Front end searching

I agree 100% with you John.

The bike is amazing but in ruts I really struggle. On my 09 570 I crashed hard nearly every time I raced it. It put me in hospital twice and one of those was in Hungary (not a pleasent A&E). I never hardly ever crash. I now got a 450 and still suffer from the searching, as well as not being able to turn in on flat bermless grassy corners. You would think with searching in ruts you could turn on a sixpence but no. if there is a good grip, a berm or rut it rails turns easily.

It is like in the ruts the front rides to low yet turning in to corners it riders to high.

The other thing I have noticed with forums in general are, when you post about what stickers to use or look at my bike everyone speaks until the cows come home but put up a real issue and everyone shuts up. I cant beleive that the only 2 riders in the forum who have this issue also know each other and live less than 40 miles apart.

Maybe everyone else is just slow and it only happens to the fast riders? :evil: That will provoke some response haha!

i resemble that remark!

look, I'm convinced it is the TCs and yet Johny says he doesn't have the variables and no part number on the bloody top of the clamps? I mean, who doesn't have a part number on the top of their clamps I ask you? 8O 8O

regards

Taffy

The ones I just took off my 02 don't have any markings on at all.

The new (08) KTM ones I've just put on not only have the part number but the Nm torque settings stamped by each bolt head - nice....

well look, measure it OK?

get the bars out the way, pull the crown nut, get a ruler and start marking and measuring! you may not have what you thought you did.

regards

Taffy

Johny,

The 2009 Berg has 18 offset stock. from 2010 they went to 22.

You have 22's on your bike I have X trig on mine set at 22. 22 is way better than 18 in my opinion, I spent a lot of time on 18 and in A & E. Late in 2009 the WEC team were using 24 mm offset. I do not know what they are using now.

I think its a fork/shock balance damping issue,. they need to stay higher in the stroke in ruts but need to sink when you brake for turns. but I am not 100% sure, sometimes it feels like its the back of the front wheel crabbing on the ruts which would suggest the back is to low and thats why it wont turn in but the pre load is correct, 100 and 38. If other think otherwise let us know.

I have just aquired some factory cone valve forks which i intend to try and experiment with, trouble is I dont ride enough now a days to get this project moving.

when u say searching do you mean the front wheel bounces side to side thro the ruts?i think all the bikes i have riden have done this & my 09 does aswell sometimes but i put it down to me/rider.sorry mate i cant help with tech info but all i do know i had a go on alex rockwells (think thats his name)390 playbike & i wouldnt mind having some of what hes go susies wise

if you measure the thickness of the coils and how many there are on each of those springs I'll check them against a home-chart I've been compiling? I can tell you what strength they are I hope. trouble is that one spring will have 4.9, another 5.0 and another 5.1mm coils. you have to be very precise when measuring.

regards

Taffy

So basically the bike is perfect except in long , straight ruts.

Trying to think about it logically, if the problem only occurs in long, straight ruts then its not likely to be offset related. Offset would manifest itself in many other areas of turn -in or cornering.

Same with the suspension, I find it hard to believe a long straight rut could upset an otherwise great suspension package. Not saying it cannot, I'm just trying to think logically. What does a long rut do to the suspension that a long rough bit of dirt doesn't? The only difference is the sidewall of the rut surely?

I have no idea of your local conditions but 16psi in the front jumps out to me as being high.

Typically I run 12psi in Mich S-12 and ride plenty of ruts and rocks. In four years I've only had handful of punctures.
It could be that at 16psi you are not getting enough side contact to grip.

Before you do anything drastic I would try a lower tyre pressure front a rear and go from there. Its easy and cheap.

Hi I had similar issues and others with setting up my 2004 550 and one of the most valuable pieces of info i found somewhere on the site was that when you back off a large four stroke the transfer of engine braking will cause the back end too sit up and the front tends too dive especially when standing, so after getting the correct spring rates front and back for your weight and setting up the sag correctly i adjusted the rebound on the shock till it felt ok on down hill rocks and ruts and then whoops on the flat then did the same with the fork compression first and then fork rebound, Down hill makes the situation seem worse and a bit of throttle will make the back end squat, it takes a bit of time too get it right but if you can imagine what happens to the bike when you back off and accelerate it makes it easier, hope this helps worked for me, don't know what bike you've got but the principle should be the same, oh yeh and i ended dropping the forks 10mm through the triple clamps too.........colin

Whilst I agree tyre pressure will effect this, I run mousses in my wheels so have no control over the pressure as such. I have similar mis handling traits to John.

If you plod along nicely there is no problem, as speeds increase you constantly find yourself correcting and over correcting in ruts.

Before the Husaberg I raced a 450 Husky and that never had the problem, the front on that bike felt planted and super reliable, you always knew what it would do in any given situation.

maicoxx said:

Hi I had similar issues and others with setting up my 2004 550 and one of the most valuable pieces of info i found somewhere on the site was that when you back off a large four stroke the transfer of engine braking will cause the back end too sit up and the front tends too dive especially when standing, so after getting the correct spring rates front and back for your weight and setting up the sag correctly i adjusted the rebound on the shock till it felt ok on down hill rocks and ruts and then whoops on the flat then did the same with the fork compression first and then fork rebound, Down hill makes the situation seem worse and a bit of throttle will make the back end squat, it takes a bit of time too get it right but if you can imagine what happens to the bike when you back off and accelerate it makes it easier, hope this helps worked for me, don't know what bike you've got but the principle should be the same, oh yeh and i ended dropping the forks 10mm through the triple clamps too.........colin

Click to expand...

What happens when you accelerate on your bike?

The rear wheel will start to move forward, pushing on the swing arm. The swing arm will then push on the bike in the point where it´s attached to the frame.

If teh point where the swing arm is attached to the bike is higher up than the center of the rear weel, the bike will "lift" itself up. Both front and rear.
If the point where the swing is attached would be below the center of ther rear wheel, then it would push the bike down on acc.

And the opposite happens when you brake the rear wheel. The swingarm will try to straighten out, compressing the suspension.

he has 100mm of sag. I've been sticking to 106 plus or minus since I got it. I also have the top of the forks above the yoke by the two lines of the fork leg.

regards

Taffy

The whole off set subject has been covered before. Here is an illustration that will hopefully increase everyone's understanding of how off set affects a bikes handling, and it's affect on balance.



As you can see, the more offset you have on your forks the less trail you have. This has two effects, it makes the bike less stable, and it takes weight off the front wheel due to the lengthening of the "arm". This equates into the bike being quicker to steer due to the shorter trail or castor, and the front will be less stable due to it's increased maneuverablility.

More offset also has the effect of increasing the fork spring rate, due to the longer "arm" or mechanical advantage of the length of the arm's distance to the fulcrum, and longer wheel base. Basic physics.

Although the difference between 19 to 22 mm offset is small, it will in effect make the front end "feel" lighter, and make the forks ride higher in the travel, and decrease the "bite" the front tire has for any given soil condition. If you are riding in "hero" conditions it is much less notable. However, when riding on a surface with less mechanical grip, it becomes very noticeable.

So, by increasing the off set of the triple trees, in effect one has increased the overall wheel base, in this case towards the front, which means less weight on the front tire, and decreased the amount of trail, or decreased the front ends natural tendency to want to go straight. And in effect, increased the front forks spring rate shifting the weight bias of the bike towards the rear.

This is why it is absolutely critical that the correct spring rates be used to maintain proper balance. As well as having the proper pre load to maintain the proper weight bias balance.

By raising the forks in the triple trees, one lowers the front end of the bike, thereby decreasing the rake at rest and throughout the stroke, and it also shifts the weight bias forward, subsequently decreasing the rear sag, and slightly shortens the wheel base in front of the balance point, and promotes over steer. That's why raising the tubes will give you a better turning bike but make it less stable. Which is also the same as decreasing the rear sag, by increasing pre load on the rear spring thus increasing the weight bias towards the front end.

So if you lower the forks in the clamps you effectively increase the rake, and shift the weight bias towards the rear, increase the sag slightly, slightly increase the wheel base, thus, making the bike more stable, but, it takes weight off the front and promotes under steer.

Raising or lowering the tubes in the triple trees is a way to fine tune your handling characteristics due to small to a small change in the weight bias and geometry. This is why a change of 5mm in fork height can make such a noticeable difference in handling, and as such is not a cure for improper spring rates.

Okay, so with all of this in mind why is your front end hunting? Well, it wants to turn more easily than when you had the 19mm triple trees on it. And, it is also not uncommon for the front tire to want to and grab the sides of the ruts since the side knobs are now in full play when the bike is straight up and down, where as normally the side knobs come into play when you start to lean the bike over. So, in effect you are getting the oscillation once you get into the ruts b/c the tire is trying to grab the side of the rut and climb out, so you force it back straight, it then grabs the other side and the cycle repeats making your front end feel like a pin ball. Add this to the fact that you changed the front end geometry by going to the 22mm offset clamps with their inherent "want to turn" and it makes this oscillation more pronounced.

Everything has a cause and effect. I had not realized that you had changed the triple trees to 22mm before, and it is no surprise to me that due to the inherent effects explained above, why your front end is twitchy in these conditions.

I hope this helps you in making some changes during testing that will give you some more desirable handling characteristics.