A half step front derailleur is what was a common derailler back in the '70's before the japanese fine tuned the alpine style of derailleur. The shifting plates of a half step front are almost parallel to one another and work well with chainrings of similar size. Newer derailleurers have the plates quite offset, so that the inner plate contacts the chain at a much smaller chainring diameter. The inner plate would be too low for the inner or middle half step ring and would push against the chainring instead of just the chain. By changing to a 52 front, you would have higher gears, but you would have what's called alpine shifting system with dramatic overlaps in the gearing between chainrings that wouldn't be as easy to keep track of.
Half step gearing is a good compromise with older setups with only 5 or perhaps 6 cogs on the back. The rear is set up with an even jump or even percent jump so that a wide range can be shifted with what feels like exactly the same shift each time. By using half step in front, you can always find the gear almost exactly in between any jump on the back in order to fine tune the shifting. This provides gears as close as an old racing setup, though it may require two shifts to get it just perfect. These close gears would typically be in the range where most of your riding is, but then you'd have a granny for the steeper climbs. Its advantages are that you can usually do your gross shifting with one shifter covering a fairly wide range of terrain and then fine tuning it with the front. The 4 tooth jump you have on the front works well with a 14-16 tooth spread of even jumps 14, 17, 20, 23, 26 or a slight variation of 14-28. I use a wider setup on my old classic that uses a 5 tooth jump on the front, with an even percent jump on the back or 14, 17, 21, 26, 32 or 3, 4, 5, and 6 tooth jumps. Combined with my 48, 53 front and an extra 13 on the back, one shifter can go from a 110 inch gear to a 44 inch gear in one smooth shift. Using the 48 chainring, its a 100 to 40 inch gear or the equivalent of an old '70's standard alpine setup, but with a gear in between each jump for fine tuning and I can use all the gears. And then there's the granny if you're using a triple.
If you were to plot two columns of gears on a semi log sheet of graph paper for each chainring, the force behind the pedal would be plotted linearly. With the half step gearing side by side, you would see just how logically set up half step gearing is and how easy it is to keep track of when you know the system.
Modern gearing systems with 8, 9, and 10 cogs on the back with such
close ratios have made half step gearing unnecessary, but they still
work well on a period bike.
>>> "Tom Sanders" <tsan7759142@comcast.net> 09/22/2003 3:25:21 PM >>>
Well I'm off again on another project. I just bought a bike with half
step gearing and I can't say that I like the idea of it very much. I
have a bike with a Specialities T.A., cyclotouriste(sp) crankset,170mm
arms, half step/granny rings, 44/40/26. My question is can I just
replace the outer chainring with, say, a 52t and be back to normal
shifting? I have heard that the front derailleur is different on a bike
with half step gearing (They lost me there!)...hopefully I'll be all
right there?
Any advice will be received with much gratitude and points will be
built up in Heaven for those doing such good deeds, I'm sure.
Thanks,
Tom Sanders
Lansing, Mi