DR650 static sag

[Bass]

Maybe I can explain it geometrically...

If the result curve is plotted, at some point there is a 'knee' where for small inputs there is a dramatic difference in output. Bikes are set up at that knee. The further a particular setting (or range of adjustment) is from that knee, the less effect it will have, and vice-versa.

Zat what you were asking?

Sorry but no. Close though.
Saying that at some point there is a 'knee' where for small inputs there is a dramatic difference in output, is simply putting it in other words.
What I am trying to figure out is why there is a knee, (in your valve example, it's a simple geometrical ratio thing). In fact, I don't accept that there is a knee. for the adjustment to have a sensitive response, the curve (or part curve) just needs to have a large slope or dy/dx = a large number.
However, that's just me being pedantic and I understand what you are trying to say. I am interested in understanding why the machine is particularly sensitive to the adjustments over some small part of their range, rather than a different way of saying that it is.

It also seems to me to be a tad dangerous. For example, Ocean1's experience of a 15 mm change in rear end static sag significantly affecting front wheel grip is not reassuring (and that's ignoring the size of his orifice).

[ducatijim]

Moving the forks 3mm in the clamps of my XR250 makes a noticeable difference in the handling.

I move my forks 45mm thru the clamps, depending on whether I am gravel riding or doing a track day. Same wheel, differant tyres. Makes fuck all diferance. 3mm ????, can't see it on a 27' rake(approx?) makin any differance. Now, on a Ducati 999, oh yes.............

[ducatijim]

You are getting a bit off topic there, aren't you mate?

Anyway, I seem to remember you doing all of that on a Honda 90 and that was built for short arses too.

PD here we come.

Off topic? you asked how to make the bitch sit up some more, I provided the answer, and pointed out that Mr Suzuki may not always be right, spot on topic as I seez it.

Honda postie?.....yeah, only 1 reel and the fuckn calf WALKED. You nowwill have every lanky Postie in the country after YOUR arse!!!!

[Bass]

You now will have every lanky Postie in the country after YOUR arse!!!!

Yeah!
Warewolf and Ocean have already warned me that I need a bigger orifice.

[Ocean1]

Sorry but no. Close though.

Beer in mind it's not a DR650. Can't recall the salient geometric details but the rake is steeper to start with.

Worth noting however that a fore/aft attitude change isn't just changing rake, it's also changing trail and weight bias. Slightly to be sure, but the changes all aim the same way wrt behaviour. You’ll be familiar with the effect compound variables can have on a process…

And yes, wrt my orifice I have been made abundantly aware that ignorance is bliss.

[warewolf]

What I am trying to figure out is why there is a knee, (in your valve example, it's a simple geometrical ratio thing). In fact, I don't accept that there is a knee. for the adjustment to have a sensitive response, the curve (or part curve) just needs to have a large slope or dy/dx = a large number.

Wasn't quite sure what you were asking. However, to continue on this theme, by sensitive I meant d2y/dx2 (delta dy/dx) changes markedly. dy/dx can be as large as you want and still be considered consistent, not sensitive.

I am interested in understanding why the machine is particularly sensitive to the adjustments over some small part of their range, rather than a different way of saying that it is.

It also seems to me to be a tad dangerous. For example, Ocean1's experience of a 15 mm change in rear end static sag significantly affecting front wheel grip is not reassuring

The answer is that it is a complex system of inter-related functions aka "I don't know" or "it just is" . And yes, it can be dangerous making changes.

[warewolf]

I move my forks 45mm thru the clamps, depending on whether I am gravel riding or doing a track day. Same wheel, differant tyres. Makes fuck all diferance. 3mm ????, can't see it on a 27' rake(approx?) makin any differance. Now, on a Ducati 999, oh yes.............

So the DR is away from the knee, the 999 right on it. QED.

Enduro riders change their pull-through by 2-5mm all the time, depending on conditions. eg Woodhill sand whoops are better with more rake, weaving between the trees is better with less. You can feel the difference quite easily - and you want it.

[Bass]

Wasn't quite sure what you were asking. However, to continue on this theme, by sensitive I meant d2y/dx2 (delta dy/dx) changes markedly. dy/dx can be as large as you want and still be considered consistent, not sensitive..

Yep. We are on the same page.

The answer is that it is a complex system of inter-related functions aka "I don't know" or "it just is" . And yes, it can be dangerous making changes.

......and probably something to be thrashed out over a beer and a few text books rather than in here.

[warewolf]

......and probably something to be thrashed out over a beer and a few text books rather than in here.

Thinking the same thing myself

[Bass]

Be interested to hear what you think about the change. Cranking the rear up 15mm on the KLX makes a big difference to steering.

Right, just to complete this discussion and to report what I found having just done about 1000 km over the weekend with the rear end cranked right up and about 15 kg of luggage on the back.
We covered a wide variety of terrain, I noticed no change in the handling and it was much more stable on the stand.

[GaZBur]

Call me a nOOB but - ride the damn things for a good year or so till your actually getting to the point pushing the limits of the stock bike, then figure out what is wrong and deal with it. You need to establish a base line and if your skills wrt a particular bike are still improving significantly your not going to be able to do this.

I know this isnt going to help you Bass but others tend to spend to much time farkling and not enough time riding if you ask me (I know ya didnt ). My speed and confidence on the DR has improved significantly over the past year and I've not changed a thing (OK got the forks serviced - seals and oil replaced). I don't even remotely consider myself ready for major changes such as ohlins (not that I'd ever do that anyway). Might do a stiffer shock spring and shock rebound revalve middle of the year but not sure I need it yet.

Cheers R

I'm with you on this. I am new too but am also pushing the bikes limits ok. I just skimmed this thread and really dont understand the geometry and changes that result from alteations.
I did have a problem with the standard set up shock as sliding into corners on the Motard track the DR shuddered with the back skipping and not maintining a smooth slide. A bike mechanic told me to just wind the spring preload as hard as it will go as it was way too soft. I wound it all the way and if fixed the problem. It is still ok for road use like that. I loaded it up and rode central and also found it handled the gravel and dirt tracks ok set like that. Seems to be OK in most situations so don't see the point in spending money on new shocks that could be better spent on tyres. Maybe when I get real good and know exactly what does what I will look into further but seems too much like hard work for little gain to me!

CORRECTION EDIT- I said I wound it up all the way - in fact it is more like 3/4 now I have checked.

[warewolf]

Your motard racing application is pretty narrow. From everything I've ever read, if you've got that much preload on a spring, the spring is way, way too soft and will cause more problems than it will solve. Note that a steady slide means you have LESS grip (slide, slide, slide) than when it was shuddering (grip, slide, grip, slide). This is the same as what drifters want: no grip for any easy continuous predictable slide.

I must take your admission that you are "new" as a bit of a negative against your comment that it is "ok for road use". Sorry to be so negative but although this configuration sounds like it is working for you, I wouldn't recommend it for everyday use!

[Bass]

Seems to be OK in most situations so don't see the point in spending money on new shocks that could be better spent on tyres. Maybe when I get real good and know exactly what does what I will look into further but seems too much like hard work for little gain to me!

The reason we are fitting new shocks is that we are going to do Outback Oz and at times will be 300 + km from mechanical help, heavily loaded, on some really rough tracks. So the change is as much about reliability as it it is about performance.

[cooneyr]

The reason we are fitting new shocks is that we are going to do Outback Oz and at times will be 300 + km from mechanical help, heavily loaded, on some really rough tracks. So the change is as much about reliability as it it is about performance.

I know they are a bunch of numptys but don't watch Charlie and Ewan's latest, The Long Way Down. Ewan and the camera man managed to blow the seals and or root the springs on two Ohlins shocks (they swaped out the BMW shocks) each during the trip. The fact that they were carrying umpteen million tonnes of gear and aren't the best riders maybe, just maybe had something to do with it. Don't think Charlie had any issues with his shock (well not that was included on the DVD anyway).

Cheers R

[GaZBur]

Your motard racing application is pretty narrow. From everything I've ever read, if you've got that much preload on a spring, the spring is way, way too soft and will cause more problems than it will solve. Note that a steady slide means you have LESS grip (slide, slide, slide) than when it was shuddering (grip, slide, grip, slide). This is the same as what drifters want: no grip for any easy continuous predictable slide.

I must take your admission that you are "new" as a bit of a negative against your comment that it is "ok for road use". Sorry to be so negative but although this configuration sounds like it is working for you, I wouldn't recommend it for everyday use!

OOPS! I said I wound it up all the way - in fact I stopped at 3/4 as it fixed the problem so will go back and edit my original post . I did find on the rutted gravel roads and moderate off roading it kept line at this. I was also told the standard spring was probably too soft as well so that probably why its working OK wound up to that level.
Perhaps I will look online for a "Setting up suspennsion for dummies!" as most of the terms used in this forum go over my head. I dont even know how to measure static sag.