jaimwa said:
If I changed to the 12-27 and a 38t inner chainring on the crank shoul Id just leave the 53t on the outside?
Would you mind explaing to me what a compact chainset is? I looked at some of the online shops and i can see visually what it is but if I changed both the inner and outer chainrings to to 50 and and a 34 does that mean I now have a compact? Or is it the other part (the crank?) that needs to be changed too? The crank - I think that's what it's called, is a 175...
There may be a marginal (little-if-any) benefit to changing the 53t to something else if you change the 39t inner chainring to a 38t chainring, so save your money.
AFAIK, "Alpine" gearing was originally a pejorative label for cranksets which did not have the "normal" 52/42 chainrings which was once typical on road bikes.
WHAT'S IN A NAME? The "
compact" designation/label seems to have been coined by PINARELLO as a euphemism when
Senor Pinarello decided to sell one of his bikes with a
110BCD crankset on it several years ago (~2004?) ...
THAT + Tyler Hamilton's epic ride with a broken collarbone gave "Alpine" gearing a respect amongst the
aficionados that it never had before. Thereafter, almost every crankset manufacturer now has a "compact" crank in their catalog.
Generally, a "double" crankset whose BCD (bolt circle diameter) is 110mm is now considered to be a "compact" crank whereas in the past that size BCD was typically only found on "touring" & MTBs (usually, with a granny) before the advent of the 4-arm/104BCD MTB cranksets.
Several years ago, I configured an older XTR crank (112BCD) with a 50t outer chainring + 34t inner (
sans granny) ... AND recently, an XT crank (104BCD) with a 48t outer ring + the 32t inner chainring that came on the crank (
sans granny) -- both would be considered "Alpine" gearing ... but, those would
not be considered to be "compact" cranks.
FYI. On most-if-not-all current Shimano cranks, the model & size are indicated on the backside of the arms -- the information encircles the pedal axle's hole. On your crank, it probably reads something like:
175 FC-7800 SHIMANO JAPAN ... (etc.)
... where "175" is the
length of the crankarm as measured between the center of the pedal's axle & the center of the BB spindle.
BTW. Although a 39t chainring is now the generally available smallest for a "regular" road crank, a 38t chainring is available for cranks with a 130BCD. Similarly, for a crank with a 110BCD, the smallest chainring which is generally available has 34t, but a 33t chainring is available from TA.