Bike gear ratio / cassette question

Smaller cassette, i.e. 12-23, 12-21.  On the cassette, the lower the number, the bigger (faster) gear it is.  Many people swap out cassettes based on course profiles

What year is the bike?  Looking at 2011 and 2012, the P2 has a compact (50/34) on the front and 12/25 cassette.  I could see how with that setup on fairly flat courses you could run out of gears. 

It really depends on what type of terrain you usually bike on and where your races will be.  Really you only have one choice, and that would be to get a standard crankset (53/39) if you want more gears.  You could go from a 12/25 to 11/25 and that would give you one more gear.  But if you want more than that the standard crank is the way to go.

HERE is a really great article that explains it all and the differences you can see.

if you've got a compact in the front, and you're running out of top end- it's very likely because you've got a 12-25 on the back.  Your tallest gear, a 50/12 will require 100rpm cadence just to go 32.5mph.  A pretty easy speed to hit on a little downhill or with a tailwind or in strong group ride.  What you need is an 11-25 or an 11-23 if there aren't steeper hills in the area.  It's an easy and inexpensive swap.  Get yourself a chain whip and a cassette tool- and you can do these yourself in a few minutes.  the 50/11 will get you out to 35 or 36mph before you get over 100rpm.  If you need to power over 40mph on a downhill- then you can look to a bigger chainring.  But for now- just a cassette change.  easy peasy.

the main disadvantage of going from an 12-25 to an 11-25 is that you lose the 16 cog, which is right in the sweet spot of a little over 20mph. 

I like this guy's gear calculator

http://home.earthlink.net/~mike.sherman/shift.html

Another choice is a larger chainring set: 42t inner and 55 or 56t outer. A 56-12 will be more efficient than a similar gear of 50-11. In general, larger chainrings and cogs will be more efficient than smaller cahinrings and cogs for the same gear ratio.

For BT poster to help you we'll need to know what size chainrings and cassette you have.

Really?  he's got a compact with a 110mm bolt circle.  you think he should change out his whole crankset to go with a beast of a chainring that few pro cyclists can even push- just to get another high speed gear?

Thanks for all the advice.

I have a 2009 cervelo p2. Im not even sure what cassette it has.  Whatever was stock with the bike.

Count the protrusions on the first cog (smallest on the cassette). Theres your first #. Do the same for the largest cog and there's your 2nd #.

I just checked Bikepedia and Cervelo website and I was very surprised 50/34 compact cranks come stock.  My recommendation is to buy a 53/39standard road crank. You can get a new Ultegra 6600 in the $150 range. A gearing of 53-12 will be more efficient than a 50-11 because the links don't have to pivot as much. Another benefit is you will be able to keep your cadence ( and heartrate) in a narrower range since the % change cog to cog will be less for the same speed as a compact crank.

A new chain or additional links and an adjustment to the FD will be in order whether upgrading to a standard crank or larger chainrings. 

Save yourself 3 minutes and just look for the stamping of how many teeth is on the gear. Sometimes hard to see, but you cogs will be stamped with the # of teeth somewhere along the side facing out away from the hub.