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Front End Chatter (SM racing suspension setup)

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I am running a brand new and completely stock KTM 525 SMC (Basically an SX with wheels and brakes). My last time out I was running Dunlop slicks with about 20 psi front and rear (cold day). There are a couple of problems I am running into on suspension setup:

01) Front end chatter when off the throttle through fast turns. Moment I get back on the throttle the chatter disappears. I am *NOT* getting any chatter on the brakes in a straight line (if that makes a difference).

02) It turns in slower then I would like. Very neutral to slow steering. I would prefer to have it "fall" or "dive" into the corner.

03) The balance front to rear is more biased to the rear during the mid to corner exit then I would like. I would prefer the rear to step or push coming out of the corner (right now the front is pushing).

I have some ideas on what todo about these problems (i.e., some more weight on the front end by increasing rear preload and/or dropping the front forks slightly). But I am pretty certain I can dial a lot of this out through the front & rear dampening (I actually had someone do this for me on my old XR650) -- but I don't have a clue which way togo on dampening setup. Ideas????

-Micah

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Mine was doing the same and I made the dampening way stiffer on the front forks and it helped alot!

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Chatter is a common problem on SM bikes. I think you're instinct to increase rear preload is correct, along with an increase in rear compression damping. If this doesn't help, start playing with the front damping..initially I would dial more rebound to the front. Saying this, I played with my front suspension in every direction, ended up replacing front tire (which helped more than any suspension adjustment, but didn't solve the problem), then sent the forks back to the fork doctor (Provalve, awesome service, thanks Nick) and he made ride height and valving changes that seem to have cured my problem... 😢

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Saying this, I played with my front suspension in every direction, ended up replacing front tire (which helped more than any suspension adjustment, but didn't solve the problem)...

What did you change the front to? And what did you have on before?

I am running Dunlop slicks and I have to say that I don't like them. Mostly because I can't figure out when they trully warm up -- which leaves very little confidence in the first 3-4 laps. But also because they don't seem to have any "give" -- meaning the transition from grip to slide seem very sudden -- which again doesn't leave me with a lot of confidence. I plan on immediately going to the Maxxis Presa 6118 & 6119 intermediates (which I have experience with on my XR).

Back to suspension setup. I have consistantly heard the mantra going to more & more rebound -- but a question is how do I tell or what are the characteristics of *TOO* much rebound? Also, what does it mean that the front is chattering *ONLY* at off throttle in fast corners but *NOT* chattering braking into corners?

-Miach

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The maxxis are pretty predictable. They aren't going to grip anywhere.

1 quick old school trick: turn up your idle a bit.

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It doesn't chatter when on the binders cause its loading your front suspension.....with no load the tire isn't being forced to the road, thus fighting for grip, crank up the rebound 4 clicks,(makes the tire want to go to the pavement faster) "generally" rebound and compression get adjusted equally at the same time.......I also would raise the forks through the clamps 6 mm (1/4" ) to start, this forces more weight on the front wheel.... you are complaining about turn in and falling over..... a 70's series tire will help the bike to flop more, the forks will also help the turn in..... This helped my MZ (standard height) also fined tuned my green bike..... I don't know about tire pressure with slicks and compounds etc but seems to me a super soft on the front at 20-24 psi should stick like shit to a blanket ??? First thing I did on both bikes is to adjust my rear sag..... (90-100mm) then make sure my tire pressure is with in MFG specs and around the same pressure as some of the other guys in the pits.... all the adjustments start in the middle so I have a baseline... and away I go..........1 adjustment at a time.... I'm a rookie so I know just enough to get into trouble 😢

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I also used Provalve in costa mesa, Nick's a good guy. Anytime my bike chatters now, it's time to change the front tire. I'm a suspension dummy, I told Nick what the problem was and all I know is it doesnt happen anymore. It was slow on turn in, too soft and too low.

MicahP I'm sure you also know that even though there's plenty of tread left on the tires that doesnt mean they're any good. They heat cycle until they die!

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The maxxis are pretty predictable. They aren't going to grip anywhere.

1 quick old school trick: turn up your idle a bit.

so you don't like Maxi's ron 😢

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Hey #6 would be fast on chen shins. Oh wait he is.

I personally have never found a maxxis tire that worked as well for me as any of the other tires that are available.

But enough smart ass comments from me, Mica at part of the corner are you chattering: entry, mid or exit?

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I also used Provalve in costa mesa, Nick's a good guy. Anytime my bike chatters now, it's time to change the front tire. I'm a suspension dummy, I told Nick what the problem was and all I know is it doesnt happen anymore. It was slow on turn in, too soft and too low.

MicahP I'm sure you also know that even though there's plenty of tread left on the tires that doesnt mean they're any good. They heat cycle until they die!

Thanx for the tip. I've dug up some old chassis design/suspension books I have. Reading the John Robinson book "Motorcycle Tuning: Chassis" he seems to indicate that the particular chatter i'm getting is caused by over extension in the rebound. Basically an oscillation in the first couple of inches of suspension movement that is not being properly damped out. I believe that getting on the throttle cures it because the suspension is not trying to hammer itself back and forth in the pavement (when in doubt gas it out). So I am hoping that incrementally increasing the rebound and compression up front will cure this badness... (or just holding open the throttle :-)

Also, with the tires, according to John Robinson and his calculations a radial tire will absorb roughly half the forces that would otherwise be input into the suspension. So my "theory" is that the Maxxis intermediates will dampen a lot better then the slicks I'm running. Plus there is the whole subjective/superstitious factor that I have already somehow convinced myself (I crashed twice on Sunday) that slicks are trying to kill me and I know and like the Maxxis tires. Which probably factors in to as much as 80% of my handling woes... :-)

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Hey #6 would be fast on chen shins. Oh wait he is.

I personally have never found a maxxis tire that worked as well for me as any of the other tires that are available.

But enough smart ass comments from me, Mica at part of the corner are you chattering: entry, mid or exit?

It would be mid corner for sure. When I'm off the gas... Everything is happy when I'm on the gas or the brakes.

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What did you change the front to? And what did you have on before?

I started with a michelin soft dot pilot, it was a few months old. I purchased a new michelin slick, soft, Can't remember the model number, its what they use on 250 gp bikes.

I am running Dunlop slicks and I have to say that I don't like them. Mostly because I can't figure out when they trully warm up -- which leaves very little confidence in the first 3-4 laps. But also because they don't seem to have any "give" -- meaning the transition from grip to slide seem very sudden -- which again doesn't leave me with a lot of confidence. I plan on immediately going to the Maxxis Presa 6118 & 6119 intermediates (which I have experience with on my XR).

Back to suspension setup. I have consistantly heard the mantra going to more & more rebound -- but a question is how do I tell or what are the characteristics of *TOO* much rebound? Also, what does it mean that the front is chattering *ONLY* at off throttle in fast corners but *NOT* chattering braking into corners?

-Miach

My 426 was also chattering off throttle in 3rd gear sweeper (among other places). To me, this was saying I was over loading the front end. An increase in ride height, along with increase in both compression and rebound damping is what cured (for the most part, anyway) my problem. After reading some of the posts here, and on SM junkie, I am convinced that the initial 2-3 inches of travel are where this gremlin comes from. I think my increased fork travel allowed for more damping control of the first few inches of travel past the sag travel. Its really hard to feel any solid damping control with a simple "squish" of the forks through only the first few inches of travel. This said, I think it takes a suspension revalve guru to really get the valve flow correct to work in the first few inches of travel. Until then, I think stock valving is not going to be adjustable (not much at least) in the initial damping (0-3 inches of stroke).

As far as too much rebound, in roadracing at least, hitting a bump mid corner, and then getting a slide from the tire immediately following that bump would tell me that the wheel is planting quick enough after the bump = too much rebound ( or too much compression not absorbing the bump) 😢

.02

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wheel is planting quick enough after the bump = too much rebound ( or too much compression not absorbing the bump) 😢

.02

I meant the wheel isn't planting quick enough, sorry. I also wrote inside the quote above.

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wheel is planting quick enough after the bump = too much rebound ( or too much compression not absorbing the bump) 😢

.02

I meant the wheel isn't planting quick enough, sorry. I also wrote inside the quote above.

That has always been my initial guess as well. But like I said in a previous post according to John Robinson in "Motorcycle Tuning: Chassis" he seem to indicate that the sort of chatter is caused by not enough rebound dampening in the front -- what essentially is happening, according to John Robinson, is that the suspension is overextended which cause the suspension to take another self induced bump back in the compression direction. Basically the suspension starts to oscillate -- thereby causing chatter. I don't know whether that is true or not but it makes sense...

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Try the 120/70-17 front Dunlop slick (Soft Compound) This is a little higher profile than the stock tire and helps the chatter. I also like to run 22, 24 psi cold. A lot of KTM racers like the 16.5 front wheel. KTM sells the complete wheel through its Hard Parts Catalog and it is pretty affordable. The 16.5 offers a larger contact patch and keeps provides more grip

Changing the trial with different offset clamps speeds up the turning on the KTM. I believe the stock claps are 20mm? I ran the 14mm clamps and it improved the turning.

As for clickers and suspension setup, every rider is different and it all about testing. Chatter can be a problem but to weed out the problem you have to start with a new set of tires. I tested the Bridgestone ultra-soft tire on my KTM 450 and it was sick. But that was after I already had the bike dialed in and it had 14mm offset clamps.

There are times that chatter comes from riding style too or it is the track. We have a track that causes even the best bikes to chatter. The only way to offset the problem is to brake early and roll on the throttle through the turn or trail brake through the apex and start rolling on the throttle as you release the brake. This way the bike never gets a chance to unweight and flop around.

Good Luck

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Changing the trial with different offset clamps speed up the turning on the KTM. I believe the stock claps are 20mm? I ran the 14mm clamps and it improved the turning.

Going to a smaller offset increases the amount of trail. How does that speed up turning? That would increase the stabilizing effect of castor/trail which I would think would make it harder to turn in but more stable coming out of corners and in braking.

Let R be the wheel radius

and theta be the head angle

and offset be the normal offset between the steering axis and the wheel spindle.

Then trail = R * tan( theta ) - offset / cos( theta )

So say for argument that a motorcycle has a rake of 27.5 degrees, and a wheel radius of 13.5 inches. With no fork offset, the trail would be 13.5" x tan 27.5 = 7". A 2.5" offset reduces the trail to 4.5"

see the diagram: http://www.motorcycle.com/mo/mcnuts/mcphotos/chass2.gif

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Chatter!!!! One of the most asked Questions I get. Scott is right, riding style and line selection will get that front end doing a lot of chatter, but that is a whole new topic. But most of it is in the suspension and the faster you get the more this is a problem. I could go into great detail about how and why, but from what you guys are posting you are in the right direction. Go find a guy who really knows Supermoto suspension real good, and get you forks and shock revalved. If done in right you should be able to adjust out most of the chatter. Now you have a new problem you will be going faster and you will have chatter all over again but a different chatter. Tires!!! the best cure for this is a 16.5 front wheel more rubber and better turn in. I know this is expensive for most people and most have 17 and thats OK. Most of the guys I see are running to low of tire pressure, this causes the tire to roll and this will cause chatter For Donlop slicks 24 seems to be a really setting but on really high speed track with high corner speed I have bumped it up to 26 no chatter! All tires are differant so you have to play a lot with the pressures to see what good for you. Now there is the triple clamps!!! changing the off set will help you with chatter but for most guys this is more money you don't need to spend unless you are really fast pro, use that money spend it on NEW Tires. The single most reason for chatter!!! 😢

Darrick

www.westcoastsupermoto.com

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Just thought of a huge problem with bike set up.....my rear tire was "rolling" played with tire pressure, front was needing low PSI....had a buddy change my tires out for me (yea I'm lazy) put on my rains for TT track etc and found the shop (last place that had installed my new tires) had reversed my tubes, back tube on front vise versa....... 😢 yup I'm not so lazy now 😢

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Chatter!!!! One of the most asked Questions I get. Scott is right, riding style and line selection will get that front end doing a lot of chatter, but that is a whole new topic. But most of it is in the suspension and the faster you get the more this is a problem. I could go into great detail about how and why, but from what you guys are posting you are in the right direction. Go find a guy who really knows Supermoto suspension real good, and get you forks and shock revalved. If done in right you should be able to adjust out most of the chatter. Now you have a new problem you will be going faster and you will have chatter all over again but a different chatter. Tires!!! the best cure for this is a 16.5 front wheel more rubber and better turn in. I know this is expensive for most people and most have 17 and thats OK. Most of the guys I see are running to low of tire pressure, this causes the tire to roll and this will cause chatter For Donlop slicks 24 seems to be a really setting but on really high speed track with high corner speed I have bumped it up to 26 no chatter! All tires are differant so you have to play a lot with the pressures to see what good for you. Now there is the triple clamps!!! changing the off set will help you with chatter but for most guys this is more money you don't need to spend unless you are really fast pro, use that money spend it on NEW Tires. The single most reason for chatter!!! 😢

Darrick

www.westcoastsupermoto.com

Darrick, you did an amazing job setting up my XR back in October. Felt like a completely different bike. The chatter I was getting on the XR was hard on the brakes. The chatter I'm getting on the KTM is through the final part of the fast long left at Stockton (or at least that was the worst part). I am also getting a big front end push through the very first part of the long left. I am definitely not going that fast.

I wish I understood or paid more attention when you were doing the bike setups in your class. But I don't have a clue on what you did. I'd really appreciate it if you could explain it a bit more.

-Micah

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