Why Stick to Manufacturer's Spec?

Just had a dude on the phone, asking about Shimano / Campag hybridisation ...

Our advice is always simple - stick to the manufacturer spec. Yes, there are cases where you *can* make allowances for performance shortcomings (and they will crop up sooner or later), there are times where you'll run a Shimano cassette with a Campag system, or a Campag cassette with a SRAM system and it'll *work* but *working* is one thing, working reliably, for the service life of the parts, on all frame sizes and compatible geometries and without constant "tinkering" ... that's something else.

All manufacturers who make groupsets test and test and test - and even then, sometimes there are mistakes made as all the three main component makers will testify - Shimano have had disc brake issues, ditto SRAM and Campag have had to change production techniques a couple of times to fix problems that occurred in the field but that didn't show up in testing.
So to take two things that were never designed to work with each other and expect them to work on a consistent basis, from the beginning to the end of their service lives, is already optimistic.

If you then look at those parts and say, "well, it's only a couple of tenths of a mm", in the case of 11s cassettes, perhaps - that may be within manufacturing tolerances when the system is new but what happens with wear and tear - it's entirely possible that the operating tolerances in production are there to account for wear and tear, in part - if the parts are marginal when new, apply a feww 100 km to them and wear might already have them outside the normal manufacturing tolerance.

Back in the day, you could merrily mix six and seven speed, then seven and eight (if you were careful with the chains) ... life started to get more complicated and touchy with 9s, then more so with 10 - and now with 11s, accuracy of manufacture and set up is everything. We see many, many bikes that don't work well, not because the componentry can't but becaue of poor preparation and poor set up - mix mis-matched components into that and you have something that is never going to be "quite right".

"My mate's done it and his works" ... well, first, what do you mean by "works" and second - in road bike terms, if your mate happens to ride, say, a 53, 54, 55 or 56 cm road frame of pretty standard geometry, then his or her chances of getting a marginally mismatched system to work are quite high. If you are also in that mid-range, you might get the same result, it's true. On the other hand, if you are at the very margins of frame sizing (and therefore geometry), say a 49, 51 cm, or a 61 or 63 cm, you shouldn't take it for granted that you'll get the same result. The same applies the other way around of course. If you are riding, say, a TT rig, you might also see differences - short chainstays, different BB height and therefore seat tube-to-chainstay angles, front mech placement, all have an effect on shifting. Again, the reverse is also true. What can sometimes be "made to" work on a TT rig might be lousy on a road bike ...

What spec you are running makes a difference, too - where a system is running easily in it's comfort zone - so, say, a Deore RD on an 11-27 cassette, with maybe a 22-32-42 combo "up front" on an MTB, then monkeying around with a "compatible" chain, cable set, cassette or chainrings might be OK. On the other hand, just as with frames, if you start to work right out at the limits of what a transmission can do, you might start to see serious degradation of performance - add to that a frame at the margins, or maybe a full sus with lots of compression / extension range, then the whole shebang can go from "works like a dream" to "total nightmare" pretty quickly.

Manufacturers, SRAM, Campagnolo, Shimano, all say stick to the spec and yes, of course there is a commercial imperative in this - they want you to buy "their" kit because if you don't, for one thing, they can't afford to develop new kit, for another, they can't afford trickle-down from, say, the "Red" level to the "Rival" level, SR to Veloce or DA to Sora ... plus of course no-one in the trade does it for fun - we all want a return on investment - yes, shock horror, we all want to make a profit!

Having said that though, there is also a mechanical requirement and as we demand more and more in terms of how our equipment performs, it becomes more and more important to heed the advice - "systems are designed to work as systems".

OK, rant over - I'm going to lay down in a darkened room for a bit now ... then I can start a new diatribe about "compatible" brake blocks and fried carbon rims ...