Any reason why i cant?

I have a Specialized Roubaix Elite.

Can I just change the wheels and tyres and there I have a cross bike? or is there more to it than that?

maybe the carbon forks and seat stays wont hold up tot he abuse?, are different gear ratios required etc? Different frame geometries?

canti brakes

from what I've been told:

different geometry between a proper road bike and a crosser. Crosser is more like a tourer in geometry, and can therefore handle road work but vice versa not so great.

Prob won't have the clearance for 'big' cross tyres to go in there.

Mud and road brakes = disaster. You'd need cantis of some sort (or mini V's) and not sure the frame and fork would have the bosses for it.

Bottom line – don't think it will work. If you want a bike to do both, get a crosser and a spare set of wheels for road stuff rather than the other way.

Cross bikes are slacker angled with more clearance around the tyres, canti brakes and generally just a little bit more overbuilt.

The likely problems with just sticking CX tyres on are lack of clearance at the frame (tyre rubbing on fork/stays/bridge), lack of clearance in the brake calipers (less problematic if they're deep drop ones but that's uncommon except on touring or older road bikes).

Some road bikes can be made to work though and one of my friends has ridden HONC several times on an old Peugeot road bike with narrow cx tyres and normal road caliper brakes without too much trouble. That said, he's a fantastic rider and would probably be able to ride a road bike as is offroad too…

In short, really you need a cx frame/fork to make the best of it.

Any reason why i cant?

I have a Specialized Roubaix Elite.

Can I just change the wheels and tyres and there I have a cross bike? or is there more to it than that?

maybe the carbon forks and seat stays wont hold up tot he abuse?, are different gear ratios required etc? Different frame geometries?

The carbon forks and seat stays won't be the problem, there are plenty of full carbon cross frames available. The issue will be clearance, most cross tyres are between 30 and 35mm, even if you can get them in the frame the first sight of any mud and it will clog.

The gear ratios aren't massively different, most cross bike will run 44ish/36 up front and 12/25 or 12/27 at the back.

what you need is

http://www.singletrackworld.com/forum/topic/kinesis-crosslight-pro-frame-and-forks

It's cheap enough to stick the tyres on and have a go. If you don't like it, then get a proper cross frame.

In any case isn't the Roubaix somewhat rough road capable as it stands?

You can ride any bike anywhere in reality, you just have to modify your riding style to suit. 40 years ago our mountain bikes were our road bikes 🙂

You'll never get cross tyres on it. it was designed to be ridden on the road, and that is about all it can do.
Fitting cross tyres to it, and running the risk of 'sawing' through your stays is just something no-one would do!

I've seen it done at the dryest courses.

The Roubaix is the slackest of their road bikes isn't it?

The Roubaix is the slackest of their road bikes isn't it?

What do you mean by slackest? Least stiff?

its this one (a 2001 roubaix elite) with the zerts inserts in the forks, seatpost & stays.

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No way will you have tyre clearance, so everything else is academic.

The carbon forks and seat stays won't be the problem, there are plenty of full carbon cross frames available

but that doesn't mean that everything made of carbon is built the same way or has the same strength.

slackest = least (road) race-y geometry. Like the one in the pic, which has a long headtube, not very steep head or seat angles (what are now called "sportive" bikes).

As others have said: cross tyres at their thinnest are 30s, and I suspect that even a Roubaix would struggle with tyres much above 26c.

If you want to ride off road on it, do. I ride my winter bike off road, and that runs 24c tyres (Pavés, natch) and full guards. I just avoid too much mud and recognize that I couldn't thrash along like I could on a cross bike. But it works fine and no-one has died.

If you google Graham Weigh's ebay shop, you'll find super cheap cross frames on there. You can F&F for less than £200. Just swap over what you can from your Roubaix, buy some brakes and cross tyres (and maybe a compact chainset) and Bob's your mother's brother.

cross tyres won't fit. Even if they go in the frame, it is unlikely that the brake calipers will have enough clearance. I have a trek 1000 which has fairly decent clearances, and I can only get a 25c slick in the forks.

It will be twitchy as owt. The bottom bracket will be too low.