Cyclocross - Why smaller for cross?

Hello to all -

I have seen several posts that mention sizing a cross frame 1-2 cm smaller than a road frame. Why is this? When you decrease the seat tube length, you also decrease the top tube length. You then must make up for a cramped fit by installing an extra-long stem. It just seems to me that any decrease in seat/top tube (smaller than your road frame size) is asking for an uncomfortable and poor-handling bike, as your weight is now too far forward (short top tube & long stem).

Am I missing something? I am in the market for a cross frame and my road frame measures 57 cm (c-c) at the seat tube and 57.5 cm (c-c) on the top tube. It seems that all manufacturers offer a 56 and a 58. Since I fit squarely in between sizes, I really want to make sure of the correct frame before I lay out the cash.

Thanks for any and all help.

Rgds,

Steve Marley

I think you want the smaller frame for better clearance over the top tube and more agile handling in the rough stuff. I'd imagine the 56cm would be great for you. If you factor in the larger tires, your standover would likely be the same as a 57cm road bike.

The bottom bracket is higher on cx bikes typically. So this would effectivly shorten your seat tube length and not the top tube. imo the top tube is the real important measurement.

Everyone measures differently anyway so try both sizes before you buy anything.