I use the time xs on my mountain bike and speedplay x series on my road bike. I love float and I love both systems. I also had some knee pain when I rode on my road bike but after getting a bike fit all is fine. Seat height, foot position, handlebars, all that is very important. At least for me it was. I can ride all day on either bike with no pain except the ones I inflict (the occasional tumble LOL) on myself.

Sue