I always know that roadies are faster than foldies and recently orgz a comparision ride. The fastest foldie I have, the Dahon Speed Pro vs 3 roadies. 9 of my Dahon Club riders (all SP and one MU P8) joined in as well. This was for a 4.5km sprint on a relatively flat road with some very slight descents & climbs.
2 of our strongest riders manage to keep up with the roadies at 35-40kmh. I max 51kmh on the slight down slope on Schwalbe Marathon tires (not as good as Stelvios for sprints expectedly). At the finishing point, #1 roadie (Ridley Carbon ridden by a young 23 yo guy) was 20 secs ahead of #1 SP. #2 position was another roadie with #2SP just at its heels. #3 roadie was in the middle of the pack.
So in this rough shootout test, roadies are indeed faster as expected. In another race over 160km (with the same rider), the difference is even greater - abt 10%. Would this be your experience as well?