Stronglight - varying chain ring tooth profile

[backnotes]

Does anyone know the fairly recent history of Stronglight chainring design?

I have a few Stronglight Speedlight triple chainsets. The replacement Stronglight Zicral rings on the one I use most are normal - all the teeth have the same profile. I have another NOS (bought in 2007) Stronglight Speedlight chainset I now want to use on another bike, and when I look closely for the first time, the profile of the teeth on the big and middle rings looks odd, with a mix of regular profile, and ones that look sharp that are just after the pins and recesses on the back of the chainring - (picture below), so it must be indexation to help shifting.

It is exactly the same on a second NOS one I bought at the same time. It is also the same on one linked here http://sscycleworks.com/components/cran ... lver-61201 - (look at the two teeth either side of the "52T" on the outer ring, but do also enjoy the comedy typo in the price...).

So, a deliberate "feature" rather than a fault. Is this what Stronglight call "CSA"- Chain Shift Assistance - or is it something else? It seems to have been used only for a short while, then dropped again. I guess it may not have worked so well across different makes of chain, or was too specific to one of 9/10 speeds, or led to premature chain or chainring wear.

I'll use the new chainset anyway and see how it goes, but I was just interested in what to expect and why this evolutionary dead end was apparently introduced for a short while and then dropped again. My older (1980s) Stronglight chainrings all look perfectly normal with a consistent tooth shape, and more recent (2012) Stronglight Zicral replacement chainrings do as well.

Anyway, thanks for any background that clarifies why I have wonky teeth!

[reohn2]

Yes though not clear in the photo Istrongly suspect it's indexing tooth profile.
But I've found on the two bikes I have with Alpine doubles 24t-39t I get just as clean and crisp shifts when changing up from 24t to the non index plain 39t ring.This is the same on both bikes one on a friction lever the other on MTB pods.

[backnotes]

Thanks. Yes - sorry - my original photo wasn't very good at all was it! I have now replaced the original blurry one with a new one done with the benefit of a tripod - hopefully this shows the phenomenon more clearly - to my eyes, the teeth change profile between the regular shape adjacent to the "52" and the one just to the left of the pin.

Like you, I have never noticed any particular trouble with shifting between Stronglight rings anyway, so as it wasn't broke, I'm not sure what they were trying to fix here.

I am sure the explanation is the pursuit of better indexing - I am just intrigued as to why this was tried and dropped. Maybe they just got a different marketing person!

[Brucey]

FWIW I think the 42T chainring in your photo is built the same way. Possibly they found that it just cost more to make, confused people, and didn't greatly improve the shifting. Another possibility is that it somehow infringes someone else's patent and they were quietly told to 'desist'.

cheers

[backnotes]

Thanks Brucey,

You're right - only the outer and middle rings have this arrangement, while the granny ring is all regular teeth, so this seems intended as a way to help the chain slide off a larger ring and onto a smaller ring.

You're quite right that this arrangement has successfully confused at least one person - hence this thread!

I will just file it under "one of those things" and see how the chainset shifts and wears over time.