I have no clue. I wouldn't say I have experienced anyone going 120-140mph but I can remember the first caravan I went on the group was going 100mph on a stretch of road that I had never gone over 65 on!
I remember just being in shock on how fast everyone drove and was a little scared to go on another caravan again! So what I do now is just go at my own speed and if thats not fast enough its not fast enough thats why I have Nav ill find the end spot
