I have a 63cm leader frame, which is 2 or 3 centimeters a little bit to big for me. I was wondering since the frame is a little big on me, should I buy a smaller crank? I'm 6'4. I was thinking about buying 170mm cranks instead of 175 or 180. Is this a smart decision?

Take a ruler and look at the size of 5mm. You won't even notice it realistically.

Either one would be fine. I would just use 175's for simplicity though.

165mm would give you better pedal clearance in turns though...

Lies. LIIIIIES.

Crank arms come in 2.5mm increments for a reason.

According to the ruler logic, I guess he wouldn't notice a centimeter or two on the top tube either, right?

My intent was based around his original post. If his frame isn't perfectly sized as is, then he more than likely isn't the type of person that will notice a 5mm change. I'm more than willing to admit I'm wrong when it comes to hardcore riders, but the average person likely isn't going to notice such a small change in cranklength.

If your frame really is 2-3 cm too big then you probably need 165mm cranks, and maybe a shorter stem too. How does the reach feel?

Especially if the OP ever rides in different pairs of shoes. I know for a fact the three different pairs of shoes I rotate between when riding have more than 5mm difference in the thickness of the soles.

In an ideal world I would have a dedicated pair of riding specific shoes, probably clipless, but I like to live practically which for me means working with what I have and overlooking minor changes

buy cheap ones and experiment

Oh, I never answered the original question.

If the frame is too big, swapping cranks won't help.

Frame sizes are like shoe sizes. If they don't fit, they won't fit.

I will gladly take that frame off your hands and donate to the foundation of the tall and needy cyclists

crank size! heh heh heh

I had the misfortune to have a frame 6cm to large for me - I called my FUJI "The Horse" - Try as I may I never got comfortable on it and eventually got a proper sized frame transfered all my components...

Grammar nazzi.

And your answer..

Frame size shouldn't dictate your crank length. Your leg length and pedaling style should.

^ That's the story, zap. I don't know how shorter cranks is gonna make a too-big frame any better for you, unless you're in a seatpost totally slammed but you're still hyperextending situation. Then I reckon the short cranks will help you shoehorn yourself onto this too-big frame.

Wear shoes with thicker soles, look for the saddle with the lowest profile - these methods would be cheaper than new cranks.