What is the most effective way to upgrade my Cervelo S2? I bought my Cervelo S2 2013 model a few years ago.

It has Shimano 105 groupset and brakes, and originally Fulcrum Racing 7 wheels which I have upgraded for Planet X Carbon 45mm wheels. The rest of the components is general aluminium stuff that does the job and I often stick a pair of aluminium Profile aerobars on.

I mostly race short 10-40km as part of triathlons, but I also use it for longer rides and even "touring" (with a rucksack rather than panniers).

I know the standard thing to upgrade is the wheels, but since I've already done that, I'm thinking maybe a better groupset?
My question to the world is: what would be the most effective upgrade to make me faster?
To get faster times, your options are:


Accelerate faster
Cruise faster
Decelerate faster


To accelerate faster, reduce rotating weight and increase bike &amp; component stiffness. Reducing non-rotating component weight will not have much effect unless your races involve a lot of climbing, especially as lighter components are usually less stiff unless you're swapping cheap alloy for good carbon fibre.

To cruise faster, reducing drag, rolling resistance and drivetrain friction will help, in order of impact. Your body and clothing are currently the greatest contributors to your drag, especially since your frame doesn't use round tubes, has internal cable routing, and your rims are deep. Rolling resistance can be decreased by increasing your tyre width, since you're not racing on perfect surfaces (such as wooden velodromes). The current fashion in the pro peleton is 25mm. 

To decelerate faster, use soft-compound brake pads. Reducing rotating weight also decreases the load on the brakes.

This review of a bike which I think matches yours lists the weight as 8.08kg. This isn't bad, and losing 1.3kg to get down to the 6.8kg UCI minimum will be far more expensive than eating less and riding more to lose body weight.

Things I would consider upgrading:


Tyres. Easy upgrade, quite cheap.
Chainset. The Praxis Turn M30 crank is about the same weight as Shimano Ultegra, but is surprisingly stiff. Praxis make a matching bottom bracket for most shells, including "old-school" BSA threaded 68mm shells.
Stem. Thomson Elite X4 is heavier than their X2 "road" model, but you'll struggle to twist the stem and the 4-bolt clamp is nice and wide.
Carbon bars, but not a superlight model, since you need them to be stiff for acceleration.


Of course, you still need to train more.