Mountain bike tires. I also ride road but not nearly as much as mountain bike.
I have to disagree a bit here, I think steel frames are way overrated. The bike frame is not meant to be a shock-absorbing mechanism; that’s what the air-filled tires are for. I’ll concede that frame stiffness may make some difference if you’re using a road bike for racing, and you’re using the narrowest tires available to cut down air resistance and shave a few seconds off your time. But for the rest of us, moderately wide tires will more than make up for a stiff aluminum frame.
Also, the kind of frame you’re talking about would typically come with antiquated components. It’ll be difficult to use for a novice, and difficult to find replacement parts.
Your knee would have been a bikefit issue, not an issue with a crappy bike per se.
Possibly, and technique may have had much to do with it, too (too high a gear, too much pedal pressure). However, the better bike is probably not particularly well set up for me, and the problem has not come back. So YMMV. But I am not using it the way I used to, just a couple of times a week for fitness.
Si
Also check with some local Triathlon and cycling clubs - I recently bought a Trek Hybrid for 200.00 used from one of the women on another message board I belong to - it was a good deal and I love my “new” bike.
Certainly blows the old MTB (free to me) out of the water.