Originally Posted by
DaveSSS
exRunner...
Also, if you compare the closest possible gear inches or gear ratios in the little ring to an equivalent in the big ring, the shifts when riding in the little ring can be smaller. As an example, the 39/17 is nearly identical to a 53/23. If you shift to the next smaller cog in both cases, you get a 9.5% (23/21) increase in the big ring and a much smaller change of 17/16 or 6.2% in the little ring. Of course this assumes that you have a 16T cog, which nearly all 10 speed cassettes do.
I think we are saying the same thing in different ways (or maybe you are using more detail then I did).
The example I was using in my head was my bike - 39/53 and 12/25 (12/13/14/15/16/17/19/21/23/25)
As you state, the 53/23 and the 39/17 are nearly identical at 60.6/60.3. Going to the 53/21 is a bigger jump (9.5%) then going to the 39/16 (6%). As the GI goes up the percentage difference makes the actual GI change greater. We pretty much agree
I have ridding buddies that say they can not tell the difference in those jumps. I can feel the 3% difference. I detest the 39 ring for that reason. I just don't feel comfortable.