I have a 2012 Specialized Roubaix with Ultegra components. Since the day I got it, there are a couple gears towards the center of the cassette where I'll almost always miss a down shift. Then, when I click again, it shifts twice. Annoys the heck out of me. No problems up shifting.

I took it to my LBS last week for it's allowed physical during the first year of ownership, and immediately the tech said the cable was too short to the rear derailleur. Now that didn't sit well with me since it was built that way, and once he realized it was passed through the inside of the frame on the Roubaix, he determined he couldn't lengthen it, and I would have to bring it back this week for the more experienced guys to look at. He also added tension to the cable since they may have stretched over its' breakin period (which doesn't surprise me), but that hasn't helped. I have 3 sets of wheels..all with 11-28 cassettes..and all of them do the exact same thing.

Do you think he may be onto something with the cable being too short ? Said it restricts the cable movement. In fact, he said the pass through frame style is a headache compared to older out of frame cabling. Didn't sit well with me either since I have about 4K in that bike thinking it was an upgrade over my 105 model that I have NEVER had problems with.

But, anyway, I'm taking it back tomorrow to see what the more experienced guys say. If the cable has to be lengthened, it appears it has to be replaced from the front through the frame all the way to the rear derailleur. Last weeks tech hadn't done that before and couldn't pull any slack through just trying to lengthen the short rear piece of cable.

This is by now an old story with the 11-28t cassette on the upper-level Shimano drivetrains.

Because of the 28t sprocket, the B-tension screw has to be turned in so far that there is a large gap between the top pulley and the smaller-middle cogs of the cassette.
The 10sp spacing is principally what makes the shifting so sensitive, as even the 12-27t 9sp systems didn't have this problem.

Short of fanatically adjusting, lubing and cleaning cables, or of pre-mature chain replacements (you are using Shimano chain, I hope) to hold side-play in check, the best way to deal with this is to swap your upper and lower pulleys. Note that the rotation is directional when re-fitting them.

This sounds rather home-spun, but I have easily doubled the service interval with this simple modification, and no need to replace chains before they reach the standard stretch wear limit. Shifting is much crisper as well on every one of the several bikes that I have done this to.
You could go one better by using an 11t ball bearing pulley in the lower position, which can be inexpensive while offering less friction than Shimano's top-pulley sleeve-bearing. I've sourced quite a few good lower ball bearing pulleys from discarded Shimno 9sp mtb derailers, and these work great. Shimano's pulleys are very high quality.

The mechanic may be right. If the rear loop is short it comes to the RD fitting at an angle. This causes extra friction, and sets up a stick and release motion on the wire. As you shift, the the resistance cause the long length to stretch under the added tension. Then when you shift a second time the tension is too much and the wire finally moves rebounding back to it's normal length.

Of course this is just a theory without seeing it, so try this quick diagnostic. With the bike on a stand (or a friend holding the rear wheel off the floor) shift to the area where you're having problems. Now try to shift, not with the lever, but by drawing the bare wire away from the downtube like a bowstring. It and the RD should move very smoothly, but if I'm right there'll be an increase in tension followed by a sort of release.

You mentioned internal cables, so if you don't have access to the wire, try the same test this way. Remove the wheel, and work the lever watching and feeling for smooth action, you might see the RD move in so of stick and jump motion.

If the diagnostic confirms the sticky wire, your best bet is to spring for a new cable, making sure the run to the RD fitting makes a nice graceful curve coming to the fitting straight on.

This is becoming a more common problem because the ferrule fit to the adjuster has gotten sloppier than it used to be in the past, and so much more sensitive to the length of the rear loop. Here's a trick that may improve it until you're ready to replace the cable. Use a rubber band to hold the loop at a smaller radius and enforcing the 180° bend, so it meets the adjuster with better alignment.

I think the technician meant that the short housing loop at the rear derailleur was too short. If this housing is too short it causes excess friction on the cable and sluggish shifting. As you shift to smaller cogs on the cassette (actually an upshift) the derailleur spring is pulling cable from the shifter and through the cable housings. Any excess friction will cause sluggish shifting. More often replacing the short housing requires replacing the cable. But if the cable is long enough it may be possible to cut the end cap off and replace the short housing by sliding the old one off of the cable and sliding the cable through the new housing and adding a new end cap. The standard length for the short housing is approximately 34 cm (13.4 inches).
I helped a friend install an 11-28 cassette on a 10-speed Ultegra drivetrain and it shifted perfectly with no changes to the derailleur or chain.

edit: I had not seen post #3 above before making my post, #4. We must have been typing at the same time.

Actually we were describing opposite effects, but they both spring from the same cause, excess friction in the rear loop.

Each of the last two times that Shimano introduced the tech details of a new shifting system (first with ten-speed, then with their hidden-cable shifters), they emphasized that they had developed a better grease to go with the new system.

I often find cables/housings apparently lubed with perhaps whatever grease the builder had handy during cable fitment, and often have to flush the thick stuff out of the housing. I usually follow up with a light application of GripShift lubricant, but here I just wanted to emphasize that only certain greases may be suitable for the cables of today's 10-speed systems, and most of Shimano's cable housings are now pre-lubricated with a very light-viscosity special grease for this reason.

And, to improve on the straight entry of the cable housing into the barrel adjuster, there are aluminum sealed ferrules available from Shimano which have a much tighter fit that the plastic ones, which, it seems, aren't even sealed half of the time.

The rear-most cable housing is particularly sensitive to friction, as any friction force here induces elastic stretch in the entire length of the cable wire, which of course compromises derailer movement resolution in both directions.

It sounds like the OP's mechanic may be very conscientious about the cabling, which today is a must imo. But without using a non-floating pulley in the top position with the 11-28t cassette, I would expect more-frequent attention will need to be lavished on the cable and housing as an ongoing hassle and expense.

I appreciate the feedback provided.

The bike is at my LBS right now. Just got home. And I talked to one of the very experienced techs there. Actually two of them including the one that assembled the bike. It seems that 2012 (and maybe older) models of the Specialized Roubaix were built with electronic shifters in mind, but they then realized they were going to be selling a lot of mechanical shifters despite their dreams. Problem with that is that the frame apparently has a point or two that basically somewhat crimps the RD cable inside the frame, and while electronic shifting can deal with that, mechanical shifters are not dealing with it well. So Specialized offered up a solution to this problem, but the LBS has apparently come up with an even better solution. Bottom line is it basically frees up the movement of the cable inside the frame work and results in smooth and consistent shifting. They said the short cable length at the RD is not the issue. They have already done this on about 20 bikes with perfect results to date. Mine will be 21. I'll be picking it up tomorrow.

But thanks again for any feedback.

For the record, the 2012 bike came with an Ultegra 11-28 cassette on DT Swiss 3.0's. I have Mavics on it now with the same cassette (not moved, but another one), but each wheelset and cassette has the exact same performance characteristics. Rode them both. And it also came with a Shimano 105 chain. Never understood why it came with a 105 chain while everything else is Ultegra, but that's how it shipped. Maybe they were trying to save $10 ? I see where new releases are now coming with 105 cassettes on DT Swiss 4.0's and Tiagra chains. Go figure.

This is an increasingly common issue with >8spd bikes, particularly with internal cable routing, and it pisses me off.

We're getting this hassle because today's derailleur is still compatible with a 6spd one, so shifters aren't pulling enough cable to be accurate about it. On top of that, return springs keep getting lighter... it's as if we're being pushed to electric systems.

Yes, the internal cable hype has me a little pissed, too. Better protects cables in weather, more aerodynamic, but doesn't work as well. They leave out that last part. Never had a seconds problem with my Allez and 105 stuff. I wanted the electronic version, but was told not to. Said out of the few they had sold, several already had problems. "Buy the mechanical version and never have problems." Yep.

Talk about bad advice...

You want a mechanical system without problems? 7spd.

Or look for more cable pull per shift; AFAIK SRAM is better in this regard.

Actually, I kinda doubt friction is the whole problem here. I gather you have a full-length housing run inside the frame, pretty much a worst-case scenario friction-wise... but it's also a worst-case scenario for housing compression, which is a serious issue with normal cable runs above 8spd. You may benefit quite a bit from ultra-spendy truly compressionless segmented housing like Vertebrae...

I'm hearing more and more how much better SRAM is than Shimano. Think my next bike, if that ever happens, might just be SRAM.

Swings and roundabouts.

All things considered, I'd say Shimano > Campy > SRAM, but there's not much in it and SRAM's coming up fast. The smart (and rich) gearhead picks the best of each, and fettles it all to play nice.

If I had a full Campy group I'd ditch the rear hub for Shimano. A full Shimano group kinda cries out for the STIs to be piffed for Ergos.

I'm pretty interested to get my hands on a pair of Doubletaps...

"Or look for more cable pull per shift; AFAIK SRAM is better in this regard."

I think that's only a valid statement when comparing brands of pre-Dynasys MTB derailers.

The SRAM and Shimano rear derailers, up till now, are roughly the same in this regard, i.e. less cable travel than Campag.

I'm told that Shimano's now 11s gruppos will have a longer cable travel, but at that level more and more riders will opt for electric.
I think that electric shifting will allow the highest gear counts, due to the absence of cable elasticity and friction.

LBS called me this evening and said it was ready to go and shifting perfectly. "If it doesn't shift great now, it's you."

I didn't have time to get it before they closed, but I'll get it in the AM and test it out. Said he would have to kill me if he told me what he did, but what it was is a shop designed retrofit to deal with that semi-crimped cable inside the frame near the RD. Not really crimped, but the path is a little restricted...or was.

If they'd have to kill you, then I'm guessing that they went wild and ran a continuous housing thru the frame, which would no doubt give the very best shift action imo.

Other than possibly being a PIA when replacement time comes around, there's isn't any drawback to internal cable routing if it's done right. Two of my bikes have it, and both shift smooth as silk.

The OPs shifting problems seem to have arisen from a specific bad cable routing, which caused some binding. That shouldn't be used as a springboard to indict internal cables in general, nor for a particular groupset.

IME, cable friction, whether from poor routing, liner wear, dried lube, or ferrule issues, is the number one cause of problem shifting. It plays no favorites, affecting the full range of systems from all 3 makers, and can make any derailleur shift like an entry level off brand, set up by the worst mechanic Walmart has to offer.

One key to being a decent mechanic is to recognize cable friction by it's effects, and address it promptly and properly.