"if you have an existing 8 speed bike why don't you just settle on gear 1 and call it a single or fixed gear bike and not shift to all the other gears? educate me please if my theory is wrong."


I see this all the time from people who have not made the conversion themselves and perceived the difference.

In bullet form:

- Chainline Efficiency. A straight chainline with no derailleurs, superfluous chain links removed and correct chain tension improves the power transfer from crank to driven wheel. Improved drivetrain efficiency. This is a difference you can feel. The smoothness and power efficiency gain is not imagined and translates into a greater enjoyment of the bicycle.

- Leaving the chain in one gear for extended periods of time without shifting will wear that one cog out prematurely. If the cog you wish to use is not in alignment with the chainwheel, the chainline will not be straight. A chain running at an angle from chainwheel to a cog with its tooth cut at an angle to aid controlled derailment held in that position by a spring in a derailleur...well you get the idea. Using a singlespeed conversion cog costs me $6 per cog and assures a perfectly straight chainline. Plenty cheap to experiment while preserving the cassette for redeployment.

- Ever damaged a low hanging derailleur on a 20" wheel folding bike? That's easy enough to happen especially if you stick it on the lowest gear all the time.

- Less maintenance. Oil the chain and go.

- Removing the cassette, derailleur, shifter cable, grip shifter and unneeded chain links lightens the bike. As a result, the 20" wheeled bike accelerates even faster with all the benefits of reduced static weight.