Three makes in this Championship (Ferrari 512S, Matra-Simca MS650 & Porsche 917K) allow drivers to choose "modern" compound tyres which have been proved to offer an significant advantage on the track.
These alternative .tyr files take away the modern compound. The option to choose them in the garage remains but you will get the vintage "hard" tyre instead of the modern tyre. This also applies to the "inters" that the Porsche offers.
To apply this fix please follow the instructions.
1) Download
this.
2) This is what you do for the Porsche 917K. Put the file P917_F70.tyr file into GameData/Teams/ExtraCars/Porsche_917_K and allow it to overwrite the existing file.
3) This is what you do for the Matra-Simca. Put the file Matra_MS650.tyr file into GameData/Teams/ExtraCars/Matra_MS650 and allow it to overwrite the existing file.
4) This is what you do for the Ferrari 512S. Put the file Ferrari_512SCL.tyr file into GameData/Teams/ExtraCars/Ferrari_512S_Coda_Lunga and allow it to overwrite the existing file.
5) The three files with .saf as an extension are the original tyre files in case you need them. Keep them safe but not in any of the folders mentioned above or GTL will crash.
6) If you join the race server without this patch applied you may get a miss-match with the server based cars.