After more than 15 years without GP4 I installed it and downloaded 1998 mod. The mod itself was good, but how performance files are organised, is questionable. The I look for more performance files and all of them lacked realism. There are two major problems with user created performance files:
1. They are based on the results and not on the real pace.
Like, if a rider has finished low or failed his qualifying attempt, he will have low performance, it's especially visible in rainy conditions. Like Frentzen on Williams had low performance in Austria 1998, lower than Shinji Nakano on Minardi in the same race. This is not real.
2. Most of performance files have the same engine power. I understand where it comes from: if you only need to adjust driver performance to come to the same gaps, it's easier than to adjust two parameters. Problem: cars underperform on fast circuits like Hockenheim or Spa and overperform on slow like Hungaroring. You have a crazy grip which cars obviously didn't have in 1998. And you cannot really use your engine to overtake as they have the same power.
This is why I decided to correlate performance files with times. But before I present here the result, it's important to resume the environment.
Base values used are: 800bhp, 15418 grip, 0 variance.
1. Correlation is performed in qualifying conditions, 0% rain, 60min session, 10 cars at the same time on track. This permits every AI driver to complete 4 flying laps before the end of the session with the least risk of traffic. So you are sure that 2-3 flying laps are traffic free.
2. 1998 circuits are used for correlation (in fact I used 1997 trackpack w/o Jerez, but the rest is the same as in 1998).
3. For each simulation I gave the same bhp, grip and variance values to all 22 drivers, mean value for each simulation was retained for the correlation.
4. Ace level is used
Bhp is varied from 700 to 800 with step of 25
Grip (or driver performance) is varied from 15018 to 15818 with step of 200 (I know it's a close range, it should be expanded to about 13-16k to draw better conclusions)
Variance is changed from 0 to 1000 (0, 100, 200, 350, 500 and 750)
Just to mention here, there are many misconceptions about the order of parameters:
[Team #00]
Name=Williams,Mecachrome
Performance=765,775,1969
First Driver=1,Jacques Villeneuve,14020,580,15031,296
Second Driver=2,Heinz-Harald Frentzen,14286,580,14785,296
It's:
For teams:
765=race bhp; 775=qual bhp; 1969=failure chance (according to GP3edit 4096 corresponds to 10% failure chance, but to my sense it's higher). Btw, I haven't yet correlated failure chance to be sure.
For drivers:
14020=race performance; 580=race variance; 15031=qual performance; 296=qual variance.
The most important conclusions (gaps in % of 1998 best weekend times, most of them are pole times except A1-Ring and Monza):
1. The most obvious: bhp and grip effects are track specific.
1.1. Bhp has the strongest effect (obviously) in Hockenheim, Monza and Montreal.
Like you have 0.8% bonus for each 25hp, but the dependence is not linear. For some reason, sometimes you have 0.9%, sometimes 0.65%.
Hungaroring is the least impacted by bhp: only 0.37%-0.47% bonus for each 25bhp.
Thoughts? Results can be polluted by internal variance or by mismatching gear ratios (for some specific bhp they can have different effect)
1.2. The same counts for grip.
Hungaroring is the most impacted with 0.57% per 200grip followed by Barcelona, Buenos Aires, Magny-Cours and Silverstone (all between 0.53-0.56%).
The least impacted are Hockenheim (0.29%), Interlagos (0.36%), Monza (0.37%) and A1-Ring (0.39%). Reason? Less corners = less impact.
But again, sometimes you have 0.05% less, sometimes 0.05% more for the same circuit.
2. Variance = 0 does not mean results will be the same.
In fact, there's still a huge spread in lap times (given that I compare 22 drivers which has 4 tentatives every session) even if the variance is 0.
But you can have 0.2-0.9% between the fastest and the slowest. This delta is also track specific. If we talk about standard deviation, it's 0.21% for Interlagos (max) and 0.065% for Imola (min). I don't know why, but it's a recurrent pattern. It's reproduced on various combinations of bhp and grip values. And Interlagos and Buenos Aires had the highest dispersion, Imola and Barcelona the lowest. On every single test.
3. Variance of 100-200 is practically invisible on some circuits.
For example: I modified variance from 0 to 100. On Melbourne I got closer field results for 100 (SD=0.126%) than for 0 (SD=0.164%). Then I increased it to 200 and got SD=0.155%. Only at values exceeding 350 I began to see some kind of effect. This is also track specific. For circuits with basic low variance like Imola you see dispersion immediately.
But even at high variances between 500 and 1000 when the effect of basic variance should be less visible there are situations when you increase the variance and the field becomes closer. It's still unclear how variance works disperses lap times.
4. What is sure that variance improves lap times.
And this is reproduced on all variance values and all circuits.
Again, the most impacted are grip-dependent circuits like: Silverstone, Hungaroring, Barcelona, Buenos-Aires and Magny-Cours.
Like, you adding 200 to driver performance in Hungaroring reduces your lap time by 0.55%. Adding 200 to variance reduces it by 0.22%.
The trick is: it's non-linear and track specific.
Increasing variance from 0 to 200 gives a different effect than from 800 to 1000.
Increasing variance from 0 to 200 gives sometimes 0.4 sometimes 0.7 of pure increasing of driver grip. In farmers words: sometimes is variance of 200 equivalent of 80-140 increase of driver performance.
This latter problem was already discussed on grandprixgames. In fact, in GP4 a random value from 0 to 1 is multiplied by variance and then added to grip (driver performance). This explains why it gives near the half of performance on average (although to my sense, the average bonus is slightly higher than 0.5).
This is different to GP3 variance where a random value from -1 to 1 is multiplied by variance (so the average remains the same).
So these are my findings grosso modo after some correlations. My times are still far from 1998 results, but they are already playable.