Recently a friend of mine got me interested into bikes, and although I don't have any interntion to do much biking, I want to get a flatbar road-bike. I found a really good one on Amazon for £225, and the RRP is usually £400. My friend said it would be a good one to start with and would match my needs. However the bike is 58cm and I'm only 5"6 and it's recommended that I get a 54cm. I'm only 14 and still am growing and would getting a larger bike be a problem. The other model availible is 56cm but thats £340.

Link?

Well that's a tough one cause you may not ever need a 58cm (or even a 56 for that matter). The top tube length on a bike that's too big can really screw up your comfort and is only finitely adjustable with different stem lengths. So that's something to consider. If you absolutely had to choose between the two, I would pay the hundred more for the 56, but that's just me.

Yeah but still £100. That's a lot.

Frames these days come in some different styles. But at 5' 6" a 58cm is too big by far for any style. I'm 6' 1" and ride a 58 that has a long'ish top tube but normally I take a 60cm classic fit road frame. So while you may grow into a 58 it'll be WAY too big for now. Even the 56 would be a stretch at your present height.

What you want to look for would be a 54 with a sloping top tube. They come in less sizes because with the right length of seat post they can be adapted over a wider variety of people sizes. A 54 of that style would do you fine until you hit around 6 feet then it would be time to review how it fits. And this last info assumes that you're a casual rider where the optimum fit isn't as big a concern. A serious rider would go through 2 in between sizes as they were growing in order to maintain the most efficient fit. But for casual riding and errands a "one size fits all" sloping top tube style bike would likely do you for a good number of years.

How tall are your parents? that has influence on how tall you will be..

but my dad was 6'3'', I stopped at 5'10'', ..
mom was shorter, some blending genetically..

get what size you can stand over.

It is still a crap shoot. I am 5'2" my brother is 6'. My mom was 5'5", dad was 5'8"

Thanks for the info guys, so would a 56 be all right?

I would find a 54, ride it until you outgrow it and sell it for probably waht you paid to get a larger size when you need it.

Dude I say re-read BCRider's post and keep shopping...you'll find as good of a deal with a little patience.

+1
A 54 may be big for you now, it may be the right size for you later.

Generally the size is dependent on leg length measured from the floor to your crotch in bare feet. I am 5' 9" and my leg length is 33.75". I ride a 57 to 59cm bike. Some bikes like Trek measure from the cen. of the BB to the top of the seat clamp On those I can ride a 60cm.

If you may still be growing and you're not sure if you'll get into biking much a good used bike would make the most sense. Lower initial cost and typically less loss when you sell.

Go to all the local bike shops and test ride their bikes. Find out what size is best for you. Remember that same size frames from different manufacturers fit differently. I have two bikes. Both 58's. One I test rode and it fits. The other was purchased off the internet and it is small. I have the seat post and an adjustable stem at their max height. It looks dorky, but the bike was a great price. You can learn from my lesson.

After riding their bikes for two hours, and using the salesman's time, tell them you want to buy a bike off the internet, then leave. It is good to be honest about your intentions. (just kidding - This presents an ethical conundrum.)

I don't know what a conundrum is. Somebody used the term yesterday, and I thought it sounded sophisticated and wise. So find the secret message in my previous note.

I think the 56cm or the 58cm would be too big but your personal comfort is better judgement. Personally, I'd look at the 54cm, you could ride that until you're about 5'10" You can always adjust the stem a couple inches either direction. Or maybe your LBS has a trade-in policy so you could upgrade size in a few years? If you get one that's too big, you're just going to have back pain.