Bicycle Mechanics - Need advice: 21 speed to 7 speed

Pardon if I get the terminology wrong. Life long bike rider, but not an informed bike enthusiast.

The bike is an FS Elite AAC 600. Aluminum frame, 21 speed with a DuoTrack 7007 front fork. Seems pretty well made, light, comfortable to ride (I had been riding a very heavy, steel framed Bridgestone MB6). I am not a trail rider. I just bike in and around my neighborhood for excercise, as well as some family bike outings in parks and such.

The left 3 speed shifter is cracked and broken. It will shift from the low (smallest) gear to the mid gear, but it's balky. I'm thinking about doing away with the shifter altogether and turning this into a 7 speed. After having experimented riding using both low and mid gear, it seems that something between the two would be ideal. So, my question is, any tricks to finding a replacement gear of the right size? How are these referred to? By diameter? Number of teeth? Are there any compatability issues?

It looks like all I need to do is remove the grip shift and front derailer hardware, and then change out the existing front gears for a single gear of the right ratio. Am I missing anything?

Thanks in advance for any advice.

On most bikes, the casual rider will spend the majority of their time in the middle chain ring.

I don't know you bike specifically, but in general what you are seeking to do is very easy. It is just a factor of removing the shifter, cable, derailleur, and extra chain rings (or just leaving them in place and not using them).

If you do want to change the remaining ring to a different size, they are sized by the number of teeth.

In addition, the distance between the bolt holes differs with different styles of cranks. This is the BCD... instead of trying to explain... look at BCD here: http://www.sheldonbrown.com/gloss_bo-z.html

I suggest staying with your current middle ring, or going down just very slightly from that, as this will be your most useful range in most cases.

If you want the cleanest possible look, you can go with a single crank, which will look very clean and sleek... Or you can simply remove the unused chainrings from your existing crank, which would just require shorter chainring nuts available from your closest bike shop.

LD, thanks, very helpful!

It began with rear derailleurs, 1910s-20s. Riders discovered that the chain could - and would - be tossed off the front chainwheel, and by the early 1930s they had developed chain keepers. By the mid/late 1930s, there were front derailleurs that, in addition to shifting between multiple front chainwheels, kept the chain from getting tossed.

Every so often somebody gets the idea to do without a front derailleur. They rediscover some sort of front chain-keeping scheme.

HTH,
TCS

Why don't you just leave the bike as is, and don't use the front derailleur?

Why don't you just leave the bike as is, and don't use the front derailleur?

The left shifter needs to be replaced or removed. The plastic housing is falling apart, has some sharp edges. Since I don't need the 21 speed capability, I figured I would just remove the extra gear, make the bike a little lighter and easier to maintain.

Retain the FD to keep the chain on your ring; or if you decide to buy a new size ring, buy one without ramps and maybe you could do away with the FD.