My Diaries

A Lurid Tale of Obsession, Depravity, Wits and Attempted Wit

Fri Jul 2, 1999

Detailed Description of AI in Gran Turismo

Newsgroups: rec.autos.simulators

Subject: (long) Detailed Description of AI in Gran Turismo

People have expressed interest in Gran Turismo as a simulator, and some have indicated that the AI cars are reasonably good. I suggested that, at lower levels, it is not so good because the cars try so hard to let you win. I thought people might be interested in more detailed qualifications.

First off, Gran Turismo has "Arcade Mode", and "Simulation Mode". Forget about Arcade Mode; it's useful for learning the general layout of some tracks, but not details (all bumps are exaggerated in Arcade Mode). And the races are all two-laps, and the AI is of the pesky and bothersome variety.

Now, in simulation mode, Gran Turismo makes you do a lot of work before you can race the races a simulator aficionado will consider "good".

You must earn three "licenses"; B, A and IA, by passing a set of 8 tests for each. The IA tests actually take over a minute for each trial, because you must complete a whole lap, in an untuned car no less. In addition, you must earn money (Credits) to be able to afford to buy cars and tune them. You start with Cr10,000 which lets you buy used cars only. A '93 Civic 3dr si is a good initial choice. You then race the dreadful Sunday Cup a few times to get cash to improve it so you can win the Clubman or GT cup, and buy something better to enter other races where you can make real money. The series with the best remuneration is the "Normal" series, which simulator aficionados may hate because you can use only "untuned" cars in it. A Dodge Viper does well here, but it's an hour or so's worth of well timed exaggerated slides to earn up to Cr400,000--about enough to build up a car good enough to enter the good races. Another approach it to take a really fast tuned car (or cheat and take a racing-model) to the fifteen-minute "MegaSpeed Challenge", and get close to Cr100,000 for fifteen minutes work.

If you have a GameShark PlayStation, ahem, "enhancer", GameShark web sites will show you how to patch around all that, but an easier solution would be to obtain the Winter 1998 Playstation Underground Jampack CD which has a memory card download which gives you all three licenses, a garage full of interesting cars, and about Cr2,000,000,000 of simulation money. That turns the game from a sort of "role-playing driving game" into more of a pick-and-choose simulator. The CD packaging for the Underground Jampack CD does not explicitly indicate the presence of the particular download. If you have a friend who already has downloaded the CD, you can copy his memory card. There might be a copy DexDrived to the Web somewhere, but I can't find it off-hand.

The Gran Turismo Manual gives the following ratings for its various series:

But, even with my semi-editorial comments, that doesn't give the whole story. Competition in the GT-World Cup is noticeably "stiffer" than in the USvsJP(etc) series, and individual races in each series exhibit different competition characteristics. E.g. USvsJP AI seems to start strong and end a bit weak, while UKvsUS starts a little weaker and ends a bit stronger. Many series allow you to cheat and enter a racing-model which generally totally dominates.

Essentially, any but the "professional" races seem to have a noticeable "handicap" algorithm which causes the AI cars to wait for you. This is very encouraging when you first begin. The algorithm is such that it gives more help to powerful cars with good acceleration. This at least allows you to set challenges by gradually using weaker and weaker cars in those series. But, in general, it gets annoying after you've mastered it.

In any but the "professional" races there seem to be two speed thresholds for each race. Achieve one speed, and no car will attempt to pass you, but they will stay right behind you. There is another threshold you must achieve in order to start leaving the cars behind. This has the unfortunate effect that if you are driving between the thresholds, discretion is really the better part of valour because, unless you are trying to set a personal best, you are better to take a tricky corner slowly and safely rather than take a little risk to go faster; unless you pass the second threshold, that same car is still going stay the same time behind you. And, as I indicated earlier, if the cars get ahead of you, they slow down noticeably to wait for you. Study the GT or GT-I Cup demos in the "Replay Theatre" and you can see this effect. Also notice how, to make a good demo, the Viper driver in the GT demo deliberately scrubs off speed on every corner so as to avoid leaving the AI cars behind).

Anyway, I've not seen a lot of other examples of AI cars, so in some sense I'm talking abstractly. But I can see a lot of good things in the AI cars in Gran Turismo. They really do seem to be governed by the same physics model you are (but of course AI finds some things you find difficult to be easy, and vice versa). That is very good.

Contrary to game reviews based on perfunctory playing of the game, the AI cars do make mistakes, both small and large. This makes things very exciting at times. Perhaps the two best races in the game are the penultimate races in the "Normal" and "Tuned" series; at "Deep Forest Racing Way ii (reverse)" in Normal, and "Autumn Ring ii" in Tuned. In the Normal Series, an AI Honda/Acura NSX usually dominates, especially at Deep Forest, but at turn 4 (assuming the preceding high speed bend is turn 3), just before the first tunnel, it often enters too fast and loses control and time as it slides wide. It will do this in a reckless bid to pass you, and also when it is ahead. So you cannot take your driving cues from him; you must drive your own race and hope to take advantage of a mistake like this. (Once I bumped the NSX off-course on the very first turn, and it got stuck behind the other star, a Toyota TRD3000GT, and finished an unusual 3rd. I watched the whole replay, and, sure enough, the NSX had tried to pass the TRD at that corner, but flubbed it).

In other places, the AI cars make mistakes in fine details of their line, usually when exiting slow corners. In contrast, they dominate most fast corners since their AI allows them to explicitly calculate the optimal speed to reduce slippage. Exceptions are corners where a drift works really well, and, also a particular fast corner after them main straight of the two reverse "Grand Valley" courses. This corner does not suit heavy drifting, but they seem to generally take it even slower than is reasonable for driving--this might have been done deliberately since, even so, early in my playing I found it very daunting how deeply they did go into this corner before braking. I made it a bit of a mission to learn that corner intimately, actually, so maybe that's why my "I" is now better than their "AI".

The only time the AI driving seems unrealistic is when some "alarm" seems to go off and they decide it is time to pass you. On some corners this is done nicely. At turn 4 (assuming the first slight esse is turns 1+2) at Autumn Ring ii, the cars will often nicely go by you on the inside as you enter a little too late and wide. But at other times they just sort of force their way around your outside, often ignoring any contact with you unless you manage to nudge them clearly off onto the sand or grass. That is somewhat aggravating. Before my skill developed, or when I tried slow cars, I had seen this happen at all levels of racing.

So, both the Normal and Tuned series provide quite a nice challenge, and also the GT World Cup (abbreviated GT-I). While the Normal Series is dominated by one car, forcing you to win almost all races in order to win, the Tuned Series is not so dominated, and this allows you the challenge of holding things together in one race to gain second instead of falling to fourth, so that you can win the series with 30 of a possible 45 points. (In contrast, in the Normal Series, you can really only afford to lose one race, so need to risk more to chance first--but, in general, the Normal seems "easier" than the "Tuned"). All three series end with the challenging but silly "Special Stage Route 11" course--a night time maze of twisty passages, made doubly silly by the fact that you, as a human, can cheat your way far ahead of the AI cars once you learn that you can get far far ahead of the AI cars by making severe use of walls. Slide gently into them and accelerate while pulling off them--much faster than taking the corners properly. Similar techniques can be applied at the two All-Night 30 laps races, since they take place on that same track.

In contrast, the jewel of Gran Turismo has to be the Grand Valley 300. This is 60 laps of a 5km (3 mile) road circuit, with many sand traps around hairpins and only one "cheat wall", (and a fairly sticky one at that, although a well-timed rear-end bounce off it usually helps more than it hurts).

As someone coming from the likes of "Superbike Challenge" on the Commodore 64, I would have felt I got my moneysworth if Gran Turismo consisted of just the Grand Valley 300, together with a set of reasonable cars to compete in it. The downside of the Grand Valley 300 is that the AI cars run very predictably. A particular AI car as an entrant will motor steadily to a particular time +-10 seconds. Sometimes you get good competition between those cars. With most of the good cars (USvsJP etc prizes, Cr500,000 models, and race-modded TVRs and Dodges and top-line Japanese models) you can easily win this race by a couple of laps or more, by keeping to a schedule. The AI cars are sort of dumb about changing their tires. I've come to the conclusion that changing every 12 laps, or 10 for some cars, is best. (15 for a race-modded TVR Cerbera) Now, obviously it is, in general, best to change tires at regularly spaced intervals, (especially since tire wear effect consists of a gradual effect followed by a somewhat sudden, and, I think, a bit exaggerated severe effect) but the AI cars do not do that, and lose time by waiting until they encounter the "severe" effect. They seem quite pathetic sometimes when you lap them while their tires have nearly disintegrated. In addition the AI cars probably do not drive quite as fast as you can. (quite?--not nearly!!) Well, except, in my case, for the NSX-R LM GT2. I hate that car. The AI one dominates the race, but I couldn't get my copy to go nicely.

Finishing a Grand Valley 300 does require mental effort and concentration, and leaves you pleasantly exhausted. (Not so pleasantly exhausted in my case when I tried it and lost with the Chaser LM; must give it a reprise sometime. Maybe. Ick.--That Toyota Chaser LM is probably the first "race-modded prize car" you will stumble across, since it is awarded for winning the relatively easy GT Cup, and it seems nice at first, but is just too heavy and clunky to be pleasant to drive, but it does sit there in the game as a "challenge" when you get bored).

The predictability of the GV300 finishing time does allow you to set challenges; you can run two lap "time trials", or do "practice runs" of the GV300 course (the latter gives you "tire wear"), and try and find a car with which you appear to be marginally capable of winning. Racing with such a car will be quite exciting because you should pit before the AI cars, drop back, and regain placings later. My wins with the special model Mitsubishi GTO (I nickname the "twintubbo"), and the prize Viper GTS-R were like that. I *think* I'd win more cleanly with those cars now, though.

I should make an additional note about the GV300 AI racing. The field consists of random entrants, and, if none of the entrants are "strong", you can get a very slow race. In particular, I saw one race in which the fastest AI car was the Subaru Impreza, and it finished in 1-43:32.9, whereas the first AI car usually finishes in 1-42:00 +-10 seconds).

Oh well, I seem to have rambled on and given an idea of the flavour of Gran Turismo, describing things I perceive a racing simulator enthusiast would like to know, but did not really stick to my stated topic of discussing the Gran Turismo AI.

I guess I'll lose marks for that.