3-4cm of clearance is plenty. When you're riding, your body does not care about standover clearance, it cares about how stretched out, or not, your upper body is. Sizing people based on standover is ridiculous. Besides, when was the last time you crashed and managed to somehow straddle the top tube? Maybe this is a problem for some, but in 15 years of riding, including racing, and many crashes, I have never had a groin to top tube collision.
I'm a similar size, and have ridden many 54 and 56cm bikes. Some 54cm frames fit while others were too small (short); some 56cm frames fit well while others were too big (long). If pressed, I'd put you on a 56 based on your comfort on a 18.5" Trek. Ride both sizes and see what feels best to you, keeping in mind that you can easily run anywhere from a 90-120mm stem without seriously affecting the handling of either.

 

I would always go smaller just to get a shorter top tube- like you said, you can use a setback post and a longer stem, and it will not effect the handling as much a sliding the seat way forward and using a 80 mm stem or something short like that. I bought a cross bike recently that felt fine on the road, but is just too stretched out for a cross course. With a short stem on it, the handling is really twitchy.

 

I would always go smaller just to get a shorter top tube- like you said, you can use a setback post and a longer stem, and it will not effect the handling as much a sliding the seat way forward and using a 80 mm stem or something short like that. I bought a cross bike recently that felt fine on the road, but is just too stretched out for a cross course. With a short stem on it, the handling is really twitchy.

But the OP wasn't complaining about reach, he was complaining about standover. IMO standover is overrated; having an inch or two more clearance is no guarantee that you won't smash your nuts in a crash or missed remount, anyway.

Some more food for thought: When you size down a bike, you are adding almost an inch to the amount of exposed seatpost. Or in other words, the headtube is shorter, which effectively moves the handlebars down and away from the saddle. So even though you're shortening the top tube, the bike won't feel "shorter" unless you add a couple headset spacers (provided you have enough steerer tube available) or use a riser stem, etc.

 

1. Find a traditional road bike that fits your leg length at your LBS. (Don't size off of a Giant) Hopefully, you won't need special top tube specs.
2. Subtract 2cm for a cross bike.

This should work for a plain old 'cross bike from Performance. There are exceptions, like an Empella, but Road Dims - 2cm will get you into something about right.

 

1. Find a traditional road bike that fits your leg length at your LBS. (Don't size off of a Giant) Hopefully, you won't need special top tube specs.
2. Subtract 2cm for a cross bike.

I strongly feel that this is bad advice. There is no reason to "size down" a cross frame.

 

I have a 56 Fuji Cross Pro. Same frame as the Cross comp.

I'm 5'11" with a 32.5 crotch to floor / 72cm bb center to saddle top. Short legs. I ride a 55 lemond road bike with a 56 effective top tube (sloping). I ride a M 2005 Specialized Epic (59cm eff top tube i think). The 56 fuji cross frame has a 56 top tube. The 54 has a 55.5. top tube. In hindsight, I'd rather have the 54 as I think it would handle better (same head tube I think, so stack is not an argument on this frame). I also run a shorter stem than my road bike (2cm) and a 1cm more forward saddle. I think at your specs, the 54 sounds right.

best,
some dude on the internet.

 

I strongly feel that this is bad advice. There is no reason to "size down" a cross frame.

agree. my overall reach is about 2cm shorter (taken off the stem), but the frame itself is almost identical to my road bike. this feels perfect to me.

my advise to the OP is to FIND a LBS that can help you....getting a good deal online won't mean much if you have to sell the frame after a few months because it doesn't fit.

btw... most shops would be willing to order you the frame, even if they don't carry it.

 

my advise to the OP is to FIND a LBS that can help you....getting a good deal online won't mean much if you have to sell the frame after a few months because it doesn't fit.

I completely agree with this.

First, bike sizes mean very little. There are several methods to measure bikes, and in some cases a 56cm may be smaller than a 54cm frame. Unless you understand how a company is measuring their bike, the number really means little. Think about it like buying a t-shirt - sometimes a medium fits you, and other times you need a large - there is no standard for sizing.

Second, the best way to size a bike is by the combination of the effective top tube length and seat tube angle. These two numbers, if you know how to look at them, tell you how a bike will fit you. The second most important dimension for sizing is head tube length, and it's often not listed for bikes.

If you know your road bike size, look for a CX bike that has approximately the same size cockpit (combo of top tube length and seat tube angle). The same size or slightly smaller (0.5 to 1 cm shorter) will fit you fine. Since you don't know your size, the advice above is best: find a competent bike shop and work with them to buy the frame.

 

Thanks for all the responses. I checked with the LBS where I got my Trek, and they can't get this one, or a cross bike anywhere near the $ ballpark. I would almost feel bad going over there and getting sized for a road bike knowing I won't buy it. Maybe I should do that though, as it would be the best bet, and I just bought an expensive mtb from them last month.

I reread all the geometry numbers and as matt tucker posted right above, the 54cm is 2cm shorter on the seat tube, but the top tube is only 6mm shorter. After re-measuring myself and thinking about the numbers, the 54 does seem like a better bet. I have short legs (5'10" and only 32" taint height) so the "Fuji" 54 seems to give me pretty much the same cockpit as the 56cm but a shorter seatpost and standover. Hmm, might be the way to go, and its nice seeing that someone with pretty much my same dimensions would be ok on the 54 as well. I could always get a 110mm stem instead of the 100mm it comes with and then I would have plenty of room.

Also, what someone said all the way up top about having a "right size" for the road bike, but being too big on the dirt of cross to manhandle and handle well was a worry.

Thanks all!
-Tom

 

My road bike and cross bike are effectively the same size. Same virtual top tube length, same head and seat tube angles, nearly identical head tube length. Use the top tube length you get fitted for on a road bike and look for cross bikes with the same top tube/seat angle combo or ratio (1 degree more slack in the seat tube with 1 cm more top tube length will give you the same reach). Then adjust stem length and bar position from there.

 

I reread all the geometry numbers and as matt tucker posted right above, the 54cm is 2cm shorter on the seat tube, but the top tube is only 6mm shorter.

That Fuji 54/56 deal is unusual. Heattube same length, top tube less than 1cm shorter, but the seattube 2cm shorter. So if the dims are for real, you would get a bit more standover while changing the fit/handling of the bike hardly at all if you went with the smaller frame. On the other hand a little less convenient to get on and off the shoulder.

 

You can't compare bikes by just top tube alone - you have to take into account the seat tube angle because steeper angles put more of the top tube in front of the bottom bracket (bb).

The starting point is the position of the saddle relative to the bottom bracket - known as saddle setback. That's the position in which the rider generates their power and once optimized, should remain constant. For a bike with steeper STA, the rider would need a seatpost with greater offset or saddle with longer rails to move the saddle back behind the BB to its proper position.

With a steeper STA and moving the saddle back, you are effectively lengthening the top tube (moving the saddle back adds distance to handlebars).

Looking at it another way, two bikes with the same top tube length but different STA have different effective top tube lengths. For bikes with steeper STA, more of the top tube is in FRONT of the bb. That's why you need the STA to compare TT lengths.

As an example, my Richard Sachs has a 72.5 seat angle (57.5cm c-t seat tube) and 56.6 top tube length. When I was figuring what size Moots Psychlo-X, I chose the 53.5cm that has a 55cm top tube but the seat angle is 73.5. That means that to get my seat to the same point behind the bb as my Sachs, I need to push the saddle back at least 1cm. And that effectively lengthens the top tube to 56cm. If I chose the next size up with the 56.5cm top tube, my effective top tube length would be lengthened to 57.5cm and too long for me (unless I use a stem that is 8 or 9cm).

 

Veloduffer....Good point on frames in general. For the OP...STA same on 54 and 56 Fuji Cross frames (73), so no worries for you on this point.

For me my road bike and cross bike have same STA, same top tube. I run less setback on the cross bike and shorter stem for a more upright position. Based on my very stale middle school math, 1 degree of STA = about 1 cm of Top Tube Length / Reach...so a 74 STA with a 55 Top Tube about equals a 73 STA with a 56 Top Tube...

Pretender...yes...sizing is weird on the fujis 54/56. Very close sizing.

 

My road bike and cross bike are effectively the same size. Same virtual top tube length, same head and seat tube angles, nearly identical head tube length. Use the top tube length you get fitted for on a road bike and look for cross bikes with the same top tube/seat angle combo or ratio (1 degree more slack in the seat tube with 1 cm more top tube length will give you the same reach). Then adjust stem length and bar position from there.

Which is a very complicated way of saying a bike with a seat tube length specification at -2cm of a road bike. What is the published seat tube spec on your road frame versus your cross frame? If one is a Giant or other compact style, the effective length is fine.

 

You can't compare bikes by just top tube alone - you have to take into account the seat tube angle because steeper angles put more of the top tube in front of the bottom bracket (bb).

On the other hand maybe the frame designer used a slacker angle for a reason, and you simply go with it. AFAIK there's no single optimal fore-aft position and it is highly dependent on the application, for example tri bikes with their very steep angles, downhill mtn bikes with their very slack ones, extreme examples of course.

 

Which is a very complicated way of saying a bike with a seat tube length specification at -2cm of a road bike. What is the published seat tube spec on your road frame versus your cross frame? If one is a Giant or other compact style, the effective length is fine.

Umm. NO! Didn't mention seat tube length at all and frankly that is so subjective in today's marketplace (C-C, C-T, etc.) that it is quickly becoming a less significant measurement. I might use ST length as a range to narrow down an appropriate frame, but would never use it as a determining factor in final selection.

I'm suggesting using top tube length and seat tube angle to determine reach and understanding the ratio/interaction the two have with each other to broaden the selection of frames that might fit past those with the exact specs of a given bike that is known to fit.

And to answer your question, believe my cross bike has a "published" ST of 48 and my road bike is a 49 or 50, but have been more than comfortable on cross bikes with published seat tubes in the 51 or 52 range if they have the appropriate top tube length.

 

Are you serious?

I strongly feel that this is bad advice. There is no reason to "size down" a cross frame.

Your advice would not work with Redline, Ridley, Empella, Salsa, Jamis, Raleigh, Cannondale or Kona 'cross bikes. The high bottom bracket on these 'cross bike translates into a meaningfully higher (effective or actual) standover spec and a top tube that will probably be too long.

Here's an example from Cannondale's site. Look at the bottom bracket height and bottom bracket drop for each, then do a little back of the hand estimation to discover that a rider will, in fact, have to size down for a couple of different reasons.

road: http://www.cannondale.com/bikes/10/cusa/model-0RCLIC.html specs (G and K)
cross: http://www.cannondale.com/bikes/10/cusa/model-0XR3C.html specs (G and K)

Cannondale is not unique in this way.

At this point, you have passed on some very bad advice that would have lead to a very expensive mistake. Please modify your opinions to reflect reality.

 

And to answer your question, believe my cross bike has a "published" ST of 48 and my road bike is a 49 or 50, but have been more than comfortable on cross bikes with published seat tubes in the 51 or 52 range if they have the appropriate top tube length.

Hey, look at that, Road size - 2cm was your 'cross bike size. Shocking. The other stuff is too much information for the average person looking for a decent bike.

Regarding riding bigger bikes because the top tube length is right. This is possible, but not likely. The local 'cross-riding pro will pass you and I just as quickly on a bike with a top tube that is too short for her than one that is optimally sized. Which is why Road size - 2cm is a good rule of thumb.

 

Your advice would not work with Redline, Ridley, Empella, Salsa, Jamis, Raleigh, Cannondale or Kona 'cross bikes. The high bottom bracket on these 'cross bike translates into a meaningfully higher (effective or actual) standover spec and a top tube that will probably be too long.

Here's an example from Cannondale's site. Look at the bottom bracket height and bottom bracket drop for each, then do a little back of the hand estimation to discover that a rider will, in fact, have to size down for a couple of different reasons.

road: http://www.cannondale.com/bikes/10/cusa/model-0RCLIC.html specs (G and K)
cross: http://www.cannondale.com/bikes/10/cusa/model-0XR3C.html specs (G and K)

Cannondale is not unique in this way.

At this point, you have passed on some very bad advice that would have lead to a very expensive mistake. Please modify your opinions to reflect reality.

LMAO. No need to "size down" if you are selecting based on top tube, not arbitrarily decided seat tube length. Maybe that wasn't clear from the quote, but that is my interpretation of what he was getting at and I think based on other's responses, they agree as well.

 

LMAO. No need to "size down" if you are selecting based on top tube, not arbitrarily decided seat tube length. Maybe that wasn't clear from the quote, but that is my interpretation of what he was getting at and I think based on other's responses, they agree as well.

Well of course. Choosing a frame size based on a single number is as old-fashioned a concept as "sizing down" a cross frame.

 

That Fuji 54/56 deal is unusual. Heattube same length, top tube less than 1cm shorter, but the seattube 2cm shorter. So if the dims are for real, you would get a bit more standover while changing the fit/handling of the bike hardly at all if you went with the smaller frame. On the other hand a little less convenient to get on and off the shoulder.

The specs are normal for a cross bike. Look at the bottom bracket height/drop. It's much higher than a road bike. A 'cross bike generally has a seat tube spec that is -2 cm from a road bike, and as you point out, the geometry works out just fine otherwise.

Which is why I recommended a traditional road bike size -2 cm.

 

Hey, look at that, Road size - 2cm was your 'cross bike size. Shocking. The other stuff is too much information for the average person looking for a decent bike.

Regarding riding bigger bikes because the top tube length is right. This is possible, but not likely. The local 'cross-riding pro will pass you and I just as quickly on a bike with a top tube that is too short for her than one that is optimally sized. Which is why Road size - 2cm is a good rule of thumb.

Actually just checked my road bike's spec sheet and it is a 48 ST length. So your rule of thumb is just that, a general principle that is not going to hold water in all instances. Maybe it is me, but I see these forums as an opportunity to not provide general advice, but very specific advice and educate all consumers, whether you deem them "average" or not. Personally I wish I understood the top tube/seat angle interaction years ago as it would have saved me TONS of money over the last few years as I was searching for better fit.

 

The specs are normal for a cross bike.

No they aren't. We're talking about two cross frames. The only differences between the Fuji 54 and 56 cross frames are a 7mm difference in the top tube and wheelbase, and the 54 has a more sloped top tube. They have the same angles and the same headtube length. This is not normal.

And just to make it painfully obvious to the denser among us, I don't recommend buying a road frame based on a single number any more than I recommend buying a cross frame based on a single number. There is far too much variation in how different companies spec their bikes.

 

Which is why Road size - 2cm is a good rule of thumb.

No, it's a bad rule of thumb. Size by top tube length and seat tube angle.

I ride a 58cm Ritchey road bike.
I ride a 58cm Ritchey CX bike.
For Independent Fabrications I ride a 54cm CX bike - a 56 would be too big, and a 58 would be barely rideable.
I have owned road biked sized between 57 and 60cm (not compact geo) were all sized the same (+/- 0.5cm of cockpit length).

There is no standard is how bikes are measured. If you ride bikes and are interested in fit, you MUST understand top tube length and seat tube angle in order to fit bikes.

 

No they aren't. We're talking about two cross frames. The only differences between the Fuji 54 and 56 cross frames are a 7mm difference in the top tube and wheelbase, and the 54 has a more sloped top tube. They have the same angles and the same headtube length. This is not normal.

It is quite normal for two different frame sizes to have the same angles. Cannondale has two frame sizes with *gasp* the same angles!!! http://www.cannondale.com/bikes/10/cusa/model-0XR5C_0XR5T.html Oh no, so does Specialized!!! http://www.specialized.com/us/en/bc/SBCBkModel.jsp?sid=06TriCross Motobecane too. http://motobecane.com/ftx_geometry.html Noooo!!!

For whatever reason, Fuji's cross bike in different sizes have similar angles. No news here.