This summer I worked up to a 53t chainring with a 17t cog for almost 82 gear inches.
Pretty tall gearing but the speed felt good.
So, for winter, and to make it easier to stay off the front brake, I went back down to 47X17, for about 72 gear inches.
Surprisingly, to me, I got around town as fast as I did with my 53X17 gearing, and maybe even a little faster.
I think my spin improved a lot over the summer and the lower gearing gives me more punch on the hills.
Anyway, I had a Shimano Biopace ring as my 53t ring, and when I put on the 47t ring I felt a big difference in "elegance."
I missed the effect of the Biopace.
So, I ordered a 19t EAI cog from Businesscyles and have gone back to my 53t Biopace ring with the 19t EAI cog, for about 73.3 gear inches.
Now I can more equally compare a round ring with a biopace ring, since 47X17 and 53X19 have only about one gear inch difference between them.
It still takes the same number of watts to get up a hill and push the wind out of the way.
Nonetheless, the biopace feels more "liquid" and smooth, and much more comfortable uphill out of the saddle.
My heart and my lungs don't feel any difference but my legs do.
Harriscyclery offers a 53t, 52t and 42t biopace in my crank's 130mm BCD.
If I can see my way clear money-wise to build a fixed gear ice bike, I think I will put the 42t biopace ring on it.
Someone looking for a different size ring might want to experiment with biopace rings, since Harriscyclery almost gives them away.
As for chain tension, I adjust mine for 1/8" slack at the tightest point and about 5/8" slack at the loosest point in the cycle.
I have a normal chainring that I feel isn't round enough. The chain tension changes a lot from the tightest to loosest, but it has been reliable. I can't imagine running a fixie with a Biopace for fear of dropping my chain on the loose parts while trying to skid.
Thanks for that. I have a 42T Biopace sitting in a bin that I've been meaning to fool with for ages.
Does it "spin out" any differently than a standard, uniformly round chainwheel?
I haven't rode Biopace on my fixed yet, but on my road bike it did spin out differently than a round chainwheel. You can keep it constant. It's really the only time i've ever the felt the elliptical shape. Your feet just get thrown through the deadspot.
Also, has anyone notice that with biopace rings you kind of get a new deadspot at like five and eleven or maybe four and ten?