Front wheel chatter?

[bucketracer]

Hi Folks I have been poking around on here looking to educate myself about suspension setup.

My problem is that my F4 race bike suffers from front wheel chatter when pressed moderately hard. I have tried changing things oil/preload, and cut the progressive bit off but made no real progress.

I was running 18" TT900 GP's 90/90F 120/80R and the chatter front and back was real bad. The bike would turn sideways, and slowed down like I had put the brakes on.

When I changed over to 17" 90/90F 115/70R slicks on the correct rims 2.5F and 3.5R the problem got better but is still a handycap.

Not only does it chatter in the dry on slicks, it will chatter on the front when running wets in the rain.

The fork springs are 28mm OD and the old damper rod type. Are there emulators or cartridges for these small forks?

Can someone point me to a thread that might help.

Thanks. BR

[F5 Dave]

Damper rod forks are tragic. But that sounds worse than they should be. Without springs I'd want to know if the forks are binding up. This will require two people to pump it up & down.

Further I would look at the rear for the same thing, I'm struggling with your description, but rear can upset the front esp if it packs down. You might be able to ride around some of it with less bar pressure & weighting other side peg to normal to see if that helps, my H counter intuitively liked the inside peg on some corners to make up for crap frame/suspension. Make sure weight is not too far back with radical rearset pegs forcing you there etc.

People often try crazy oil weights but will only lead to hydraulic lock, I'd stick with 10w for a ripply track like mt wgtn.

But yeah some emulators might be nice to try, I'd try to find if there are other reason first lest you spend a bit & only 1/2 fix the issue.

I'm assuming you aren't running silly amounts of preload & have some static sag.

[Shaun]

I am assuming of course, that you ballance all wheels correctly, also that you have cheched the wheels and discs for run out, as well as checking the axles for being true, play in the stearing head bearings can also cause chatter

[bucketracer]

Damper rod forks are tragic.

People often try crazy oil weights but will only lead to hydraulic lock, I'd stick with 10w for a ripply track like mt wgtn.

I'm assuming you aren't running silly amounts of preload & have some static sag.

Last time out, cut the soft part of the progressive spring off and ran 20wt, preload minimal sag 1/4 of travel F&R with rider aboard, weight distribution 45%F 55%R with rider in riding position.

Jacked the rear pre-load up and made things worse.

Will check for fork bind, last time someone bounced the bike up and down they said there was no/little rebound damping in the front?????

Will try again with two pairs of hands, then planing on removing the springs and seeing if the sliders go up/down OK.

The pistons on the rods dont have a piston ring like I have seen on other bikes, just relies on the close fit in fork tube I expect.

Thanks for the suggestions.

.

[bucketracer]

I am assuming of course, that you ballance all wheels correctly, also that you have cheched the wheels and discs for run out, as well as checking the axles for being true, play in the stearing head bearings can also cause chatter

Wheels ballanced by the shop when they fitted the tyres, runout OK but they are spoked wheels, axil runout? will have to check, stearing head?? will have to re-check that carefully too.

Swing arm and frame braced, swingarm rubber bushes replaced with bronze bushes. This bike has allways suffered from chatter whereas I know of other bikes like mine (without the bracing)???? have not had any problems.

Thanks for your ideas, I will check "all" the things you have suggested.

[Shaun]

Wheels ballanced by the shop when they fitted the tyres, runout OK but they are spoked wheels, axil runout? will have to check, stearing head?? will have to re-check that carefully too.

Swing arm and frame braced, swingarm rubber bushes replaced with bronze bushes. This bike has allways suffered from chatter whereas the other Suzuki GP125's in the team have not had any problems.

Thanks for your ideas, I will check "all" the things you have suggested.

Do not trust the shop ballance mate, I have seen/re done many a wheel ballance from a shop, 1 in paticuallr in the Auckland area

Wheel rim, discs RUN out check also mate, and the axles could be bent from prior crashes?

[Robert Taylor]

Beyond all the totally valid points that Shaun has made chatter is a ''frequency interaction''. It often happens on the racetrack because the spring rate and or preload is incorrect ( usually insufficient ) It can also happen because the low speed damping is weak and allows the suspension to blow through its stroke too readily to the compressed part of the stroke. Damper rod forks have this undesirable characteristic and emulators will certainly provide a major improvement in that and other areas, money well spent. You also need to establish exactly what the spring rate is.

[bucketracer]

RT thanks for the tips.

Before I got started looking on these threads I had purchased some YSS PD fork valves No 238. I would have liked Gold Valves but did not know where to get them, Sorry.

Are Gold Valves in this size available? Price?

I am begining to suspect that there is to much clearance around the piston for the rebound to work. There is no piston ring on the piston.

The piston measures 23.7mm are there emulators that small that will fit my forks?

.

[Robert Taylor]

RT thanks for the tips.

Before I got started looking on these threads I had purchased some YSS PD fork valves No 238. I would have liked Gold Valves but did not know where to get them, Sorry.

Are Gold Valves in this size available? Price?

I am begining to suspect that there is to much clearance around the piston for the rebound to work. There is no piston ring on the piston.

The piston measures 23.7mm are there emulators that small that will fit my forks?

.

Yes I think there are and will check.
The poppet springs on those valves you purchased sack out very quickly ( we have tested some ) and the bypass hole size is on many sizings too large leading to too little low speed compression control. Once the anodising wears through ( from spring rubbing ) it also gets ugly with alloy chards contaminating the oil and finding their way into the bushings, embedding into them. They are a very substandard product and a very poor copy, typical of so many mainland Asian products.
Race Tech emulators are more expensive but with good reason, they are a reliable product that also work properly and with full backup / tuning knowledge.
Yes the damper rods should seal properly and theres a lot of detail points for proper emulator installation and therefore function.

[bucketracer]

RT thank you for your reply. I would be interested to know if there are emulators and/or Gold Valves available.

The bike/rider combo weighs 190Kg all up with 45%F 55%R weight distribution with the rider on board and in the riding position.

I was planning on removing a fork leg, putting a cable tie on the stanchion to measure compression travel and using a set of bathroom scales measure how much weight I can apply to the fork leg.

From the weight and distance compressed I should be able to get an idea of the spring rate in Kg's a Cm.

Is this idea workable???

Are spring rates even measured in Kg's/Cm ???? this is how little I know.

I had better go and read up some.....

Many thanks for your help

.

[Robert Taylor]

RT thank you for your reply. I would be interested to know if there are emulators and/or Gold Valves available.

The bike/rider combo weighs 190Kg all up with 45%F 55%R weight distribution with the rider on board and in the riding position.

I was planning on removing a fork leg, putting a cable tie on the stanchion to measure compression travel and using a set of bathroom scales measure how much weight I can apply to the fork leg.

From the weight and distance compressed I should be able to get an idea of the spring rate in Kg's a Cm.

Is this idea workable???

Are spring rates even measured in Kg's/Cm ???? this is how little I know.

I had better go and read up some.....

Many thanks for your help

.

I will pm you on monday with sizing and pricing of emulators. We have a digital fork spring rating load cell set. If you purchase a pair of emulators we will test the fork springs foc.

[cowpoos]

RT thank you for your reply. I would be interested to know if there are emulators and/or Gold Valves available.

The bike/rider combo weighs 190Kg all up with 45%F 55%R weight distribution with the rider on board and in the riding position.

I was planning on removing a fork leg, putting a cable tie on the stanchion to measure compression travel and using a set of bathroom scales measure how much weight I can apply to the fork leg.

From the weight and distance compressed I should be able to get an idea of the spring rate in Kg's a Cm.

Is this idea workable???

Are spring rates even measured in Kg's/Cm ???? this is how little I know.

I had better go and read up some.....

Many thanks for your help

.

take a fork leg off...and see how much forward and backward play there is in it.

[bucketracer]

Thanks CowPoo's

Very Good Idea. Will do that.

[bucketracer]

I will pm you on monday with sizing and pricing of emulators. We have a digital fork spring rating load cell set. If you purchase a pair of emulators we will test the fork springs foc.

The best discription I heard was "it was like the springs bouncing the wheel up and down like a Yo Yo".

Thanks RT, I am looking forward to getting the price, testing the springs, that will be great many thanks.

.

[bucketracer]

I will pm you on monday with sizing and pricing of emulators. We have a digital fork spring rating load cell set. If you purchase a pair of emulators we will test the fork springs foc.

Thanks RT, got your PM, I have replied with Visa details etc.

.