Front suspension question

Sometimes when cornering on my 1250 the front end feels a bit skittish if thats the word.
Sort of like a slight wobble mainly if hitting even very small bumps, tyre pressures and tread depth are ok.
I've been on the same roads on other bikes and haven't had this happen. This is at normal cornering speeds.
Front pre-load is on 3
What causes this and what can be done to correct the problem

V17R wrote:Sometimes when cornering on my 1250 the front end feels a bit skittish if thats the word.
Sort of like a slight wobble mainly if hitting even very small bumps, tyre pressures and tread depth are ok.
I've been on the same roads on other bikes and haven't had this happen. This is at normal cornering speeds.
Front pre-load is on 3
What causes this and what can be done to correct the problem

What km on the bike, what front tyre type, what km on the tyre, what pressure are you running? Any front end mods?

You should be 36-38 psi.  If pressure and tread are OK, I'd check the forks are properly installed, no loose mounting bolts and that steering head bearings are OK

its got 19,000kms, 36f/42r psi, Michelin road pilot 2 about 1/4 worn bike is stock
I will check every thing over the w/end although it just had 18k service at Suzuki, Id hope they checked the basics

A common cause of poor bump compliance in non adjustable forks like the Bandit is the fork oil being treated like power steering fluid - that is, it never gets changed. (As far as I know, it is not done as part of routine servicing by workshops - but I could be wrong there, cos  I don't use commercial workshops)
Fork oil is past its best at 24000k and has turned to fish oil by 48000k. (Suspension gurus like 12000k changes)
At 19000k it maybe a bit early for damping to be suffering big time as you describe, but can be considered.

Next, steering head bearing too loose could give problems like you describe.(edit-I just noticed kewwigs answer, but here's some more detail) Easy to check - put the bike on the centrestand and get somebody to push down on the arse of the bike to lift the front wheel. Grab the bottom of the forks and push forward and backward. If there is any movement in the forks your bearing is way too loose. Too tight causes the bike to weave, so doesn't fit your symptoms. Damaged/notched bearing doesn't quite fit either.



Another - GSF Bandits are chronically undersprung in the forks and stiffer springs are at the top of most guys list when fettling these bikes.

Read up on how to set your suspension sags (Google how to do it, you'll get hundreds of hits) . If you have standard springs and you weigh more than 60/70kg you'll note that your sag will be too low when you have your preload set to maximum and if so, to get the bike to handle safely you'll need stiffer springs. a couple of hundred bucks will usually get you out of it.



Other guys will post up more possibilities, work your way through them.

+1

Yes, front suspension is one of the cost saving areas for Suzuki on these bikes. I have a '09 model which had 26,000km on the clock and weigh 100kg, front would dive severely under modest straight line braking and if you were too hot into a bend and applied a little brake she would toss you around like buggery.
I put 1.0kg non-progressive springs with 15mm spacers in the front with 1 notch adjustment on the screws.
This alone won't fix the problem as the dampening design is cheap.
I took it to a suspension guy in Mulgrave called Promecha, he has had years in the racing game.
He suggested that bandits need re-valving & anti dive mechanism installed with 5W oil.
This cost me $365, he disassembled did the job & I picked the bike up 2 days later.
The suspension does feel a little softer but rides really well over bumps, under braking the lack of dive is very noticeable.
The performance around bends even with a little braking is firmly planted.
All up I spent $120 for a set of sonic springs which I fitted and $365 for the suspension guru to weave his magic.

thanks for the replys, I checked the steering head bearings , no movement
front sag 25mm, rear sag 30mm thats from bike standing to with me on it

From those sags it sounds like the original owner has installed stiffer springs.

A small point , though. Your post sounds like you've measured the  difference between the suspension position from when the bike is on its wheels and when you've climbed on.

If so : You have to measure from when the suspension is fully topped out - that is put the bike on the centrestand and get your first measurement when each wheel is lifted off the ground and then measure how far the suspension has dropped when you are sitting in your normal riding position on the bike. This is called dynamic sag and its what we're interested in.
The difference between topped out and then with the weight of the bike only is called static sag and is useful for working out some things but the dynamic sag is what you need to set.

The accepted sag is 1/4 of total suspension travel for track and 1/3 of total travel for road.

In the Bandit that works out as between 32.5 mm and 43mm front and 34mm and 45mm rear.

Can you confirm that you've got them in that range and then we'll keep stabbing in the dark as to what's causing your problem.

thanks !Tag I did it wrong , will measure again

No worries - all this is good though. Setting sags is really important for getting your bouncy bits working proper like but not all that many riders go to the trouble of learning how to do it. Once you've learned though, you'll get the benefits for ever and ever more  

(Crap, I've just used an emoticon - I'm turning into an Ewok)

!Tag wrote:No worries - all this is good though. Setting sags is really important for getting your bouncy bits working proper like but not all that many riders go to the trouble of learning how to do it. Once you've learned though, you'll get the benefits for ever and ever more  

(Crap, I've just used an emoticon - I'm turning into an Ewok)

You've got a long way to go!                                                                                                                                                      

The journey is long Master.

As ever,
Your Padawan

I remeasured the sag front and rear
took 3 measurements wheel unloaded off the ground, bike standing by itself and with rider on board

front 36mm difference from wheel off ground to bike by itself 
front 46mm difference from wheel of ground to rider on bike

rear 12mm difference from wheel off ground to bike by itself
rear 34mm difference from wheel off ground to rider on bike

make of that what you may because it doesn't mean that much to me

Good stuff, V17R

I make of that that we've ruled out another possibility of your less than user friendly front end.

It means you've got stiffer than oem springs (unless your a jockey) and the springs are suited to your weight.
If you want to make it exact I'd go down one ring on your front preload adjusters (screw the adjuster down into the fork) and that should put it in the ideal range.

A bit of background before I keep flapping my gums at you:
Preload adjustment is a suspension travel adjustment only, it doesn't make your suspension or the ride comfort or your penis or your soft fluffy washing any harder or softer. It's a fatarse adjustment only. As you've seen your suspension can move up and down 130mm. If you are the size of King Kong when you get on the bike it sinks down much lower in the suspension stroke and you need to increase preload to lift it back up till its resting at one third of its stroke when your riding down a smooth road. This gives two thirds travel to absorb big compression bumps until it bottoms and your bike turns into a rigid tail Harley, and one third of its travel to allow the wheel to reach down into potholes, depressions and broken surfaces. Now if it couldn't do that you'd end up with a front end that was skittish and unstable. (Thank god, your saying - he's finally got back to the original question.)

Your rear is a bit high but that is with you only. If you carry a pillion or load up a shitload of luggage it will be a bit low. So if you want a compromise between loaded/ unloaded , then your current setting is not too bad (you should change your rear preload every time you ride with a different load and that's fine if you've got a bike with remote preload adjusters but in these Bandits altering rear preload is a PITA.

The downside is your setup a bit nose down (rear sag higher than front sag). When the bike is adjusted nose down you get faster steering but this also increases instability. That is the bike reacts faster to any input from the rider or road surfaces, and feels skittish and unstable.

One thing I forgot about your steering head is check to see if cabling and hosing is not interfering with free movement of the front end . If you've installed heated grips, GPS a 12v outlet and a toaster or if your brake hoses are wound around the forks twice then all this will bind your front end and make it feel - you guessed it - skittish and unstable.

I've probably set fire to your eyeballs by now so I should just shut up at his point. If you can't get the problem tracked down post up again and I can give you more possibilities if you can put up with my rabbiting on.

!Tag wrote:The journey is long Master.

As ever,
Your Padawan

Patients you must have .....................

what a reply !Tag,

I just got back from a ride so jumped on the scales 86kg with gear
so I will wind down the front preload 1 ring and remeasure 
does this mean with standard springs it would have more sag?
seems strange it would have stiffer springs got all the receipts with the bike but who knows.
now what about that rear rebound dampener adjustment....

once all this suspension stuff is sorted I will give the bike a few runs at the drags (Sydney) just for the hell of it
I have drag raced cars for years but always love watching the crazy's on the bikes
feel free to keep on rabbiting on!
Thanks,
John

By the looks of that reply, I hereby rename Tag "suspension master"   
When I have someone around that can read a tape measure, I'll get them to give me a hand to measure things up & pm you the info to see what you think oh masterful suspension master

AAARrrrgh goddammit, I just spent the last two hours with one eye on the footy and one eye typing up a whopper response only to have the whole thing disappear into electronic limbo when I finally hit the submit button.

And it wasn't footy it was a 75 minute bitch slapping session with 5 minutes of footy         - what the hell is the green snail for Ewok?

So I'll post up some replies in little bits to be safe.

paul wrote:

!Tag wrote:The journey is long Master.

As ever,
Your Padawan

Patients you must have .....................

Hehe, I see what you did there.

Quote John :
does this mean with standard springs it would have more sag?
seems strange it would have stiffer springs got all the receipts with the bike but who knows.

Sentence 1 ; yep.   Sentence two ; nope. (of course I don't know what's been done to your bike but the numbers you posted are consistent with a spring upgrade.)

The GSF's are chronically undersprung and are often upsprung. The GSX got a major spring and damping rate upgrade and is much better.

You'll probably find this vid interesting BUT BEFORE YOU WATCH IT - (sorry about yelling but this bits important) . The vid is by Dave Moss who is a suspension legend because of the huge amount of technical vids he has made. But in this vid he makes a false assumption. He says the Bandit has a damping rod setup. It doesn't it has cartridge dampers. This is a picha of a disassembled Bandit cartridge. In the middle on the left is the compression valve and on the right is the rebound valve:
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This is important because later in the vid he makes recommendations on oil weights. DISREGARD any of these recommendations. They are right for a damper rod fork but the Bandit is not.

So, roll the video:

https://www.youtube.com/watch?v=eXvobTB39Kc

Quote John; "now what about that rear rebound dampener adjustment"

Rebound is pretty easy to get your head around too.

A suspension tech uses black magic to be able to get a close approximation to correct damping because he has to set a bike on the spot.
The owner has the luxury of being able to dial in rebound across the life of a tyre. The best all round rebound setting (it can be altered to perform better in one area at the expense of another but I'll guess you'd prefer the best overall) also gives perfect tyre wear. If your tyre, at the end of its life, has scalloping, tearing or ridges on the tread grooves at the shoulders and edges then theres a high probability that incorrect damping caused it.
Check the grooves of your tread toward the edges and if one edge is rounded and the other edge has a raised ridge, your rebound is out.
If the ridge is on the leading edge give your shock adjuster a quarter turn softer (towards "S" on your adjuster). If the ridge is on the trailing edge go a quarter turn harder. Give the tyre 500-1000k to wear in to the new setting and keep repeating until you get a smooth tyre.

Good pichas and words on this site, I've just added English interpretation to suit the Bandit adjuster. 

http://biketrackdayshub.com/motorcycle-tyre-wear-guide

Quote John: "once all this suspension stuff is sorted I will give the bike a few runs at the drags (Sydney) just for the hell of it"

NOOOO John, now we've got too concentrate more on chassis geometry than suspension action to get the bike to transition to a rear net anti-squat as early as possible in the run.
For that you'd better get a copy of Tony Foale's "Motorcycle Chassis and Handling Design - The Art and the Science" because Tony Foale is the benchmark in chassis design.

I'll bet by now you've run screaming from the room and I'm talking to myself.

Kiwisteve wrote:When I have someone around that can read a tape measure, I'll get them to give me a hand to measure things up & pm you the info to see what you think.

 If you think I might be able to help on anything that's got you scratching your head post up or PM and I'll have a shot at it.
As an aside the only thing I'll ever post up or pass on will be what I've learned from experts. I'll never be posting what I reckon as my uninformed best guess (or if I do I'll soon tell you - use my ignorant guessing at your own peril)

bloody hell, here I was thinking it would be a peace of piss!
I need to do some serious rear tyre study regarding this rebound business 
looking at that video those original springs must be like a old mattress 

with my lack of experience on a sticky drag strip on a bike, I wont be needing the book just yet.
 I know how you felt when everything disappeared!

ok, finally got back to the bike again.
I wound down the preload down to 2 lines instead of 3 now it measures 48 mm from wheel of the ground to me sitting on it
does this sound right?