Need help from the suspension guys

To measure preload, just measure the height/protrusion of the cartridge before and after you tighten the footnut (without compressing the spring, but still touching it).

can you give a little more detailed description on how to measure the preload? I think I understand but I want to be sure

Put the cartridge on top of the spring, measure distance from the top of the outer leg to the top cap (or whatever 2 points are convenient).  Make sure the weight of the cartridge isn't sagging the spring.

 

Then install the footnut on the cartridge and make sure the footnut is bottomed out on the rod (gap between footnut and jamnut).  Then take the same measurement again up top.  Outer leg dropped all the way on the stanchion for consistency.  The difference in the measurements is your spring preload.  ~5mm is normal for mixed use.  Some offroad guys like 1-2mm.  MX guys up to 6mm maybe (don't know for sure).  I do know that the 10mm or so that comes on them is way too much and doesn't really serve any purpose well.

Awesome thanks

I agree, but I was being simplistic so as to not over complicate the issue for the OP

Yes the spring rate has go to be correct first, but the point I was trying to make in a simple way was that even with the correct spring rate, if the valving is too harsh then it will still feel harsh

 

So, if you leave your presumably satisfactory valving in place, then substitute a pair of 2.00 kg/mm springs with an appropriate preload for the right ride height, that would not feel harsh?

 

 

Stock rate in the rear is 6.0kg, front is.50kg.

 

 

The manual for the '14 calls out .50 and 5.9 (4.9 n/mm and 58 n/mm)

So, if you leave your presumably satisfactory valving in place, then substitute a pair of 2.00 kg/mm springs with an appropriate preload for the right ride height, that would not feel harsh?

Gray, what are your thoughts on reducing the preload as suggested?

Preload is a secondary consideration, but can be necessary in front just as the sag settings in the rear.  Like the rear, there's a "ballpark" way of estimating spring rate suitability from the measurements.  According to Dwight Rudder:

 

That bike has 310mm travel in the forks. You are looking for 43mm static sag and 77mm rider sag (+ - 2mm). If you are not in this range you need different fork spring or a bit of preload. About 5mm preload should be good.
The 450 has 315mm rear wheel travel. You should be looking for 35mm static sag and 107mm rider sag. (+ -2mm). No more than a max of 10mm preload on the spring. I like much less.
These numbers are based on a formula of percentages that can be used on all modern bikes.

 

The difference between free sag and rider sag will be the same for the correct spring rate whatever the actual free sag is, so check that first.  If, for instance, you have a 30-35mm difference between free/rider sag, but your free sag is only 30mm, then you need to loose some preload to get into the right range.  If the preload is only 30mm, but you only have another 15 or 20mm more sag with you on board, the spring is just too stiff.

 

Cutting the perches as described is the simplest and most workmanlike means of reducing the preload, IMO.  The perch slides onto the cartridge tube and stops against a steel ring that rides in a groove on the cartridge tube.  People lowering the bike seriously for things like flat track will normally cut new grooves farther up and relocate the ring, but the ring has a rolled on retainer over it, so it's not as simple as it sounds.  Cutting the perch is reversible by either shimming, or by simply replacing the perches. 

Machine off material from the top of the spring seat.

To measure preload, just measure the height/protrusion of the cartridge before and after you tighten the footnut (without compressing the spring, but still touching it).

Excellent, thank you!

so I found 10mm of preload. To reduce it I would shave material off of the spring seat here?

1435971060121.jpg

The guys commenting previously know there stuff, but I think they are over complicating things. I'm pretty specific when it comes to my suspension and have had every bike revalved. The new yzs have great stock suspension. I'm 208 lb B rider. The stock valving is good. The recommended sag for the yzs is 90-100mm which is different then just about every bike. I use 95mm. As for your original question, unless the guys telling you that its to soft are your speed and weight, its best to go with what the suspension company's recommended for your weight.springs are a easy swap and are worth getting. I would start there more then messing with pre load.

Edited by guntoter535

The guys commenting previously know there stuff, but I think they are over complicating things. I'm pretty specific when it comes to my suspension and have had every bike revalved. The new yzs have great stock suspension. I'm 208 lb B rider. The stock valving is good. The recommended sag for the yzs is 90-100mm which is different then just about every bike. I use 95mm. As for your original question, unless the guys telling you that its to soft are your speed and weight, its best to go with what the suspension company's recommended for your weight.springs are a easy swap and are worth getting. I would start there more then messing with pre load.

I get what your saynig. I ordered springs and I'm considering adjusting the preload while swapping. Somewhere I read a post that I believe Dwight rudder wrote. In the post it mentioned that reducing preload will make the first tad bit of the stroke act like a softer spring and then revert back to the actual spring weight.

Something I think we are all familiar with is washboards on a gravel road. Bassically my take on it was that it would make small bumps like those all but vanish. Idk maybe I'm wrong.

Well if your gonna try pre load then you can test it by raising or lowering one fork leg while its in the clamps. This will create pre load as well

Something I think we are all familiar with is washboards on a gravel road. Bassically my take on it was that it would make small bumps like those all but vanish. Idk maybe I'm wrong.

 

Lightening the preload won't fix that, because all it does is adjust the "ride height" of the suspension unit.  The response of the suspension to its environment isn't affected by it. 

 

Series small bump compliance is reduced by too high a spring rate, too little float in the midvalve, too much damping resistance in the mid valve or compression valve, or by too much initial rebound response not allowing the fork to recover quickly enough from each bump.

So I got the New springs today. They are fc .46. Something odd I noticed is that they are about 7mm shorter than the stock springs. That reduced the preload from 10mm to 3mm. Seems fc is onboard with reducing preload.

Most aftermarket companies are.  Well, most everyone except KYB/Showa.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now