I've done 16 miles round a resovior on a Base t19 with 22-18 gearing, was a challenge I must admit, I've ridden around a bike track called Bedgebury a number of times if anyone on here knows of it, I think it was around 15 odd miles, It's good fun, and if your with mates its great, you forget how far you actually ride and you wind up racking up the miles before you know it!