I am currently riding an old Brompton (about 10 years old I think). I cycle 2 miles to the station, then 5 miles across London each day, each way and have been doing so for the last 5 years. Over the last year I have been getting knee problems for which I have been having physiotherapy for the last 9 months with only limited results and now facing a trip to see a consultant surgeon. The knee problems started when I started upping my road bike and mtb mileage, but has been lurking for many years (I don't run any more either). One of the things that I have noticed over the last year is that my knee gets sore when I get on the Brompton after having done some longer (35-85) mile rides over the weekend, or recently I managed 8 pain free days over xmas (160 miles in 8 riding days out of 12, av 30 miles a trip) only to get on the Brompton and get a pain in 10 mins. It appears that the Brompton is often the straw that breaks the camels back, one factor in the equation to be eliminated.
I can't help feeling that the riding position is to blame. I ride my other bikes well set up (e.g. according to Andy Pruitts book) and the Brompton with as long a seat as I can get and seat as far back as I can, but I still feel upright.
Looking at the new S-Types I wonder if this position would help change my geometry on the bike enough sort things out. I have heard that the more recent Bromptons are longer than my 10 year old is that true? Or do I need something more stretched out?
I am looking for any opinions or suggestions. I am open to the idea of buying a new bike or modifying my existing one. I am not tied to the Brompton, but the compact fold is very important for the train leg of my journey. I have not got around to test riding an s-type yet or anytyhing else, but it is on my list of things to do when I can get over to a shop with them in.