I normally ride a 52X17 (80.4") Sugino/EAI chainring and cog setup.
I experiment all the time and also like 47X17 (72") for the control and versatility.
Looking for something new to try, I came across Sheldon Brown's article and Shimano Biopace chainrings.
Apparently, Shimano tried to market these in the 90's and it didn't work out for them.
A few people who have tried them really like them, and a few "scientific" tests regarding them proved inconclusive.
So I ordered a 53t chainring from Harris Cyclery.
I guess no one wants them.
Anyway, I put it on my Pista with the 17t EAI cog, which comes to 81.9".
I adjusted the chain tention at the two tightest points so that I had about 3/16" play, with effort.
The chain would probably feel too tight to most people.
That left it about .5" - .75" slack at the two loose points in the spin; pretty loose for me.
On the work stand, I got the wheel and crank up to speed and then let them coast down a few times.
The crank spun forever and stopped at random points, so I figured the tight chain wouldn't cause any issues.
Going out to test ride it, I went on my usual 12.5 mile training ride and threw in a little detour just to add some spice.
My training ride has a dynamic range of about 800-1000 feet in elevation changes, and takes me through both urban and suburban traffic with a couple of very intimidating hills.
I average 13 to 16 miles per hour for the whole ride, including stoplights and the like.
My first impression involved a sense of powerful fluidity and speed.
I mean, I didn't do a warp 9 or anything, but I definitely felt faster for less effort.
In fact, it felt like I'd gone down a tooth on the chainring instead of up, and I felt noticeably faster.
Long climbs in the saddle felt more comfortable.
I had better acceleration, almost "squirty."
I also noticed more control going downhill, and no tendency to "bob."
My knees seemed to like this new chainring, too.
I couldn't feel the slack at the loose points and the chain sounded as silent as usual.
Well, I thought maybe I just had a good day.
So I asked my seventeen year old son, the world's most physically fit human being, to take it for a test ride.
He disappeared for a long time and came back with big grin.
"Fast," he said.
He doesn't talk much.
That represents about four days conversation for him.
Anyway, I'll ride this for a week and report again.