'70 TR6R final drive gearing

When I rebuilding/restoring this motorcycle I replaced the countershaft and the rear sprockets. I selected the sprockets from the parts book that were identified as the ones it was originally shipped with: 19 counter and 46 rear.

As this motorcycle is breaking in I have noticed that this gearing is on the (very) short side; I can start from rest in second gear fairly easily.

After some digging I learned that I can fit a 20 tooth counter without modifying the access port in the primary, but would need to do some grinding to fit a 21.

I have found that a 43 tooth rear is about the lowest available. I'm thinking about doing the 20---43 gearing, but would really like to hear from members that have experience in this area on a TR6R, 650.

Any suggestions for good all around gearing for street operation where I can cruise in the 40 to 60 MPH range (light to moderate engine load) with out lugging the engine in 4th gear are appreciated.

Best

20/43 is 4.30 overall gearing..I think that's a bit much for a 650 at normal road speeds..19/43 is 4.52 and better in my opinion..Stock was 4.84 overall for the T120 ?

Back in the late 60s it was, in the states, all about quarter mile work. Domestic gearing wasnt quite so low.

Something wrong with a 650 if it wont pull a ton in third ! .

Generally , 100 at 7500 in third IS about right .

Bit tall for ISDT type stuff , bit short for the I.o.M. , but for the road , not to bad .

I roadraced a Triumph for 25 years in AHRMA on a very high performance 750. My base gearing just about anywhere was 4.6:1, or 20/46 on standard sprockets. That gives a good first, a raceable second (not too short) and about 117 mph at 7000 in fifth gear—about 17 mph/1000 rpm, on 25-1/2 or 26 inch tires. A very good all round gearing. I used 4.3 at Daytona. That gives a fairly tall first, and about 126 or 18 mph in top, but rare is the Triumph that will pull that gear to that rpm, it was even a bit much for my low to mid 60’s hp engine, and the loss of acceleration was noticeable. I ride both T120 and T140D Bonnevilles on the street and find the 19/46 or 19/47 gearing (around 16 mph/1000 rpm) to be a bit too short and I’m changing both to 20, and perhaps changing the T140D to 21 if 20 isn’t enough—that’s about like a 20/44, or 4.46. They both accelerate nicely geared short, but the problem in both bikes is too many rpm on the highway in those short transits between twisty roads.