Rear Derailleur question
 

I have Tiagra rear derailleur and it's starting to get hard to shift into the lowest gear or two. Any suggestions for a fix or is it just that the nature of the Tiagra????

Thanks.

I doubt it is your RD. Much more likely that your shift cable & cable housings need to be replaced. Also check the cable guide underneath your BB and replace if it looks worn / gummed up (the guide can create a lot of friction when worn and it is a very inexpensive part to replace).

Swap the RD cable and housing.
Spray a lot of WD-40 into the brifter mechanisms. This makes a mess, do it outside. Let the solvents do their job and clean the gunk out. Spray some lubricant on the mechanisms. Shift up and down the entire cassette to work the lube in.

Voila.

What Grambo said. Depends what you mean by 'lowest gear or two'. This is often hard to understand on forums.
Upshifting is technically stair stepping Down the cassette. Are you speaking of lazy shifting to the smallest cogs?
This is generally due to cable friction as Grambo said. The way a derailleur works is the rotory spring rate is most challenged on the outboard i.e. smallest cogs because the spring is less coiled within the derailleur. So generally increased cable friction due to worn/dirty cables will affect outboard rear shifting the most. A tip is...if you leave your bike for a long time...generally shift it to its smallest cog which relaxes the derailleur spring the most. Same with front derailleur but a bit less of an issue.

As has been stated...check replace the cable and housing...maybe only the short length of housing from the chain stay to the rear derailleur is gunked up and restricting cable movement if that is a problem.
Before replacing the cable and housing though thoroughly clean the rear derailleur and chain, readjust the cable tension.

If it started suddenly, it could also be a bent hanger. Plenty of things to check. Take it to your LBS if you aren't sure about checking or fixing these items yourself.

+1 In my experience a bent hanger maybe the single most overlooked reason for poor rear derailleur indexing.

When I say "lowest" I mean like first gear in a car vs 6th or your "granny gear".

I'll lube the cables real good & see if that helps. If not, off to the shop.

I asked about the Tiagra b/c I've already (about 2,200 miles on the bike) replaced the front derailleur. The front was getting jammed up to easily - probably b/c of lack of cleaning on my part. The shop said that they don't seem to have that problem as often with Ultegra & the price difference was small anyway.

If the RD only has 2,200 miles and the DH hasnt been bent you probably just need to adjust you cable. I hate to say it but your LBS may be looking to up-sell.