Geared to the moon? - Triumph Bobber Forum
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post #1 of 37 (permalink) Old 05-11-2019, 10:45 AM Thread Starter
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Geared to the moon?

I'm coming from a Thruxton R which I just didn't ride "hard" enough to keep it around. I loved the motor though, and the instant torque at any point in the rev range was welcome. I figured I'd like the Bobber's engine even more given the way I ride most of the time. That said, though it does have more torque in the range where I typically ride, it doesn't feel like it. I then looked up the gearing which really surprised me. The Thruxton uses 16/42 (2.625:1) and the Bobber is 17/37 (2.18:1). No wonder it feels so much different. Rather than swapping both out right away, I'm planning to start with a 16t front sprocket and go from there.

Has anyone else changed their gearing? I wonder why Triumph geared them so radically different. I also wonder what the ratios in the gearbox are, and if they differ between the various 1200 models.
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post #2 of 37 (permalink) Old 05-11-2019, 01:08 PM
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I tested a Thruxton a while ago and a Speedtwin and T120 this morning. The Thruxton and ST are geared the same (lower) with 6th being tractable from 45 mph whereas the T120/Speedmaster/Bobber you can't really get into 6th until well over 50, approaching 60. It was the biggest thing that I had to get accustomed to on the Speedmaster....

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post #3 of 37 (permalink) Old 05-11-2019, 01:20 PM Thread Starter
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Yes, 6th gear is really only for the interstate. I don't get into 6th until I've crested 60, preferably 65. It still feels a bit long legged there, as the highway pull is not nearly that of the Thruxton. Since I commute with a lot of lunatics, I like being able to shoot away even when I'm doing 75 or so. At that speed, the pull is actually similar to that of my Bonneville with the 865cc mill.
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post #4 of 37 (permalink) Old 05-11-2019, 01:51 PM
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Yes, I switched to a 16-Tooth front sprocket and it launches much better and routine take-offs are much smoother without needing to pamper the clutch lever. 6th gear remains pretty useless under 75mph though and the engine isn't screaming even at 105, so I feel it's still geared slightly too low. I'm not sure I want to go to 15 because it would be hard on the chain, so at some point I will probably see if I can find a 38 or 39-Tooth rear made of steel (I've given up on aluminum sprockets because if you ride hard at all the teeth always bend, regardless of hardness).

-GPz/Gary

Last edited by GPz; 05-11-2019 at 01:55 PM.
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post #5 of 37 (permalink) Old 05-11-2019, 04:47 PM
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I run the thruxton R 16 front & a 39 rear.
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post #6 of 37 (permalink) Old 05-11-2019, 05:37 PM
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Yes, I switched to a 16-Tooth front sprocket and it launches much better and routine take-offs are much smoother without needing to pamper the clutch lever. 6th gear remains pretty useless under 75mph though and the engine isn't screaming even at 105, so I feel it's still geared slightly too low. I'm not sure I want to go to 15 because it would be hard on the chain, so at some point I will probably see if I can find a 38 or 39-Tooth rear made of steel (I've given up on aluminum sprockets because if you ride hard at all the teeth always bend, regardless of hardness).

-GPz/Gary

Hey Gary....Did the 16 tooth sprocket affect your speedo reading ? were you able to adjust the chain enough to get good tension or did you have to remove a link or two ?

Last edited by Mar-Vel; 05-11-2019 at 05:45 PM.
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post #7 of 37 (permalink) Old 05-11-2019, 07:50 PM
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Hey Gary....Did the 16 tooth sprocket affect your speedo reading ? were you able to adjust the chain enough to get good tension or did you have to remove a link or two ?
You can vary the final drive ratios infinitely ( from what options available to us) without impacting on speedo reading. Only when you change rim size or tire profile does it affect the reading as it's determined by the outer diameter of the tire and rotation.


If the speedo sensor was in the gearbox like Harleys and other marques then we might have to purchase one of those speedo recalibration modules. This I had to do on my Buell, not the case fortunately with Triumph as the sender is a component of the ABS rotors.
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post #8 of 37 (permalink) Old 05-11-2019, 08:36 PM
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You can vary the final drive ratios infinitely ( from what options available to us) without impacting on speedo reading. Only when you change rim size or tire profile does it affect the reading as it's determined by the outer diameter of the tire and rotation..
Ooops, should read the tire circumference not diameter......
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post #9 of 37 (permalink) Old 05-11-2019, 09:37 PM
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Hey Gary....Did the 16 tooth sprocket affect your speedo reading ? were you able to adjust the chain enough to get good tension or did you have to remove a link or two ?
Mar-Vel: Speedo is fine. Rear axle is way back but still able to keep the chain tight w/ standard 108 links. I'll probably take a link out anyway just so the bike is a little easier to wheelie.

-GPz/Gary
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post #10 of 37 (permalink) Old 05-11-2019, 09:48 PM
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Ooops, should read the tire circumference not diameter......
Actually, you were right both times.

-GPz/Gary
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