If I'm close to 6' tall, will a 54cm frame be too small or manageable?

I would have to say that a traditional geometry 54cm will be WAY to small for you. I am ~5'11" and ride a 56cm with a fairly long stem. Keep in mind that this is a very general statement since there is much more to bike fit than your height. For instance, I have a long torso and quite short legs. (32" cycling inseam) So, depending on your build, you may even need to go to a 57 or 58cm depending on the manufacturer. Your best bet is to go to a local bike shop (LBS) and get a proper fitting done.

Good luck!
Bob

Here's a "fit calculator" that someone else posted...

https://www.competitivecyclist.com/za...sex=M&units=cm

Sweet! Thanks for posting that, CheesyD!

If you have average proportions you will probably end up at about 58cm for most brands. A race setup might put you on a 56 but no smaller. To ride a 54 you will need a mountain seat post and a pretty long stem. Also, the crank arms on a 54 might be a little short for your liking. A lot of compromising to ride a frame that doesn't fit.

Pants come in waist sizes and leg lengths. You have to get them both right or they won't fit.

Bicycles come in seat tube and top tube lengths. Not only do you have to get them both right but all the bike manufacturers don't even measure them the same.

Bike riders come in different porportions of torso's vs. leg lengths. Consequently, two riders who are exactly the same height might have different bike sizing needs.

I wouldn't put too much reliance on advice given by someone who has never seen me and whose background and experience are unknown to me.

Problem is, one "model" of pants comes in a "grid" of waist sizes and leg lengths. Typically, one model of bike comes in a "linear" selection of frame sizes, with the seat tube and top tube lengths increasing proportionally. To get the right seat tube / top tube combination, you either have to shop among different models (potentially compromising on quality, componentry or features) or go custom-made. So yeah, it's a lot more complicated than simply going by overall height. It's even more than just upper-body vs. leg length. Ratio of upper-leg and lower-leg length determines crank length, seat height, fore/aft seat position, stem length, stem height, etc.

I just sold a 56cm semi compact goemetry frame that was a hair too tall for me but I liked the length so now I am on a 54cm with a 120mm stem and it is just right . I am 5-9 with a 31 inseam. I you are 6 ft it is way too small for you . You would probably need a stem that is not avilalable, I may be wrong but I think they only go to 130mm.