Adding more preload to stock forks?

[RC390 Fan]

My R fork was missing the washer next to the preload spacer you show in your pic. Also found that getting the oil worked back into these forks is a real be-atch. Very messy! Any tips on that? I still gotta do the other one.

Edit: The L fork was also missing the washer next to the spacer. Doesnt seem to be a big deal though.

Also now that both forks are shimmed with more preload (12mm) and 5w weight oil, I think it is better. Def less fork dive under braking. But after testing (street only) I think I should go with 7w as suggested. 5w doesnt feel very different than stock in the rebound dept. I may also reduce preload to 8mm.

Here are a couple more pics
View attachment 1229View attachment 1230

 

[OldVet]

Informative thread thanks guys...

 

[RC390 Fan]

Update.

Update on preload project: Decided to add more fork oil to my current setup (12mm preload/5w oil) instead of going to 7w, and I am fairly please with the result. Added @ 10cc per and forks feel firmer but not harsh, and there is almost no dive if you dont stab the brakes. Still needs more rebound control but it's not bad for the effort.

Starting to think i may be able to mess with the stock valving to help slow it down on rebound. Wonder what would happen if I somehow were to preload this spring a bit, just to put a bit more pressure on the rebound shim. ? Hmmm.... Any thoughts from you tuner types out there?

 

[SPG]

That shim is just a check plate which is held loosly in place with that spring. The actual valving is from the holes in the piston. You would need a pretty massive increase in spring rate to affect the damping with that spring. If you built a stack of shims instead of the check plate, you might have some success though...
-Sean

 

[RC390 Fan]

Ok I get it now. So what if I put a larger diameter shim in the rebound side?

I'm just surprised by how light the springs are on the 'check plates'. Seems like it would take very little force to open them up.

 

[psych0hans]

Why don't you ask race tech if they have replacement valves for your bike? They would provide you with the shims as well.

 

[Ash797]

I may not totally understand what you're trying to achieve but have you seen the preload adjusters from TYGA? There is also a set I saw on japan.webike.net
CRAFTMAN : Initial Adjuster [W-1404-103]

 

[Formula390]

I may not totally understand what you're trying to achieve but have you seen the preload adjusters from TYGA? There is also a set I saw on japan.webike.net
CRAFTMAN : Initial Adjuster [W-1404-103]

He's trying to adjust the valving on the stock cartridge, basically. The Tyga adjusters (and the linked Craftman as well from the looks of them) preload for the springs, and wouldn't much impact rebound or compression. Obviously additional preload on the springs will have SOME impact, but not nearly as much as say the weight of oil used, oil level, and the valving settings in the cartridge. The heavier 7w oil is mostly for us bigger boys and racers. We are basically just finding the 4w oil inadequate. KTM had to build suspension that would do "well enough" for riders from the 95# 16 year old kid who's got it as their first bike, to the 240# greybeard flogging in through canyons and the occasional trackday... So, compromises are made at the factory that mean it's not setup correctly for anyone really. LOL So now when you have a known rider weight and riding style/place, you can tune for exactly how you use it. The Tyga adjusters allow you to dial in the preload on the spring for setting sag and tuning the springs, but won't have any impact on the cartridges. Generally you can adjust those settings with oil weight, without having to touch the valving. I think the stock cartridges (such as they are) are basically "good enough" for tuning... you just gotta play around with it a little bit to get it dialed in just right. That said, the Tyga adjusters are looking AWESOME and I can't wait until I've got 'em in stock for folks... as well as myself. Having to do a complete disassembly to drop in a new spacer to slightly adjust preload on the springs... SUCKS!!!! My current sag is ALMOST right. I'm just too lazy to tear into them to make the small final adjustment necessary. Having the Tyga adjusters will allow me to do that in about 4 seconds as opposed to the full scale ordeal of getting that front end all the way apart AGAIN just to swap out my spacers to add another ~3mm to 'em. {bleeagh!!!}

 

[hydroz1]

He's trying to adjust the valving on the stock cartridge, basically. The Tyga adjusters (and the linked Craftman as well from the looks of them) preload for the springs, and wouldn't much impact rebound or compression. Obviously additional preload on the springs will have SOME impact, but not nearly as much as say the weight of oil used, oil level, and the valving settings in the cartridge. The heavier 7w oil is mostly for us bigger boys and racers. We are basically just finding the 4w oil inadequate. KTM had to build suspension that would do "well enough" for riders from the 95# 16 year old kid who's got it as their first bike, to the 240# greybeard flogging in through canyons and the occasional trackday... So, compromises are made at the factory that mean it's not setup correctly for anyone really. LOL So now when you have a known rider weight and riding style/place, you can tune for exactly how you use it. The Tyga adjusters allow you to dial in the preload on the spring for setting sag and tuning the springs, but won't have any impact on the cartridges. Generally you can adjust those settings with oil weight, without having to touch the valving. I think the stock cartridges (such as they are) are basically "good enough" for tuning... you just gotta play around with it a little bit to get it dialed in just right. That said, the Tyga adjusters are looking AWESOME and I can't wait until I've got 'em in stock for folks... as well as myself. Having to do a complete disassembly to drop in a new spacer to slightly adjust preload on the springs... SUCKS!!!! My current sag is ALMOST right. I'm just too lazy to tear into them to make the small final adjustment necessary. Having the Tyga adjusters will allow me to do that in about 4 seconds as opposed to the full scale ordeal of getting that front end all the way apart AGAIN just to swap out my spacers to add another ~3mm to 'em. {bleeagh!!!}

What exactly is your spacer setting Matt? I forgot to ask you since we are about the same weight.

V

P.S. Yes, removing both fork sides and basically doing an entire rebuild to change sag settings sucks.

V

 

[hydroz1]

Swapping out the springs sucked! Took way more work than I expected.

It will require several special tools or some rigging to get then apart.

Thanks to DCMoney for the tip on making the special tool required to remove the fork cap.

I can't believe how much locktite KTM uses for the fork cap. It's absurd.

Anyway, I have also taken a pictures of the amount of blue locktite on the fork cap, showed Matt from Formula390 and he agreed that the locktite was too much.

I use locktite all the time in our shop here at work and I don't use the entire squeeze bottle to thread something to go into flight at 300+ knots.

Anyway, take a look and see how much locktite there is (much like DCMoney's fork cap).

 

[CDN Duke]

I'm swapping my Duke forks to RC390 345mm spring soon. Based on my lowering thread here, http://www.rc390-forum.com/forum/wh...-difference-travel-springs-duke-rc-390-a.html, I have reduced the travel to match the RC390 at ~125mm.

How much preload have people added to the stock spring and at what rider weight? I'm 145-150 without clothing/gear. I am planning to add between 5-10mm of extra preload, probably less rather than more as I am on the lighter side I think, as is my wife who's about 125lb. I'm using 5 weight oil.

Any thoughts on starting point? Perhaps 5mm is enough to start?

thanks
Andrew

 

[Fangfactor]

I'm swapping my Duke forks to RC390 345mm spring soon. Based on my lowering thread here, http://www.rc390-forum.com/forum/wh...-difference-travel-springs-duke-rc-390-a.html, I have reduced the travel to match the RC390 at ~125mm.

How much preload have people added to the stock spring and at what rider weight? I'm 145-150 without clothing/gear. I am planning to add between 5-10mm of extra preload, probably less rather than more as I am on the lighter side I think, as is my wife who's about 125lb. I'm using 5 weight oil.

Any thoughts on starting point? Perhaps 5mm is enough to start?

thanks
Andrew

Im 200 (220 in riding gear) and 15mm extra preload changed my rider sag measurment from 52mm to 40mm.

It does help firm them up a little as well as the preload compresses the soft part of the progressive wound standard springs so the firmer part cuts in a little sooner.

My guess would be about 10mm extra would be a good start for you


Heres a link to a youtube clip of my suspension mods in action

https://youtu.be/cCnGVPPaPF0

 

[CDN Duke]

Im 200 (220 in riding gear) and 15mm extra preload changed my rider sag measurment from 52mm to 40mm.

It does help firm them up a little as well as the preload compresses the soft part of the progressive wound standard springs so the firmer part cuts in a little sooner.

My guess would be about 10mm extra would be a good start for you


Heres a link to a youtube clip of my suspension mods in action

https://youtu.be/cCnGVPPaPF0

Thanks for that Fangfactor. I'm hesitant to go too big to start, particularly as my wife is only 125lbs (not riding the bike currently though)... however I reviewed my notes from the previous work and because I already have a 2mm spacer with the white 2.5mm spacer on top of the spring now, for 4.5mm 'preload', I'll look to remove those and go with a 10mm spacer in total I think. Granted, I think the 320mm Duke spring is softer and not really a proper comparison but will plan to use this as a starting point. I'll take some measurements before starting the work planned for Weds night.

In your setup, do you have any of the OE spacers plus your 15mm or is it 15mm total?

 

[Fangfactor]

Thanks for that Fangfactor. I'm hesitant to go too big to start, particularly as my wife is only 125lbs (not riding the bike currently though)... however I reviewed my notes from the previous work and because I already have a 2mm spacer with the white 2.5mm spacer on top of the spring now, for 4.5mm 'preload', I'll look to remove those and go with a 10mm spacer in total I think. Granted, I think the 320mm Duke spring is softer and not really a proper comparison but will plan to use this as a starting point. I'll take some measurements before starting the work planned for Weds night.

In your setup, do you have any of the OE spacers plus your 15mm or is it 15mm total?

Ive got a total of 20mm which includes the 5mm OE spacer.
I suppose I do have a tendency to leap into the deep end and If I cant swim I'll scramble out, but if I can and its comfortable I know Ive reached my goal a lot sooner.
Also if it is too far you feel the result and can calculate what would be about right and adjust. Then on some occasions you learn its still not enough and there is still further to go.
With my set up Im tempted to add another 5mm, but am a bit concerned about the spring binding at the end of the stroke
Ahh the fun of tinkering in the garage

 

[CDN Duke]

New 10mm spacer with nothing else has resulted in what looks to be 20mm static sag and ~37mm rider sag, sans gear. Note that this is on my modified Duke setup using stock RC390 345mm spring with 30mm white Duke spacer and 27mm travel reduced strut assembly.

Haven't had chance to ride yet but optimistic that it will work well.

 

[Fangfactor]

New 10mm spacer with nothing else has resulted in what looks to be 20mm static sag and ~37mm rider sag, sans gear. Note that this is on my modified Duke setup using stock RC390 345mm spring with 30mm white Duke spacer and 27mm travel reduced strut assembly.

Haven't had chance to ride yet but optimistic that it will work well.

Those numbers sound good
Look forward to your thoughts after a ride

 

[CDN Duke]

So far so good. Using 95mm of travel on city/highway mix, no big bumps or compressions. Not far from the 100mm I had before but less sag so it's not as soft to start, less dive, so I'm quite satisfied at this point. Will continue to put more miles on.

Posted link to the clip on mounts for fork re&re in the other thread.