Tires in AC

I've thought about this for a long tine but never asked. What the heck is a semi-slick?

I'm familiar with slicks, DOT 100s and 200 and up street tires but I have no idea how semi-slicks fit into that.

I'm mostly curious because I drive a Porsche 981 GT4 in AC and the only option in is semi-slick but my actual 718 GT4 came with Dunlop Sports Max Race 2 [80TW but not a DOT] and the other standard option is Michelin Cup2 [180TW]. I actually use Goodyear SC3 [220TW].

In AC I use a Green track grip which seems to get me pretty close but not exact. Overall AC is a bit faster but I know from actual on track experience that I have more grip in certain places than I get in AC. Fast might get the grip closer but it would result in unrealistic lap tines. Optimum is just insane. It is all a bit confusing. I live with it but I'd like to know what I can do to be closer.

 

I compared longitudinal grip data between the sim and actual on-track and found the sim is anywhere between 0.15G and 0.3G higher. That's actually pretty significant, although weather could have something to do with it. Lateral Gs are also a bit higher but not quite as much, maybe 0.15G max. So semi-slick tires have a little more grip than 200TW tires using a Green track grip setting. Unfortunately, I still have no idea what that means in the context of my original question.

 

This is weird. Doesn't anybody know? I'm sort of thinking semi-slick might be a European thing but it ought to relate to something I can get here in the US.

 

Semi Slick:

Source: https://fmic.eu/198069-emperum-semi-slick-225-45r17-emp-2254517.html

You may know them as cut slicks I think?

 

That's definitely not a street tire. Those are nothing like a Goodyear SC3. They look pretty close to what I would call a 100TW tire. I wonder why AC only allows semi-slick for the GT4? I suspect most folks who take their car to the track on a casual basis probably run on the OEM tires, which for a GT4 would likely be a Michelin Cup2. That's around 200TW.

 

Is there a file where tire grip levels are set? I'm not above fiddling with that to get what I want.

 

I found a very old thread that suggests AC's semi-slick tire aims to represent a very high end street tire like a Cup2. One post mentioned that Cup2s were actually shown on an AC car using semi-slick. In spite of that I find the semi-slick tire on a Porsche GT4 running on a Green track generates a little more grip than the Goodyear SC3 on my actual car and Optimum is ridiculous.

Another post mentioned tires.ini for tire settings. I'll have to check that out when I get home. It may be possible to tweak the settings to get the tire closer to the GYSC3.

One problem with the Green track is in certain situations the semi-slick tire breaks loose a lot easier than the real tire. I have no idea why that should be. It may have something to do with the track setting itself. Maybe a tire with less grip on a Fast or Optimum track might work better.