One-hand-steering? What's that???
That is precisely why my road bikes have SunTour barcons. Two hands on the bars at all times. I might lessen up on the pedals a bit during the up-shifts - I really don't know. I haven't really given the concept much thought. I'll have to try to remember to look tomorrow on my commute...
I mainly shift just the 13-21 rear six speed anyway, mainly using the 13-14-15-17 rear cogs.
The MTBs that I ride (cheap disposables) for going to the corner store, etc have thumbies on the bars - again, both hands on the bars at all times.
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'75 Fuji S-10S bought new, 52k+ miles and still going!
'84 Univega Gran Tourismo
'84 Univega Viva Sport
'86 Miyata 710
'90 Schwinn Woodlands
Unknown brand MTB of questionable lineage aka 'Mutt Trail Bike'
Plus or minus a few others from time-to-time