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Setting front preload

L

loz16h

Joined Oct 2007
231 Posts | 0+
Vancouver Island BC
I checked the static sag at the front and have 55mm. Target static sag is 20 - 35mm so I figure I want to reduce sag by 25 - 30mm.

Pulled the forks apart and the packing shims measure 11mm. When I re-assemble without the packing shims the spring is tight up to the cap. No gap.

This seems contrary to what I have read in the doc. I also notice that I can create a 15mm gap between spring and cap by pulling the damper tube down against some spring pressure in the damper rod.

So now I'm confused. Should I meassure the gap without pulling the damper tube down?

What I also want to know is should I add packing shims to reduce the sag or change the spring?

If I add shims how much preload packing would equate to a reduction in sag of 25mm?
 
Loz,

All good questions.

How about some more info? Do you have stock springs? If not what rate are they? Has the static sag always been this much?

I am not an expert in this area, but, what I do know for sure is that you want to be careful about how much preload you put on the main springs, or you will compress the top out springs and things will not work very well indeed. That's the spring pressure you feel in the damper rod I believe.

It definitely sounds like you have too much static sag. It kind of sounds like they are sacked out, which doesn't happen as severely as it used to in the old days.

And more importantly, how much do you weigh? You might well be looking at re springing the front and the rear.

You might want to contact member Steve in NSW Australia. If memory serves he is pretty up on suspension.

Have you checked the "fork tuning for enduro's" thread?
 
Thanks Dale,

I have not been in the forks since I bought the bike last fall so spring rates etc are unknown.

Static sag has increased a little since I first got the bike. I checked sag when I first got it and found Static sag = 48mm, Loaded sag = 81mm. I weigh about 200 lbs.

Given that sag is too great I was kind of surprised to see that there was no gap twixt spring and cap. Can anyone offer explanation of this?

Hoping for more input on how to measure the gap.

I'm guessing I should be looking at new springs but need to be sure about how to assess these things.

Loz out.
 
loz16h said:
Thanks Dale,

I have not been in the forks since I bought the bike last fall so spring rates etc are unknown.

Static sag has increased a little since I first got the bike. I checked sag when I first got it and found Static sag = 48mm, Loaded sag = 81mm. I weigh about 200 lbs.

Given that sag is too great I was kind of surprised to see that there was no gap twixt spring and cap. Can anyone offer explanation of this?

Hoping for more input on how to measure the gap.

I'm guessing I should be looking at new springs but need to be sure about how to assess these things.

Loz out.
Click to expand...

There is always going to be some preload between the cap and spring, I'm just not sure how much, a guess would be about 10 mm's or so.

You are about 20# heavier than me, with riding gear on I'm 210#, and I run .44kg springs in my 04 550. And I run a PDS 8 in the rear.

I can try and find out how much pre load my suspension guy puts on my fork springs.
 
loz16h said:
Thanks Dale,

I have not been in the forks since I bought the bike last fall so spring rates etc are unknown.

Static sag has increased a little since I first got the bike. I checked sag when I first got it and found Static sag = 48mm, Loaded sag = 81mm. I weigh about 200 lbs.

Given that sag is too great I was kind of surprised to see that there was no gap twixt spring and cap. Can anyone offer explanation of this?

Hoping for more input on how to measure the gap.

I'm guessing I should be looking at new springs but need to be sure about how to assess these things.

Loz out.
Click to expand...

Those sag numbers look pretty good to me? You should change the top-out springs to the 05 up part number though as the 03/04 is REALLY soft and prone to breaking?
 
So I changed the seals and put in fresh Belray 5w oil up to 130mm air gap.

On the next ride the zip ties i put on the tubes were pushed to within 1/2" of the bottom of the tube. This seems OK for the air gap but I'm still thinking I have too much sag and I'm using all of the travel too easily.

Can anyone recomend a suitable spring for a 240lb rider with gear?

I still don't understand why I got no gap between spring and cap without packer shims.

Comments?
 
who ya talkin too? :lol: :lol:

ok here is my take on it. you should, on a standard fork have a gap between the top of the spring and the underside of the cap.

to get a gap between the spring and the cap you would PULL the cap up or with the cap off, PULL the rod up.

the only thing that can give or lose you this extra space is the top out spring.

the only thing that makes the spring a touch fit to the cap is the longer top out spring. you'll note that the KTMs got the longer 50mm top-outs and we didn't.

so you have two things connected here. it would pay when you next strip the fork, to look at the top out springs and measure them. 50mm and the conversion is done and that's why you'll have no gap.

the spring for a 240lb rider would be a .48 or even a .50 but i'd stick to the 48s if you are fun trailing etc.

regards

Taffy
 
Steve,

Your 400 has the stock 42's in the forks. I run 46's in my 550, 5w oil, 120mm gap. I weigh 200lbs w/gear. I would guess you'll want the 46's too, especially if your running the Clarke tank all the time.
 
Depends on what type of riding you do? If you spend the bulk of your time in 3rd gear or below, riding lots of rocks, then .48 should work...if you ride a lot of 5th gear sand whoops and not many rocks then .50 would be better.

But you really need to do some valving work...a REAL mid-valve with .48 springs will help a ton and work pretty well everywhere...

Have you looked at The Doc? Do you understand how the top-out springs work?
 
Taffy said:
who ya talkin too? :lol: :lol:

ok here is my take on it. you should, on a standard fork have a gap between the top of the spring and the underside of the cap.

to get a gap between the spring and the cap you would PULL the cap up or with the cap off, PULL the rod up.

the only thing that can give or lose you this extra space is the top out spring.

the only thing that makes the spring a touch fit to the cap is the longer top out spring. you'll note that the KTMs got the longer 50mm top-outs and we didn't.

so you have two things connected here. it would pay when you next strip the fork, to look at the top out springs and measure them. 50mm and the conversion is done and that's why you'll have no gap.

the spring for a 240lb rider would be a .48 or even a .50 but i'd stick to the 48s if you are fun trailing etc.

regards

Taffy
Click to expand...

Thanks Taffy, I was actually talking to you of course. :wink:

As you say when pulling the cap and rod up I get no gap unless I pull harder against the top out spring. This seems inapropriate for measuring the preload gap so I assume any gap (or not) should be measured without pulling agaist the top out spring. Correct?
So... the top out springs would seem to be the new type.

I did noice that when screwing the cap back on, it bottomed out on the top of the damper rod thread. To get the cap to lock off against the nut at the top of the spring guide, I had to wind the spring guide nut up to the cap from that point on. This has the effect of reducing any spring gap. Again, I assume this is the way that spring gap is supposed to be measured.

If the above are both true then my fork must be running 11mm of pre load (at least) as this is the size of the packer stack I have in there. As I seem to have no gap at all with out packers and the spring still has pressure on it I'd guess at around 15mm preload. This is a fair way off the recomendations in the doc (0 < 6mm).

Maybe I'm making too much of this. My aim here is a supple fork that can maximise it's travel. The terain here is pretty lumpy with a good amount of rocks and roots. I don't ride many jumps. It's mostly tight woods stuff.

Sounds like maybe I should just change the springs (.46 / .48 sounds about right) and see what that does for the ride.

Thanks for all the helpful comments. Keep 'em coming. :idea:
 
so far so good.....

i do feel you need to strip the fork because the TO springs are the only valid reason for no gap: everything else is trouble....

regards

Taffy
 
Well Steve you got some different opinions on spring rates. The guys are right, I believe for your riding weight the 48's or 50's are the recommended springs. I run th 46's cause I'm a bit lighter than you. I wouldn't run 48's myself because i find the 46's are already stiff enough on trail junk like rocks and roots. Knowing that you are mostly on the tight single track and rarely jumping I would think 46's or 48's would be right for you. 48's are a bit on the stiff side for your type of riding in my opinion. i don't think you would use the full travel on a typical ride, unless you are hitting big air. That being said, I am no expert. I have to drop about 10ft to lightly bottom my forks. Thats a 3rd gear pop off a drop-off to flat ground. Just bottoms mine out. I wouldn't want it any stiffer in rocks, etc.
my 2 pence
Aaron.
 
In my 07 650 I run 46s. I do lots of single track and firetrail. 47s are be OK too, but 48s tested too stiff for me. 47 = 48 + 46! For MX, 48-50 would be OK I guess. I run a 9.6 SR in the back to get the sags right with my 116 kg geared up (250-260 lb). With valving mods to suit and 90-95 mm oil height it rarely bottoms and ride is magical, but dependant on the valving to make it work. Standard compression valving is way off, its too harsh, for rocks and rugged terrain IMHO.

Steve
 
ktmlew said:
bushmechanic said:
48 springs will help a ton and work pretty well everywhere...
Click to expand...

wow, 50s even .................

more music for taffys ears :twisted: :twisted:
Click to expand...

What spring would you rec for a 240lb rider? :roll:
Click to expand...

never quite understood why some countries understand sarcasm more than others. I agree with your recomendation just that ..........

taffy weighs 220 + and your slightly rude post in his thread with bunny pic suggests very strongly that he is a fool for running stiffer than .46s

:?:
 

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