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'70 TR6R final drive gearing

Discussion in 'Triumph (Classic)' started by RoadScholar, Aug 30, 2019.

  1. RoadScholar

    RoadScholar VIP MEMBER

    Dec 28, 2008
    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.

    nortriubuell likes this.
  2. Hillbilly Bike

    Hillbilly Bike

    Oct 18, 2018
    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 ?
  3. Onder


    May 11, 2010
    Back in the late 60s it was, in the states, all about quarter mile work. Domestic gearing wasnt quite so low.
  4. Matt Spencer

    Matt Spencer

    Jul 25, 2010
    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 .
  5. linker48x


    Aug 2, 2011
    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.
    Last edited: Jan 23, 2020

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