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Thanks in advance for indulging my beginner's questions. I see cross bikes have shorter head tubes and longer top tubes. Is it better to have a longer top tube than you would have on a road frame? If so, how much longer? Thanks!

I should say, should one err on the side of (a) longer or (b) shorter?
 

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Hoopy Frood
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Generally speaking, you want your reach to be a little shorter and a little higher on a cross bike than on a road bike. The theory is that this type of setup provides more confidence on steep downhills and off-road stuff.

I've always selected cross bikes with the same top-tube length as my road bike sizing and then adjusted my reach with a shorter stem. Recently, I've been running the exact same top tube and stem length on my cross bike as I would on a road bike and I don't have any handling issues off-road (at least, none I can blame on my setup). I'll probably go shorter when race season rolls around, though.
 

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The difference between my road bike sizing and cx bike sizing was gone about a little differently as compared to 'Khill'.

I normally ride a road frame with a 56.5 TT length with a 110mm stem, with the CX frame sizing, I went with a 54.5TT length and 110mm stem.
I've logged more than 1000 miles on this setup and have also switched between my road and cx bike during my weekly riding schedule. I have found that the 2cm difference in length between my cx bike and road bike was not as noticeable as what I had previously expected. I have setup my cx bike to have a more upright seating position as compared to my roadie, This contributes to a more comfortable position and easy transition between riding on the hoods and onto the drops. So, basically, I went shorter on the TT length and flipped the stem up to bring the handlebar height higher. As measured, my seat to handlebar drop on my roadie is 7.5cm, while on my cx bike it's 4cm.

So, I hope this info is useful to you, good luck in zeroing in on your cx fit/sizing!
 

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I second the vote for a slightly smaller total length acrost the top and somewhat less handlebar drop. A too large frame will be a real boat in the woods, I have ridden as much as 2cm smaller than the 58 I ride on the road, generally now I like 57 TT for cross and 58.5 for road-works for me..
 

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Newbie to drop bar bike riding.

Mountain bikes aplenty but I wanted a cx bike for road training. My question for jroden is: I have a 57mm Poprad with a 110mm stem and it "seems" a little like my weight is too far fwd. I'm 6" with a 33" inseam. Since you prefer a 57 cx frame as well,how does this compare to your size? I flipped the stem to get my bars up and I've ordered a 100mm stem anyway. Maybe that will move me back enough to "feel right"?
 

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shoot, I know these measurments off the top of my head, from BB center to top of saddle is 30.5 inches, then from nose of saddle to center of bars is about 23 inches. For cross, I tend to move the seat fore and aft on the rails to get the balance right in terms of the handling on the bike and worry a little less about getting the perfect setup over the pedals. I think you are smart to worry about the fore-aft weight distribution and play with the stem rise and saddle position to get this right. I have always belived that I can ride a slightly smaller bike faster is slippery conditions, but maybe it's in my head. I think the weight distribution is so important in low traction situations, really an under-rated part of the whole picture.

If you are riding a 57 TT, I can go out and measure the other dimensions if it would be helpful, but we may not have the same body type and riding style, I'm sort of a klutz.
 

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I measured the BB to seat top and it's 32" That's actual on a slight diagonal. The front of the seat to the bar CL is 22". The seat height seems OK but I still think I've got to get the bar closer to me.

On another note; I took the bike on some mountainbike trails today. Just fireroads with some mud holes and the bike handled it surprisingly well. I worried about the skinny front tire digging in and endoing me but we blew right through the soft mud where some drainage work had been done. And then; to my surprise, I was able to spin through as well as my 2.3 mtb tires would do (wet slimy stuff, it's been raining for 40 days here). The light weight was a surprising advantage to me riding off road. All of my mtn bikes weigh 32 to 38 pounds, gotta toughen up the sit bones if I do much off road riding with this bike though.
 

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Part of your answer lies in what you intend to do with your CX bike. For racing, a lot of people will go with the purist approach, shorter top tube and higher bottom bracket (compared to road). For some this works fine, but don't be afraid to go with a CX setup that's identical to your road setup. I've done this for the past three race seasons and it's worked out very, very well.
 

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what does that look like in real life, the top tube seems so long that you would have to get a bike with a shorter seat tube to replicate your road position across the top, but you would still sit much higher on the bike--with an off the shelf frame, it seems like it would be difficult to really replicate your road position on the horizontal and vertical planes, or am I missing something? For example, to get close to my road setup across the toptube, I end up riding a 1 cm shorter seat tube bike, which still has maybe an inch or two more standover.
 

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Well it probably depends on what your road position is like, too. Me, I like a semi-compact frame for both road and cross, somewhere around 51cm seat tube with a 55.5 sloping top tube. I also prefer a BB height that's only a little higher than road. This is also very close to what a lot of reputable builders (Sycip to name one) do as stock cross geometry. I take my CX bikes and racing very seriously and this works great for me, but of course your results may vary.

edit: My bikes are all custom. You're right, with many off-the-shelf brands it's not easy to do this.


jroden said:
what does that look like in real life, the top tube seems so long that you would have to get a bike with a shorter seat tube to replicate your road position across the top, but you would still sit much higher on the bike--with an off the shelf frame, it seems like it would be difficult to really replicate your road position on the horizontal and vertical planes, or am I missing something? For example, to get close to my road setup across the toptube, I end up riding a 1 cm shorter seat tube bike, which still has maybe an inch or two more standover.
 
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