Where exactly are you getting time penalties? I've only managed to pick up some small penalties in the NGP section of the track in the two fast chicanes. Going 2 wide through those is tricky.
At least in the '17 Lexus softs work fine for a lap. They still have better grip than hards on a no stop run, yet they do have a less grip in the last third of the track. Since pretty much everyone runs softs now it doesn't really matter.
I haven't tried the 911 yet. I like the fuel economy of the Lexus. ...
One section would be Hatzenbach I suspect. There are real delays for me before I know I received a penalty. You come off the F1 track and do a continuing left turn, then you are on the Nordschleife, and you then do a tight left turn in first or second gear, then a short straight bit to an important right hand curve, where if you get to the left before the right hand corner, and you clip the right hand apex the higher speed you can get around there the better and you will carry the speed down to the next left right kink sort of ... I think I crossed the curb at that next left right bit because I felt I had lost a bit by not being clean there .... later I got the penalty. Otherwise I did not cross curbs except for where the curb is paved for going wide, which surely could not be a penalty.
I've also got one I think for crossing the curbing at Flugplatz ... when you leave those first twisty bits of the Nordschliefe, entering the high speed part you have a right then left kink and then you go to the high speed sections. So you leave the kink behind and full power you go and there is a time check as you go under something I think, and you have a high speed right hander coming ... after that high speed right hander, I try not to back off there at the right hander high speed curve but I have feathered for a micro second there (not sure which is fastest because the lifting of the throttle can change the car's direction) but I have also gone through there without backing off ... and I did in the beginning of the race and I then went marginally across the left curbing after that right hand high speed curve ... but not by much ... and I picked up I think a 5 second penalty for doing so. And I thought I did the corner perfectly at the time.
I will try the softs and pay attention to the tyre wear.
The mediums though - I am not much slower in practice on the hards curiously, but in the race (I have not had many though) the cars around me out accelerate me and that must be tyre grip I reckon ...
I was in second place last race coming towards the end of the F1 circuit on the first lap on mediums, having started in 4th or 5th place, and the pole sitter who was an S or an A+ who had an 8:05 time was coming up behind me, he had got hit in the first corner at the end of the F1 starting Pitstop straight... so I was approaching the end of the F1 circuit in 2nd place on mediums, things looked good for me. The right curve/corner which leads onto the fairly long straight which leads onto the left turn before the Nordschleife - the fast driver came off that right hand corner fast and was gaining on me in a Supra on that straight ... I pulled over and just let him slowly edge by ... I sure paid for that though, because some way behind, the 4th guy did not brake for the next sharp left hander corner leading onto the Nordschleife, he hit me very hard and I went into the red and white bollards on the right side of that entrance to the track ... I had to reverse out, and by the time I got back onto the track I was 16th. I think I also got a warning and a 5 second time penalty for driving too fast ... sheesh I just had thrown the race away ... on softs I would have been 2nd and 1.5 seconds further up the track.
I think I will turn my power down to half way after the first corner, and that should save the tyres. I'll have TC on 2 and that should save the tyres. Which is the tyre to watch out for?
The front left seems the most critical but on the mediums I had a fourth sown up but went into the sand at the Schwalbenschwanz which is the left hander before the final Karussel ... that must have been the right tyres I reckon ... darn that hurt I had someone close behind me and the section before that which is fast and winding but flat, I can go full bore there without lifting, the Porsche is amazing there, and I opened up a big gap there ... but i forgot about temperance and I was afraid of him behind me on the long straight, so I went for the corner hard and I guess the tyre may have had some wear there, who knows ... I got stuck in the sand and finished way way back ... with softs but I would have to be careful there I reckon...
I've not had a clean race and not had many either, and I love the Nordschleife ... its a bit frustrating.
It does not really matter if you back off either after making a mistake it just takes like 0.2 off the penalty and you lose more than that backing off.
B/S to B/B in two races not my fault , got punted from behind and got 8sec penalty wtf thats silly ...
. Help me Obi-Wan Kenobi, you're my only hope 
