road to reach that conclusion was long and bumpy.

Firstly let’s start from describing what Shift 2 by Slightly Mad Studios really is from physics engine side. In short both Shift games are based on Image Space Inc. pMotor engine used in GTR, GTL and GTR2 simracing titles by Simbin. Later on ISI made pMotor 2 used in rFactor which has improved tyre physics model (among other important changes but let’s stick to the rubber for now).

SMS owned older version of the engine with quite obsolete tyre model. However instead of buying rights to updated pMotor they decided to hire Eero Piitulainen which was a physics developer for Richard Burns Rally simulator. If you don’t know RBR is THE best rallying simulator made to this day. He was also responsible for physics in Driver’s Republic. Never heard of this title? Well unfortunately it was never released so it’s natural to know nothing about it. However both RBR and DR had few things in common – cars felt natural to drive, over the limit control was good and force feedback effects were top notch. But let’s see how good it really was with our own eyes in the astonishing 240p!

Quite decent isn’t it? So let’s get back to Shift 2. Mr. Eero was hired and he coded new tyre model for SMS new title. However somewhere between release of first and second Shift he was no longer a part of the team. He was either fired or his contract ended. SMS stated the latter but who knows. What we do know for sure however is that this tyre model was flawed and actually never finished in both of the Shift games. Tyre stiffness was not dynamic and weight transfer was too sudden at times. Also there was quite a bit of delay in steering. Lagged steering is a ‘no-no’ for any racing game, not to mention a sim. Many of the issues were corrected in SMS newest child – Project Cars – but the company had to hire another physics developer to debug the model. They are still (end of 2013) working to get it just right for various cars. Patch for Shift games never appeared.

However back in 2011 I didn’t know about any of the issues with tyre model. Official statement of SMS was that tyre stiffness was just lowered to allow easier control for gamepads and keyboards. This sounded sensible to me and the other modders. First tyre mod for Shift 1 was made by a guy nicknamed Juls. It was called Sharp Tyre Mod and a lot of people liked it, me included. Tyres were stiffer, cars easier to control and it fixed some of the problems. Another thing made by this smart fellow is a small .dll file which decreased steering input lag. Later on Juls made updated version strictly for Shift 2.

The first version of PTM was made between 2010 and 2011 fueled by our need of even stiffer tyres. At first we tried to just multiply the vanilla stiffness values. Around PTMv2 it came to me that this simple solution won’t work the best. Next iterations of PTMu are a mix of gathering real stiffness data, trying to plug it into the files, testing, balancing. We end up with decent result overall but still not enough for us. Too little data was actually useful and tyre model wasn’t really cooperating with it. The biggest problem was the inability to use same tyre stiffness for front and rear tyres on RWD machines. Car would turn very aggresively even with little steering inputs (mind you – on the understeering setup based strictly on real data). Undriveable really. The only working solution to this was fixed stiffness ratio for front tyres – 70% worked quite well. However this created another unpleasant thing – tire induced understeering. It was not so bad because setups in S2U are mostly oversteering so the “driving feeling” was evened. We decided to stop at version 1.74 because we thought there is no other way to improve the mod. Stiffness is set to as realistic levels as possible as well as grip. Slip curves, slip peaks and load settings were not working as in ISI sims or were limited so those were chosen literally to “do no harm”. For example LoadSens (curve of grip to load relation) is fixed for front and rear tyres for particular tyre file. But one file represents not only one compound but five compounds. So we get stock, high performance, semi-slick, slick and super slick tyre upgrade covered by only one file. Thing is only stiffness and grip values have multipliers that change tyre physics based on the current upgrade. In the end we get range of Prius-like narrow rubber to GT slick with only one LoadSens curve – which is a bummer. Same for slip peaks, slip curves, camber effects, speed effects, rolling resistance.

Anyway – year later our mindset was changed a bit. After all there is an option to make stiffness values dynamic. So we will improve the mod. It will be more of a evolution than revolution though. At this moment PTMu 1.75 is on our workbench along with a little comeback of PTMuArcade. This time modification will also include engine files with corrected engine braking as well as chassis files with updated inertia. We can’t give any release date other than overly used “soon” because PTMu is only one of our current projects.

In the meantime you can take a look at how Zonda R handles with PTMu 1.74 on Green Hell. If you would like to try the mod it’s available to download in Modifications or through Nogripracing website .