I have also had trouble tuning some of the cars for race C not sure which, I also couldn't get the game to save the settings think it could well have been the TS050.
I had the gearing lengthened on the Group C cars. I did that by changing the setting in arcade mode time trial with BoP on. The settings I had for the time trial were kept for Race C. Speaking of which.....
I gave Race C another go, this time with the R92CP, despite my previous bad experience. Driving the other two Group C's had helped. I shaved about 1/10 off my Sauber time, and qualified P12

. The first 2 positions were DR/A, P3-P11 were DR/B, a couple of Bs, Ds and a C behind me, and behind them with no qualifying time, an A, B and C. Full grid of 20. Let the mayhem begin! There was a guy in P5 running a Sauber, the only other Group C. I wished them luck. In the end I did decided to post a warning that I'd be braking early in pre-race.
The race starts and I'm surprised that I'm still P12 by the time we hit Mulsanne and no one ran me off the track. I picked up a position on the strait, but just couldn't quite catch P10. I'd get close but then we hit corners and I was almost keeping up. Watching the replay, the guy behind me was having all kinda of trouble trying to get past me, and just when he was in position, we'd hit a strait and I'd pull away

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He fell back and I was being harassed by a guy in a 787B. A few times he got ahead of me but then I'd get ahead of him on the outside as I was turning. I thought all was good and my passes were clean, but looking at the replay, I was constantly in his way on many of the corners and on those occasions where he did get ahead briefly, I'd get ahead on the outside cut across him. The reason I looked at the replay was because on the final lap he was coming up on the outside, when he got a 2/3 overlap with a car's width gap between us (ie, enough room for 3 cars side by side), he rammed me with the front corner and slammed me off the road. I didn't know the cause of his road rage so I wanted to see how I'd slighted him. Turns out one time when I'd turned in front of him there was contact and he ended up in the sand. I'm guessing he'd had enough

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The punt aside from slowing me down unsettled the car and I ended up in the sand and loosing a place. The race timed out with me in P12. He ended up with a red SR. As for the guy running the Sauber, he finished 2nd

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So the end result. SR remained 99, DR went up by more than 300. Another day above DR 1

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