Picked up couple gear cables from the lbs as I was replacing my apex shifters to some red shifters. When I was feeding the new, uncut, cable to the rear derailleur (with the original cable housing) it was like 5 inches too short for it. I thought those new gear cables are made for all kinds of derailleur systems. Did I do something wrong or simply I need a much longer cable for it?

That's really weird. Usually the cables are much too long to accommodate virtually any frame, as you say. Are you sure it's routed through everything and you don't have a big loop somewhere?

Sounds like the LBS gave you a bogus cable. If it's really that short return it and ask for a different one.

some kit come with a long (rear) and a short (front) cable.

If you bought the cables as a set, there is often a long and a short cable. If you bought individual, non-specific cables, they should be long enough for the rear.

I should clarify myself, I bought couple shifter cables (individual, non-specific) from my LBS and all of them are measured the same length as about 80 inches long. I thought 80" must be long enough for the rear but I can't get it long enough to reach to the RD. I know there is no loop or anything somewhere as I pulled the cable couple times to make sure. I am using the same cable housing so it can't be that. I am confused

That's how I routed my cable. Cable goes into the right shifter, along the handlebar and then goes down to the cable guide which is on the bottom of the BB shell. Straight into the cable housing on chain stay, loop around and goes into the RD.

A "standard" rear inner wire is typically 2000mm or about 80". That seems to work for most folks, but if you have a tall frame, or longish housing loops from the handlebar to stem it's very possible that it won't reach.

Problem for you is that the next common size is 3,000mm, and they're not as common, and cost almost double.

I don't think my frame is that big? It's just a 58cm frame, a Specialized Allez Comp Apex. That's strange and ridiculous when an individual gear cable won't fit it's RD! Cable housing loops being too long?

If you needed an inch or so you might be able to trim housings a bit. But you're over thinking this. If you bought an 80" or 2000mm inner wire and came up short you need a longer one. What is, is. It's not a problem to solve, just buy wires long enough for the job.

BTW- the 2000mm "standard" wire length goes back a number of years, predating Campy Ergo, to when Shimano STI wires took the shorter route out the side of the lever. It's fine for older road bikes, and mtn bikes, but apparently can come up short with the current under the tape routing on road bikes. It's possible that Campy and Sram added a few inches to the cables they provide in their kits, but it's hasn't trickled out to the aftermarket stuff yet.

I think the housing looks too swept forward below the handlebars. With shift cable running under the bar tape, there's no need to come forward of the handebars once the housing exits the handlebar tape. Have it go towards the other side of the bike just past the middle of the headtube, and then back as it goes to the side of the lower part of the headtube and to the cable stop on the downtube. You have a fairly large frame and you're adding a good bit of unnecessary cable length by going forward after the cable comes out from under the bar tape. That's why the standard length cable is too short. It would probably be fine with more efficient routing as it exits from under the bar tape.

Here's a link to a bike with a tall head tube, a similar setup as your bike. Look at the way the shift cables drop pretty much straight down. They look jumbled when viewed from the side, but if they go towards the other side of the bike after they exit the bar tape as I described above, there will be plenty of slack for turning the bars.

https://www.jamisbikes.com/usa/thebik.../12_quest.html

And here's one of my bikes with the shift cables under the bar tape. You can't tell it from the side, but there's plenty of slack in the cable to turn the bars because after the cable exits the bar tape it comes down in a nice gentle arc and then goes by the lower headtube and to the cable stop. Not forward at all.

That's a very good point. I never pay attention to that and seems like the guy at the LBS who built my bike didn't cut enough of those derailleur cable housings. I assumed once I trim the cable housing like FBinNY mentioned, the 80" cable should fit right into the RD. Will try that again tomorrow to make sure.

+1

One of my bikes, I forget which one at the moment, requires longer cables than the typical default. I don't try to shorten the bike. I just keep a small stash of the longer cables on hand.

Sorry to hijack but that is one Beautiful bike!!!

Thank you!