Originally Posted by cyccommute

Your problem is that you are thinking of bicycle gearing like the gear box of a car. It's not a straight linear progression. This calculator will help you see how your gears work. You shouldn't be trying to get into the big/big combination because that gear exists elsewhere. Generally, on a triple, shift off the large ring in the middle of the gearing (the 18 tooth cog in this case) while downshifting and use the middle. If the hill becomes too steep, shift off the middle to the inner before you get to the lowest gear on the cassette as well. In the other direction, shift up when you hit the middle of the range.



MRT2 has a point. Here's what your proposed gearing looks like compared to what you have now.. If you look closely, you'll find that you'll need to use the two rings mostly independently of each other. The transition from the outer ring to the inner ring is large and the difference in cadence to make up that difference is difficult to accomplish. For example, if you are riding along at 90 rpm and 15mph in the 50/24 gear combination and you need to downshift, you have to slow down 5 mph for the gearing to catch up or your have to increase your rpm to 130 to maintain that speed. It feels like you have dropped the chain.

There's also the issue of expense. Swapping from an 8 speed (possibly freewheel) would require new shifters, new cassette, new brake levers and, maybe, new wheel. It's not impossible to do but it would add significantly to the cost of a relatively inexpensive bike. I suspect about $200 in parts and $100 in labor.