Front-end chatter under heavy braking (track)

[discotex]

Since I've started braking harder and later I've found a chatter problem under heavy braking. It feels like my front suspension bottoms out or bounces. Hard to describe exactly.

I thought setting up my front sag would solve it and although it seemed better yesterday it's still limiting how hard I can brake.

Anyone got any ideas where I should start attacking the problem short of a re-spring/re-valve? I think I'm on 30mm sag without digging out notes. Worth dropping it down to 25mm?

Guess I need a zip-tie to see if I'm hitting mechanical bottom as well?

[Tony.OK]

Yeah you def need a zip tie to confirm if you are bottoming.
I had the same issue with mine early on and thought the same thing, after checking the stroke and seeing it was well awy from bottoming it turned out to be too high an oil level causing it to cavitate/hydraulic when really hard on the brakes.

[JayRacer37]

Just a few thoughts:

-CBR600RR have no slipper clutch, do you still get the chatter if you don't downshift when you brake? (Rear chat can often feel like front chatter/movement)

-Steering head is nice and tight?

Chatter would be a pretty unexpected outcome from the front if it was bottoming. Bottoming usually feels like a whack through the palm of your hands. Unless you are a really big guy grabing the brakes reallly hard initally its not that likely you are actaully bottoming - -Tony is right, try a zip tie round the fork leg and then go do some hard stops. Don't do a big ride then check 'cos you can often have big bumps that will make the fork extension zip-tie move more than it is on braking.

Jay

[Robert Taylor]

Since I've started braking harder and later I've found a chatter problem under heavy braking. It feels like my front suspension bottoms out or bounces. Hard to describe exactly.

I thought setting up my front sag would solve it and although it seemed better yesterday it's still limiting how hard I can brake.

Anyone got any ideas where I should start attacking the problem short of a re-spring/re-valve? I think I'm on 30mm sag without digging out notes. Worth dropping it down to 25mm?

Guess I need a zip-tie to see if I'm hitting mechanical bottom as well?

This most often is because the spring rate is too light / under preloaded and it arrives at the compressed part of the stroke too readily. That in combination with the harmonics of the tyre creates a chatter frequency.
The stock springs in the CBR are usually progressively wound and they need chucking as far away as you can throw them. Also its probably arriving at the hydraulic lock mechanism and a great part of that needs disarming. Also as Tony said if the oil level is too high that can sometimes create the problem.

[discotex]

Thanks guys. Good to have a starting point so will get a zip tie on pronto.

Pretty sure it's not the rear as I'm used to locking it up if I botch a downshift and know what that's like. Had a doozy yesterday when I dropped into 1st by mistake inbetween T12 and T13 in the wet lol. Thankfully I realised as I was letting the clutch out and it started to go or I'd have gone down for sure.

It's not a hard clunking feeling. More of a juddering feeling. Sounds like that's probably not bottoming out then.

My steering head isn't loose but it's not nice and tight either. I had problems with the original bearings and that was a kind of notchy feeling. Probably worth figuring out how to tighten them up anyway tho.

[discotex]

This most often is because the spring rate is too light / under preloaded and it arrives at the compressed part of the stroke too readily. That in combination with the harmonics of the tyre creates a chatter frequency.
The stock springs in the CBR are usually progressively wound and they need chucking as far away as you can throw them. Also its probably arriving at the hydraulic lock mechanism and a great part of that needs disarming. Also as Tony said if the oil level is too high that can sometimes create the problem.

It's definitely underspring. I'm 75kg without gear and it was at least 40mm sag on the front before I added a heap of preload.

I'm getting the feeling I've probably just hit the limit of the stock suspension. Tempting to just bite the bullet and have you take a look rather than waste hours chasing an unfixable problem.

I'm still stitting on the fence about whether I want to put the cash into my road bike or buy a separate track bike. For the money I'd spend on fairings, suspension, slipon, etc I could probably get a 2nd hand pro-twin or 400 that I could take racing. Bit of a compromise after a modern 600 tho. Hard to know what to do really

[Shaun Harris]

It's definitely underspring. I'm 75kg without gear and it was at least 40mm sag on the front before I added a heap of preload.

I'm getting the feeling I've probably just hit the limit of the stock suspension. Tempting to just bite the bullet and have you take a look rather than waste hours chasing an unfixable problem.

I'm still stitting on the fence about whether I want to put the cash into my road bike or buy a separate track bike. For the money I'd spend on fairings, suspension, slipon, etc I could probably get a 2nd hand pro-twin or 400 that I could take racing. Bit of a compromise after a modern 600 tho. Hard to know what to do really

Use the Moto-Dynamix work shop service plan, to go through the bike 100% professionally, and then make your decision

[YellowDog]

Great thread. I was on a completely different track considering disc skimming and fork wear. Some really good tips to note down for future reference.

[discotex]

Use the Moto-Dynamix work shop service plan, to go through the bike 100% professionally, and then make your decision

Will have to till she's out of warranty for the full-on service plan but I should at least come see you at Frosty's and see what you think eh?

[dipshit]

Will have to till she's out of warranty for the full-on service plan

Huh? Has Honda got you locked into only getting serviced at Honda dealers to keep warranty valid or something?

[Shaun]

Will have to till she's out of warranty for the full-on service plan but I should at least come see you at Frosty's and see what you think eh?

It is already out of Warranty IF YOU ARE RACING IT!

[sinfull]

It is already out of Warranty IF YOU ARE RACING IT!

Haven't quite talked him into a clubmans round yet !
(His times are getting to the point where he should be i might add !)

[discotex]

Huh? Has Honda got you locked into only getting serviced at Honda dealers to keep warranty valid or something?

No they don't but I wouldn't want to give them any reason to deny a claim so I'd still have to get the regular services on-top of Shaun's workover.

I'd rather just have him look at specifics such as the head bearings and maybe do some work on the forks without doing the whole service until the warranty expires.

It is already out of Warranty IF YOU ARE RACING IT!

I'm just trackdaying it so far. It's my work transport which is why I have the dilemma of buying another bike for the track rather than pouring money into this one. I'd never be able to race it to it's potential worrying about crashing it. At least with trackdays I'm covered with a massive excess (hence thinking about race fairings and suspension mods)

Haven't quite talked him into a clubmans round yet !
(His times are getting to the point where he should be i might add !)

Not in the wet though lol. I really only went out incase I go racing so I don't totally shit myself on a wet day.

My other problem is the only local racing is at Puke. Not keen to race there at all (and the wife to be would veto it) so hoping for racing at Hampton Downs next year.

So really trying to get the most out of the stock stuff until the planets align for me to go racing (on something else)

[dipshit]

No they don't but I wouldn't want to give them any reason to deny a claim so I'd still have to get the regular services on-top of Shaun's workover.

I think you're being a bit overly paranoid. They can't deny a warranty claim because you got it serviced. Like with my Suzuki you have a two-year warranty and the only stipulation is that you have the first two services done by an authorised Suzuki dealer. That's it.

[discotex]

I think you're being a bit overly paranoid. They can't deny a warranty claim because you got it serviced. Like with my Suzuki you have a two-year warranty and the only stipulation is that you have the first two services done by an authorised Suzuki dealer. That's it.

You misunderstand my point. I'm not saying Shaun's service won't void the warranty - that'd be mental.

Howver they can deny a claim if the maintainence schedule isn't followed for that part. My only problem is that it won't be the Honda approved schedule so I'll still have to book it in for a service that it probably doesn't need after Shaun has looked at it.

No longer an issue from December once my 2 year warranty expires anyway.