What would result in more stability?

[cowboyz]

are you saying I am fat?

seriously. I will re-read your post in depth later on tonight when I have more time. thanks for the input.

[Robert Taylor]

All of the following assumes that the bike is straight and the suspension components are in good / serviceable condition.

Not wanting to knock anybody's abilities but reading through this thread there are a couple of things that have changed it would seem from a previously stable bike.

1/ The weight of the rider has gone up!

2/ The front suspension has been adjusted!

One of the most common things that riders get wrong is they mis-adjust their front suspension (well actually both ends) by way of applying way too much rebound damping.

If this has been done this will cause the front end to dynamically ride lower in the stroke than it will sit at rest. This is due to the time it takes for the forks to extend after each compression cycle being increased (by way of too much rebound damping). This mans after successive compression cycles (read several a second) the forks will ratchet (or pack) down as they have not had enough time to extend between compression cycles. This results in the bike sitting lower in the front at speed and the suspension compliance degrading as a function of how much the front end is packing down.

This has several undesirable effects firstly it makes the front sit lower which effectively decreases the steering head angle and the trail (both critical to stability). Additionally it makes the response of the forks abrupt for the size of the bump encountered. This could quite conceivably add up to an unstable bike at speed.

If the front is already sitting low because of the increase of rider weight (assuming it was not adjusted to compensate), given the packing down effect described above the bike could be beginning to enter the region of front suspension travel that is dominated be the effects of the internal hydralic bump stop, if this is the case due to the aggressive action of the same it will make for a very frightening ride at speed. And given the history and symptoms would be my guess assuming all of the parts of the bike are still serviceable.

This suggestion is just that a suggestion after reading the information posted with a whole bunch of assumptions, but if I were a betting man its where my money would be.

The ZX9 has soft springs from stock, at your advertised weight and height at a minimum replacement fork springs should be on your shopping list!

Thats all very very correct. The reality check is that this bike has 9 years and many tens of thousands of kilometres of wear issues. The damping fluid at both ends will be well well past its best, as will be wear components inside the units. Trying to adjust something that is worn will only achieve a limited result.

One thing I also didnt mention was checking condition of the headrace bearings. Also I am not a fan of mixing different brands of tyres front to rear, except where they are the same tyre with different labels. (The bike is not a GN250! ) Different brands of tyres will have different carcass construction and different characteristics with a differing frequency response that can exacerbate any underlying chassis stability problems. Not saying this is the problem here but this can often be an issue.

But undeniably the bike is undersprung for the rider stats. Its dynamic ride height is too low and the effect of the oversoft springs is more keenly realised at the front rather than the rear, where TDC correctly stated it affects the steering geometry / stability of the bike.

Just winding up oversoft springs is really a statement ''Im in denial that I really need to fit appropriate springs ( at BOTH ends for balanced action )and recondition the suspension to make the bike work properly and safely'' Its also a matter of filtering out the ''advice'' that whilst well meaning is less than sound.

I get to bounce on so many bikes that have too much rebound damping cranked in. That appreciably reduces ultimate mechanical grip and is one of the biggest causes of riders crashing.

[cowboyz]

thanks for the input. Am I reading it right where you are suggesting looking at the front springs?

i should note that the rear was a conti road attack2 and recently replaced. The front is due for replacement soon so that should match the tyres up in the near future. I have a metz racetec tyre that I got of a track and the very sides of the tyre (where I wouldnt get to) are worn but 5/6th of the tyre is good but had less than favourable suggestions about riding that tyre on the road so thinking I might scrap it and put a michellin on the fron tto match the rear.

[sugilite:Me]

OKDOK, I've been following this with interest and was not going to post again with 2 obvious experts offering their advice.
However after reading the "well meaning advice part" I'll add in a few more cents worth to explain why I did what I did.

I met up with cowboys for a group ride and he described some suspension issues he was having.
Having raced this exact model and with Richards help transforming it into one of what I believe the best handling examples of it's model on the track I figured I'd see what I could do to help. Bearing in mind it was with a standard issue Japaneses bike tool kit on the side of the road. I quickly ascertained that it was bottoming out the moment he hit the brakes as it was so soft (yes I'm well aware this model has way to soft fork springs standard, and he is no waif like flame eh Drew) I'm fairly familiar with Cowboyz sensible road style and figured he would bottom out under brakes and suffer various other ailments from a way to soft front end than he ever would from over vigorous use of the throttle. So choosing what I believed to be the way lessor of two evils I set the front forks with the range accordingly with what I had to work with at the time. The rebound, while not perfect, was in the realm of acceptability in my limited experience.

As to the original question, I voted steering dampener as there is no guarantee that stiffer fork springs will fix this issue as it could be any number of things causing the problem, however I'm bloody sure a steering dampener will. Whether it is masking the original issue or not, the end result is no more twitches from the front end. If Cowboyz has a large budget to go through everything to find it, then by all means go for it Robert has offered very sound advice as has TDC. If you have the bucks, get the internals refurbished and fork springs installed and prob some rear shock work as well.

As an aside, I do not test ride peoples bikes unless specifically asked, end of story there.
Nor do I try and set peoples bikes up to suit me, as I have a VERY different ride style to most. I make changes and get them to ride their bike. If it's better, then all good.

BTW, A big Hi to Robert. Sugilite = Anthony Bradford

[Robert Taylor]

OKDOK, I've been following this with interest and was not going to post again with 2 obvious experts offering their advice.
However after reading the "well meaning advice part" I'll add in a few more cents worth to explain why I did what I did.

I met up with cowboys for a group ride and he described some suspension issues he was having.
Having raced this exact model and with Richards help transforming it into one of what I believe the best handling examples of it's model on the track I figured I'd see what I could do to help. Bearing in mind it was with a standard issue Japaneses bike tool kit on the side of the road. I quickly ascertained that it was bottoming out the moment he hit the brakes as it was so soft (yes I'm well aware this model has way to soft fork springs standard, and he is no waif like flame eh Drew) I'm fairly familiar with Cowboyz sensible road style and figured he would bottom out under brakes and suffer various other ailments from a way to soft front end than he ever would from over vigorous use of the throttle. So choosing what I believed to be the way lessor of two evils I set the front forks with the range accordingly with what I had to work with at the time. The rebound, while not perfect, was in the realm of acceptability in my limited experience.

As to the original question, I voted steering dampener as there is no guarantee that stiffer fork springs will fix this issue as it could be any number of things causing the problem, however I'm bloody sure a steering dampener will. Whether it is masking the original issue or not, the end result is no more twitches from the front end. If Cowboyz has a large budget to go through everything to find it, then by all means go for it Robert has offered very sound advice as has TDC. If you have the bucks, get the internals refurbished and fork springs installed and prob some rear shock work as well.

As an aside, I do not test ride peoples bikes unless specifically asked, end of story there.
Nor do I try and set peoples bikes up to suit me, as I have a VERY different ride style to most. I make changes and get them to ride their bike. If it's better, then all good.

BTW, A big Hi to Robert. Sugilite = Anthony Bradford

Thanks Anthony, actually it was very clear that your work was sound and totally in the right direction with what you had at your disposal.

The ''well meaning'' advice statement was a generalisation because I have seen some suggestions in many posts generally that frankly I have just shaken my head at. I would hate for someone to be injured ( or worse ) because some very bad ''advice'' was taken on board. Many bikes have serious potential to get people into trouble, its peoples wellbeing and lives we are dealing with.

Motorcycle suspension set up has become more and more a specialist field and point of fact when motorcycle mechanics undergo their training there is very very little taught about this. The trade is in fact more diverse than many think and it is fair to say that as a mechanic you just cannot do justice to every single facet of the trade. At the risk of an uproar from certain quarters I would have to say that much of the work that I have evidenced is horrifying.

When time permits I think a post on generalised ''springs and clickers'' set up would be well justified.

[Robert Taylor]

thanks for the input. Am I reading it right where you are suggesting looking at the front springs?

i should note that the rear was a conti road attack2 and recently replaced. The front is due for replacement soon so that should match the tyres up in the near future. I have a metz racetec tyre that I got of a track and the very sides of the tyre (where I wouldnt get to) are worn but 5/6th of the tyre is good but had less than favourable suggestions about riding that tyre on the road so thinking I might scrap it and put a michellin on the fron tto match the rear.

You need to change both front and rear springs at the same time to achieve the correct dynamic ride height control and to keep the bike balanced. Heavily preloaded oversoft springs will actually feel harsh in the top of their stroke because there is so much ''pre-energy'' wound into them. But they are still soft when you strike something abrupt or brake suddenly.

Appropriate springs correctly preloaded for your personal stats will actually feel more compliant at the top of their stroke because there is much less pre-energy wound into them and this also achieves the correct correlation of free sag and rider sag. Sounds nuts but you fit firmer springs to make the bike feel plusher but more controlled! More reactance means more ability to keep the bike stable and more mechanical grip.

There will be more control because the springs are firmer and this will be especially noticable in the front when braking hard. As the ride height will be a little higher and suspension shaft velocity mostly slower at later stages of travel there will be less tendency to reach the sudden abrupt kick in compression damping articulated by the front fork hydraulic bottoming out cups. In truth it would be a further improvement to minimise this over zealous bottoming control function by approximately 75% and I have very specific tricks for doing so, more detailed than some will think. But it is not my intention to divulge all of my experience to the mechanics that frequent this site, unless theyd like to subsidise the cost of my many overseas trips that I have incurred to help learn my craft, etc.

In the rear end the more abrupt part of the rising rate linkage curve will not be reached as early as it is presently. Keeping the rebound damping fast ( but not so much so as to induce wobble ) will ensure that the bike rides high in its stroke. So a win win situation.

If you want more info please pm me, I can direct you to a very capable road focused suspension technician.

[F5 Dave]

. . . and suspension shaft velocity mostly slower at later stages of travel there will be less tendency to reach the sudden abrupt kick in compression damping articulated by the front fork hydraulic bottoming out cups. In truth it would be a further improvement to minimise this over zealous bottoming control function by approximately 75% and I have very specific tricks for doing so, more detailed than some will think. But it is not my intention to divulge all of my experience to the mechanics that frequent this site, unless theyd like to subsidise the cost of my many overseas trips that I have incurred to help learn my craft, etc.
. . .

Bugger ‘cause that was precisely the question I was about to ask. So in public domain much of this information is common knowledge (Read; I don't think I will be giving away any of Robert's trade secrets here, my question was to which you thought was the most useful direction & what is currently being favoured in modern high quality forks. I guess only that last part of the question may be answerable without giving away too much (rightly so, experience is worth the money).

In reading a book I mentioned before (Kevin Cameron’s Sportbike performance) it probably simplistically explained the effect of the hydraulic stops & the downside that they are symmetrical in action (ie: both down & up) hence keep the forks stuck at full compression too long.

My YZF has been modified by way of drilling bleed holes in the stops to reduce this effect later in the stroke & lessen the issue. I understand Maxton (UK suspension co.) as par for the course replace the stops with springs. On my bucket (don’t laugh everything needs good suspension esp. light bikes) I replaced the stops with suspension bush material of a similar, but slightly stiffer consistence to a rear shock’s bump stop material.

These are of course simple Damper forks however I have made deflectors on the top of the rod to redirect squirting oil from being pumped into the top of the tube & had designs for a spring loaded blow-off to sit on top of the rods to replace the compression holes, however the scale of the tiny tubes made it a bit impractical to fit inside. I later discovered that Gold Valve emulators aren’t too dissimilar in concept. This really did improve the action, however I had to concede that the (very early but shim) RS125 forks on my other bike were indeed better.

[slowpoke]

The ''well meaning'' advice statement was a generalisation because I have seen some suggestions in many posts generally that frankly I have just shaken my head at. I would hate for someone to be injured ( or worse ) because some very bad ''advice'' was taken on board. Many bikes have serious potential to get people into trouble, its peoples wellbeing and lives we are dealing with.

I reckon this is just as important as the technical advice you have given, Robert. Too often we accept or look for advice without any regard whatsoever where it has come from.
Nothing against you cowboyz, 'cos we have all been baffled by something or other at some stage, but if we are seeking a solution on an open forum or while chatting at the top of the 'taka's then we have to be extremely discerning about who's advice we are going to follow and the rationale behind it.
Some people may have no idea who RT, TDC and Sugi are and might attach no more weight to their years of unseen experience than to Joe Blow's Bourbon induced midnight ramblings.
I'm just glad you used the "Robert Taylor" moniker on KB, rather than "Foggy Bottom" or some such, so we can attach the appropriate weighting to your advice. Hang on....that is "you" isn't it Robert....Roobbbeeeeeeert...you got some ID there fella...? LOL

[Pussy]

I reckon this is just as important as the technical advice you have given, Robert. Too often we accept or look for advice without any regard whatsoever where it has come from.
Nothing against you cowboyz, 'cos we have all been baffled by something or other at some stage, but if we are seeking a solution on an open forum or while chatting at the top of the 'taka's then we have to be extremely discerning about who's advice we are going to follow and the rationale behind it.
Some people may have no idea who RT, TDC and Sugi are and might attach no more weight to their years of unseen experience than to Joe Blow's Bourbon induced midnight ramblings.
I'm just glad you used the "Robert Taylor" moniker on KB, rather than "Foggy Bottom" or some such, so we can attach the appropriate weighting to your advice. Hang on....that is "you" isn't it Robert....Roobbbeeeeeeert...you got some ID there fella...? LOL

You want some ID? Accuse him of being a Labour voter, freind of Helen etc..... and see what sort of response you get!! It will then be confirmed that it IS indeed Robert Taylor

[cowboyz]

Nothing against you cowboyz, 'cos we have all been baffled by something or other at some stage, but if we are seeking a solution on an open forum or while chatting at the top of the 'taka's then we have to be extremely discerning about who's advice we are going to follow and the rationale behind it.
Some people may have no idea who RT, TDC and Sugi are and might attach no more weight to their years of unseen experience than to Joe Blow's Bourbon induced midnight ramblings.

Exactly. Any advice has to be taken in context how it was given. And it goes the other way too. Indeed alot of people dont know who TR TDC and Sugilite are. So there advice, however warrented may go by the way simply because it is either misunderstood or doesnt have the deserved repect behind it. I know Suglite but not the other two so having Suglites affirmation that Robert Taylor knows what he is talking about is a big plus.

It is alot like I know there is not alot I dont know about computers. Worked with them for many years. However i ventured into a dairy farming career and am now a greenskeeper. It was particularly entertaining when a guy came in to setup the new irrigation system (which is computer controlled) and obviously a salesman rather than a technician and the moment things didnt go exactly to plan my boss asked the guy if he would like me to look at it. The response was a very blatent "what would he know about it" Partly because the guy was having trouble with his own system and partly because he didnt know me from a bar of soap so why should I know anything about it?

When getting free advice it pays to sort it according to source. There has been some useful and informative ideas being thrown round in this thread. I am not going to go out and spend $1000 tomorrow on the basis of someone elses ideas. Nor does this mean that others ideas are wrong or unimportant. I just have to spend a while to decide what the most credible advice is.

[DEATH_INC.]

what aboot the front tyre pressure? wouldn't that make it feel a bit nervous with 42psi? and mebbe acentuate the suspension problems?

[JayRacer37]

You need to change both front and rear springs at the same time to achieve the correct dynamic ride height control and to keep the bike balanced. Heavily preloaded oversoft springs will actually feel harsh in the top of their stroke because there is so much ''pre-energy'' wound into them. But they are still soft when you strike something abrupt or brake suddenly.

Appropriate springs correctly preloaded for your personal stats will actually feel more compliant at the top of their stroke because there is much less pre-energy wound into them and this also achieves the correct correlation of free sag and rider sag. Sounds nuts but you fit firmer springs to make the bike feel plusher but more controlled! More reactance means more ability to keep the bike stable and more mechanical grip.

There will be more control because the springs are firmer and this will be especially noticable in the front when braking hard. As the ride height will be a little higher and suspension shaft velocity mostly slower at later stages of travel there will be less tendency to reach the sudden abrupt kick in compression damping articulated by the front fork hydraulic bottoming out cups. In truth it would be a further improvement to minimise this over zealous bottoming control function by approximately 75% and I have very specific tricks for doing so, more detailed than some will think. But it is not my intention to divulge all of my experience to the mechanics that frequent this site, unless theyd like to subsidise the cost of my many overseas trips that I have incurred to help learn my craft, etc.

In the rear end the more abrupt part of the rising rate linkage curve will not be reached as early as it is presently. Keeping the rebound damping fast ( but not so much so as to induce wobble ) will ensure that the bike rides high in its stroke. So a win win situation.

If you want more info please pm me, I can direct you to a very capable road focused suspension technician.

AMEN to that!!!

[Robert Taylor]

Bugger ‘cause that was precisely the question I was about to ask. So in public domain much of this information is common knowledge (Read; I don't think I will be giving away any of Robert's trade secrets here, my question was to which you thought was the most useful direction & what is currently being favoured in modern high quality forks. I guess only that last part of the question may be answerable without giving away too much (rightly so, experience is worth the money).

In reading a book I mentioned before (Kevin Cameron’s Sportbike performance) it probably simplistically explained the effect of the hydraulic stops & the downside that they are symmetrical in action (ie: both down & up) hence keep the forks stuck at full compression too long.

My YZF has been modified by way of drilling bleed holes in the stops to reduce this effect later in the stroke & lessen the issue. I understand Maxton (UK suspension co.) as par for the course replace the stops with springs. On my bucket (don’t laugh everything needs good suspension esp. light bikes) I replaced the stops with suspension bush material of a similar, but slightly stiffer consistence to a rear shock’s bump stop material.

These are of course simple Damper forks however I have made deflectors on the top of the rod to redirect squirting oil from being pumped into the top of the tube & had designs for a spring loaded blow-off to sit on top of the rods to replace the compression holes, however the scale of the tiny tubes made it a bit impractical to fit inside. I later discovered that Gold Valve emulators aren’t too dissimilar in concept. This really did improve the action, however I had to concede that the (very early but shim) RS125 forks on my other bike were indeed better.

I think that many oem forks have rather ''aggressively long'' hydraulic bottom out devices so that the forks dont actually bottom with a heavyweight rider on board. This so there are no product liability issues and demands for firmer springing etc.

The Maxton idea is sort of okay but I hope that absolute bottom of travel is not coil bind. Many suspension companies over-rely on secondary air spring effect to help control bottoming out. Ohlins do it a very effective way and if you purchase a set of cartridges or forks off me you will be able to view it to your hearts content!

Have a look inside DR350 forks, probably where Race Tech got the idea from, but they actually made it work as intended.

[Robert Taylor]

You want some ID? Accuse him of being a Labour voter, freind of Helen etc..... and see what sort of response you get!! It will then be confirmed that it IS indeed Robert Taylor

Yep, thieving, conniving, self serving communist control freaks who give hand outs rather than a hand up. If I paid less tax it would mean I could employ that same guy who is on the dole, being subsidised by my tax.....Conservative thinkers also have compassion.

And oh, they are spending too much money making our roads smoother......

[Robert Taylor]

AMEN to that!!!

I didnt realise you were religious Jay! BTW, looking forward to seeing you remain upright this weekend.