Can a MTB survive the urban commte?

Eggyolkeo

Brief backgound. I own a Kona Dr Dew, and a 15yo steel mountain bike (solid forks). I commute 25kms each way to work, twice a week on the Kona. On the weekend I ride about 2hrs offroad on the old steel girl. I'm actually borrowing a mate's old MTB with suspension forks at the moment so I don't break my wrists! The old one has got to go.

Question is, I really need a better bike for the off-road riding I do. It’s crazy. But I can’t afford/justify two bikes. So I’m contemplating selling the Dr Dew and buying a hardtail (eg Kona Blast Deluxe) with dual purpose tires. Will this totally suck on a 50km urban road trip, or can I get away with it so that my off-road weekend trips are heaps better?

Would a dual suspension mountain bike be totally off limits on my road trips (weight) or again, is it ok?

I hate the thought of selling my Dew as I love it, but is really is road-only. At least a MTB is genuinely dual purpose.....

weedvspeed

My commute is the same distance, I'm doing it every day on an aluminium solid MTB.(vintage Claude Butler)
Yes you will be a little tired come Friday.

You could get a hard-tail with lockout front forks to kill the suspension on the road.

Or see if its practical to get some lockout forks for your Dr.Dew, ask your LBS.

You can always ALWAYS justify a new bike. Read thread
http://www.cyclingforums.com/t428689.html

DO NOT get a full suspension MTB for road use.
That rear shock will soak up all the energy you're trying so hard to get down.
Riding 50km would be slow and tiring.
Weight counts for relatively little on the flat* is it hilly?
Its more about drag (riding position) and roll resistance and the frame putting all the energy from the cranks into the wheel.

*note 1 [acceleration will be affected by weight]

Personally I'd keep the Dew if you're liking it, splash the cash and get a hardtail too for weekends, its not like it costs as much as a car.
Then get a road bike too, for when you wanna go fast/far