3rd gear

Question
I have a fairly cheap mountain bike, a mongoose xr250 and i cannot get it to shift into 3rd gear. I can shift into 3rd but the derailer will not move the chain enough to change gears do you know how to fix this, and also would you recommend sliming my tie to prevent flats? thanks!!

Answer
When you say "3rd gear" I am assuming that you mean the big, or outer, chainring - the "gears" on the crank. If so, this is a fairly easy fix. I am thinking that it is just cable stretch and the cable that runs inside the housing needs to be tightened.

Look down on your front derailleur and you will see where the cable attaches with either a hex head bolt like an 8mm or a Allen head bolt that is either a 4 or 5mm. Place the bike in the lowest gear, the small chainring, loosen the bolt holding the cable, pull the cable snug using a pliers, and tighten the bolt making sure it is clamping the cable.

The other possibility is that the front derailleur got knocked out of alignment. Again, fairly simple but you are dealing with two planes - making sure it, the outer part of the cage, is parallel with the chain and also just clearing your big chainring by 2 to 4 millimeters. You will find a bolt that clamps the derailleur to the frame, loosen that up and then make your adjustments. Like I said, fairly easy but you have to keep in mind the two different planes that you are working with.

I would check cable tension first, since that is very common.

I personally don't like the feel of Slime in my tubes, but if I was riding in a place where there were a lot of thorns I would get over that really fast! If you are using your bike for a city commuter I would consider using tire liners, like Mr. Tuffy. They protect the tube a bit better from punctures from glass and the like. Slime works best, I have found, on the really small holes like from thorns and not so well on big cuts like from glass.

Oh, one last thing... you have a couple little screws on your derailleurs, those are to limit the travel of the derailleur and really should not be adjusted "in the field." They are better left to a bike shop, or have someone show you what they do. It is very rare that they ever need to be moved once set by a qualified mechanic.

Good like! Keep riding!