Bicycle Mechanics - Tires and Rims

I've got a hybrid with 700 x 35 tires, and the typical hybrid tread. I am eventually going to try to go with a narrower tire but on the same rims. Is that possible? If so, how much smaller can I go? I still want stability for the occasional detour (usually induced by traffic or people walking across the length of the bike path) into dirt or stone. Could I could to say 700 x 32? How much increase in speed would I expect?

Second, how would 700 x 28 feel as far as grip (not related to same rim issue)? I am not interested in slicks or a road bike, but I do want a little less road resistance. I've heard lots of talk about the Specialized Sirrus (not available in my area), which to me seems like the perfect bike as long as it doesn't seem to "delicate" (ie semi-dangerous in stone dust, dirt, grass, etc). I have no plans to mountain bike but I do sometimes ride on stone dust or 1/4 in stone trails.

The smallest I can seem to go on my wider hybrid rim (don't have a measurement) is 28mm without getting flats. If you stay on the road (no soft ground) they handle very well and smooth out the ride. As far a speed goes, I noticed a difference but can't say it did nothing more than make pedaling a bit easier.

If it is a commuter and you don't go ultra long distances, I go with a 32mm no-tread tire.

Just do not run a tire narrower than your rim is wide.

Here is a link from the Harris Cyclery web site. Sheldon Brown writes some great articles on many facets of biking. Scroll down on the page below to see a chart that tells you what size tires you can fit on what sized rim. It's way down at the bottom with green and red boxes.

http://www.sheldonbrown.com/tire_sizing.html

Heh, I'm upgrading to 28's... I've been running 23'ish's @ 120psi for a while now... and they handled alright on soft ground, snow, ice, dirt, etc... took a little coaxing, but they were alright... I'm hoping the 28's will soften the harsh Somerville/Cambridge roads a little though. So, I wouldn't worry about the 28's grip...

Heh, I'm upgrading to 28's... I've been running 23'ish's @ 120psi for a while now... and they handled alright on soft ground, snow, ice, dirt, etc... took a little coaxing, but they were alright... I'm hoping the 28's will soften the harsh Somerville/Cambridge roads a little though. So, I wouldn't worry about the 28's grip...

The 28's will fit where your 23's are now; they should also handle soft ground, dirt, snow etc better than the 23's and soften the ride a tad. With the 28's you should be able to air them to 100 PSI which will help in the ride department as well.

This is probably cool, but I am pretty bike dumb. How do I know my rim size? Here's the spec I have: Weinmann 519 Alloy 700C 36h Silver Anodized. What is the 700c equivalent to? I'm having trouble understanding the conversions above the green and red chart.

700 refers to the theoretical rolling diameter of the tire in millimeters.
"C" is a measure of width, like in shoes.

I don't think that I would try to put anything narrower than about 32mm onto a Weinmann 519 rim and I don't think that I'd recommend using more than about 85psi on it. That's a pretty cheap rim.

Use a caliper to measure the inside width of your rim. That is the number used in Sheldon's chart.

700 refers to the theoretical rolling diameter of the tire in millimeters.
"C" is a measure of width, like in shoes.

I thought the "C" meant "Clincher"?