I have an older cannondale f300.
my tires are 26 x 2.10" IRC Mythos XC. looking to replace them.
do i have to get 26 x 2.10" or will 26 x 1.95" work as well?
26 x 1.95 will work fine. The '26' is the size of the wheel they fit on (you must use 26" tires - other sizes simply won't fit) but the second number is how fat the tire is, which you can choose as you like, within reason (huge tires might result in clearance issues, for example). 1.95" tires will be a little skinnier than your current ones, of course.
According to BikePedia, your F300 came with 26" Weinmann ZAC19 rims. 26 x 19mm MTB rims are typically rated for 1.5 to 2.3" tire widths, so 1.95's ought to be fine.
Tire width is a fairly forgiving criteria, there's usually quite a bit of leeway there. 1.95 will do just fine. If you stay mostly on hard, even surfaces you may even consider narrower and smoother tires. Keep in mind though that the 26" designation is a bit messed up, and holds several subsets. You're better off staying with the ETRTO size(559 mm) to ensure that you get the right size.
Any 26" tire should work, what you choose all depends on where you ride, the general trend now seems to be for bigger (wider) tires off road, but if mainly used on-road, you can go as skinny as you like.
ah, that's good to know. i mostly ride on the street now with a few grassy patches thrown in for short cuts.
my last pair of 2.10s wore out really fast on the street so it's good to hear i can get some more road friendly tires.