Moved to Road cycling from Intros.

As far as geometry numbers go .... you should be able to find the geometry numbers (top, head, and seat tubes, chain stays, wheel base, tube angles) for each on Fuji's site. Stack and Reach are pretty much telling .... but ...

if the numbers are pretty similar, then with a slightly longer or shorter stem, more or fewer spacers, seat setback ... you can make a bike fit over a pretty wide range of frame sizes.

Most important thing is ultimately, how it feels to you ... if the numbers say it is wrong but it feels right, ti is right.

Also, there is no universal size system as there is with shoes (well, I guess there are three with shoes ... ) One vendor might measure and name its bikes differently ... and another vendor, using the exact same frame frim the same factory, might call it something else. Some might measure the seat tube and call it a 46-cm, and some might measure the Virtual seat tube and call it a 52 ... you never know.

We need more info ... can you link to the two bikes please?

Why are yuo worried (besides the number difference?)

Best money you can spend...most of us here have been at this for decades...if considering a new road bike purchase without a track record of previous bikes and related niggles due to less than ideal fit, is to consider a professional bike fitting.

Now, there are a couple of ways to do this. Inquire with the bike shop if they will give you a break on a pro fit...or, ask around at your local bike club and find out who the go to fitter is in town.

Fit is no.1 and even transcends your choice of bike. Fit is king and a pretty critical ingredient to your enjoyment on the road.

So, get a pro bike fit. If you are buying on line, you of course miss this vital step which many of us no longer need and we can buy a bike right to the nos. But you don't have this database in your hip pocket yet until you have owned a couple of bikes.

Good luck
PS: if you look at the chart...you will see reference to C to C versus C to T. These two references differ because of how a frame is measured. Center to Center is from center of crank to center of the top tube...even more complex is...with a sloped top tube is...'virtual sizing' as if the frame had a horizontal top tube. Center to Top is how frames are measured more conventionally...to top of top tube...again virtually if the bike doesn't have a horizontal top tube, and most don't today.

For you...your conventional bike size according to Dave Moulton who built this chart based upon thousands of fittings...you should be a a 48. A 46 is for the smallest among us...those in the 5' to 5'1-2" range. At 5'3" your sweet spot is closer to 48 C to T. That is a starting point and frames vary a bit mfr to mfr even within the convention of virtual seat tube sizing because of variance of of top tube length.

Your flexibility and even desire to ride aero affects your nominal position on the bike as well. So there is a lot to consider and no substitute for a fitter seeing you on the bike who will get a sense of your athleticism and even temperament for wanting to ride fast or more passive personality of just being out there on the road and smelling the flowers along the way. Some just want to hammer and their bike set up reflects this. Most don't however.

I have to disagree with camapg. A good fitting can cost a few to several hundred dollars .... and is really best for people looking to get a little more out of their bodies, not for a basic, "Is this bike the right size" sort of issues.

No reason not to go to a fitter if you really want o ...and can afford it ... but do a Lot of research to make sure you are getting a good one, and one who will listen and set you up as You want to be set up, and who will work with you if you ride more and your "optimal" position changes.

or .... you could do the same amount of online research about bike fit, and get a decent understanding yourself of what your options are, what different ideas are out there about fitting, and how they might apply to you and your body and your riding style.

You already have a drop-bar road bike. Are you comfortable riding it for an hour or more? if I were you, I might get my saddle/bottom bracket relationship dialed in---how far from the center of the bottom bracket (where the pedals connect) to where the saddle clamps to the seat tube) when the saddle is at the right height. I would also play with moving the saddle a little forward or back if it wasn't comfortable.

Then I would see how I sat on the bike----was I reaching too fr forward and carrying too much weight on my hands? Was I sitting more upright that i preferred? i would grab the handlebars at different places to try different body positions, to see what felt best.

Then I would measure the top tube, and find the length and angle of my stem, and reach of my handlebars. I would look at how far below my saddle, my bars were.

if the bike fit as it was, i would look for the same measurements on the new bike. if it was a little too long or tall or short, i would look for better numbers.

Gran Fondo geo chart Fuji Bikes | Gran Fondo 2.3

Those are two very different bikes.

I have the aluminum version of the Gran Fondo, the Sportif. Nice ride.

Comparing the 46-cm Gran Fondo and the 50-cm Newest. Hard to believe both of these fit you properly. (Not Impossible---I generally ride a 56, but I have a 50 Dawes which is Really comfortable. I also have a foot of seatpost exposed, and a hugely long, up-angled stem, and a gigantic stack of spacers. My "right" frame size tends to be a 56.)

Here is another tool which helps some but not others: https://www.competitivecyclist.com/S...ulatorBike.jsp I like this one because I have an oddly proportioned body, and "standard" fit charts don't work for me at all.

Based on what i see here, you do not need a very expensive professional fit ... you need a very simple, very basic fit done by someone with no agenda and no desire to sell you a particular bike. A pro can adjust your body for maximum power and such ... but you need to figure out what riding position suits you best first. You shouldn't need to spend hundreds of dollars to get an accurate basic fitting.

if I met you and you were asking me these questions in person, the first things i would ask you would be, "How long can you ride your Newest comfortably? How far do you usually ride, and how long?" Then i would look at you on the Newest for a while and see how it seemed to fit you ... if your Newest has an adjustable stem i might play with that, or swap in a couple different stems, or play with seat height and setback and such .... unless you were already supremely comfortable on that bike.

if the Newest fits really well and you can ride for hours comfortable, then you want to pretty much duplicate the same spatial relationship of contact points---pedals, saddle, bars---on your new bike.

I cannot help much more without actually seeing you on the bike.

(The Gran Fondo is considered an "endurance-geometry" bike, designed for the rider to be sitting more upright than on a "racing" bike. The Newest looks to have more "racing" geometry. What attracts you to the Gran Fondo? is it what is in the bike shop and it looks nice? I know the basic design is good (because I ride the Sportif) but if you prefer a racier frame .... you might want to shop around.))

Shakes head. Ummm Maelocks...you contradict yourself. What a surprise.
Your last sentence. If you saw her on the bike. That is what a fitter does. Can't this up..lol.

I have been doing fittings for 25 years OP. Word to the wise, be very weary of advice you get on the internet. ^^^^

If you want your best fit, ask your local bike club who does the best fittings in the area. If your bike shop can couple this to your purchase for a discount, all the better.
Fit is king. Unless you are a savant, your chances of nailing your fit algorithmically are slim and none and slim rode off on his bike.

I think Campag does not understand me, and is offended because i dared say i don't agree with him. Once i said I didn't agree, he didn't bother to look at what specific thing I didn't agree with--I became The Enemy. Welcome to the Internet.

Seriously, Fit is King. i Wholly agree.

What i do not agree with, is paying several hundred dollars for a professional bike fit. For a more casual rider, it is a waste of money. Any caring person with a clue about cycling should be able to help you ... for free. Any bike shop with staff which want to fit you on the right bike (as opposed to selling you whatever bike is on the floor and telling you it fits) will be able to help you find what's right for your body and your preferred riding style.

What he says about bike clubs is really good advice. if you meet local cyclists, not only will they have a lot of information gained from experience, they will also probably know which shops have trustworthy and competent staff. Quite possibly those very shop staff and owners will be in one club or another.

Campag 4 Life--i am not looking for a fight. The only advice i disagree with is telling casual riders to spend a third or a half the price of a bike on a fitting, the benefit of which they won't fully realize. In my opinion, pro fittings can be really helpful for people who want to get a little extra out of their riding time ... and for some folks who have never been fitted even halfway sensibly by someone for free or along with a purchase. Most people can get a sufficient beginner fit from a salesperson at a bike shop for free just for buying a bike.

Shall we not fight further, please?

No need to fight Maelochs. To me, you are mixing things up which you do time to time. I said nothing of a price tag for a fitting. Truthfully, $200 if picking a number is the best money a novice cyclist can 'ever' spend being placed on the right trajectory to enjoying the sport. An in depth fit isn't essential. A more generic fit is an OK starting point. If working up to riding 5K miles per year where further repetition can manifest an overuse injury, fit is even more critical. Cleat position for example is a science unto itself....how a foot tracts throughout the pedal stroke affecting knee health for example. Fit is extremely complex and too nuanced even for somebody with a heavy science pedigree like I have starting out. Too much to digest and apply. In fact, the study of fit is life long. Even after 10 years of riding, a student of cycling may and will learn something new about position on the bike that will either improve comfort or power or both, sometimes not at the exclusion of each other.

Btw, its ok to disagree. What the forum is about, to compare ideas. We won't all agree because we come from different walks and have difference experiences.

I will state again, the best money anybody who is willing to spend $1K more on a bike is a bike fit by somebody who does it for a living. If she lived near me, I could perform one for her. I end up fixing many club fits and help local cyclists with their fit issues. Even having a basic bike fit performed at the local bike shop is no guarantee of success. Fit is a work in progress.

I started riding back around 1980. I knew nothing about cycling. So, I bought Greg LeMond's book. In it, and other books, I read two things that still ring true. The first is that there are a range of frame sizes that can work. The French, Competitive and Eddie fits. The second is that the way to get into that range is to measure your inseam...socks w/no shoes...convert to cm and multiply by .667. That will give you your base frame size when measured Center to Center. Funny how it still works for me.

With respect and no quibble it works for you, it may not apply to others. But yes, old stand by of .667 x inseam will fit a large population of riders. But the landscape is quite a bit different today with un-square frame proportions aka endurance geometry frames many seek for a bit more upright position. Skewing of this proportionality may work well for a given rider or may work against them...depending on torso to leg length ratio. So selecting frame size today in particular with all the different geometries available is a slippery slope. But never been a better time to buy a bike today with all the frame geometry options. Issue is...sorting through the complexity what may work best for a given rider.

As an example, I am longer of inseam and shorter of torso. A Roubaix will fit me identically to a Tarmac for another rider the same height with opposite proportions aka long torso and short inseam.

Just to clarify....I have no issues with a professional bike fit. I have done several and would do it again. What I have found is that they put me pretty much where my estimate would be. For me, they are great for getting at details. I was just trying to give the OP an idea of how to determine if a particular frame size was "workable" so to speak. I ride both a 58 Masi Gran Criterium S and a 55 Guru Sidero (steel) and both work really well for me. The 55 is optimal and required little modification. The 58 w/ shorter stem and a couple other tweaks is just as comfortable. I agree that individual proportions will drive frame size. That's the place to start.

It's hard to tell unless you test ride the bike. I am firmly in category size 54cm for Trek and was even sized up for a 54cm (could hardly call it a fitting) and ended up being way too long.

I'd skip the pro fit as well, let the bike shop do a basic fit and you should be good to go, OP. People often WAY overthink fit, imo. It's true that the right fit is of paramount importance, but achieving a good basic fit doesnt require spending several hundred dollars with a professional fitter. Get the right size frame and go from there.