Mountain Biking with Heavy Rider and Rigid Bike I ride an early 90's Trek MultiTrack 700. It's a completely rigid, Cro-moly frame with 700c wheels, and, except for a new rear wheel (double wall rim) and cassette, all of the components are original. I want to begin riding some basic MB trails. Nothing fancy, no jumps or DH riding, just basic hardpack trails. However, I'm 6'2&quot; and 235 lbs. Will a fully rigid frame withstand the abuse of roots and ruts with a rider of my size? Or will I constantly be buying new rims, or risk breaking something more vital? According to my LBS, suspension forks for this style of bike are pretty much nonexistent, so if I need shocks, I'll wait until I can invest in a new frame.
Thanks for your help!
Edit: I rode my first hardpack yesterday, and it was a blast! I'll get a better feel for technique as time goes on, but the bike seemed to handle it like a boss.
The Multitrak is really a hybrid designed for light off road, on road and touring. You are right not to try and upgrade the bike parts. As long as you stick within its limits it will be fine. Enjoy the ride you have. If you enjoy it enough to justify it, save up for a new(er) bike.
Your legs and arms are the suspension.  If you learn to 'ride lightly', there is no reason the bike will not handle moderately rough trails. You need to unweight the wheels as you come up to bumps like roots and ruts, stand on the pedals and let the bike 'float' under you. The geometry is more aligned to road use, so its agility and stability won't be that of a full mountain bike.
You will need to pay close attention to the tire pressures - too much and you will have problems with traction, too little and you will have problems with punctured (snake bites from pinching the tube).  With no suspension its unlikely to can run low enough tire pressures for best traction and completely avoid snakebites, a tiny mistake can result in a heavy hit onto a trail feature (root, rock etc). I suggest starting with higher pressures and lowering them a little at a time if you feel the traction is too 'sketchy'. If you get a snake bite puncture, think about why, and decide of you need to bring pressures back up.