Finally got some shorter cranks, so I decided to update my results.
I thought I had a line on some 165's last Winter, but that fell through. Budget matters!
I saw this mentioned on the Mechanics Forum (I think) and couldn't resist the price, even if they didn't work out.
http://www.nashbar.com/profile.cfm?sku=20985
$7.49 + S&H! I couldn't resist, so I bought 2! After S&H, that averages $10.37 per set!
Obviously, these are cheap cranks and only fit sq. taper BB's. Also, they are ONLY 160MM long.
Now some things are a bit different this year, than when I switched to the 170's from 175's.
Because of the WINDY weather and some illness, I haven't been riding as much. In fact, I hadn't gone over 5 miles in a day for a couple months.
I decided to do a 10 mile test, on basically flat, paved terrain. About 50-50 city-rural.
In "cruising mode", my cadence was about 83, or 10 RPM higher than with the 170's. That's 20+ higher than the 175's.
My average for the entire trip was 12.6 MPH. That's probably 2.5 MPH faster than my average with the 175's.
I was facing an estimated 5-10 MPH headwind during about 2/3 of the "cruising" stage, so that probably slowed me down 1 MPH?, since I have to sit VERY upright because of my back.
About 1/3 of the way in, I realized something wasn't quite right. I wasn't extending my leg far enough. I than realized that I forgot to raise the seat an additional .4"!
At least I was "in tune" enough to notice, so that made me feel better
I didn't notice any adverse effects except I could use bigger cogs in back or smaller rings in front. The smaller rings isn't going to happen, since these are the riveted kind.
Right now, I'm using a 13-14-15-16-17-19-21-24 cassette and stayed on the middle ring the entire time. I didn't go above the 15T cog except for a slight down hill at the start of my ride.
I wish I had a 14T top cog, so I could throw in an 18T for the "stiffer" head winds. I've found I'm most efficient in a very narrow cadence range and there were a couple times where neither the 17 or 19 were quite "right".
Maybe if my conditioning was a little better, it wouldn't matter though.
Anyway, overall I give a thumbs up, considering the price.
It would be an excellent chance to experiment with 160's, if you have a sq. taper BB.
Just keep in mind that your cassette WILL feel like it has smaller cogs.
These cranks also may be usful for "kids" riding adult bikes.