Hi everyone...

Need some advice please: I currently ride on a custom built Cannondale CAAD10 with Shimano 105 componenets. I've realized that 10 gears is not enough for me, as I find myself often times over-paddling going downhill (as in missing another gear to up shift to). I *assume* (?) that replacing the cassette with an 11-speed one, would help things out? I guess I just don't know if the additional gear is for the lower end of things or higher (or rather compensates for both)?

Also, if an 11-speed setup is recommended, what would be a decently priced set? Would the "105 HG (11-Speed)" fit?

I'm really clueless when it comes to the 'mechanics' and technical part of my bike

Thank you in advance

You can't run an 11-speed cassette on a 10-speed (rear) bike. You need the corresponding derailleur, shifters, crank, and chain as well. Also a compatible wheel. Mucho dinero! What you can do is change your 10-speed cassette to one with a smaller cog (higher gear), namely the 11-tooth cog, if you don't already have that on your current cassette. Or if you want an easier gear, get a cassette for 2X10-speed with a larger cog than you now have. Or you can have both larger and smaller. Just keep in mind that you have to give something up, if not a cog at one end, then one or two in the middle of the range.

Pretty much all stock bikes (including 10 speed) come with a lowest cog of 11 or 12 tooth. If all you want is a bigger gear so you can pedal downhill and you have a 12, you can just swap the cassette for one with an 11 tooth cog. Or get a larger chain ring if you have a compact/mid compact. That being said, pedaling downhill where you're already maxing out your speed (35+ mph) is not really an effective use of your energy due to aerodynamic drag.

count the teeth on your rear smallest cog and get back to us.

Other ways to address the problem are to cultivate a broader range of comfortable cadences so pedaling rate can compensate for the missing gears or learning to shift more easily between front chain rings.

IF you hit escape speed (meaning too fast to pedal), try going to an 11 tooth. If you still hit it, then you are reaching a terminal velocity, where pedaling is actually more inefficient than tucking. Thats when you grab the drops, tuck as hard as you can, and get aero. Thats how you gain speed.

Sounds like you might be up the proverbial YKW creek without a paddle.

@Dannydyn: as you've read, 11-speed doesn't offer a "faster" high gear than 10-speed (and so on?).

You would pay ~$380+ for a Shimano 105 "5800" set of components plus whatever you'd need to pay to have an 11-speed rear wheel plus installation. What you'd get on the rear cassette is one more gear choice in the middle. (There are other differences; (almost) everyone is enthusiastic about 5800. But 5800 does not give you a higher gear.)

Two comparable options:
With a Shimano 105 5700 cassette, you can get 11-12-13-14-15-17-19-21-24-28.
With a Shimano 105 5800 cassette, you can get 11-12-13-14-15-17-19-21-23-25-28.

What everybody said already... If the smallest cog on your cassette is 12t then get one where 11t is the smallest.

Or you can save money by learning to pedal faster. I've ridden 40 mph on a flat road with 12t as my smallest cog. (For you doubters, I was drafting a car.) Once you're above a certain speed rolling downhill, just tuck and coast tho...

And count the teeth on the large front chainring.
Most probably the solution is learning to pedal at a faster cadence. 85-100 is considered by most to be the optimal pedaling cadence on flat & downhills. Climbing up steep hills is often done at a slower cadence.

If you're ever in Norwalk during the week day, I'd be happy to meet up and take a look at your bike, go for a spin and offer any tips.

bigger chainring

Hot or not ?

does that come in oval?

The smallest cog that will physically fit on a rear wheel these days is an 11-tooth cog, which provides some "top end" improvement over a 12-tooth cog. If you want big changes though, you need to address the front end of the gearing -- i.e., bigger chainrings, not smaller cogs.

One other thing to consider -- as the tooth-gap of the front chainrings increase, shifting gets progressively worse. i.e., compact chainrings have a 16-tooth gap (34 to 50), which is "pushing it" in terms of the jump that the derailleur can handle. i.e., put a dramatically bigger chainring on and you might need a bigger "small chainring" as well which is going to affect your low-end gearing rather dramatically.

What sort of speeds are you maxing out at? Most people stop pedaling around 35, 40mph -- the power output required by you to push the speed higher as the speeds creep up into the 40mph range is "a lot".

If you want to get faster on downhills... get deep-section rims or work on your tuck. Aerodynamics are your friend at downhill speeds.