Ages ago I plotted a 120k route to extend my max square to the southwest. This involved a lot of riding round Coleshill, Birmingham airport and northern Coventry and another 50k there and similar back home. I kept putting it off but finally did it as a mandatory route 200k audax a couple of weeks ago. This bagged 94 tiles and bumped my max square up to 48*48.
Urban routes can be fairly efficient in terms of distance for picking up tiles as there are a lots of roads to use. The traffic, traffic lights and junctions don't exactly help your speed though.
I also had a few mechanical issues resulting from a puncture picked up on a bit of canal towpath. I somehow managed to reinsert the rear wheel incorrectly and damaged the rear derailleur. This was beaten back into some sort of functional shape with a rock using a convenient cattle grid as an anvil
A 150k ride out to the Kettering area on Tuesday added another 20 tiles and bumped my max square up to 50*50.
To my eye that top edge 'needs' tidying up a bit and I reckon that a trip to Newstead Abbey and Southwell should sort it out