As many have pointed out there are a ton of variables for candidate bikes for mid-drive conversions. There is also the issue of what the bike is to be used for. Recreational pedaling on smooth ground doesn't require an especially burly bike, but even there it helps a good bit for certain components on the bike...especially drivetrain and wheels. Now, for actual mountain biking...not just dirt bike paths...the bike had better be a decently built frame with very solid components.
Even as an older guy myself, I absolutely pound my Santa Cruz Nomad/BBSHD in rough terrain. My Nomad weighs about 50 pounds without the battery...I use a backpack setup. So far I notice the rear wheel takes a serious beating, requiring more attention to spoke tension. I have broken one good quality rear derailleur...clutch failure. I use an XT rear hub with a solid bolt axle with track nuts. The cassette body is steel, most aluminum cassette bodies should be avoided. And if your bike is full suspension, I highly recommend all-mountain, enduro, or DH level models for pivot and suspension component durability. I even run a dual crown fork on mine. Strong, quality hydraulic disc brakes are a must. Again, this is all for serious mountain biking in rougher terrain.
View attachment 101393 I’m more the casual rider that would like to go off road now and then but not too rugged terrain like some wooded trails etc. etc.
