Im going to get flamed for this but…

I have a ridged mtb for off road c2c type rides. 26 inch wheels. 1.8 slick tyres. And for the life of me i cannot get beyond the idea that a proper cyclocross bike would be faster / more efficient.

The only thing that should count here is weight and tyre width / resistance isnt it?

“hides under table”

Wind resistance is a huge factor. Often accounting for waaay more than half your effort.

rough approximations follow:

Mtb’s position the rider in a more upright position, with their arms further apart.

Drop-bar bikes position the rider in a lower, narrower, more aero position.

And (just possibly) the idea that a drop-bar bike is faster, might encourage the rider to wear tighter-fitting/less flappy clothing – reducing drag a bit more.

ridged bikes are always faster, the ripples help with the laminar flow of air

Body position on a CX bike makes it quicker when pedalling – they aren’t that far off road bikes for geometry

i kant spel gud.

I tend to ride on the top of the bars on my road bike so is there really much difference??

even with your hands on the hoods or bars rather than the drops you will be presenting a much smaller frontal area compared to having your hands on the grips of wider MTB bars.

Going from my road bike to my anthem 29er, (okay its full suspension but covers the ground quickly for a mountain bike) feels so wrong, the road bike leaps forward when you pedal in comparison. The Anthem feels heavy, sluggish and unresponsive in comparison.

The road bike riding position also feels so much better when it comes to putting down the power.

Even your 1.8″ tyres are fat and squishy compared to a road or fast Cx tyre.

My fastest time on my local XC ‘enduro’ trail was on a CX bike – a good few minutes quicker than my MTB primarily due to the lighter weight, and reduced rolling resistance of the narrower tyres.

you carry a lot more momentum due to the two factors (wind and rolling resistance) and go further/faster for the same effort ime

I’ve been doing it wrong then. 26″ rigid mtb with 1.5″ City Jet tyres and riser bars covers my recent 20 mile canal commutes in the same time as my drop barred 700c Salsa with Marathon+ tyres..

??

once your down on the drop handle bars the air flow over you creates a venturi affect. Farting in said position produces a backwards thrust effect giving you more speed

A lot depends on how your MTB is setup. I use a long stem (negative degree) with narrowish bars (600mm) and my position is very similar to my position on a road bike with hand on hoods.

What I am missing is the in the drops position which I rode in for around 50% of the time when using a track bike (which I road off road).

I have got close to the times I posted on my cross bike but never quite matched them apart from a few more technical/rooty/twisty sections where I have better control on MTB and wider tyres.