Road cycling on a MTB

With the right tyres and clothing it won't actually be as much slower than the road bike as you expect.

I used a Zaskar in the city, fitted slicks and a carbon fork. It was lighter than my old Trek 1200 roadbike.

I used to love the handling and sliding over a 6 mile city commute.

Cycled from Bristol to Bath chasing down road bikes and spinning out - one hell of an aerobic workout.

Set the bike up with the leg in the same angle/position as your roadbike so you work your heart & lungs (not full out quads). 15 miles each way.

Also you could use it as a cruising recovery ride to avoid overtraining.

A GT Zaskar shouldn't be set up all that differently to the roadbike, if it's an XC machine. Top of bars about same height, etc.

Just get some slicks and use the MTB, you'd have a bit more air resistance and that's about it.

Though that's too nice an MTB to keep locked up out of sight and in public.

It'll be nicked just as fast as the roadbike would.

Having acquired some rather nice vintage tubeless wheels from eBay for proper offroading, I recently put a set of these on my 26" hardtail GT for road use / daily commute.

http://www.chainreactioncycles.com/michelin-country-rock-mtb-tyre/rp-pro...

Difference on road is huge. I regularly do the Sunday club ride on it when the weather is bad and sometimes struggled with the big old knobblies.

I wouldn't worry so much about 'wrong kind of cycling'. For a start, unless you like getting to work as a sweaty morass, you won't be working at anywhere near your limits.

Another +1 for Schwalbe City Jet tyres.  Assuming your frame is hardtail (a quick google of GT Zasker suggests it is) you could also look at swapping your suspension fork to a rigid - not much point doing this if full-sus.

Or if you have the budget, storage space and understanding partner required for a N+1 do as BigShape suggests and get yourself a commuter/winter bike.

treat yourself to a commuting bike

Treat yourself to some slick/hybrid MTB tyres.

When I was commuting into London on my MTB a few years back, the 16 miles went from 1:05 to 50-55 minutes just by swapping the tyres.

The MTB won't be as efficient as your road bike on the blacktop but otherwise that's it.

The way I see it, there really shouldn't be any concerns about working the wrong muscles. If anything, the smaller wheel size could potentially help you develop a better spinning technique, because the smaller MTB wheels will have greater rolling resistance vs your 700C road bike wheels.

If you can challenge yourself to avoid freewheeling and keep pedaling for as long as possible, your pedaling smoothness should improve. I believe they call it "souplesse"

For even better souplesse improvements I'd recommend an even smaller wheeled bike. Think 20" folding bike or less