Is there a big difference between a mountain bike and a commuter or road bike effort-wise?

There is a huge difference between a road bike an a mountain bike. I would fix the flat on your bike and change the tires to ones they use on comfort bikes. Knobbie tires eat up a lot of energy and are not very comfortable on the road. Kenda Kross tires will also work but are a little heavier.

Yes, a road bike or commuter type bike would be better. However, there is a cure to your problem keeping the same bike. Change tires! Change them now to Kenda Kross Plus tires. Link below. You will be AMAZED at the smoother ride & increased speeds. Keep them inflated to the proper pressure...40 - 65 psi. I would stay toward the top end, around 60 psi. But, I'm a big guy. Beats buying a new bike dollar wise.

If you constantly have a slow leak, replace the tube. It costs a few dollars. Air leaks overtime and you are supposed to check your tire pressure before each ride. Look at it this way, riding a heavy bike on hilly terrain makes you stronger. :) I know the temptation of getting a faster bike but you should be OK with what you have. You should learn to use the right gears and switch as appropriate. No matter what bike you have, there is always a better and lighter bike you can get that makes you ride faster.

eric of course the bikes are easier as narrow tyres 700c rims and light weight will make easier but for the distance you travel its not worth the trouble changing. your bike from the pawn shop might not fit you how did you know it was the correct size, and smooth slicks 26 x 1,5 could make a hell of a diffrence as well but dont do that till you sort out wether the bike fits you you need to got to a bike shop and find out on one of their bikes and take note of size and what yours is as well'

Where i live, it is not cost effective if you already got a bargain-priced mountain bike (a road bike cost very much more) Perhaps you could inflate the tire a little more Clean the chain and gears more regularly Lubricate the chain before each trip with some light penetrating oil like WD40 Change the gears more often when going uphill/downhill Replace with narrower tire when they worn out

Yes, a road bike would be faster, but for a ride that short its not going to save you THAT much time. Your old bike is probably fine for a commute like that. Just buy new tires and tubes. You can fit slicks or semislicks on those rims that will reduce your rolling resistance quite a bit.

Your front tyre keeps going down? this is an easy fix. Go to your lbs and get a new inner tube or a repair kit. Go to the how to videos section of this site and see how to repair a flat: www.parktool.com Mountain bike tyres are fat and nobbly. The low tyre presssure that you are probably running at doesn't help. Fat, nobbly tyres are great for absorbing hits when going XC, but lousy for road use. A road bike will be better suited for road use, but there is no reason to get a new bike. You have 26" wheels. These do not have as high a top speed as a road bikes, but are very nimble around corners and technical sections. I have raced against cyclocross bikes and, while they will have me on the straight, I can usually do nasty things to them as soon as it gets twisty. But overall, that is not a big issue. All that you need to do is change your tyres to road pattern: http://www.sjscycles.co.uk/product-Panaracer-Panaracer-Hi-Road-Folding-Tyre--26-Inch-(559)-1890.htm Remember to buy tubes for these, since they will be slimmer. In any event these tyres will increase your average speed. Your mountain bike gears are actually helping you on the hills. You do not make as quick a progress, but it is easier and you actually develop a smoother peddling action than the roadies. That said, you might want to change your actual gear ratio. The casset below will make you slow on the hills but better on the flat: http://shop.ebay.co.uk/items/__dura+ace+9+cassette_W0QQ_dmdZ2?rvr_id=&crlp=2107591478_228459_228460&UA=WXI7&GUID=04be3d731290a0aad4307fd0fe071f87&agid=857854358&MT_ID=10&keyword=dura+ace+9+cassette&ff4=228459_228460 These are 9 speed cassets, although if you look for similar dura ace cassets for your bike. In any event, go and talk to your lbs and see what they can match to your wheel. This will give you more of a road gearing for your back wheel. In any event, these changes should make your ride a bit quicker. Luck P.S. Don't listen to people that tell you that you do not do enough miles. I do 11 miles to work each day and that is enough to develop my stamina and muscle tone. If you want more, go out at weekends and evenings.