Road Cycling - Road vs. Mtn.

I have arthritis in my knees and am curious if a road bike would be less stressful on them than a mountain bike is. Kinda vague, I know, but any (reasonably intelligent ;)) thoughts on the matter would be appreciated.

Well, you left the door open for me when you asked for "reasonably intelligent" replies!
In my limited experience, this is what I have observed: road bike riding results in a more or less constant and consistant effort with the legs, and you rarely have to leave the saddle. Mountain bike riding, however, also gives periods of furious activity when climbing steep trails, as well as a lot of time spent standing on the pedals while going downhill. I believe that road riding would be much easier on your knees. As a matter of fact, last year after tearing the cartilage in my knee, my orthopedic surgeon allowed me to keep road riding....as long as I avoided hills! So, in my opinion, I would stick to the road bike.

One key to reducing knee stress is to use low gears and spin the pedals faster rather than PUSHING on big gears which is an invitation to injury even on healthy knees. Some people report improved joint function from cycling. I had chronic ankle pain from a poorly healed ligament tear from 30 year old skiing injury that cleared up after just a few months of daily bicycle commuting. As long as your riding is on the road a road bike rolls MUCH easier for the same effort. Whatever you do, just take it easy and enjoy the ride.
FWIW,
Raymond

A standard road bike would have a gear range too high for bad knees. Some of us here have geared down so we can ride comfortably at non-athletic rates, but keeping up a reasonable pedalling cadence.

Apart from gearing, MTBs have longer cranks, for extra leverage on really steep terrain. This is probably not such a good idea for bad knees. You would be better with standard sized cranks using a lower gear.

For general road riding, a range between 28" and 100" should suffice. You should find this range on good touring and hybrid bikes.
Gear inches = (teeth in chainwheel/teeth in cog) xwheel diam

I concur. Use low gears, and make sure your saddle height and foot rotation are optimal. A pedal retention system with lots of lateral "float" may help, as well. I own a road racing bike, two road touring bikes, and a mountain bike. For a given pedal cadence and gear ratio, I find no difference in stress on my knees, including my almost 52-year-old, twice-dislocated, left kneecap.

A roadbike is alot more comfortable on all my body parts.I rode a hybrid for 6 years and my road machine offers many more riding positions.Never going back.

I find that mountain bikes require a lot more pedaling. This is probably due to the increased roller resistance from fatter and softer tires.

In any event, my road bike allows me to do a lot more coasting or at least more relaxed pedaling.

If there is any correlation between the amount of pedaling and the pain in your knees, then a road bike might be better than a mountain bike.

Thanks for the input everyone. Guess I need to put a bit more effort into getting the Gitane back on the road.