I’ve been asked several times lately if it’s possible to attach a triplizer—either the 122 Stronglight version or the newer 144 version—to the outer position on a crankarm, then bolt a 74 BCD inner ring to the triplizer to create a compact double with a 42-tooth big ring.
That just won't work. The space where the inner ring would fit under that scenario is already occupied by the crank spider arms. (In fairness to the questioners, that problem is immediately apparent if you hold a crankarm and a triplizer in your hands, but it’s a lot less obvious when you’re picturing the situation in the abstract.)
That just won't work. The space where the inner ring would fit under that scenario is already occupied by the crank spider arms. (In fairness to the questioners, that problem is immediately apparent if you hold a crankarm and a triplizer in your hands, but it’s a lot less obvious when you’re picturing the situation in the abstract.)
With a suitable chainring guard and a triplizer ring, any Stronglight 93 crank can be set up as a double with much lower gearing that you could get with conventional rings. The catch is that you're limited to 42-tooth big ring and an inner ring ranging from 26 to 34 teeth. It works well, and to my eyes the setup even looks pretty good.
But cheer up! You can do pretty much the same thing by mounting a triplizer and an attached granny ring in the usual inner-ring position, using the same spindle or bottom bracket cartridge you’d ordinarily use for a triple.
If you’re not the fussy type, you can just leave off the outer ring altogether and secure the triplizer with a set of single-ring chainring bolts instead of the double-ring bolts you’d use if you were including an outer ring. After bolting the assembly in place, all you have to do is adjust high-gear limit screw on the front derailleur so it won’t shift onto the now-absent outer ring before riding happily off into the sunset.
The only drawback to that approach is that it looks just awful to run a crankset—especially a nice-looking vintage crankset—without an outer ring. The usual way around that is to install what’s various known as a bash guard, pants guard or chainring guard in the outer position. That used to be a fairly common setup back in the 1960s and 70s. Stronglight actually made a great big chainring guard that came as standard equipment on the Raleigh Super Tourer, among other bikes. Whatever you call it, it’s basically just a toothless chainring, sized to be slightly larger than the next ring inboard. (If the chainring guard is too large, it will get in the way of the front derailleur and prevent the chain from shifting onto the large ring.)
If you’re not the fussy type, you can just leave off the outer ring altogether and secure the triplizer with a set of single-ring chainring bolts instead of the double-ring bolts you’d use if you were including an outer ring. After bolting the assembly in place, all you have to do is adjust high-gear limit screw on the front derailleur so it won’t shift onto the now-absent outer ring before riding happily off into the sunset.
The only drawback to that approach is that it looks just awful to run a crankset—especially a nice-looking vintage crankset—without an outer ring. The usual way around that is to install what’s various known as a bash guard, pants guard or chainring guard in the outer position. That used to be a fairly common setup back in the 1960s and 70s. Stronglight actually made a great big chainring guard that came as standard equipment on the Raleigh Super Tourer, among other bikes. Whatever you call it, it’s basically just a toothless chainring, sized to be slightly larger than the next ring inboard. (If the chainring guard is too large, it will get in the way of the front derailleur and prevent the chain from shifting onto the large ring.)
 Here's a Model 93 with an old-school Stronglight chainring guard mounted in place of an outer chainring. The chainring guard and both inner rings--a 52 and a 42--are mounted on the same set of extra-long chainring bolts. The guard and big ring are separated by the crankarms, and the inner ring stands off from the outer with a set of spacers. See how the front derailleur just clears the edge of the chainring guard? |  Compare the original-style chainring guard to the homemade version at right. Using the big one with a 42-tooth ring would have necessitated mounting the front derailleur much too high to be functional. I fashioned the smaller guard by cutting the teeth from worn-out a 47-tooth chainring. A lathe would have been faster and neater, but as a character-building exercise I did the job with a hacksaw and a file. |
Being an inquisitive guy, I recently set up one of the bicycles in the Red Clover Components Test Fleet with a homebrewed compact double setup, using a 42-tooth triplizer and a 28-tooth small ring. I had an original 70s-vintage Stronglight 122 BCD chainring guard--and a big dinner-plate sized chunk of aluminum it is--but since it was designed for 52-tooth ring, it was no use to me here.
Instead, I improvised one of the right size by digging up a worn-out 47-tooth 93-pattern chainring, cutting off the teeth one by one with a sharp hacksaw, and carefully rounding off the resulting rough edge with a double-cut file, followed by a single-cut file and some fine emery cloth. The whole process only took about an hour, and to me the result looks pretty good.
Assembling the inner ring, triplizer, and chainring guard was a snap—the whole thing just bolted together.
Instead, I improvised one of the right size by digging up a worn-out 47-tooth 93-pattern chainring, cutting off the teeth one by one with a sharp hacksaw, and carefully rounding off the resulting rough edge with a double-cut file, followed by a single-cut file and some fine emery cloth. The whole process only took about an hour, and to me the result looks pretty good.
Assembling the inner ring, triplizer, and chainring guard was a snap—the whole thing just bolted together.
Here's a view of the setup from the back side. Notice how the triplizer ring and chainring guard are mounted on the same set of bolts, with the inner ring on its own smaller bolt circle. The toothless 47-tooth ring is just the right size to cover the 42-tooth triplizer. A 48 would probably also have worked, but a 50 would have been too big. If you look closely you can see that the 47-tooth ring (now the chainring guard) must have been run for a long time with a badly worn chain--the chain sideplates wore little scoops in the edge of the chainring below the level of the original teeth.
I installed a 7-speed 13-15-17-19-21-24-28 freewheel in back, mostly because I happened to have one handy. With the 42-tooth triplizer ring in front, that gives a high gear of only about 86 gear inches with 28C tires. That would be too low for a lot of people, but I’m old and feeble—the gearing on most of my bikes tops out in the high 80s or low 90s—so it’s adequate for my needs. Rejiggering the gear ratios for a 12-tooth small cog (as I probably will when I have the chance) would give a high of 93 or so; an 11 would bring it up to 102 gear-inches. The setup I chose gives a nice even gearing progression, with a double shift in the middle from the 42-21 combination to the 28-17 then back up to the 28-28 from there.
After bolting on a circa 1981 mid-cage Suntour Vx in back and a matching front, I took the bike out on a hilly 25-mile test run. The rear derailleur shifted perfectly, as I had expected. And I was pleasantly surprised by the crisp, accurate shifting in front.
Why surprised? Conventional wisdom says that a front derailleur should work best when the curvature of cage--as viewed from the side--conforms closely to that of the outermost chainring. Like most road fronts, the Vx was apparently designed for use with a 52-tooth big ring; in the photos at the top and bottom of this page you can see that it describes a significantly larger arc than the smaller 42-tooth ring I actually used.
Even so, it shifts just fine. I can't say for sure that the same setup would work equally well with any front derailleur meant for a road double, but my guess is that most road doubles should work.
Although I haven't tried it yet, I'd expect the same compact double configuration to work nicely with a 144 triplizer in a Campagnolo crankset or Campagnolo clone. As it happens, an Oregon company called BBG Bashguards (http://www.bbgbashguard.com/Cyclocross.html) seems to make a reasonably-priced 144 BCD bash guard sized for use with a 42-tooth ring. That could do away with the need to fabricate one from an old chainring, making the 144 conversion even simpler.
After bolting on a circa 1981 mid-cage Suntour Vx in back and a matching front, I took the bike out on a hilly 25-mile test run. The rear derailleur shifted perfectly, as I had expected. And I was pleasantly surprised by the crisp, accurate shifting in front.
Why surprised? Conventional wisdom says that a front derailleur should work best when the curvature of cage--as viewed from the side--conforms closely to that of the outermost chainring. Like most road fronts, the Vx was apparently designed for use with a 52-tooth big ring; in the photos at the top and bottom of this page you can see that it describes a significantly larger arc than the smaller 42-tooth ring I actually used.
Even so, it shifts just fine. I can't say for sure that the same setup would work equally well with any front derailleur meant for a road double, but my guess is that most road doubles should work.
Although I haven't tried it yet, I'd expect the same compact double configuration to work nicely with a 144 triplizer in a Campagnolo crankset or Campagnolo clone. As it happens, an Oregon company called BBG Bashguards (http://www.bbgbashguard.com/Cyclocross.html) seems to make a reasonably-priced 144 BCD bash guard sized for use with a 42-tooth ring. That could do away with the need to fabricate one from an old chainring, making the 144 conversion even simpler.
I know this photo makes the fork look a little bit bent. But believe me, it's really not.
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