Can someone explain in simple terms how this works and why/when one would want it? Thanks.

You understand the gear set up, right? The half step chainrings are to add an extra gear between the cassette gears. For example the shift from the 5th cog to the 6th cog may be a change from 70 gear inches to 78 gear inches. But the theoretical rider wants to be riding in 74 gear inches. A triple/double setup won't let him do that, thus he has two chainrings that are close together to add an extra jump between rear gears.

And then the granny gear is for steep hills.


I realize that's not very simple, but someone else can explain it simpler

This was a popular gearing set-up back in the day when bikes had 5- or 6-speed freewheels and folks wanted triples set up for touring (for example).

In front, you have two chainrings that are pretty close to the same size -- say, a big ring of 52 and a middle ring of 47. Then you have a third chainring, a granny gear that is pretty small -- say, only 24T or 26T.

You then have a freewheel spaced so that each time you change cogs in the rear you are making a "full" gear change, but because the chainrings in front are so close together when you shift between the big and middle chainrings in front you are making a "half step."

So -- if you are quickly moving through the gears, say when you encounter a moderate hill or slowing down, you make big gear changes by shifting to different cogs in the rear. Then you can "fine tune" the gear you want by making "half step" gear changes in front. Finally, for climbing big hills, you drop into your granny gear.

A properly set up half-step triple is (was) a thing of beauty. Because your two big chainrings in front were only about 5 teeth different, your shifts in front were really smooth. You sometimes had to make double shifts (make a big shift in rear, and then fine tune in front), but the shifts were easy to accomplish. There was a big gap between the middle chainring and the small chainring, but since you only used the granny gear when encountering a big hill, that was not such a big deal.

Back in the day, I had two touring bikes set up this way, and I loved it.

As I understand it, the need for half-step gearing pretty much went away when rear cassettes starting coming in 8, 9, and 10-cog versions.

OK, so with this setup instead of shifting from say 5th to 4th via the cassette you can shift to 4th and a half gear by shifting the front down from the 52 tooth to the 47 tooth (or whatever) and leaving the rear alone. I'd think it could become confusing a little more easily than a standard system. I can see where 27-30 gears to choose from could obsolete it.

I found it a little easier once I got used to it. With "standard" gearing, you sometimes have to put some thought on whether you're going to go to the trouble to shift from your biggest chainring to the middle chainring. Especially in the old days, with downtube or bar end shifters, making a change in chainrings was more of a "big deal"

With half-step gearing, you have a choice of two relatively simple ways to shift -- either make a "full" gear change by shifting in the rear, or a "half" gear change by making a (very smooth) shift in the front. Or say you make a "full" shift in the rear, but then the grade changes slightly -- you're then only a "half step" away from finding the right gear.

Half step gearing is a beautiful thing when it is set up properly... I use it on both of my touring bikes which run 6 and 7 speed freewheel blocks in the rear which also has the advantage of having a wheel with less dish and narrower dropout spacing.

One can always find that perfect gear to maintain a comfortable cadence.

Although it was rendered somewhat obsolete with the advent of 8-10 speed cassettes that can have very close steps a great number of people still prefer it.

Hey guys. I'm pretty new to cycling and I could use some clarification on this. Please forgive my simple newbie talk.

The way I understand what you've been saying is that if i'm in the 2nd gear upfront and the 4th outback, I will feel a bigger difference if I stay in 2nd up front and swith to 5th outback... rather than switching to 3rd upfront and staying 4th outback. But I've always felt like swithing the front gears makes a huge differnce, and switching the rear gears only made a small difference.

Could you please explain this some more.