Originally Posted by
cyclezen
I'm not sure how you could even start comparing between the 2 bikes... 42/28 + 5lbs vs 34/28 ?
It's pretty simple kinematics, and 5lbs is usually a small enough difference to total system weight that even rough approximation can paint an accurate-enough picture to address the question.
For instance, if a bike+rider is 167lbs, a 5lb increase represents a 3% increase in resistance from gravity. So for example, on a steep climb where you're going slow and bottlenecked by gearing, that 42T chainring on the Miyata would be like using a chainring slightly larger than 43T on the Emonda.
Ok, 5-6% grade isn't much, but I was trying to put into a frame work which I see a lot of riders struggling. But let's make it 'real' 8-9%+ and, for whatever reason, you're barely turning 55/60, on a current bike with 34/28, 25mm rubber - you're goin about 9 kph (6ish mph) - you drop into a 30 or 32 - I would put big money that, after about a 20 yd surge
Why are we assuming that the rider will "surge"?
If you're at 55 rpm, you're already DONE/cooked and 30/32/34 isn;t going to save you
What point are you even arguing? I mean, obviously if your legs want to climb at 70rpm, and your gearing currently pegs you doing a lot of 55rpm, going from 28T to 32T may not produce a totally-optimal situation. But it's still an improvement, and if a rider wants even lower, they can set their bike up with even lower: the OP's question about lowering gearing was quite open-ended.