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I've been riding/racing road for a number of years but looking to get into cross. Been offered a really sweet Stoemper Ronny single speed CX bike, would really like to make it work but concerned it is too big, so thought I'd pose the question to those of the Internet.
I ride a 52 cm road bike - 49 cm seat tube, 53.7 top tube, 110 head tube w/o spacers to a 110mm stem, saddle height from BB is 67 cm. (compact geometry)
The CX frame measures - 52 cm seat tube, 54 cm TT, 120 head tube (traditional geometry)
I've always heard go a size down from your road when fitting a CX bike but others have said just stick with your road geo more or less and adjust with stems. I'm less concerned with the reach/stack of the CX bike it's the stand over and using only about 12 cm of seat post + saddle since I've got shorter legs. But the other thing that makes me think it'll work OK is my road bike is compact geometry while the Stoemper is traditional with a horizontal top tube.
In short, if it is too big, it will probably be the clearance when standing over the top tube which is probably more important on a CX than a road bike.
fork + Headtube = Total height
370 + 110 = 480mm
400 + 120 = 520mm
Difference = 4cm#
However you also need to take b/bkt height into account but it's usually only a few mm.
CrossRob wrote:Don't forget wheelbase either. I was advised to go down a size and sometimes get caught out by my toe hitting the front wheel in sharp turns.
That was one of the problems for me on a smaller frame, had to be very careful in slow sharp turns.
First, you have to throw away many of the rules you'll hear from other bigger ridders -- like pedal/front wheel overlap, stand over height, etc. You'll never get stand over height in a small frame; just plan on tilting the frame over slightly when you stop so you lower the top tube and can get both feet down. But honestly, you never have to have both feet on the ground, do you? One foot on a pedal, bike tilted over and one foot on the ground. Similarly, you'll get a slow long bike if you try to avoid toe clip overlap (sorry for the old fashioned term) on a small frame. Everything on a small bike is just too tight. Same for insisting on shallow seat angles -- you'll have a steeper seat angle and less setback, which you'll have to handle with a setback seat post if necessary, but you probably have shorter thighs anyway and don't need the same setback as bigger riders anyway. And every centimeter of setback gets you more performance gain than it does on a bigger frame anyway. Same for bottom bracket drop -- don't go to a low bottom bracket simply because you think you need top tube clearance. Instead, choose bottom bracket drop to suit the kind of riding you do and your riding style.
Overall, as a smaller rider you'll need greater flexion at the waist to get a low position. You run out of head tube length on a short frame anyway, but the better position for a shorter cross rider is to go to a slightly longer stem and extend your torso forwards rather than just down. You'll get the same aero position but with a position that acts a little bit more like being on aero bars. Use narrower bars (you can be a good candidate for 38 cm c-c bars like 3T Ergonovas), don't go deep with them, and don't think you need to be on a short stubby stem. One problem on a small bike is getting your weight balance right, both for handling and for personal power generation, and being slightly stretched out is a plus.
Shouldering your bike? Hard or impossible with tiny bikes. There's no triangle in front to stick your shoulder into. So you have to pick up the bike differently. It's inefficient to pick it up in your hands all the time, but plan on putting your shoulder into the triangle at the seat lug and hold the opposite side of the bars rather than the front wheel. You can help by pointing the frame downwards a bit more than taller riders do -- not great but once you get used to it, it works well. Frames with sloping top tubes might seem contradictory for small riders, but they let you put the bike higher on your shoulder so you can handle the frame better. Again, don't worry about stand over height on a small frame.
Your frame size might be a candidate for 650 wheels. I'm always loath to suggest them because then nothing is compatible and gearing and everything else is suddenly different. The smaller wheels do give you a slightly easier lift and carve some room in your frame design, but honestly, I'd think about joining a circus first. We short riders aren't served by 650 wheels unless we're just touring and that kind of thing.
The basic point is that you need to break rules in your frame design and equipment choices. I'd say to go as small as you can for your saddle height (67 cm from bottom bracket axle to top of saddle?). A 48 would work, a 50 would be OK, a 52 is probably too big. I'm on a 50 with a 70.5 cm saddle height and could have gone a size smaller if I could have gotten one. Big riders are focused on top tube length but you'll have your top tube defined by your overall frame size. Use seat post setback, choice of saddle, and stem length to set your horizontal dimensions on the bike. Again, if you make the top tube long you just ruin the overall handling of the bike, to no good end.
Small bikes are a compromise. That's all there is to it. But you can race them really well if you don't stick with design rules that don't make sense for small riders.
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