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This is what I did to mine...

And all it did was make the wheelbase a minor 0.19 inches longer, according to GearingCommander, so it adjusted right out and didn't require changing the chain at all.
 

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I also went with a 43 tooth rear and i am happy with the results, bike just feels better at low speed town riding and I feel it hasn't lost anything mid range or top end.
Fitted the 43T and much happier with the low end and still pulls well, still need a PCV etc to reduce the jerkiness.
 

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Hi all, new to the forum but came across this thread and thought I would pass on my set-up.

I have a 2017 390 Duke which I use for commuting, touring and squirting in the hills.

With the stock 15/45,

1. Commuting (20-60 kmph) was painful as I had to constantly change gears if my speed varied by 10-15 kmph. The bike was also quite jerky at the initial throttle opening and closing as a result of the gearing.

2. Touring (80-120 kmph) was painful as I had the bike sitting between 9-11 rpm which is not good for the motor on long stretches or my body as the thing would vibrate a lot.

3. Squirting was painful as the decel from high rpm (8+) would unsettle the chassis too much for my liking but if you got a stretch that required 4th it was the sweet-spot!

So, after experimenting (playing with gearing is both cheap and easy) I settled on 16/42. I can commute in 3rd at any speed other than from a stop. I can tour all day at 110 kmph sitting at 6 rpm flat (no harm to engine or overtly vibrating) and squirting is fun in 3rd - 5th which covers the useable speed range up in the hills.

Other than stunting, I cannot understand why some folks go even shorter gearing than stock. At 16/42, the bike has more than enough punch for street riding with the only qualification being overtaking in 6th. You need to plan ahead and then drop it too fifth for that quick pass but that's common for a lot of bikes under 1000cc!

To give context to my comments, I also own a Ducati 999S (2005 - road bike) and a Gixer 600 (2004 - track bike). I bought the 390 for a commuter but honestly, I find myself riding it more often than not now, it's just a blast in any situation and it truly does them all with the right set-up.

I sorted the gearing and suspension (Andriani fork inners & Yamaha R6 shock swap) and a floating disc at the front (Bikemaster) with pads to suit.
 

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Hi all, new to the forum but came across this thread and thought I would pass on my set-up.

I have a 2017 390 Duke which I use for commuting, touring and squirting in the hills.

So, after experimenting (playing with gearing is both cheap and easy) I settled on 16/42.

Other than stunting, I cannot understand why some folks go even shorter gearing than stock.
Perhaps because not everyone has the same view of riding as you. For example, and yes he stunts and yes it is a sales video but he could easily also sell longer gears if he agreed with you.

 

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2020 KTM Duke 390
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I run a range of sprockets, All Supersprox and Bagaros, depending on if I'm commuting, Hooning in the hills, Hitting a trackday or Stunting it. I have 4 chains at different lengths and run between a 44 to 50 rear and 12 to 16 fronts. 12 is the smallest front I've been able to find running the 12/45 gets me close to a 15/54 rear for stunting without the hassle of pulling the wheel to change the rear sprocket. Just unclip the chain, switch out the the front sprocket and clip in a the shorter chain, then back to the 15 again for heading to work after the weekend.
 

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That video uses the crudest and least accurate timing method I have ever seen
 

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2019 KTM Duke 390 w/RapidBike Evo ECU piggyback
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I run a stock 15T in the front and 43T in the back and I think it’s a big improvement as 1st and 2nd gears are actually useful now; however, I lost a wee bit torque on the top end with speeds over 100 km/h, so if I would do it again I would get a 44T in the rear. No observable change in fuel economy on the 43T sprocket. I ride 60/40 hwy city.
 

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I run 15T/45T for long rides, 14T/45T for the twisties and 12T/45T or 12T/48T for stunt work depending on the available space I'm riding in.
All Supersprox front and rear with orange EK QX ring chains and clip links for easy chain swaps
 

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2020 KTM Duke 390
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I run a stock 15T in the front and 43T in the back and I think it’s a big improvement as 1st and 2nd gears are actually useful now; however, I lost a wee bit torque on the top end with speeds over 100 km/h, so if I would do it again I would get a 44T in the rear. No observable change in fuel economy on the 43T sprocket. I ride 60/40 hwy city.
Thats weird as I gained torque all over with 14T45T (which is almost the same at 15T43T). reduced my top speed to 154kph at 10000rpm. I'm running a BMC filter with an opened airbox lid, Rapid Evo piggyback, Decat pipe and Arrow Pro Race exhaust on 98 fuel
 

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The Duke 200 has a 42 T rear sprocket as standard. I replaced my 45 with the 42 giving 15/42. Chain length is fine and this gearing works very well for me. 3rd is now a usable overtaking gear.
 

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2019 KTM Duke 390 w/RapidBike Evo ECU piggyback
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Thats weird as I gained torque all over with 14T45T (which is almost the same at 15T43T). reduced my top speed to 154kph at 10000rpm. I'm running a BMC filter with an opened airbox lid, Rapid Evo piggyback, Decat pipe and Arrow Pro Race exhaust on 98 fuel
That’s not weird as more teeth in the back gives you more torque at the expense of higher rpm (lower top speed). I found that there is a world of difference between 43T and 45T that I ran before switching to 43T.
The character of the bike is completely different. (Stock 45T is a torque monster hooligan and the 43T is a mature lean mean speed machine with loooooong gears, but a wee bit less torque and acceleration). 2 teeth make more effect than it seems. I think the sweet spot is actually 44T for a duke.
 
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