Have i not been changing gears correctly?

Yes, you're missing alot!  Assuming you've got 2 rings up front, you're only using "half" your bike....maybe less as I think most actually use their big ring most often  Short version - use big ring up front on flats and downhills, small ring up front for hills.  Also, you almost NEVER want to be in the small ring up front at the same time you're in the small cog on the rear.  Same with big/big.

I'm sure others more knowledgeable then I will chime in about gear ratios, cross chaining etc. 

No, you're not necessarily missing anything. Unless you're "spinning out" while on your small chainring, there's no reason to go to the big one. By spinning out, I mean spinning >110 or so RPMs where you're effectively not applying power.. This would occur in  your 39-13 gear at around 27-28mph.

The other thing you need to watch for is "cross chaining," where you have the chain on the small chainring and the small cog in the rear. This puts excessive strss on the drive train.

On a most of my training rides I stay in my small chainring. Folks who stay on their big chainring and average <20mph need to look at their candence.

I have to disagree with The Bear, which is not to say he's wrong I just have a difference of opinion on this. I have two attributes when it comes to cycling, the first is high wattage output for very short bursts which translates into being a good Sprinter. I'm the protected one when we race as a team. Sit in till the end then BOOM for 15 seconds. I can not however push the same wattage for long periods as my mates.

The other is a stupidly high cadence. When riding with team mates I am consistently 10-20% higher on my cadence than my two buddies who are just more powerful than I. IN MY OPINION (and please read as MY OPINION) you need to start working intervals in your "large" ring to build power and Threshold endurance.

If you know your avg cadence when cruising you can start going into the large ring and starting from the inside run up the rear cassette in 1 minute intervals trying to maintain that avg cadence. Some cal these spin-ups.

Find a gear combo (I don't know what you're running as far as your gears) that you can cruise in Z3/Z4 and start running 5 or 6 minute intervals. Eventually you can work up to twenties, that's twenty minute intervals in a high gear staying just sub-threshold.

When I'm barreling down the road at 27 mph I can promise you I'm not in my small chainring...

Good luck...

Eric J

first, thanks for the comments thus far.

however, i really need some explanations in easy to understand language Alot of what you just said Courage makes no sense to me.

if possible, i just need a short tutorial on when to use the small or big front ring and when to switch the rings on the back.

for example, if i need to use the big ring up front for the majority of flat riding....just tell me.  if i need the big ring up front for hills....just tell me.   

i just want to learn the absolute basics and go from there.   if what i am doing now is fine, then someone tell me so.  i just want it broken down really simple for me.

You don't "need" to use either ring for general cycling. Find a comfortable cadence, then find a gear that you can spin at that comfortable cadence at the appropriate heart rate for the training you're doing. Most people on here can find that gear combination for general training without leaving the small chainring.

What Courage is talking about is intervals- speedwork if you will- and should not be attempted by a rank beginner. Even when it is used by more experienced cyclists, many on here can do so from the small chain ring.

It's cadence and effort folks, the gear you're in is mostly irrelevant  and primarily a function of those two.

Im with you.

I'm lost. What is spinning out?

 I DO know my gears, but the terminology you guys are using makes us newbies lost.

I tend to stay in the big ring and smallest ring on downhills and flats, then move to the middle ring on the front and adjust the back for other stuff.

 but like she said. I need gear shifting for dummies LOL

Never said "no gear changes," go back iand read my last post. Particularly:

I have a triple, and my first year doing triathlon, almost exclusively used the middle ring on the front.  Only when there was a brutal uphill would I use the small ring, and only when there was a steep downhill did I used the big ring.  I always tried my best to keep my cadence around 90-95.

My legs got stronger over the past year, and now to keep my cadence in that range, it is necessary for me to use the big ring much more.  So no, don't worry about staying in the same ring all the time.  As you spend more time in the saddle, you will get stronger, and have more opportunity to use the big ring.

Sorry Bear I mis-understood as I read "a gear" as singular.

Latrina, by spinning out we mean your legs are spinning so fast with no resistance rather than using the revolutions of the pedals to give your bike more power, does that make more sense?  

thus far in my training, the only "issue" i ever have is i do spin out occasionally going fast downhills.

saying that, i should shift from small to big up front and smallest in back instead of small up front and smallest on back? does that sound about right?   will that give me more resistance?

and i should never be small up front and back or big up front and biggest in back?

so besides the spinning out i get downhill, i really don't have alot of spinning or cadence issues in my early stages of training.  so should i basically stick to what i have been doing, other that the change i mentioned above about my spinning out issue?

yes i do have a computer i use on my bike and yes i try to keep a cadence of 85-90.

Here's an easy way to learn how to use your gears.

Go for a ride on some rolling hills. Your goal is to keep your cadence unchanged as you ride up and down the hills. 

Think of your gears this way.  The small ring at the front is for your low gears.  The big ring at the front is your high gears.  Lower gears at the same cadence will move the bike slower than higher gears at the same cadence, but YOUR effort to pedal will be less with the lower gears (ie. you don't have to apply as much force to the pedal to move it, or think of it as less resistance for you to push the pedals).   On the back, as you've learned already the big cog is the easiest (ie. lowest) gear and the smallest cog is the hardest (or highest, or fastest) gear.

Now go to the hilly road and ride... you want to keep the cadence and effort the same on up and down hills.   Let's say you are riding along on a flat area and you come to a hill.... you are in the small ring on the front and the middle at the back.... when your cadence starts to slow (remember we want the effort to stay the same) you will shift to an easier (lower) gear, so you'll shift to a bigger cog on the back (I like to do this when my cadence drops to about 85) keep pedalling and every time your cadence slows drop down a gear.. if the hill is big or steep you may run out of gears an end up in your lowest gear ..... keep pedalling, when you get to the top of the hill shift up to the middle cog at the back and as you go over the hill and start down the downhill shift your front ring to the big ring... keep pedalling !!... if it's a big downhill you can shift the back to the smaller cogs (higher gears)... if your cadence falls below 85 you want to shift to lower gears again, which may mean shifting back to the small ring on the front, or you may be able to cruise along on the flats in the big ring for a while.  Always shift the back into the middle cogs before you change rings at the front (ie. don't have the chain on the smallest cog at the back and try to shift from the big ring to the small ring at the front.. this is the chain crossover other's talked about and can make you chain come off as you shift).

After a few rides you'll get more comfortable with shifting gears and you'll learn to use all of your gears.

Hope this helps.

What's your rear gearing when you are spinning in this range of cadence?  Assuming you're on a flat road with no wind.

So, if your using the small chainring and the smallest cog and your cadence is outside of your comfort zone (>90rpm) you need to shift to the big ring.

thanks guys for the explanations.

I need to get a bike computer. I'm somewhere near 75-78 rpm. Not to hijack the thread, but in order to get faster, continue riding and increase my mileage weekly right? (I read that here)

Something else you might want to consider is the wear and tear of your chain and cassette if you don't use your front gears. Let me see if I can write this down easily:

Basically, the idea is to keep your chain in as straight a line as possible. So, you'd use your small front ring with the 6-7 leftmost rings on the back. Likewise, you'd want to use your big front ring with the rightmost 6-7 rings on the back (yes, there's some overlap).

If your chain is often diagonal, it'll wear down rapidly, leading to shifting performance issues. Worse, it'll wear down your cassette quickly as well. Replacing this can be a relatively expensive exercise.

Just my €0.02