19t Sprocket

It will not just be LOWER gear torque that you feel you've lost.... bear in mind the gears are ratios so upping the final drive ratio effectively spreads the gears i.e. bigger gaps, obviously the inverse is true.
A 1 tooth smaller front sprocket than standard usually gives the bike more zing and closes the ratios for a torquey ride naturally at the expense of fuel, revs and noise.
I have a 675R which is -1 tooth on the front and it suits me.

No such thing as a free lunch as they say.
Factory gearing will always be a compromise due to the variety of customers needs.

 

2004 Speedmasters came with a 16t front sprocket and most owners went up from there

I ran 17t and 18t both through a tire change and found I lost top end speed while still often searching for a 6th gear

I did appreciate (at times) the taller gears, but when I went back to a 16t, I knew I was home and never changed it again, other than to renew

Made absolutely no difference in my fuel economy that I could tell, and I never leave the house going short of 30 miles one way, and all highway and Interstate at that.

The roll-on with the lower gear ratio was simply superior and that little 790cc motor was very happy running the higher revs, not to mention the engine braking on roll-off

I’m happy with the gearing on the T120, but knowing my experience with the Speedmaster brought me back to stock gives me pause to change anything here today

I’ve learned to trust Triumph engineers and their team of crackpot test riders. They figured all that out so I don’t have to.

 

I’ve just gone from 17 to 16t on mine and the improvement is massive…to the point of not selling the bike.
No more revving and clutch slipping to pull away on anything more sloped than flat ground, always in the right gear 30/3rd, 40/4th etc and much more instant overtaking. 6th now gets used and I don’t really care about any speed over 80 nowadays.
The gearing on the T120s is ridiculously high but, to be brutally honest, I found my previous Street Twin far too underpowered for quick overtakes so don’t regret that change.

 

I find the gearing on my T120 too tall and have considered going to a 39-tooth rear sprocket. Would the general wisdom be to go for -1 on the gearbox sprocket instead?

 

39t makes a nice difference. Closes the gears up a bit, makes second better for rolling through junctions ( not more fanning the clutch) and makes 6th more useful.
No chain alteration is required and it moves the rear wheel to the centre of the adjustment range.
Easy to do and 100% reversible.

 

That will be the way I go then. Thanks for the feedback.

 

I can appreciate that improvement afforded by the 39t rear sprocket for a T100 or T120.

I make 1st gear at most junctions and I’m quick backing down from 6th in traffic - even at 70 mph. Most of my miles are all over 80 mph, though, and I’m more comfortable with stock gearing than I was at first. Still pushing 4000 rpm in 6th often enough.

If I had anything besides flat gulf coastal plain to ride, I’d change for sure. Every road around here is flat and straight, for a 150 miles, anyway.

 

My T120 now has a 39T rear sprocket fitted. An x-pipe was fitted at the same time. The bike now feels much better as the gearing feels more natural. No clutch-slipping at junctions and roundabouts. The x-pipe has changed the tone of exhaust slightly and the engine feels like it is breathing a little better. Not a drastic change but a small improvement. Early impressions are that both mods were worth doing. Now if I could only get the fueling feeling like carbs......