fork springs (again)

[popkat]

I found setting the rebound damping correctly is not something to be over looked. It needs to be set at the fastest possible return (when you push down on the handlebars and allow the front end to return on it's own), but under control. Somewhere around one full turn out from fully in, give or take a quarter of a turn either way is where you'll probably end up.

Sorry i think thats a little misleading. As a basic static set up your forks should return at about the same rate as which you compress them, this is standing beside the bike pushing down on the fork, if they return too quickly the bike will kick off bumps and spring back too fast, too slow and it could "jack down" which means they won't fully return by the next bump..

A vague feeling front end is usually too much compression, increase air gap to get more feel (ie less oil) but it could also be the progressive springs floating (setling on the soft part of spring) causing vagueness, for track work linear is the way to go.

As for fork height i agree these bike are a bit fussy with it, i used to run mine 10mm through but needed a steering damper as it would like to wobble on track if not. for the road i'd take them to 5mm and it felt alot better. Small amount makes a big difference.

Hope this helps.

[Stephan]

Sorry i think thats a little misleading. As a basic static set up your forks should return at about the same rate as which you compress them, this is standing beside the bike pushing down on the fork, if they return too quickly the bike will kick off bumps and spring back too fast, too slow and it could "jack down" which means they won't fully return by the next bump..

My point of view:

Static sag - should be somewhere close to recommended
Rebound - as described, fastest possible return, but under control. Under control means, that bike is steady after passing some roughs. When rebound is to slow, both, front and rear has tendency to bump when braking hard
Compression - stiffer, softer, just as you like, depends more on your preferrences or tire wear on track

[budd]

Static sag - should be somewhere close to recommended
Rebound - as described, fastest possible return, but under control. Under control means, that bike is steady after passing some roughs. When rebound is to slow, both, front and rear has tendency to bump when braking hard
Compression - stiffer, softer, just as you like, depends more on your preferrences or tire wear on track

one of the issues with the OE VTR forks is the lack of independent adjustment of compression and rebound damping, adjust the rebound and you also adjust the compression, I think if you get the compression damping right then you end up with to much rebound damping I believe the tapered rebound rod helps in this regard by fine tuning the rebound, but in the end I'm stuck with bump and rebound been linked.

[popkat]

By saying misleading i'm not saying either of you are wrong, i'm just saying it a different way which i think others will understand better

[Stephan]

one of the issues with the OE VTR forks is the lack of independent adjustment of compression and rebound damping, adjust the rebound and you also adjust the compression, I think if you get the compression damping right then you end up with to much rebound damping I believe the tapered rebound rod helps in this regard by fine tuning the rebound, but in the end I'm stuck with bump and rebound been linked.

I don´t think that rebound adjustment is connected with compression on VTR forks unless you do it by changing oil viscosity and air gap. But there is no point to do it, you can adjust compression by these and then just turn rebound screws to get correct dumping, it is not linked.
Maybe there are some forks or shock units having this, but VTR forks not.

[budd]

[/quote]

I don´t think that rebound adjustment is connected with compression on VTR forks unless you do it by changing oil viscosity and air gap. But there is no point to do it, you can adjust compression by these and then just turn rebound screws to get correct dumping, it is not linked.
Maybe there are some forks or shock units having this, but VTR forks not.[/quote]

so the compression damping is fixed ? and to fundamentally adjust this would required a change of shim stacks ? Any adjustment via oil viscosity / air gap could only really be termed as 'tweaking'.
I was assuming the forks would operate in a similar way to after market car dampers (coilovers) which often (at least on cheaper models) feature a single damping adjustment that effects both the bump and rebound, the ratio or balance between the two been fixed, it seems strange the other than opening up the fork leg it's not possible to change the compression setting.

[budd]

[/quote]


A vague feeling front end is usually too much compression, increase air gap to get more feel (ie less oil) but it could also be the progressive springs floating (setling on the soft part of spring) causing vagueness, for track work linear is the way to go.

As for fork height i agree these bike are a bit fussy with it, i used to run mine 10mm through but needed a steering damper as it would like to wobble on track if not. for the road i'd take them to 5mm and it felt alot better. Small amount makes a big difference.

Hope this helps.[/quote]

I have a 4mm spacer on the rear damper and the forks are dropped through 5mm, I tried it at 10mm but it started to get a little 'slap happy' not as bad as some things I've ridden but deffo on the verge of needing a steering damper, 5mm is a good compromise and doesn't demand a damper, I've got a personal aversion to steering dampers after one went through my shin when I went over the bars of an FZR 1000 !! I know the newer dampers are mounted on the yokes unlike the frame mounted item that shattered my tibia but I still don't like 'em.
I think the vagueness I'm feeling is probably down to the progressive springs, the transition between low and high spring rates may be the cause, of course this isn't an issue with a linear spring as the rate is constant, the other problem is setting the sag normally sag is set without the rider on board ( this assumes the spring rate is correct for the riders body weight) due to the progressive springs variable spring rate the advise is to set the sag with the rider on board and I don't seem to be able to get the desired 25mm static sag, normally I'd chop a few mm off the spacers but my springs are 410mm long so no spacers to shorten, I'm going to have another go with setting up what I have, re-set static sag / pre-load, reduce air gap (to 130mm) and have a fiddle with the rebound damping but I think linear springs are probably on the cards.
I actually don't mind fiddling with the settings and components as it all helps me understand what the forks are doing and what effect the changes make to the overall handling an feel of the bike.

The other thing to note is my own physical issues, a serious crash almost 20 yrs ago left me with a
very badly damaged left leg (if not for crowtree leathers I don't think I'd still have it at all) the resulting injury as left me with limited flexion ( ability to bend my leg at the knee) in my left leg, it' was greatly improved with a total knee replacement some years ago but it's still as limited movement which is a major problem in trying to move about on and steer a 200kg motorcycle, this is one of the reasons I need total confidence in the bike as I can't easily compensate with body weight / position, basically I struggle to ride round handling problems (at least on left enders right hand corners are less of a problem) also I know what it feels like to be very seriously injured and have no intention of spending another 3 months in hospital!!

[tony.mon]

Tend to agree on the 10mm ride forks through yoke comments.
Got a proper tankslapper cranked over once with 10mm showing when I drifted out over cat's eyes- not big or clever and caused a dry cleaning moment.

Actually I'm back to std fork position at the moment; dropping them 5mm speeds the steering up but the 6mm spacer under the rear shock mount does that well enough all by itself.

Some makes of tyres cope with it better than others, and new tyres will forgive a lot more than work ones, no matter what the brand.
I'd advise a tyre pressure check before changing anything, though- it's easy not to notice a few psi drop.

[budd]

Tend to agree on the 10mm ride forks through yoke comments.
Got a proper tankslapper cranked over once with 10mm showing when I drifted out over cat's eyes- not big or clever and caused a dry cleaning moment.

Actually I'm back to std fork position at the moment; dropping them 5mm speeds the steering up but the 6mm spacer under the rear shock mount does that well enough all by itself.

Some makes of tyres cope with it better than others, and new tyres will forgive a lot more than work ones, no matter what the brand.
I'd advise a tyre pressure check before changing anything, though- it's easy not to notice a few psi drop.

I must admit I thinking of returning to std fork position and adding a couple mm under the rear if neccessary, is 6mm thr most possible before you run out of adequate thread on the top mounting ?

front tyre is a diablo corsa which I'd expect as quite a radical profile, although it's not unstable, BTW what tyre pressures do you favour ?

[budd]

also Tony you mentioned in a earlier post that your springs were the correct lenght (410mm) and required no spacers, my progressive springs are exactly the same 410mm no spacers required, do you have any issues getting the correct 25mm ish static sag? and how do you arrive at the setting rider on or off the bike ?

[Stephan]

so the compression damping is fixed ? and to fundamentally adjust this would required a change of shim stacks ? Any adjustment via oil viscosity / air gap could only really be termed as 'tweaking'.
..
it seems strange the other than opening up the fork leg it's not possible to change the compression setting.

Yes, as you write.

[Stephan]

I have a 4mm spacer on the rear damper and the forks are dropped through 5mm, I tried it at 10mm but it started to get a little 'slap happy' not as bad as some things I've ridden but deffo on the verge of needing a steering damper, 5mm is a good compromise and doesn't demand a damper

Standard forks have quite weak compression, 4 mm space itself adds load on this, then 5 mm dropped forks, 140 mm air gap and 7.5 wt oil make it even worse.

[budd]

I have a 4mm spacer on the rear damper and the forks are dropped through 5mm, I tried it at 10mm but it started to get a little 'slap happy' not as bad as some things I've ridden but deffo on the verge of needing a steering damper, 5mm is a good compromise and doesn't demand a damper

Standard forks have quite weak compression, 4 mm space itself adds load on this, then 5 mm dropped forks, 140 mm air gap and 7.5 wt oil make it even worse.

This could be part of my issues I've been under the misapprehension that increasing the rebound as been in turn increasing the compression
so what's required is so increase compression via thicker oil (10wt) and a decrease in air gap (130mm) ? in the short term and ultimately K-tech compression kit.

[Stephan]

budd: yes, I´d try 10wt oil, 130 mm gap, return forks back to original position in triples - staying only with rear 4mm spacer, and than see. But opinions how to solve your problem can vary :-)

[tony.mon]

I must admit I thinking of returning to std fork position and adding a couple mm under the rear if neccessary, is 6mm thr most possible before you run out of adequate thread on the top mounting ?
also Tony you mentioned in a earlier post that your springs were the correct lenght (410mm) and required no spacers, my progressive springs are exactly the same 410mm no spacers required, do you have any issues getting the correct 25mm ish static sag? and how do you arrive at the setting rider on or off the bike ?

6mm spacer gives you about 18-20mm lift at the rear of the tail, so it's quite a bit.
You have to lift your leg higher when getting on and off, until you get used to it you'll keep leaving black boot marks on the seat hump...

Re static sag, mine just sorts itself out- sag's about right, with the WP springs fitted, and a 6mm spacer, so I haven't bothered playing with it.
As A McQ said, it feels good as it is, so I've left it alone.

To find sag, put a tie wrap round the fork leg, push it down at rest onto the top of the seal dustcap, then lift the bike up until the leg is fully extended.
(on the sidestand is easiest) the gap form the top of the seal to the tie wrap is the static sag at the front.

For the rear, just measure from either the ground or the centre of the rear wheel spindle to a marked point on the tail plastic vertically above the spindle. same applies, really; you just need to know how much travel is used up as the bike settles under it's own weight.
You need some so that the suspension doesn't top out over bumps or undulations all the time.