compact or triple

im going to get a trek 1.7 at moment i have a triple on my bike 8 speed 52/42/30 and 12/25 rear cassette, to match this will a 105 compact with 50/34 on front and 11/27 on rear be about the same or do i need a bigger rear cassette if they make one
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I would not worry about a small difference like that, but only you will know whether it would suit you.
But will a 105 rear mech take a 28 tooth cog? Maybe, maybe not. I do know that if you need a bit lower gearing that you can buy a 33 tooth front ring from TA Specialties.
Dennis Noward
'Cos triples aren't cooooooool enough. Tch, don't you know anything
That is a fact, that's why I ride a compact. A triple is fine for a tourer if that's what you're into, but it simply looks uncool on a racer.
2008 Rocky Mountain ETSX
2008 Ribble
It's a lot less cool when you have to get off and walk
See, they return, and bring us with them.
Triples are not just about smaller gears (though they do help). They're also about keeping your cadence steady by reducing the change you get when moving between the front rings. Most times you'll only change between the big and middle rings. The granny is there for when you really need it. Plus you can also reduce wear by keeping a better chain line with a triple.
Mostly the decision depends on where you ride. If your hills are not steep, then a double is fine. But once you hit 20% or more, a triple is well worth the extra few grammes.
- JimW