MBP is right - No Preload adj. on ZX7R!!!

[HemiDuty]

This website that MBP linked us too a while ago is completely right about the so called 'preload' adjusters on ZX7Rs. I think there was some question of its validity somewhere on this forum, but cannot be bothered searching for it. I was kinda hoping to prove it wrong, since then my preload would actually be adjustable, but alas this is not the case.

I wound the adjusters all the way out and then all the way in, and did the measurements throughout, and sure enough all that changes is the ride height. It is like the preload adjuster just moves the spring up and down the fork tube. It doesn't matter what I do, I cannot set the preload anywhere other than 40 friggin millimetres. Why does the damn manual say its a preload adjuster?!? Why do we get 2 different options of adjusting ride height (the adjuster and pulling the forks through the triple-clamps), and none for preload? Seems like a mighty stupid cock-up to me........

I'd just like to add that this is the ONLY reason Brett can keep up with me round the twisty bits at the track.......

[Jonno]

Hemi, you are on the right track. I can't tell ya what brett does, but hey, what you have worked out seems to be fine right?

[MadKaw]

Spacers and Thicker oil if its that bad....
40mm is little soft for the track.....

Mine was fine and could be adjusted to 25 to 30mm quite easily...
The preload adjuster did make a difference on mine....

[HemiDuty]

40 mm is too soft for anything I reckon. So yours worked properly huh MadKaw? I wonder what the bloody go is then.... Did yours also alter the ride height? And could you adjust it up to 40mm preload if you wanted to (not that you would)? My measurements went something like this:

7.5 rings out: 138mm unloaded, average of 98mm with my bonsai human frame on it.

1.5 rings out: 149mm unloaded, average of 109mm loaded.

Measured from fork seal to stantion.

So as you can see all mine did was move the whole shebang up and down the bloody fork legs. Was yours definitely stock then?

[Barrabob]

Hemi I would be inclined to pull the forks to bits one day for a look see, could even just pull them out and take them somewhere because i recon there light on for oil myself.

when you go to no rebound and bounce them and then go to full rebound and bounce them there should be a diference in the rate it rises and as i remember there wasnt.

And as madkaw sugested you can cut spacers and sit them on top of the springs (already probably has some just make longer ones) and your in buisness.

[mrmina]

i felt mine on the zx7r-p2 did make a difference.

maybe ur forks are stuffed

[MadKaw]

yep, mine was stock.. You may be having some fork tube stiction, although it shouldn't be that much.
Have you changed the fork oil, cause if you haven't for a while it will be like sludge and not helping the situation. You should also check the level of fluid in em..

Now, if the front is a ride height adjuster, it must therefore be lengthening and shortening the amount of travel. So if that is the case and you have say 120mm travel (fully extended) and 40mm sag. If you wind the preload adjuster all the way down does the travel increase.???
I don't believe it does as the travel is the maximim dimensions the forks will come apart.... Therefore I believe the preload adjuster does as its supposed to and compresses the spring..
Pop the fork caps off and have a look at what goes on... I believe it does change the spring preload... which will alter the ride height, with you on it and that is then altering the sag....

[HemiDuty]

Actually that is the problem Madkaw, it is altering the travel. Travel goes from 138 mm with 7.5 rings showing to 149mm with 1.5 ings showing. Now I didn't actually try to compress the springs all the way down to see where they stopped (as in if they stopped before the top of the stantion hit the dust cover) but either way it isn't going to make a difference. Because I get the same difference in loaded and unloaded measurements no matter what the setting, it just alters how far up the fork leg these respective measurements are taken. I did the stiction negating method outlined Here too, so that has nothing to do with it.

I think these front ends may fool some people because the scenario goes something like this:

1. Lift up front of bike and measure distance from dust cap to top of stantion = 138mm

2. Jump on bike (after putting front of bike down again ). Have assistant (read: missus) push down on bars and let up slowly. Take measurement = 93mm.

3. Now get said assistant to lift bars up and let down slowly. Take measurement = 103.

4. Now average the 2 measurements to remove stiction from the equation and get 98mm. Therefore sag at this point is 40mm.

5. Wind in preload adjusters from 7.5 rings to 1.5 rings (I actually did it with more and smaller increments than this but to save space here...) and do the 2 measurements again to get an average measurement = 109mm

Now at this point most people would say "Yep, that's it, 138mm - 109mm = 29mm, my preload / sag is better". BUT, the next step kills that theory:

6. Lift up front of bike again and measurement = 149mm !!!!

So if you do not measure the unloaded sag AFTER moving the preload adjuster you would think you have fixed the problem but alas this is not the case.

Now the 10mm of stiction (the difference between the 'push-down' and 'pull-up' measurements) is consistent all the way through the suspension stroke, and is typical for these forks. Either way it has no bearing on my results.

Sorry for the long post, I just want to get to the bottom of this. I am not trying to prove anyone wrong or win an argument or anything, I just think that maybe these forks really do not have preload adjustment. When I read the article about this at the site linked in my first post, I didn't believe it. Unfortunately it is becoming more and more believable.....

Thanks for your help and input everyone, I hope we can discover what is really going on here. One thing I keep thinking is maybe they made them like this to enable quick ride height adjustments at the track, as preload must be manually pre-set with shims etc.

Whaddya reckon?

EDIT: Fixed some grammatical and BBCode errors.

[I-K]

7.5 rings out: 138mm unloaded, average of 98mm with my bonsai human frame on it.

1.5 rings out: 149mm unloaded, average of 109mm loaded.

Measured from fork seal to stantion.

So as you can see all mine did was move the whole shebang up and down the bloody fork legs.

That's all it's supposed to do, dude; vary the height at which your front end sits when there's no braking or acceleration acting on it. It doesn't, and can't, alter the difference between how much the bike sags on the forks with a rider on board compared to without.

The problem would appear to be that you're measuring your sag kinda wrong.

The two kinds of sag are:

-static sag, measured as the difference between the length of the forks at full extension (ie. the length of the forks without any weight at all resting on them, as you'd achieve by, say, heaving the bike onto the sidestand so the front wheel's in the air) and the length of the forks with just the bike's weight resting on them.

-loaded sag, measured as the difference between the length of the forks at full extension and with rider aboard.

What you've found is that changing your preload from seven rings showing to one ring showing alters your static and loaded sag by 11mm. What you still need to find out is the length of your forks at full extension.

The difference between your static sag and loaded sag is a function of spring constant, not preload. If you want the bike to sag comparatively less when you hop aboard, you need to change your springs.

[MadKaw]

Very interesting.....
How much do you weigh.??

It just seems to me that if you increase the travel by winding the preload up or down it must either extend or compress the spring to do this, therefore changing the preload on the spring...
Theres only washers and spacer tubes on top of the springs so what is it extending the travel.??... Don't worry I don't know either, other than I could set mine up just fine..
As I-K said you may have a too light spring, are they stock.?

[Yankee]

just ride it man!
all this cafuffle about saggy bullshit versus the rock hard type! me? i prefer not to mess with such issues!
hey, you coming out monday night anyway?!
also, hope you get to the bottom of those tubes soon mate!

[HemiDuty]

I.K., I think I may have to clarify something here. The 138mm and 149mm measurements were the full extension measurements. I think I might have thrown you with that one. And the sag I am measuring is loaded sag.

That is what I am getting at; the actual full extension of the forks is changing when adjusting the preload. It goes from 138mm to 149mm, taking the sag measurements with it. In other words, it doens't seem like the adjuster is actually compressing or extending the springs, it is just moving them up and down the fork tubes. I dunno......

I guess it comes down to this: Should preload adjustment change the measured full extension of the forks?

BTW Madkaw, I weigh about 58kg. Having 2 ruptured discs in my back has lost me half a dozen precious kilos...


It just seems to me that the preload adjuster should actually adjust the preload of the springs, as in how much they are compressed before any weight is applied to them. If they did this, then they would be 'harder' to compress when applying weight to them, and therefore there should be less movement from full extension to loaded sag.

But it is 40mm no matter what I do. I hope there is some simple part that I can buy and fit to get it to adjust preload. Coz I sure cannot afford new springs.....





Yankee, I will do my best to get there. If I stack it on Sunday I may not be in the best shape to go out!!! And lately mate, the only thing I haven't hit the bottom of is this damn fork issue

[Yankee]

have a top day sunday mate!! but we will be wanting a full report monday night, so don't come off! and get some good pics to bring too!!!

see ya Monday!

[Steve_TLS]

I guess it comes down to this: Should preload adjustment change the measured full extension of the forks?

The answer is No.

Something weird going on there for sure.

It sounds like the preload adjusters are doing / undoing a damper rod or something. Pull a leg out, pull a cap and take a picture

[HemiDuty]

Thanks Steve. Will take picture if and when I dismantle the Forks.