Changing the plotting width in bar-, column- and combo-charts of googleVis works identical and is defined by the bar.groupWidth argument. The dot in the argument means that it has to be split in R into bar="{groupWidth:'10%'}".

Example

library(googleVis)
cc <- gvisColumnChart(head(Population,10), 
                      xvar="Country", yvar="Population",
                      options=list(seriesType="bars", legend="top",
                                   bar="{groupWidth:'10%'}",
                                   width=500, height=450),
                      chartid="thincolumns")
plot(cc)

Session Info

R version 3.0.1 (2013-05-16)
Platform: x86_64-apple-darwin10.8.0 (64-bit)

locale:
[1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] googleVis_0.4.5

loaded via a namespace (and not attached):
[1] RJSONIO_1.0-3 tools_3.0.1