3v1lD4v3

I just put an Sugino XD700 on my Shogun 800 to replace the SA Sakae 48/52 it came with. The four tooth difference seems somewhat laughable.

Would this have been a flatland racer or something?

rhm

It's a half-step. The gearing difference between your chainrings is supposed to be half the difference between any two cogs.

Road Fan

Yes, for a half-step. With a freewheel selected as RHM described, you'd get 10 distinct gears with no overlap. With 2 x 5 it was hard to get a wide range and still have decently close steps, but 2 x 6's were also possible. The compromise in both cases was the shift pattern - half of the one-step changes required a chainwheel shift and a cogset shift.

3v1lD4v3

So I guess the next question would be when would you want half step chainrings? Normal chainrings are 39-53, or 14t. Compacts are 34-50, or 16t.

I've always thought of chainrings as larger steps, so the small one is a normal or climbing ring and the larger one is a normal or speed ring, depending on one's riding style.

big chainring 

The half step gearing wouldnt give you a really small climbing gear. I think 49/52 chainrings were an option on racing Paramounts. They give you closely spaced gearing. For instance i used 49/52 combined with a 15-24 freewheel when I started racing as a Junior. 52 by 15 was the gear restriction. The combination gave me a low gear of 54" and top of 93". With this arrangement you would alternate between the front and rear derailleurs to get to the next higher gear.

Best way to see this is to go to Sheldon Browns gear chart and enter in chainring and cog sizes so you have a visual as to gear progression with the half step system.

Road Fan

Well, this is C&V. Back in the old days the widest freewheels you could get had 5 cogs, in around 1972 and earlier. The most common gearings or gearing systems were half-step and Alpine. The half-step gave you a simple but labor intensive shift pattern, small steps, and full use of all 10 gear combinations. The problem was getting a really wide range of gears. In addition the 5-speed cogset had to be carefully selected.

Shifting up through the gears, such as to maintain cadence, was a lot more cumbersome than shifting up across the cogset, then across to the big ring, then up the cogset again as we do today. That pattern of today is called a "crossover." It is made possible by the advent of 8+ cogs in the back. With so many gear combinations in the system, who cares if you have some duplication?

Alpines were also called "step and a half." The chainring step was about 1.5 times the cog to cog step. The cranks were often 50/36, like our modern compacts. The cogset was selected for even spacing, like a half-step, but with the low small ring, the system had a similar range available as modern doubles. But there were still only 5 cogs in the back, not 8 to 10, so they wanted full use of every gear combination, no waste. So the cogs agian were carefully chosen to give even steps with zero duplication, but this time the shift pattern was cumbersome, and in my opinion, just too hard. Frank Berto wrote "If rats can run mazes, cyclists can shift Alpines, but I never got the hang of it.

With half-steps, you could have a bail out third ring, to make the common half-step with granny, if you wanted grunt-free mountain climbing torque.

Why don't we do these today? We have wider cogsets, and can afford to install gearing systems that have 20 gear positions for which only 14 might be usable, considering duplication and extreme cross-chaining.

Why do we care today? We're vintage freaks, and its worthwhile to know how to tell when a part that falls in our laps will be useful to get a half-step gear train to work the way it's supposed to, and enjoy that aspect of the vintage experience.

rhm

Great explanation!

kendall

Think a lot has to do with riding style.
I am normally in the big ring, 52 on three bikes, 53 on one (just sold it last week) and stick to the smallest three cogs for typical riding. With all but one of the bikes the small ring is in the 42 tooth range, and for me it drops the ratio so far that I'm just not comfortable riding it.
With one bike I have 52 and 46 rings, those extra teeth spread the gearing just enough to give me a wider comfort range. I do have larger cogs on the low-range half of the cog on that bike so I have climbing gears if I need them, but they are seldom used.
There are only a few large hills around here, so it works great, possibly wouldn't make sense at all in more hilly areas.

Ken.

Road Fan

Actually I think this geartrain would have been for flatland racing. Riders made more out of each gear in those days, spinning wherever possible. With a 5-speed rear end and a 13 tooth cog, the big cog would have been a 24, so the smallest gear would have been 26*52/24 = 56 inches! The top gear around 104 inches. For more hilly terrain, might have used a 47 small ring and a 14 tooth small cog. Then the big cog would have been 30 teeth, for a 26*47/30 = 40 inch low gear.

The traditional Campy-style road race setup, say 52/42 and 13/24, gave you a 26*42/24 = 45 inch low gear, clearly a compromise between the flatland half-step and the hilly half-step, but a big step up from the flatland half-step.

You can see in teh hilly half-step how close the system is to the limits of the derailleurs of the day. 30 teeth would have been a humongous racing cog in the '60s. You can also see why there is little point to adding another cog, to make a 6-speed - the big cog would be way too big.

Road Fan

Ken, sounds great for a modern Michigan geartrain!

oldbobcat

Half-step is also rationalized by the chain-tensioning capabilities of old single-pivot, short-cage parallelogram derailleur designs. A 52-49 / 14-22 has to pull less chain than its 52-42 / 14-18 counterpart. It's funny because while the rear derailleur was generally happier with half-step, the front was not. Downshifting over such a small difference in chainring diameters was a big effort for the front derailleur spring.

cyclotoine

Tom Boonen won paris roubaix running a 53/46 this past spring. When you're strong in the right conditions is makes sense.

prathmann

I remember the 'half-step' gearing arrangement being more popular with touring cyclists than with racers. The idea was that with 5 (or sometimes 6) cogs in the back the difference between consecutive cogs was typically about 18% (a very popular touring/casual freewheel was 14, 17, 20, 24, 28) and this was a pretty big jump between gears. By using chainrings that differed by about 9% you could cut the size of this jump in half.

For example, my touring bike has 'half-step plus granny' gearing with chainrings of 50, 46, and 30. The 30 tooth is pretty much reserved for substantial hills/mountains and the other two are used for most riding. So when riding in the 50 & 20 combination and wanting to shift up to a higher gear I can either jump all the way up to 50 & 17 (an increase of 17.6%) or I can shift in both front and back to the 46 & 17 combination for an increase of only 9.2%. Check out all the combinations and you'll see that this half-step arrangement gives pretty even spacing of gears at 9% intervals, but at the expense of needing to do lots of double-shifting with both derailleurs. Touring cyclists facing long stretches of riding between shifts could afford the extra time to do the double-shift when needed in exchange for getting just the right gear for the conditions.

Most racers of that period preferred the alternative arrangement (sometimes called 'alpine') with closely spaced cogs in the back (say 13, 14, 15, 16, 17, 18 for a 6-speed) and something like 54/42 in the front. Almost all shifting is then done using only the rear derailleur and the front is used to choose the rough range: the 54 for flat or downhill stretches, and the 42 for climbs. Made for quicker shifting to respond quickly to attacks by competitors.

The move to 10 cogs in the back has essentially eliminated the rationale for half-step gearing which is why it isn't found on current bike models.

Sixty Fiver

I just set up my sister's vintage Mixte with a touring triple with a half step gearing and she is loving it... her bike currently has a five speed rear and she already appreciates the smaller gearing jumps when she alternates between the middle and outer ring and having a 28 tooth chain ring with a 14-28 rear block means that towing 100 pounds of twin girls is a breeze.

My new old Cooper has a 42/52 and I just swapped in a 13-28 Suntour 6 speed (had a 13-24) which gives me a 40-108 range and I also have a 13-21 I can swap in if those lower gears are not needed.

Half step gearing is really nice when you know how to use it.

bbattle

Save that crankset; you can use it to make a multi-geared fixie out of a frame with horizontal dropouts. I did this with my Sprite; 48-44 up front and 19-17 in the back. I get three usable manually changed gears this way. 75.5 gear inches to 62.5 gear inches.

wrk101

My "favorite" is the vintage Stronglight crankset I have. Its a 51/49. Tightest half step I have seen.

If you look carefully at this pic, the chain is on the small ring.

gear freak

the question when did 48-52 tooth chainrings make sense is inacurately phrased. depending on what size cluster cogs you selected, say a 13-15-18-22-26-32 this what be what is called a half step which works very nicely with triple cranksets. shifting across the 13 tooth to 22 tooth cogs on the rear gives you relatively coarse steps while shifting betwen the two chainrings allows you to fine tune the gearing because shifting between the chainrings equals half a shift on the rear. you have to be a bit smart to us this & some of my friends never learned to use this, emily picked up right away, it took me a year & a half to teach jeanne how to use it while dinny would not listen to me & never mastered it.i actually built six bikes for 4 four of my friends with 13-15-18-22-26-32 clusters & 26-46-50 tooth cranksets.

Road Fan

Good explanation, gear freak! Frank Berto a consummate gear freak, said in one of his books something like "if rats can learn to run mazes, cyclists can learn to shift Alpines." In my case, he was wrong. All my bikes are crossovers. I'm working on a 13-28 half-step, but the right crank hasn't jumped up and bit me yet.

Picchio Special

At the top levels of racing, half-step began to give way to crossover gearing in the early 60's. Anquetil apparently used early versions of the 144bcd Campagnolo cranks to accomplish a crossover setup circa 1963. This per "The Dancing Chain."