cx newbie question

Especially for light weight issues concerning cyclocross / touring bikes & parts.

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by dmoneysworks

sorry for such a wet behind the ears question...

so do I buy the same sz cx machine as my roadie with it's same spec's - i.e. frame eff. tt, h'bar width & crank-arm length?

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by euan

Some will say size down. But generally all you need is a little less reach and a little more stack which you'd find in the "same size" bike. But "same size" is quite general without seeing the geometries in question.
"Step forward the climber and all those who worship at the altar of lightness" - R. Millar

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by mattr

Start from the same size and work from there.
As long as you aren't oddly shaped, all you shouldn't need to change much. Personally speaking, i've not changed anything, my contact points are *virtually* in the same place (allowing for the fact that my road bike is custom made for me, and a different brand to the CX frame!)

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by gt5504b

I feel like if you can ride a mountain bike, keep the stack and reach the same as on your road bike. If not maybe one (stem) size down for the reach.

If you are comfortable on the bike you ride, I agree with mattr that you don't want to mess with your contact points' layout.

Now on a different type of bike (ie, different angles, bb drop, etc.) the "size" may not stay the same to get the stack and reach that you need.

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by BSUdude

Lots of people say size down, but as other posters in this thread have said, you want to keep pretty much the same dims as your dialed road position. Usually the saddle gets lowered *slightly* maybe 2-5mm or so to make remounts easier, then your bars probably get a little higher and reach gets a little shorter, and some will angle the bars/shifters up to some degree to aid in keeping a good grip on them. Probably better to get a frame that is pretty much the same geo as your roadie then maybe add some spacers and shorten the stem. Most people generally don't want a 120mm+ stem for CX as it is viewed as having a negative impact on bike handling. So if you have a 120mm stem on your roadie you could easily get a CX bike with the same top tube length and shorten your stem. If you are already running a 100mm stem or shorter on your road bike, sizing down to a shorter top tube for a cross bike might be advantageous. As far as cranks go, I use 2.5mm shorter cranks for my CX bike but crank length is personal preference. For cranks I would either stay the same as what you're used to or maybe go slightly shorter. Only advantage of slightly shorter is a little more clearance above the ground.

As a caveat, make sure you read the geo charts for CX frames. Lots of companies have wacky names for their sizes that don't actually correspond to the dimensions of the bike.

Another dimension that will greatly affect the feel of your CX bike vs your road bike is BB drop. 70mm of BB drop is pretty standard for road frames. Lots of companies are making CX bikes with a BB drop of 70mm, or within 2-3mm of 70 (specialized, cannondale, many more). However some brands have much higher BBs. Ridley and Raleigh are two that are in the 55-60mm range. This will feel a lot different than your road bike. If this is your first cross bike I would try to find a frame with about 70mm of BB drop. Unless you get really serious about doing CX RACES, I wouldn't worry about a higher BB bike, and even then it's a matter of personal preference.

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