Theres a special ride height measuring tool? Not just some string and a tape measure??
Im in Hertfordshire, about 10 mins north of Hertford.
Having thought about it a bit more, 245mm ride height cannot be vertically from the rear axle to under the cans - it would be like riding a chopper with front out and the back really low, serious handling issues, even if it could be lowered that much, which I doubt.