Road bike terminology "Compact" what does it mean?

[tjdixon911]

There seems to be two meanings, one relating to the Gearing, from what I can gather the front chain rings are smaller (less teeth) to help with climbing but reduce top speed, the other relating to frame design, what does this mean, and what is the difference between this and normal*? I've been told a normal* is better for me but I don't understand why!

• I don't know what the term for a Normal frame is..

When looking at bikes, where they state "compact" is this relating to Frame or Gears?

for example http://www.paulscycles.co.uk/products.php?plid=m7b...

Thanks

Tom

[paranoid airbag]

in that case it's referring to the crankset - the two chainrings are 34 and 50 teeth, a 'normal' is 39/53. You could fit a 39t and 53t chainring on a compact (if anybody makes them) as the word refers to the smaller arms the chainrings bolt on to. You couldn't fit a 34t chainring on a 'normal' crankset as the bolts would be too close to or even outside the edge of the chainring.

A compact frame means one with a sloping top tube, IIRC, some supposed handling advantages but the main thing is manufacturers need fewer frame sizes compared to a horizontal top tube to fit 99% of the population, i.e. just a S,M,L (maybe XS and XL).

[yellowjack]

As paranoid airbag has said, the difference between a 'standard' and 'compact' chainset is the circumference and consequently the number of teeth on the chainrings. This is further complicated (or simplified?) by the fact that manufacturers use a different spacing diameter for the bolt-holes of each type. I don't know the figures off the top of my head, but a 'compact' usually has a smaller Bolt Centre Diameter than a 'standard'. I wanted to increase the size of the chainrings on my roadbike from a compact to a standard, as I felt I was running out of RPM on downhills, but was told it was not possible to do so without changing the whole crankset.

I don't know if they are still available, nor can I remember the brand (but it may have been FSA?), but when I had to travel up to Norfolk earlier this year (while the TdF was on) I stopped in at http://www.fatbirds.co.uk/default.aspx and happened to mention this issue, and from behind the counter, one of the guys in the shop produced a pack containing 'standard' sized chainrings, with 'compact' sized BCD. It's not much help, and I can't see the product on the fatbirds website, but a call to the shop might shed some light for anyone (like me) who wants larger chainrings without shelling out for a complete crankset. I didn't have the funds at the time to buy the rings (they weren't cheap), and I've since accepted that as I get older, my need for a 'standard' or traditional sized crankset has diminished, and I have other priorities for upgrades on the bike, so I had filed this info away until I saw the title of this thread.

(FWIW, I seem to remember that fitting of the larger rings onto the compact crank would also involve re-fitting the front mech further up the seat tube, along with the possible need to tweak the gear indexing.)