Stronglight 99 question
 

Messing around a little during recovery and I had my daughter bring a couple of cranksets to me for inspection and clean up. One is a Peugeot branded Stronglight 99 with 52/40 chain rings. I know this is an 86bcd crankset. The outer ring has 2 extra holes in it. I'm assuming the furthest one out would have been for a chain protector. But what about the middle hole?

I've had this crankset in a drawer for awhile and never really looked at it. The outer hole in the big ring is countersunk on the back side but the middle hole is not on either ring.

Any wisdom in why the extra holes are there?

https://cimg3.ibsrv.net/gimg/bikefor...7864b42010.jpg

Even though it doesn't look like it, they may be for a triple setup, they made plenty of them and some had some very serious drillium for factory spec.

https://www.google.com/search?q=stro...nt=firefox-b-1

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this set is the second generation "G2" or "Mk.II" edition created by Ets. Verot-Perrin reworking the original in 1981

the outer C/W is mis-mounted in that the small hole is supposed to go under the crank arm, it is threaded and takes a small bolt with spacer/sleeve which is designed to keep the chain from wedging between the arm and chainwheel in derailments to the outside

here is the manufacturer's catalogue page showing the model 99BIS of 1982. the holes are just there for lightening/appearance.

https://cimg6.ibsrv.net/gimg/bikefor...eed3d71aee.jpg

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99 triple for ref. Correct mounting puts the Stronglight mark opposite the crank arm. Agree that the larger holes prob for weight / looks.
https://cimg6.ibsrv.net/gimg/bikefor...c4ca787dc7.jpg

Maybe I'm misunderstanding you but the chainrings are mounted properly. Has to be the way it is to be flush with the ring mounting surface (other than the Stronglight stamp isn't in line up properly). The outer goes over the top of the crank arm and the inner ring goes under the bottom. If definitely see you you would use a spacer to create a triple.

https://cimg3.ibsrv.net/gimg/bikefor...42e4a7083.jpeg

https://cimg6.ibsrv.net/gimg/bikefor...43ae3e46a.jpeg

As mentioned, the outer of the three large holes on the big ring is countersunk on the back. I can't figure out the purpose unless it's for a chain guard. If those extra large holes are there to save weight then why would you make them that big. Just looks awkward like that. But, that's also personal opinion. I like that you could make a decent compact double with a combination of rings but... those extra holes, ugh.

Actually, may have found part of the answer to the outer hole and the countersink on the back of the ring from the photo of the bike I this came off I acquired a couple of years ago. This is how it was on the bike.

https://cimg5.ibsrv.net/gimg/bikefor...f7d9a750af.jpg

The five 10 mm holes outboard of the 86 mm BCD holes are at 122 mm BCD. This means a 99 ring of that type can be used as a middle "triplizer" ring on a Stronglight 93 or other 122 BCD crank. I don't think they intended for it to be used that way, it's just a happy accident. I think they had the die for punching holes at 122 mm, so some clever industrial designer said "eh, why not just punch some holes there with this punch we have already, little lighter and looks nice..."

To use it as a triplizer, you need to counterbore the 122 mm holes, or else the chain will hang up on the protruding head of the chainring nuts. You also need to saw off the five little shelves on the backside of the spider arms on the 93 crank, similar to making it into a track or 1x crank. Here's a modest example:

https://cimg4.ibsrv.net/gimg/bikefor...35c06940a3.jpg

Mark B in Seattle

He is referring to the outer ring being clocked incorrectly. The hole for the chain stop pin, visible at 3:30 in your photo, should line up with the crank arm. Minor issue, since the pin is missing anyway.

Thanks - that makes sense. I hadn't thought about those middle holes being at 122 bcd, but hey, it's French and I can see that. I'll have to have one of my daughters go out to the shop and grab my calipers so I can measure them.

The outermost set are 159 BCD, by my measure.

And they can hold a press-fit plastic chainguard.