Cyclocross - MTB Drawbacks?

Other than upsetting purist sensibilities, what are the disadvantages to competing with a mountainbike as opposed to a cross bike? Sorry if this is well traveled ground, but I'm new to the sport and haven't found a similar thread. Thanks.

Weight is one, rolling resistance another, no power-sucking suspension another. A decently outfitted cross bike will tip the scales much less than a mtn bike. You'll definently feel the difference on a course with a steep run-up. The big mtn bike tires may make for a smoother ride but that is a lot of rubber in contact with the ground and more contact means more resistance. When you accelerate, none of the energy transfer to your pedals is sucked up by the suspension. If you have a lockout suspension, that will help a little but then again that takes us back to the whole weight thing.

Ok so say you have a 19 pound hardtail mtn.bike with a rigid fork and Conti 1.5 tires.Let's say you use a double chainring in the front like a 48/36.When you shoulder the bike the bottom of the saddle sits on your shoulder instead of a cross bike's top tube.How much of a difference now?

Ok so say you have a 19 pound hardtail mtn.bike with a rigid fork and Conti 1.5 tires.Let's say you use a double chainring in the front like a 48/36.When you shoulder the bike the bottom of the saddle sits on your shoulder instead of a cross bike's top tube.How much of a difference now?


Definitly getting better, but I find that my 30mm cross tires always roll a lot faster than my mountain tires (admittidly only 1.9 semi-slicks) - I think the course layout probably decides how much of an advantage it is. A course with a lot of pavement is going to favor the better rolling 700c wheels more, wheras some courses might actually be faster with the mountain bike (causing some consternation among cross purists). Carrying the bike (as I often have to do) the lighter bike is really nice.

Depending on your wheels too, you might end up carrying less. My cross bike has fewer places to collect mud than my FS mountain bike, and the wheels (cosmic elites) V section sheds better, so I probably carry less mud overall.

However, all of this is assuming identical riders, etc. Truthfully, the engine makes things go, and as many in this forum have pointed out, the weight/style/ride/material of the bike really is secondary to the engine. Ride what you can afford, and are comfortable on.

murph

A 19 lb mtn bike hardtail with a set up like that sounds like a great rig and if that is what you race on then you probably have no problems. However, if you are going to go to all that effort (fork change, tire swap), why not just get a cross rig? Then if you want to go ride a good mtn bike trail you wont have to swap all that stuff back.

No I don't own that bike.I was just curious how much of a disadvantage it would be if you had a really nice mtn.bike.My mtn.bike is about 24 pounds even with a rigid fork.I wouldn't want to lift that bike in a race.

19 pound mountain bike sounds like a real expensive machine ...

actually, if you swap the suspension fork for a rigid fork, and go down to 1.5" or 1.3" tires, you could probably turn a pretty ordinary upper-end mtb into a 19-lb bike.

Thanks for the feedback. I have put the 1.5 contis on my bike, which has made a huge improvement over the knobby 2.0s I was running. I will probably pass on swapping out the fork. I can learn on the setup I have, and would rather put the money towards a cross rig.