of 10 how much will my speed and? performance improve,generally,if i swap my suspension fork for a rigid one?also if i change my crank from a 42 chain ring to a 44.could you give me details to what makes such a difference.thanks
you don't need to change your fork for a rigid one you need a lock-out fork see here;http://www.performancebike.com/shop/profile.cfm?SKU=25531&subcategory_ID=5231 and the difference in a 42 over a 44 tooth chain ring is not all that great get a larger rear cassette 12/28 or larger that will make a difference not in the front. There isn't much to rate here if you get a fork that has a lockout then you just lock it out when you're commuting...nothing to it!
Your performance will increase a bit with rigid fork, larger chain wheel (as long as you can push the bigger gear) better, thinner tyres etc etc.
However if you want to really improve your speed and performance, the only positive route you can take is to invest in a good road bike.
The reason that a rigid fork will help is because it will be lighter and take less effort to propel along the road. The bigger chain wheel will enable the cycle to travel further per crank revolution, as long as you have the power to use the gear.
Most road bikes are much lighter than a mountain bike and generally use a 52 tooth chain wheel.