Thruxton R gearing - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 27 (permalink) Old 10-17-2016, 02:57 AM Thread Starter
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Thruxton R gearing

Just a thought whilst doing a decent ride yesterday about the overall gearing on the R being too short. At 100kph its reving from memory at about 3800prm (correct me if I'm wrong)

Just feel a couple of teeth smaller on the rear sprocket might be the way to go without sacrificing too much pull or the need to work the gearbox much more often.....any thoughts?



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post #2 of 27 (permalink) Old 10-17-2016, 04:11 AM
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I found the same issue. I couldn't find any 39/40 tooth rear sprockets, so changed the gearbox sprocket to the 17 tooth one from the t120. Seems to have worked a treat - cruises better on the motorway with sacrificing any pull.
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post #3 of 27 (permalink) Old 10-17-2016, 04:48 AM
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At 100kph GCom gives me 3290 rpm in 6th on the R and at 100 kph an extra tooth (17) will lower your rpm by 194 rpm.

Is this enough?


Last edited by Tricolour; 10-17-2016 at 04:59 AM.
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post #4 of 27 (permalink) Old 10-17-2016, 06:07 AM
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All the same bikes and different results, I thought mine was 3500rpm in 6th to do 100km/h Talk curve and HP curve normally cross around 5000rpm. I found mine wants to get pulling around 4500rpm in 6th and shoots up over 5000rpm no worries and at that speed bye bye license. Try accelerating with halve throttle in top from 3000rpm to 6000rpm, that might let you feel where it pulls best. If you find the sweet spot in the rev range and it lands at 100km/h in 5th it should be good for dropping one and over taking. I've had mine up to 180 and it got there easily, how fast do you want to go? I doubt I would change mine. That's my thoughts.
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post #5 of 27 (permalink) Old 10-17-2016, 08:30 AM
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Talk curve and HP curve normally cross around 5000rpm.
Tq curve ALWAYS crosses HP curve at 5252. Mathematically impossible to do otherwise.
It's one of the most misunderstood concepts in motorcycling. Engines convert the chemical energy in fuel to kinetic energy. How much of this it can do in a given period of time is power. Rotational power is proportional to tq*rpm. With gearing you can trade tq at the rear wheel for speed(rpm) however you like.
It's like a 10 speed bicycle. You can put it in first gear and have a lot of torque to pull you up a hill slowly. You can also put it in 10th gear and get a lot of speed going down a hill while applying much less torque. The power provided by your legs is the same.
At some point, trading speed for tq in the gearing won't work as the engine won't have enough power to overcome friction and windage losses.
Whichever way you change gearing by changing the sprockets, you ARE exchanging speed for tq or vice versa. There's no free lunch.
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post #6 of 27 (permalink) Old 10-18-2016, 01:13 PM
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Did you have any issues with rear wheel adjuster running out of room to move it forward to provide more slack in the chain to handle the extra tooth? Also, have you noticed any issues with the ABS, traction control or ride modes since making the change?

I have a standard Thruxton and have been looking for a 39 tooth rear sprocket. Contacted all the sprocket makers and no interest so far. I added a one tooth larger gearbox sprocket to both my '04 Thruxton and my '07 Tiger 1050 and found that made the acceleration curve more acceptable to me. I will order up the T120 sprocket.

Thanks for the info.
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post #7 of 27 (permalink) Old 10-19-2016, 03:15 AM
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The chain adjuster is still within the range and no issues with the abs, riding modes or speedo accuracy. Revs drop by about 300 at 90mph, which you do notice even though it doesn't sound like much!
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post #8 of 27 (permalink) Old 10-19-2016, 04:27 AM
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You noticed a difference of 300rpm at 90 miles per hour.

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Last edited by Tricolour; 10-19-2016 at 04:29 AM.
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post #9 of 27 (permalink) Old 10-20-2016, 06:58 AM
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Just feel a couple of teeth smaller on the rear sprocket might be the way to go without sacrificing too much pull or the need to work the gearbox much more often.....any thoughts?
If your 18 stone and the girlfriend 12 stone, higher gearing wont help the engine at all. On the other hand, if your 12 stone and rarely carry a pillion, all these old tarts would handle taller gearing. One or two teeth bigger on the gearbox, if such is available would do it.. RR

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post #10 of 27 (permalink) Old 12-04-2016, 10:25 AM
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New rear sprockets

SuperSprox now has available a range of rear sprockets for the 2016 Thruxton & Thruxton R.

https://www.supersproxusa.com/products.php?cat=1125795
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