A couple of months ago I bought a Mongoose XR-Comp mountain bike. Over the last 2 months I've covered about 380 miles on it, mostly over desert terrain. I really like this bike, however, I had to return it to Wal-Mart because of the quality of the inner tubes and unavailability of aftermarket alternatives to the inner tubes that Pacific Cycles provide with the bike.
During the two months that I had the bike both the front and back tire inner tubes split. I am guessing that this happened for one or both of the following reasons: (1) The inner tube supplied is 1/4 inch smaller in diameter than the wheel diameter and/or (2) they are very low quality.
Usually this wouldn't be a concern because you can buy high quality replacements from companies like Bell. However, because of the design of the wheels these inner tubes require an extra long valve stem and even though I live in the 6th largest city in the US no one carries stock of this type of inner tube. Even if they did it's inconvenient having to replace one a month.
The only way that I managed to replace the inner tubes was by calling Pacific Cycle on the East Coast and having them shipped which means that I have to pay for postage as well as the new inner tubes.
When I read the reviews about this bike there was one person who marked the bike as "not recommended" for the sole reason of the inability to buy an inner tube. I'm not sure why that didn't concern me at the time but it should have. If Pacific Cycle stop making or supplying those inner tubes then the wheels on this bike become useless and your have to spend several hundred dollars replacing the wheels.
It's a real pity because it's a great mountain bike.