Chainset / cassette query?

Yedders

I have a 2012 specialized allez 16. The bike came with the shimano 2300 groupset. While I love the frame the groupset is cheap and problematic. I want to upgrade to shimano 105, but am somewhat confused as to what chainset / cassette combination to go for. The allez has 39/59 rings and a 13/26 cassette. I'm really disappointed with the lack of speed I can achieve in the highest gear and the lowest could do with being a bit lower for tougher climbs. I've been looking at a 105 standard 39/53 and 11/28 combination.

Is this a viable combination, or will the difference in gearing be too great?

crankycrank

Perfectly viable combo but as you've mentioned the differences between gears will be greater possibly leaving you without the "perfect" gear at times. For some it's not an issue, others will hate it. Maybe the only way to know is to try the wider spread and see how it works out for you or consider a triple or a compact 34/50 option with an 11-25 combo which would give you a fairly close ratio cluster and both a higher and lower gear than what you have now. Of course you could also wait for the new Shimano 11sp to come out soon. By the way, a 53t-11t is much higher than the 13t and you may find a 53t-12t will be high enough for you. Gearing calculator here. http://www.bikeschool.com/tools/gear-calculator