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Longer and Softer Enduro forks for Duke 390

19K views 35 replies 17 participants last post by  KTMasean 
#1 · (Edited)
Hello

The stock KTM duke 390 forks are not adjustable and very stiff . I need more travel + softer . I need more ground clearance + softer travel for mild or light offroading .

Has anyone converted the front End shocks of Duke 390 to 690 Enduro forks ?

Or any other way to increase the front end height , add atleast 3-4 inches softer travel ?

Any thoughts ,suggestions or links , conversions appreciated .

NOTE :I have already install R6 rear monoshock .
 
#3 ·
Nfsnfs, Since your bike is new and not yet broken in, before you start thinking about changing the front forks you should get them operating well. As delivered, the 390 front forks are often misaligned at the factory. You can perform this simple maneuver to release the front forks, make them more supple and compliant, and use their full travel potential:

Experience has shown that many/most 390's are delivered from the factory with a misalignment of the forks which causes binding and stiction. Apparently, at the factory the right (looking forward) fork leg is tightened on the spindle/axle first, then the spindle nut on the left leg is tightened down. This procedure - which really should go in the opposite sequence - results in a tension between the two fork legs that tends to pull each towards the center, and perturbs the alignment of the fork sliders with their respective legs.

The remedy: On the right fork leg there are two pinch bolts that tighten down on the spindle/axle. Loosen these bolts. Then, grasping the handlebar grips and applying the front brake, pump the forks up and down 6-8 times. Then retighten the pinch bolts. This allows the tension to release on the fork sliders and permits them to align naturally with the upper fork legs. The improvement in fork compliance is astonishing.
 
#4 ·
Nfsnfs, Since your bike is new and not yet broken in, before you start thinking about changing the front forks you should get them operating well. As delivered, the 390 front forks are often misaligned at the factory.
Thanks Diploman .
My bike has run over 30000 kms , It has seen 2 tyre changes ,sprocket -chain set changes , one cone set changes . Both the forks were removed and reinstalled .
 
#7 ·
The Duke already has above average suspension travel with 150mm at both ends, but the stock suspension is horrible. The rear is harsh and the front end sags a huge amount. My forks dropped 75mm with me and gear on the bike. I've swapped to an R6 shock and now have some stiffer fork springs on the way. Handled the dirt very well with just the R6 shock but the front bottomed out way too easily which is why I've got for upgraded springs. They haven't arrived yet though so I'll have to report back.
51660
 
#8 ·
As the good and always helpful forum member Diploman mentioned back in July 2017 almost ALL Dukes/RC's need to have their forks aligned correctly as per procedure he described.
Stating that the OEM shocks are horrible is, to say the least, not correct with 99.9% of the Duke/RC riders experience on a daily basis.
Can they be improved, oh well of course as can the brakes?
It is hardly the bikes fault when packing this naked bike with a rack sticking out some 15-20cm behind the pillion seat and loading it as a mule that the OEM rear shock and front end have difficulty to cope.
With my 78-80kg and my small backpack (I estimate 8 to 10 kg) riding the dirt roads in Asia, I do have the front and rear shock hit the end stop very occasionally and mainly if I ride too fast to be able to brake in time for a huge pothole or washed out crack in the road.
My sag is about 3.2 cm rear, with your 7.5 cm there is either something wrong with the shock (if you set the pre-load at max) or you weigh close to 170 kg.
 
#9 · (Edited)
Few corrections there mate. Firstly, that rack was put on after the R6 shock. And the 4kg swag I had mounted on it had almost no impact at all. The R6 shock handled the dirt absolutely perfectly and never bottomed on me with my 75kg weight, a 10kg bag on the back seat and a 4kg swag on the rack. As I said, it was the front bottoming out, not the rear. Check your fork sag. They are dual rate springs which are 0.62kg/mm at the heavier end. RC guys use 0.75kg/mm and above straight rate springs. That's significantly firmer than what comes stock on the Duke.

Now about the standard rear. It's harsh and lacks good damping characteristics. Just like all budget shocks. Just as bad as my MT07's was before I put an Ohlins on it. The R6 shock on the Duke is superb if you're a lightweight like myself and can be dialled in to suit the kind of riding you want to do with the bike. As someone who's owned plenty of bikes with good suspension, and plenty with bad suspension, the Duke is towards the bad end of the scale. Maybe horrible was too harsh, but bad is definitely a reasonable description of the rear shock at the least. The forks themselves aren't bad but the spring choice is. It's not balanced with the rear at all and some stiffer springs will go a long way towards getting more travel out of the forks.
 
#10 ·
I will never understand why humans purchase a machine that is meant for a purpose, then Attempt to turn it into something that it is not. Is it because you liked the looks of it sitting on the showroom floor? Was it the price?
If you want a DRZ400 or Africa Twin, why not purchase one rather than convince others about the shortcomings/inadequacies of the machine that you own and are using for a purpose other than it was designed for?
 
#13 ·
Can't comment on why the original poster wants enduro forks on the Duke. But for me, I run a group for riders dedicated to custom scrambler builds. We do it for the fun of it. We have Ducati's, MT03's, a W800, Triumph Bonevilles, SV650's, basically any naked bikes that have been converted to run a mix of road and dirt (aka Scramblers). It's incredibly fun and you have just as much fun riding to the dirt roads as you do on them. I've had plenty of Scramblers in the past as I tend to build, ride and then sell every couple of months just to keep things interesting. For my latest build, I specifically picked the Duke 390 for a number of reasons.

Size and weight - It's small and light. Much smaller and lighter than what the others guys in my group run. I'm a small/light guy and I don't like wrestling with 200kg bikes.
Ergonomics - It has a great riding position which lends itself well to off-road style riding, albeit it's too cramped to be able to comfortably ride standing on the pegs.
Power - Just the right amount to make road riding fun and not so much that you're constantly wheel spinning whilst on the dirt.
Ground clearance - No nasty header pipes or oil filters hanging underneath the engine, and you can buy bash plates already made.
Suspension travel - This little thing has 150mm front and rear. That's well above average for a road bike. It actually has more than the CB500X and Versys 300X.
Price - Second hand these are dirt cheap. I got mine for $2,600 AUD because it had a few scratches already from a carpark fall.

So those are the reasons I chose the bike before actually owning one. Once I bought it and test rode it a few things were realised. On road this bike is incredibly fun and one of the most fun bikes I've owned. The rear suspension felt cheap and harsh, but other than that I couldn't fault it. Based on this, I sourced an R6 shock and threw it on expecting that it would not only improve road riding performance and comfort, but that it would also benefit off road riding by being slightly longer and allowing me to tune the damping for additional comfort. Then it came to testing the bike off road. Almost everything from my above list was spot on. Size, weight, ergos, power, ground clearance. Where it fell quite short of expectations was suspension travel at the front end. 150mm should be plenty of travel. At the rear it was more than enough to never bottom out even loaded with a bit of gear, but when you take into account the highly excessive sag (especially for myself as a lightweight rider at 75kg), I was left with an effective travel at the front end that was far short of this number. This should be an easy fix. The travel is there, the valving is competent enough, it just needs more suitable springs. And so I've sourced some 0.75kg/mm fork springs to swap out with the 0.62kg/mm standard springs. If I set these up with about 30-40mm rider sag then I'll have an addional 110-120mm usable travel at 0.75kg/mm before I bottom out, which is significantly better than the 75-85mm of travel at 0.62kg/mm that I have now. This should be plenty enough to allow my bike to do what I'm asking of it and be a **** of a lot of fun to ride while doing so.

The reason I've specifically picked on the front forks of the standard Duke 390 is because I haven't had this issue before with any other road bike being used off road. And all of the other road bikes I've ridden off road have had LESS suspension travel and so my conclusion that the standard front springs are very sloppy is based on the ease at which they bottom out especially considering their long travel. If you Google or search on this site for the standard front sag numbers people are getting on this bike you pretty much come up with nothing, but take some measurements yourself and you'll be surprised.
 
#14 ·
Can't comment on why the original poster wants enduro forks on the Duke. But for me, I run a group for riders dedicated to custom scrambler builds. We do it for the fun of it. We have Ducati's, MT03's, a W800, Triumph Bonevilles, SV650's, basically any naked bikes that have been converted to run a mix of road and dirt (aka Scramblers). It's incredibly fun and you have just as much fun riding to the dirt roads as you do on them. I've had plenty of Scramblers in the past as I tend to build, ride and then sell every couple of months just to keep things interesting. For my latest build, I specifically picked the Duke 390 for a number of reasons.

Size and weight - It's small and light. Much smaller and lighter than what the others guys in my group run. I'm a small/light guy and I don't like wrestling with 200kg bikes.
Ergonomics - It has a great riding position which lends itself well to off-road style riding, albeit it's too cramped to be able to comfortably ride standing on the pegs.
Power - Just the right amount to make road riding fun and not so much that you're constantly wheel spinning whilst on the dirt.
Ground clearance - No nasty header pipes or oil filters hanging underneath the engine, and you can buy bash plates already made.
Suspension travel - This little thing has 150mm front and rear. That's well above average for a road bike. It actually has more than the CB500X and Versys 300X.
Price - Second hand these are dirt cheap. I got mine for $2,600 AUD because it had a few scratches already from a carpark fall.

So those are the reasons I chose the bike before actually owning one. Once I bought it and test rode it a few things were realised. On road this bike is incredibly fun and one of the most fun bikes I've owned. The rear suspension felt cheap and harsh, but other than that I couldn't fault it. Based on this, I sourced an R6 shock and threw it on expecting that it would not only improve road riding performance and comfort, but that it would also benefit off road riding by being slightly longer and allowing me to tune the damping for additional comfort. Then it came to testing the bike off road. Almost everything from my above list was spot on. Size, weight, ergos, power, ground clearance. Where it fell quite short of expectations was suspension travel at the front end. 150mm should be plenty of travel. At the rear it was more than enough to never bottom out even loaded with a bit of gear, but when you take into account the highly excessive sag (especially for myself as a lightweight rider at 75kg), I was left with an effective travel at the front end that was far short of this number. This should be an easy fix. The travel is there, the valving is competent enough, it just needs more suitable springs. And so I've sourced some 0.75kg/mm fork springs to swap out with the 0.62kg/mm standard springs. If I set these up with about 30-40mm rider sag then I'll have an addional 110-120mm usable travel at 0.75kg/mm before I bottom out, which is significantly better than the 75-85mm of travel at 0.62kg/mm that I have now. This should be plenty enough to allow my bike to do what I'm asking of it and be a **** of a lot of fun to ride while doing so.

The reason I've specifically picked on the front forks of the standard Duke 390 is because I haven't had this issue before with any other road bike being used off road. And all of the other road bikes I've ridden off road have had LESS suspension travel and so my conclusion that the standard front springs are very sloppy is based on the ease at which they bottom out especially considering their long travel. If you Google or search on this site for the standard front sag numbers people are getting on this bike you pretty much come up with nothing, but take some measurements yourself and you'll be surprised.
Hey Cedar Drew,
I'm doing the exact same thing with a Husqvarna Svartpilen 401 (aka KTM Duke 390)
I've done a lot of work on the bike (for fun) already which includes Nitron rear shock, raising the rear ride height, crash bars, exhaust, ecu, bar mods, bash plate, TKC 80 frt /Motoz Tractionator Adv Rear, Tubeless conversion of the spoked wheels, the list goes on..
Now to my forks.. I've added preload by inserting spacers in the top of the fork tubes (10mm) and have also upped the fork oil to 10wt which has had a great result, no more bottoming out and nice and stiff (im 80kg plus kit)! I've dropped the forks as far as I can through the triple clamps to raise the front ride height but would still like to get another 15/20mm.. I'm scouring the interweb to try and find some extensions or custom tube caps to do this but cannot find them yet.. I saw a guy on YT do this on an MT07 build he was doing... Result was perfect.
I may need to find a friendly guy with a lathe!
Where are you guys based? I'm in Point Cook near Melbourne...
 
#24 ·
A guy in Thailand just replaced his OEM forks with the latest BMW310GS forks.
He claims these have longer travel and softer dampening.
I do agree on the softer dampening as I did a test ride 2 years ago or thereabouts.
What I would question though is the balance of the bike.
It will probably work okay in the dirt but will be totally off on the roads I guess.
 
#28 ·
Hello

The stock KTM duke 390 forks are not adjustable and very stiff . I need more travel + softer . I need more ground clearance + softer travel for mild or light offroading .

Has anyone converted the front End shocks of Duke 390 to 690 Enduro forks ?

Or any other way to increase the front end height , add atleast 3-4 inches softer travel ?

Any thoughts ,suggestions or links , conversions appreciated .

NOTE :I have already install R6 rear monoshock .
Hello

The stock KTM duke 390 forks are not adjustable and very stiff . I need more travel + softer . I need more ground clearance + softer travel for mild or light offroading .

Has anyone converted the front End shocks of Duke 390 to 690 Enduro forks ?

Or any other way to increase the front end height , add atleast 3-4 inches softer travel ?

Any thoughts ,suggestions or links , conversions appreciated .

NOTE :I have already install R6 rear monoshock .
Hi, I am using wr250 forks on my ktm, with a 19 inch spoked wheel in the front. Works like a charm. The bike is a but taller but handles well. I have done a couple of motocross events on the same as well. ( won a couple of them too) .
 
#30 ·
Also, I'll revive this thread on original topic: I'd also be interested in getting a longer travel / softer suspension for some rougher roads -- i.e. push the Duke closer to a supermoto without going full ADV.

I believe this thread was started before the 390 Adventure existed. Anyone know if the forks / swingarm are swappable to the Duke? I also posted in the Adv forum as well: 390 ADV forks + swingarm swappable to 390 Duke?
 
#36 ·
I have seen a guy in Thailand fitting fork legs of a BMW 310 adv to his Duke 390 (first series).
I have done a test ride on the 310 std. and adv. and can confirm they are way 'softer'.
Not sure though how this mod will change the ride of the Duke 390.
No info on the rear other than for example a Nitron shock fabricated to your weight and riding situation. These can also lift the rear about 2 cm if I recall correctly.
 
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