Today I tried out a bike and the top tube came up to my crotch exactly, if i was standing flatfooted the tube would barely touch. The bike was a size 56cm. Now I know the bike is slightly too big, but what are the disadvantages of having a slightly too big of frame? the guy at the bike store said a 54 might be on the small side and the 56 is slightly on the large side. however a 54cm bike isn't available. would i be making a mistake as to purchasing the 56 anyway?

A larger bike will feel sluggish in steering compared to a smaller bike. I just took a test ride on my new bicycle today, which is a lot larger than the too-small Huffy I recently re-homed to someone else. It feels larger; it's difficult to describe.

But you also need to consider things such as reach and comfort while riding. If you can acquire the 54cm frame version of the bike, and get a slightly longer stem, it may be very much worth the wait. If the 56cm is too large, it won't be so great a ride.

I had a synapse that I bought off the floor and it was a 56 , well it got warranted and I just said give me a new 56 EVO and all is good had a high tech 3d, video, fitting and love it , then I decided to buy a regular supersix for a backup / winter bike and when I asked the same shop what size I should get they said a 54 would be perfect . Long story short I have both bikes set up (the 56 and the 54 ) the same in relationship with the crank , seat, and bars so when I'm riding my pedal position is the same BUT I like the compact size of the 54 better.. of course the EVO is a better bike and performs better but I wish it was a 54..If your buying a bike you plan on having for a long time and spending a lot of money get it right the first time..... Hope this help

What bike are we talking about? It seems very unusual in this day of curved and/or sloping top tubes for stand-over to be any sort of limited factor. Ignoring stand-over, how is your fit on the 56? What stem length, what seat to handlebar drop?

Mainly, a bike that you can straddle that's still too large will stretch you upper body and arms out over the top tube. You might be able to get the handlebar high enough that you won't get shoulder pains, but the bike will be difficult to control.

The most important factor to fitting a road bike is correlating top tube length to the length of the torso in a cycling position. Then factor in leg length, arm length, general flexibility, and athletic aptitude.

The frame sounds too large, particularly if the TT is sloping, then it's definitely too large - may be two sizes.

The idea that the next size smaller would be too small is nonsense. Most adjacent sizes only require one size shorter or longer stem to have the same reach. The stack height or handlebar height difference is often larger - in the 10-25mm range.

What you really need to do is post your true cyling inseam, or better yet, an accurate saddle height and some more info on the bike.

As for the bike feeling sluggish, that's not too likely, since the weight balance would only be slightly different that it would be for someone who fit the bike perfectly.