Steering / Handling Issues - Suggestions?

[stevebussard]

   I'm looking for some helpful ideas on what I can do to improve the handling of my '00 M750.  My issue is, any time I ride over 70mph, the front end starts to dance.  Not to the extent of a full on tank slapper, but it's quite unnerving to say the least.  So far I've tried raising / lowering the rear shock setting, different air pressures in the tires, and I installed a 10 position ohlins side mount stabilizer.  Currently the rear end is a high as it will go, the tires are at ~42psi (front and rear), and the stabilizer is at 7.
   To be brutally honest, NONE of the things I've tried have really helped much.  What seems to help most is just throwing my feet up on the passenger pegs, and sliding my rear end back about 4-6".  I'm currently working on a set of custom rearsets to take advantage of my this discovery (and because it's a more comfortable position for me to ride in).
   The root question then is what next?  I've heard something about raising or lowering the forks in the triple tree.  That's easy enough I suppose, but how much should I move them, and what effect will raising or lowering them have on the stability, and handling?  The other modification I've been wanting to do is swap out the bars for clip-ons.  My fear (if you will) with this, is any ill handling that may come with it.  Since the bike seems to get more unruly the further my weight is shifted forward, would this modification be asking for trouble?
   As always, any help is much appreciated.

[BMiller]

Are the forks even?  Is the wheel straight?  Is the tire cupped?  Is the damper properly mounted with the front straight and not causing it to fight you at speed?

Just a couple ideas off the top of my head.  I would suggest removing the damper and trying it to eliminate that right off.

[wasta]

The tyre pressures appear to me to be way to high. I ride front at around 32 and the rear around 36 to 38.

[GK]

The tyre pressures appear to me to be way to high. I ride front at around 32 and the rear around 36 to 38.

Agreed.

When I had tyres fitted to my 900 6 months ago, the guy at the tyre shop recommended 35/36 f/r.

I've since dropped that to around 32 each end.

GK

[Howie]

Seems like you are trying to fix a bike with a handling problem by masking it.  42 psi tire pressure is way too high, raising the rear will make the bike less stable in a straight line.  Adding a steering damper to a bike without fixing the root cause is not a good idea.  Position 7 to go straight at 70    This bike is trying to throw you on the ground!

Start off with checking all components.  Wheels straight and balanced?  Tires good?  Wheel bearings?  Head bearing?  Swing arm bushings?  Swing arm bent?  Engine mounted tightly in the frame?  Frame cracked?  Engine case cracked where the rear engine mount bolt goes through?   Forks and triples straight?  Forks doing their job of damping?  Shock in good shape?  Worn or seized rear suspension rocker?  Any previous modifications to the bike that may be causing the problem?  And I'm sure a bunch of stuff I missed.  After that, start with a stock set up with correct sag.  Then make sure the springs are at least approximately close to your weight.  If you cannot get anywhere close to loaded sags the springs are too light.  Now you are ready to go to work on modifications for better handling.

Oh! this post would do better in Tech.

[Ddan]

+1 to everything Howie said, some of what you've done is making the problem worse.

[BMiller]

42 is not high if he has Conti Road Attacks, but for a normal sport bike tire, yes.

[stevebussard]

Seems like you are trying to fix a bike with a handling problem by masking it.  42 psi tire pressure is way too high, raising the rear will make the bike less stable in a straight line.  Adding a steering damper to a bike without fixing the root cause is not a good idea.  Position 7 to go straight at 70    This bike is trying to throw you on the ground!

Start off with checking all components.  Wheels straight and balanced?  Tires good?  Wheel bearings?  Head bearing?  Swing arm bushings?  Swing arm bent?  Engine mounted tightly in the frame?  Frame cracked?  Engine case cracked where the rear engine mount bolt goes through?   Forks and triples straight?  Forks doing their job of damping?  Shock in good shape?  Worn or seized rear suspension rocker?  Any previous modifications to the bike that may be causing the problem?  And I'm sure a bunch of stuff I missed.  After that, start with a stock set up with correct sag.  Then make sure the springs are at least approximately close to your weight.  If you cannot get anywhere close to loaded sags the springs are too light.  Now you are ready to go to work on modifications for better handling.

   Thanks Howie.  I definately agree that my attempts are masking some underlying issue.  I'm just not sure what.  I do know the motor casing where it mounts to the frame is not cracked, and the frame itself is not cracked.  The tire pressure I raised in an attempt to make a difference, with no noticable change (other than a harder ride).  I just set it to the max pressure the tire was rated for.  I will try lowering it.  The steering stabilizer was a similar story.  Trying to make a difference with no real results (good or bad).
   From what I can tell, everything is straight, but I don't know for sure.  Are there measurements I can make to tell, without taking it ito a frame shop?  I'm wondering if the previous owner may have changed the position of the fork tubes, and not gotten them exactly rite.  Do you know what the stock fork tube position is from the top of the triple tree?  The forks and rear shock dampen fine.  Do you know what the sag is supposed to be at the stock settings?  It seems good, but I don't know what it "should" be.

[bond0087]

Afraid that I don't have too many insightful suggestions, but I do know that you can find frame dimensions on page 100 of the factory service manual .

[ducpainter]

Replace your steering head bearings

[WTSDS]

When you align the rear wheel don't rely on the markings on those silly plates, do the measurements from the centre of the axle to the centre of the swingarm pin. And get a new retaining washer for the front sprocket, a little bit of wear can have your chain outa line.

But, yeah, steering bearings may well be the problem.

[koko64]

Do you know how to set the rider on sag?
You will need a buddy to help. Aim for zbout 30-35mm sag with you on the bike. Check the Ohlins site to set sag and the search function on suspension. Also Facts section on suspension.
Is the rear ride height stock? Did you adjust that or just the spring on the shock?

What are the damping settings on the suspension?

What tyres you running and how many miles? Too high tyre pressures are going to have the bike bouncing off the road. The front tyre will deflect off each bump.

You need to establish a standard setting and adjust one item at a time to test.
Try a moderate tyre pressure 32-33 front/35-36 rear.
30-35mm rider on sag.
Factory damping settings (or mid way settings/clicks if you cant find a manual)
Stock front and rear ride height settings (check manual)
Ensure nothings broken or out of alignment ss previously suggested.
Write it all down each step of the way.

[Howie]

Frame dimensions:

Print and turn right side up  Sorry, new equipment

Factory fork height is 279 mm. from the bottom of the lower triple to the top of the fork (not including cap)

Factory rear ride height is 238 mm from center of bolt securing helm joint to center of bolt securing the hoop to the suspension rocker.

Koko gave you the sag.

Hope this helps.

[stevebussard]

This is great guys.  Thanks so much for the info.  I'm going to try and work on this stuff today (if the kids let me).  If setting everything to the stock settings doesn't help, I will try replacing the head bearings.

[stevebussard]

Okay,
   I removed the steering damper, set all suspension settings to stock, and did the critical frame measurements.  Frame looks good and straight.  The sag was way too high (about 55).  I increased the valve setting on the rear shock and now it's about 32.  I lowered the tire pressure to 32.6 on the front, and 36.7 on the rear.  The tires are a Metzler Z1 on the front (~4,000 miles), and a Metzler Z6 on the rear (~2,000 miles).  I raised the front end up, and couldn't feel any play in the head bearings (I was hoping I wouldn't with only 6,800 miles on it).  Took it for a quick spin, and everything feels great.  Turn in is MUCH faster, and feels much more confident.  I haven't had a chance to take it up to highway speeds, but hopefully tonight, or sometime tomorrow.  I'll keep you guys posted, but so far it just looks like it needed to be set back to stock and tweaked a hair.

Thanks again everyone.