This will be a long one, but please take your time to read. Actual answer on your question will come at the end of the overview 👍
Few bulletpoints for the start:
[*]beauty of Gran Turismo is that you can drive it as you like with tyres which you like
[*]default compounds that come with cars are not *factory spec* (with exception of race cars which come on Racing Hard compound which is *factory-spec* for race cars)
[*]*stronger* compounds than theoretical *factory spec* are always default on street-cars in Gran Turismo series because of the playability for the less-demanding drivers
[*]default *stronger* compounds are also fitted with controller players in mind - in order to experience *factory-spec* compounds and no-ABS driving, driving with the wheel is absolutely recommended
[*]tyre-compounds differences in GT series are not made to resemble any particular real-life tyre. In their base they are very simple multipliers of the basic-grip model, as detailed by the great research done by
Calan in his original thread. Follow the link in his post to see Google Docs spreadsheet of cars/compounds combo he researched in detail
[*]the complete logic of tyre-compounds in GT series is not *finite* by any mean, it is very arbitrary. For instance, you can't say how one tyre type resembles some particular real-life tyre except when you get strict notion about such from the PD (example of such can be found on
Japanese GT official site where it clearly says how the Japanese finals for FT86 championship were driven on Comfort Hard (N1) compound:
[*]the beauty of Gran Turismo comes for need to discover things - and search for the good combination of compound is one of the greatest beauties of the game
[*]have fun and start exploring - because in Gran Turismo series the actual journey is always more exciting than the destination
Purpose of the Comfort/Sport (even Racing for race cars) tyres is not to teach people about fact how grip is limited but to try to simulate as possible as true-to-real grip/physics experience - in constrains of GT5 tyre-model as said above - when driving a particular vehicle. So in order to *learn* either tyre/vehicle dynamics you should always try to opt for the type of compound that resembles the factory-spec as much as possible.
And to answer the ultimate question about which type of tyres are factory-spec for each vehicle I have to C/P this overview I did for one other forum.
Comfort tyres of GT5 are evolution started in Gran Turismo 2 game with the introduction of the Control/Simulation tyres.
Gran Turismo 2 was the first GT game that introduced adequate suspension and tyre physics in the series (first GT was very simplified in that area, despite being above majority of other games backthan). With that came the first fundamental introduction of selection of tyres as we know it today, but in the slightly different form. We had Sports, Racing Slicks, Dirt and Control tyres.
Control/Simulation tyres were the first step towards mimicing the *real-life* tyre slip/grip in the series, which is absolutely described in both in-game explanation and in game-manual. None of the cars were initially equipped with the Control/Simulation compound but player could do it for himself in order to experience the more *accurate* feel of the car. As manual says, Control/Simulation Tyres are tyres which are as close as possible in characteristics as real tyres... (player) can experience a simulation of real driving which does not feel like a game. Those tyres require quicker braking, careful steering and delicate work with the accelerator. Those are tyres specific for the surfaced roads.
Gran Turismo 3 continued the philosophy of Simulation (compound), clearly explaining how those tyres offer only slightly more grip and are only suitable for professional drivers.. Same logic for compounds remained, with offering Sports, Race and Dirt tyres for *normal* selection.
Control/Simulation tyres in both games were always very cheap - same philosophy that remained later for GT4 and GT5 - in order to make them accessible for interested drivers in any moment. Also, no cars actually came equipped with those - road cars were always equipped with Sport compound while race cars were equipped with the Race Hard compound - logic we still have today.
Gran Turismo 4 was the first game in the series that introduced Standard/Comfort compound by name (if I recall, US game was naming them Standard, while EU release called them Comfort - in Japan they were already called "N" if I recall well from my Japanese copy of GT4) as *normal* selective compound with A-B-C range (hard/medium/soft or as GT4 was naming it, Economy/Luxury/Road), again with lowest price possible (Standard tyres carried no price - 0 Cr - in order to make the fully accessible at any moment). When you were purchasing the car (road vehicles) there was a special disclaimer after each purchase that said ...(cars are) fitted with the Sports Medium for circuit racing. For factory spec purchase Comfort (Standard) compound.
GT5

rologue introduced *Japanese* naming for compounds for the first time in the western-releases, as famous "N"/"S"/"R" (1-2-3) logic. N1 were Comfort Hard, N3 were Comfort Soft, etc.
Also, in the in-game manual - that majority never actually read properly - there was extremely detailed explanation of tyre-types and logic of their use. All cars were coming equipped with the Sport Hard/Medium compound by default (Racing for those few race cars), but with following explanation presented in the options - providing a comprehensive list of fitting-recommendations for various *types* of the cars, covering majority of similar models in game depending of production year/power/drivetrain type/weight
Gran Turismo 5 continued the same philosophy/principle where Comfort compound should the one that corresponds with almost all *factory-spec* vehicles, with notable exclusions of some supercar models that would probably be equipped with Sports Hard compound as their factory-spec tyre, but those are minority.
Greatest *issue* of GT5 is omission to actually present that philosophy in any of game-manuals, as Prologue did: either game-manual, in-game digital manual and even in Apex book that came with Collector's Edition.
However, in some points game clearly implies such selections, such as Comfort/Soft tyre-compounds being mandatory in some Seasonals (latest Classic Car seasonal being an example of imposed Comfort compound, of recent F1 seasonal where you can race F1 only on Race Hard), etc. But all those *implications* are unfortunately very vague.
Me and my friends are driving GT5 with the above Prologue list used as foundation for tyre-compound-choice since the very first day of GT5 release. After Spec 2.0 update it all come to place 100%, and current introduction of latest physics model (post 2.06) made it even more enjoyable. Of course, we use the above list only as guideline and we never use any compound other than Race Hard for the ultimate racing models.
Now, to finally answer your question
In order to "learn" you should go from bottom to the top. So, in my opinion, true way would be Comfort > Sports > Racing. However.
It is not about where you will *start*. It is about what you will actually *use*. In my opinion - and that is the logic my driving friends are also using - we only use factory-spec cars on proposed (suggested by above list) factory-spec compounds.
For in-game racing (A/B Spec races, Seasonals) I always use the same compound as AI is using and I try to find factory-spec car that can win particular race without any tuning. It became the ultimate way to experience Gran Turismo for me and I would never come back into the realms of heavy-tuning or any type of tuning than rudimentary necessary one. When I look at my GT1 garage and see all cars made to be 700-900HP with all installable-parts on I only laugh
If you opt to drive majoirity of cars under virtual *factory spec* than you should try to think in the line of: what tyre compound would fit on this car in the real-life? And list above can provide you with the necessary guidelines and give an insight on the logic of the game.
But there is one thing to take into concern, and that is ABS. Experiencing tyres is absolutely connected with driving with no ABS (at least if you are so lucky to drive with the wheel).
However, that is even lengthier subject than above

so if you are interested please check this overview:
https://www.gtplanet.net/forum/showthread.php?p=6921935#post6921935
You should *learn* from the bottom up. If you learn to control cars on Comfort/Sport compound you will have no problem to push to the limit with the Racing compound. BUt if you start with Racing compound on all cars, you will be lost with the grip-properties of lower-grip compounds.
👍