Is it possible to make a larger bike fit a smaller person?

Lowering the saddle to the lowest level and see how it affects your overall position on the bike is a good start point. Coincidentally, a colleague and friend of mine has done exactly the same, and I almost thought it was you until you mentioned about school :p. Some people would stand-and-pedal, but that is not ideal to do all the time!

Another thing to try is that if your saddle slides front-and-back, see what position you require it to be fixed. This is to get your heap ergonomics right. I hope you have got your allen-key turner available at home :)

UPDATE Mind you that frame sizes for road bikes and MTBs vary a bit. What I mean is that the if you want to buy a road bike, the appropriate frame size for you will be slightly bigger than its MTB counterpart (e.g. 19" road/hybrid bike fr == 18/17" MTB fr).

If you are in the UK, the bike shops usually have charted measurements available for you to find out the optimum height and frame size for it. It would really help us if you give further information such as what exactly is the problem that you experience with this current frame size? Bob (or whoever the guy you spoke to) might have said things to sell a bike to you, but he could very well be right about the size. Coming back to the colleague of mine's bike, it was a carrera 18" MTB and his height is 5' 7". It was just about right, but he could have used a smaller frame. But when we adjusted the seat post height, it was alright although we could have used a slightly smaller bike size. If your round trip ride does not contain too much of steep hill climbing, you should be fine pedalling through. Again, it would be good to know what your height is and the size of bike frame you have.

Try lowering your saddle first and meanwhile, let us know your height and frame size. To help you understand, I am 6' 3" and have a perfect fit bike of 19" frame (48 cm). I can probably do with a smaller frame, tried in the past.

A couple of things to tide you over:

1. Obviously, put the seat down as far as you can. If the post can't go any lower, you might see if you can get a shorter post, or have the current post "chopped" to a shorter length (although that will probably cost you).

2. Move the seat as far forward as possible. To do this, you loosen the seat from the post using a hex-wrench; move the seat up, and then tighten back up. To really get the most possible, you can even try tilting the seat forward, although this might leave you feeling like you're sliding off of the bike (this is what my wife did to fit into her antique 3-speed).

3. You can loosen the handlebars and turn them upward, so you're not as stretched over the frame. To take it one step further, you can remove the handlebars, turn them around, and put them back on backwards ("bull horn" handlebars), but that will require re-taping and doing some more serious cable adjustments. It sounds like you just want to make a quick fix without too much work.

In general, being 3" too short for a bike probably isn't too bad. All of these fixes will lead to the overall fit changing. Stay on the lookout for someone who looks a tad too small for their own bike, and maybe you can engineer a trade at some point!

Getting the seat/pedal distance is the first important measure so that your extension is optimal, usually about 30 degrees. With that set, then reach, fore/aft & the other variables can be dealt with & if it doesn't feel comfortable after a couple of 40-50 mile rides, get the proper size. All bikes feel good at first, but the best test is comfort for knees & back.

As @WTHarper and @amcnabb have mentioned, you can't do much if your top tube prevents you from standing with your foot flat. You'd be replacing too much of the bike to lower it (wheels, crank, etc.).

You are not alone though. I also ride a bike that is slightly too large for me, but closer to .5".

On casual rides, I can overcome this by wearing shoes with a slight heel. If you're a lady, some wedges could easily take care of 3". Cowboy boots are also a nice option.

You probably can't mount your bike without already knowing this, but it also helps to angle the bike when standing over the frame. There isn't any reason why the bike needs to be perfectly perpendicular to the ground.

Your best option is to sell your bike and buy another better-fitting used model.

If that isn't possible, know that bike fitting is as much by convention as by natural law, and that many early safety bicycles had what we now consider very large frames for the rider: http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Columbia_Model_40_Mens_Safety_Bicycle%2C_1895.JPG/1024px-Columbia_Model_40_Mens_Safety_Bicycle%2C_1895.JPG To compensate, bicycles of that era used rear-facing handlebars, which significantly shortened their reach. Velo Orange makes similar handlebars today, and you could potentially refit your bike to fit you by purchasing a pair. Be aware that the handlebar diameter may differ, and you should learn and research what that means for your stem/brake levers/shifters.

You may want to add a top-tube pad to protect your crotch in the case of rapid dismount, as well.

I am in a similiar position. I can stand over the cross-bar alright but its a bit of a stretch to the handle bars. I adjusted the seat and that felt alright. I just tried reversing the seat post so that the curve goes forward. I'll be cautious. The seat points up more than I would like but my initial impression is that this will work.

I have also thought about bending the seatpost - I'll consider this but its not easy to recover from this and would make the bike difficult for a 2nd owner.

Another suggestion would be to put 1/2 inch or 1 inch 'lifts' (would or plastic) on the pedals to shorten the reach. Likely using raised shoes may be more practical.

In the old days when I got my first grownup bicycle with the seat at the lowest my dad used block of wood on my pedals so I could reach ... not the best looking deal but a fix.

Try aerobars that are adjustable so you can move the elbow padding closer in the direction of the seat. Be sure to test this going downhill as you would changing the handling characteristics with more weight over the front wheel. If it feels unstable, send your aerobars back.

There are in fact two most important dimensions that determine how you fit the bike (from my experience):

• the distance between the bottom bracket and the top of the saddle, which should match your inseam lengt
• the distance between the saddle and the handlebar mount (where the bars meet the stem), which should match your trunk (torso) height and arms length

The former is determined by the combination of the frame height (thus frame size) and the seat post length.
The latter is determined by the frame length and the stem length.

In your case the frame size is fixed so

in order to make your bike fit better you can play with seat post height and stem length only.

The rule of thumb is that with those parts you can virtually "adjust" the frame by +/- 2 sizes. I'm afraid that it is still outside of your optimal size.
Me myself, I'm 178cm tall and I find one of my bikes with frame size 54 (length is 54 c-c if I'm not mistaken) with 11 cm stem a bit to large (I can live with the frame height, but the length is giving me lower back pain on longer rides).

Furthermore, if your road bike is of the older (vintage) type and you want to change the stem length, it means that you either

• replace the stem requires either putting the threadless stem quill adapter, modern and shorter stem like RJ the Bike Guy did in his tutorial on How To Convert Quill Stem To Threadless Stem With Adapter On Vintage Bike, or
• you replace the stem quill for the older type (provided you find a short one) and rewrap the bars, etc.

Both are costly options comparing to the value of the bike.

As suggested earlier, the best (most cost efficient) option for you is to swap this bike for something smaller.

Check out a triathlon bike post. They bent forward.