Gear Ratios

[pinkbikes]

There are some useful discussions about gearing on this thread here if you need general info about gearing.

http://forums.teamestrogen.com/showt...t=30141&page=2

But if you are looking to find out where your overlap is, then I just did a little spreadsheet with the chainring teeth down the left hand side and the cog teeth across the top. You probably know this, but the usual way to express gears (well the old fashioned way) is in "gear inches" and the formula is:

Wheel diameter (in inches)xChainring teeth/Cassette teeth

Generally a 100inch gear is considered to be a big gear and hard to push, 90 pretty much a common top, 80 a speed gear, 60-70inches most often used. 40-50 for hills. Below 40inches would be for very hilly terrain and for carrying heavy loads. So sayeth "Richard's Bicycle Book" circa 1984! Lots of things on bikes have changed since then but probably not basic human physiology and how we propel a bike!!

The ratios spreadsheet for my tandem looks like this and it is easy to identify the overlap zones (the shaded bits) you are trying to find. Btw I just used 27" because I don't really care about the tiny error in converting from 700c!

As you can see from this, using say the smallest ring on the front (30teeth) and the 4th gear (19teeth) on the back is a 42.6inch gear. Whereas using the middle ring on the front (39 teeth) and the 1st gear (25teeth) on the back is indeed just ever so slightly easier at 42.1inches. Too small a difference to call but that's the point at which the ratios start to overlap, which is what you were looking for I think?