I have one on my Bonnie and love it, although I might wind up going back to the 18 for extra mileage on my road trip this summer.
Burphel, you could possibly find that increasing the size to 18T, albeit lowering the revs for a given speed, actually has the opposite effect on your fuel consumption, which could see it actually increase.
I take it thats what you mean by "for extra mileage".
If your Bonnie is jetted well (assuming its carb'd) for your present gearing you'll likely find it enrichening at the lower revs you'd be running with the 18T.
This is due to engine loading being a contributing factor to the resultant a/f ratio.
Have a look at the following thread, from Gumps post on...............
http://www.triumphrat.net/twins-tec...s-to-lowering-your-gearing-6.html#post1925868
Gump has an A/F gauge fitted and his jetting was fairly optimal for the 18T.
Increasing to 19T led to richer running and increased consumption.
Of course this could be recovered by rejetting again, but how many of us do that when changing sprockets!
Its all down to the engine loading being increased for a given speed at the lower revs, and the effect this has on decreasing the a/f mixture.
On a separate note, Gump and I have been on many long road-trips together.
Up to recently he ran a 19T front and I a 17T. Both bikes running a/f gauges with spot-on jetting.
At every 100'ish mile fill-up, on every trip we've done, we were only a couple of cc's different on the fuel used.
Almost exactly the same every time. Same distance, same speeds, same consumption.
Its not the tooth size that makes the difference to consumption, its the a/f setting at that particular gearing/engine loading.
All IMHO of course!!
Would be interesting to hear others experience on this! Sure we will!!
V.