Quote:
Originally Posted by ERK55
Apologies if this has been previously discussed.
Are the new Campagnolo 12 speed cranks backward compatible with an otherwise Campy 11 speed group + chain?
I was thinking specifically of the Chorus 12 crank which offers the option of sub-compact chainrings.
Thanks for any information.
|
In some cases it works OK, in some cases it's flaky and in some cases it really doesn't work very well at all.
There are a lot of variables.
Companies, be they Campag, Shimano or SRAM spend a lot of time testing variables. It's one of the things you pay for ... so if they say "we don't recommend it", sure, there's a commercial imperative but they will almost certainly have found some good mechanical reasons not to do it, too ...
We are not directly part of Campagnolo and as a mechanic, I like to know what does and doesn't work, so at Velotech we've tested Chorus sub-compact on 11s systems, knowing full well this question would come up. We also speak regularly to the other Service Centres and Campagnolo branches around the world and so can also aggregate their experience. The end result - pretty mixed degrees of success.
Some of what we have seen (not exhaustive, just a cross-section) ...
Fully crossed, running a 32 or a 34 at the back, you can get chain-scrape at the top of the CH, RE and SR FDs. With PO and CE it's better as the cage design is slightly different but still not perfect. Move the FD up far enough to kill that and on small frames the chain over-throws to the inside. Limit that with the limit screws and / or cable tension and the trim clicks are sometimes OK, sometimes "off", it depends on the rear triangle length. Poor chain engagement or flaky chain engagement on the inside ring is also a problem, leading (as Pez comments) to increased rates of wear and potentially to damage - we'd go further by pointing out that it's not just to the transmission but also to the frame that can end up showing damage.
Small-small crossed we saw a return of the "chain suck" type effect that was almost totally engineered out on HO and 12v RE and SR, by narrowing the chain (in 12v), changing the outer chainring inner surface profiles and widening the chainring spacing - because the 11s chain is 0.5mm too wide to interact in the way intended with the crankset, designed for the narrower "gate" and differing shift system in 12v front derailleurs.
You can also try to fix some of the above by using a third party FD clip in such a way as to move the 11s FD forwards relative to the seat-tube but then you tend to mess with the ability of the FD to upshift correctly as now the lift ramp on the FD is in the wrong place ... plus the ring spacing is different and the chain width / FD interaction doesn't work as intended because of that ring spacing change. If you have a FD fixing on the frame, you are potentially denied even this possible route to changing how the front shift works.
In other cases, generally with narrower cassettes (11-27 for instance) on shallower seat angles around 73-ish, we had fewer problems. As usual, it's the extremes that provide the biggest issues.
Bear in mind, if you mix and match and you claim on the warranty, you may find your warranty rejected. Most of us who look at warranty know what failure modes to expect and what failure modes have what cause - and generally we also know the ones that typically result from mis-use that would invalidate a warranty claim, as do the factory. It's not a case of rejecting warranty for the sake of it but we have to be reasonably sure that where we replace components or repair assemblies, we will get paid for our work ...