I've done a couple of 50-70 ft gaps but last time I tried one that size (~65) I thought the way many have said above : 'Better hit it a bit too quick than too slow...' Result : I must have flown about 90 ft, crash-landed on the flat behind the gap, broke a vertebra and wasn't able to do any sport for the next 6 months...
So what ever you do, watch a pro or someone else take the gap before you do it, and only then estimate the speed u will need, or even ask the guy directly...
So what ever you do, watch a pro or someone else take the gap before you do it, and only then estimate the speed u will need, or even ask the guy directly...