Forks Bottoming?

7304 Views 25 Replies 9 Participants Last post by NewRedRider, 6 d ago

pbcrisp

Discussion Starter · Jul 13, 2010 (Edited)

Please help me with this.
At a recent trackday...my 3rd:
http://www.600rr.net/vb/showthread.php?t=194926
http://www.600rr.net/vb/showthread.php?t=192924

I noticed A LOT of chatter under heavy braking:

Click and watch.
I tried various techniques to minimize the chatter throughout the day. I tried getting on the brakes smother, locking my arms, staying down in a tuck, saving my downshifting until the very end...with varied results.

Still, when riding aggressively, there was big chatter under hard braking.
Everything else about the bike seemed planted. I dont have the suspension settings written down right now, I will try to post them latter if needed. I know they are pretty off, because I cant set sag for my weight. I am 195 without gear on.

1) Am I bottoming the forks during hard braking? Thoughts?

2) What are the stock fork spring rates?

I understand they are dual rate, but I have read various stock rate numbers depending on where I search. Also, Racetech's website gives the stock rates as 1.00 kg/mm.
http://old.racetech.com/evalving/Sp...00RR&formuse=form1&SpringType=Fork&bikeid=209
07-08 Honda CBR600RR

Type of Riding:
Street
Racing
Rider Weight (without gear): lbs kg
Bike Weight (semi-wet): lbs kg
Note: Bike Weight is critical for Road Race applications where significant amounts of weight have been removed.
It is common for a race ready sport bike to be 25 to 50 lbs less than displayed.

Rider Weight: 195 lbs.
Bike Weight: 425 lbs.

FRONT FORK SPRINGS
Recommended Fork Spring Rate for Racing: 0.998 kg/mm (use closest available)
Stock Fork Spring Rate: 1.000 kg/mm (stock)
Available FRSP S3627 Series Springs are:

Part NumberDescriptionPrice Select to Buy
FRSP S3627080 RT FRK SPR 35.5x33.5x270 .80kg$109.99
FRSP S3627085 RT FRK SPR 35.5x33.5x270 .85kg$109.99
FRSP S3627090 RT FRK SPR 35.5x33.5x270 .90kg$109.99
FRSP S3627095 RT FRK SPR 35.5x33.5x270 .95kg$109.99
FRSP S3627100 RT FRK SPR 35.5x33.5x270 1.0kg$109.99

Please let me know what you think on the 2 questions above, and any other bits of info you think might help.
Thanks.
-PB

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1 - 20 of 26 Posts

G

· #2 · Jul 13, 2010

Stock rate is 1kg/mm.

Only happens in that one turn? Could just be bumps in the braking area since a lot of cars go around Mid-Ohio.

What tire and pressure? Comp and rebound settings? You may be in for a reshim or revalve.

Jim Moore

· #3 · Jul 13, 2010

What's your front preload set at now? For your weight I'd go with 2-3 turns out from full hard.

G

· #4 · Jul 13, 2010

Jim Moore said:
What's your front preload set at now? For your weight I'd go with 2-3 turns out from full hard.

Learnin' time.

Preload numbers for sag setting isn't that easy. It all depends on the weight balance on the bike, weight balance of the rider (type of build makes more of a difference then people think), fluid weight and fluid level, and friction.

By the way, when do you want to trade those books?

Jim Moore

· #5 · Jul 13, 2010

I hear ya, but there is a difference between the perfect setup, and someone trying not to bottom out his forks. I'm gonna say you can get pretty close with the stock springs buy saying 130 lb guy = 3 turns from full soft, 160 lb guy = middle of the range, 190 lb guy = 3 turns from full hard. Hell, all 15 turns will only net you about 10 mm on the stock setup.

I gotta get in touch with my boy out in San Diego. He still has the book.

pbcrisp

Discussion Starter · #6 · Jul 14, 2010

2

All-righty-then. I just took my suspension measurements. Yes, I could stand to loose a little. Included current sag measurements thanks to an understanding wife.

Fork Preload = 3.5 turns in from full soft.
Fork Compression = 2 turns out from full closed.
Fork Tension or Rebound = 1/2 turn out from full closed.

Shock Preload = 8/10 (or almost max preload).
Shock Compression = 7 clicks out from full closed.
Shock Rebound = 1 full turn from full closed.

Front static sag = 25mm
Front Rider sag = additional 10mm

Rear static sag = 0
Rear rider sag = 20mm

Yes, I think I could bump up the front preload. Thoughts on this part??
-----------------------

Still, I am under the impression that our forks are dual-rate.

http://www.peterverdonedesigns.com/05fork.htm

I was under the impression that the 07-08 (and 09-10) 600rr has essentially the EXACT same forks as the 05-06's...painted black instead of anodized gold. What springs are in our forks? A dual-rate something like these pictures?

I would like to replace my fork springs with a linear 1.00kg/mm, BUT only if necessary.

Thanks for the info so far.
-PB

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G

· #7 · Jul 14, 2010

pbcrisp said:
All-righty-then. I just took my suspension measurements. Yes, I could stand to loose a little. Included current sag measurements thanks to an understanding wife.

Fork Preload = 3.5 turns in from full soft.
Fork Compression = 2 turns out from full closed.
Fork Tension or Rebound = 1/2 turn out from full closed.

Shock Preload = 8/10 (or almost max preload).
Shock Compression = 7 clicks out from full closed.
Shock Rebound = 1 full turn from full closed.

Front static sag = 25mm
Front Rider sag = additional 10mm

Rear static sag = 0
Rear rider sag = 20mm

Yes, I think I could bump up the front preload. Thoughts on this part??
-----------------------

Still, I am under the impression that our forks are dual-rate.

http://www.peterverdonedesigns.com/05fork.htm

I was under the impression that the 07-08 (and 09-10) 600rr has essentially the EXACT same forks as the 05-06's...painted black instead of anodized gold. What springs are in our forks? A dual-rate something like these pictures?

I would like to replace my fork springs with a linear 1.00kg/mm, BUT only if necessary.

Thanks for the info so far.
-PB

The forks from 05-06 are completely different then the 07-08. Basic measurements are the same, but valve types, the cartridges, valve shimming, fork springs, internal preload, and coatings are different. OE is a single rate 1.0kg/mm spring.

Try setting your preload a little stiffer; get that sag setting around 25-30mm total.

You might want to also raise the oil level about 5mm, which will give a little more bottoming resistance.

zenodamper

· #8 · Jul 14, 2010

...years ago we used to discuss stuff suspenders related stuff on that Traxxion website; then we started IBSF - Peter were one us mods then, no idea what he does nowadays; but point being is I have perhaps wondered about the wisdom of all the spiel there on the site - part explanations and truths seem to do as much damage (maybe more) than no info at all!

2007-10 fork is different to 05/6, in that the cartridges are not stamped (like big deal), so actually easier to take apart; the springs are now linear and stiff; indeed using lighter is good with the right damping set-up (not stock) - the pistons or valves are the same - the bottoming facility has altered in that there is an additional rubber cushion in the 07 stuff - the dimensions for displacement are same as they ever were - so all in all similar but not same!

The bike moves weight differently, ergo a different construction and tuning methodology is needed.

My suggestion to the poster with the problem is to run the preloading at 6-10 turns from minimum - start at 8t? You will need to boost up the compression damping screw, start at 3/4 from max. Do not despite the lack of rebound they suffer keep adding rebound, as this will screw it up entirely - wooden and will not steer! Showa intended you to use the rebound bleed open a bit and let the top-out catch it on the return. Yes they are weird Showa; but they are doing their thing isn't it!?

Good luck!

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[email protected]

· #9 · Jul 14, 2010

Some of what I found with the stock OEM suspension.

Front preload- You will never get rider sag # close to 30mm, unless you weigh around what Paris Hilton does. When you add preload on these forks it does'nt change sag... Puts on flame suit..:flamethrower:

Front comp- Anything past 1.5 turns out and your living in dreamtime if your wanting any kind of control.

To start with, Does the bike feel quit biased to the front ? I would set front preload at about 7-8 turns in from soft, Depending on Tires.
Leave rear preload at pos# 8 for now. (Thinking you may need more) Are you sure you have 20mm of sag? I was 175lbs without gear and had 31mm on pos# 8. Can you recheck?

Jim Moore

· #10 · Jul 14, 2010

pbcrisp said:
All-righty-then. I just took my suspension measurements. Yes, I could stand to loose a little. Included current sag measurements thanks to an understanding wife.

Fork Preload = 3.5 turns in from full soft.
Fork Compression = 2 turns out from full closed.
Fork Tension or Rebound = 1/2 turn out from full closed.

I think your front preload and compression damping are both too soft. You may well be bottoming out with those settings. Who set it up for you? I would try 3 turns from full hard on your preload, and one turn out (or even a little less) for your compression damping.

pbcrisp

Discussion Starter · #11 · Jul 14, 2010

Based on the responses so far, I am going to have to say You all are most impressive.

Stock Spring = a linear 1.00kg/mm = pretty much exactly what I should be running = good to know.

Bump up the preload and possibly a little more compression damping, and see what its like.

I set the settings you see above. I am not one to just grab settings off someone else's post and run with them. I have watched Dave Moss's dvd repeatedly, and twiddled on both my bikes a bit. Again, everything about the bike is feeling pretty nice...with the exception of the braking chatter. MAYBE - more preload and compression will feel just as nice, and solve the bottoming.

Thanks
-PB

Jim Moore

· #12 · Jul 14, 2010

pbcrisp said:
Based on the responses so far, I am going to have to say You all are most impressive.

Stock Spring = a linear 1.00kg/mm = pretty much exactly what I should be running = good to know.

Bump up the preload and possibly a little more compression damping, and see what its like.

I set the settings you see above. I am not one to just grab settings off someone else's post and run with them. I have watched Dave Moss's dvd repeatedly, and twiddled on both my bikes a bit. Again, everything about the bike is feeling pretty nice...with the exception of the braking chatter. MAYBE - more preload and compression will feel just as nice, and solve the bottoming.

Thanks
-PB

I wasn't trying to give you a hard time, lol. When the suspension guru set mine (with OEM springs), he set them right at 7.5 turns out from full hard. I weigh about 165 geared up, so based on that I think you need significantly more preload than 7.5 out.

Here's an interesting tidbit on compression damping. If you get down and turn your adjuster, you will find that you have about 5 turns of adjustment. OK, fine, yours is set roughly in the middle. Well, not really. The way the plunger is designed, your orifice is essentially fully open after two turns or so. Basically your range of adjustment is from fully closed to about 2 turns open. So at your current settings you are significantly too soft on your preload and you have virtually no compression damping.

Whatever the case, play around with it some and let us know how it works out.

OveRReV

· #13 · Jul 14, 2010

have you tried removing the oil lock valves on the rod? they could also be causing your problem.

max600racing

· #14 · Jul 14, 2010

I'm also having the similar chattering problem. I thought that the chattering was caused by fork bottoming. But after I put a cam to see how does the front fork look during chattering, I found that it happens before the fork bottom out. In the vid, the zip tie is about 106mm and it is close to its maximum travel (110mm). The front starts to chatter before touching the zip tie. This kind of chattering happens at various locations. Any idea to sort out this problem?

The front fork is Ohlins 30mm cartridges so it doesn't have the oil lock. Now the sag is 20mm and rider sag is 32mm. The compression/rebound are set to the recommended setting by Ohlins.

Jim Moore

· #15 · Jul 14, 2010

I have no freaking idea, but GREAT job with the camera angle!

pbcrisp

Discussion Starter · #16 · Jul 14, 2010

max600racing said:
I'm also having the similar chattering problem. I thought that the chattering was caused by fork bottoming. But after I put a cam to see how does the front fork look during chattering, I found that it happens before the fork bottom out. In the vid, the zip tie is about 106mm and it is close to its maximum travel (110mm). The front starts to chatter before touching the zip tie. This kind of chattering happens at various locations. Any idea to sort out this problem?

The front fork is Ohlins 30mm cartridges so it doesn't have the oil lock. Now the sag is 20mm and rider sag is 32mm. The compression/rebound are set to the recommended setting by Ohlins.

http://www.youtube.com/watch?v=J8X1xLCc_bY

I am assuming the Zip-tie is at max travel while riding...not max travel in garage/simulated situations.

Where do you get the 110mm max travel number from? Is this measured travel during garage testing? Or a number from a spec sheet? I am mostly just curious, but if the number is theoretical, then the Zip-tie might be at the ACTUAL max travel. I would then want to know what type of bump-stop is in your fork. even a hard rubber one might allow a few mm of cushion (travel) that would allow for the difference between your Zip-tie, and the area where you notice chatter.

Seriously though...I am just making stuff up here. I have not much of an idea.

pbcrisp

Discussion Starter · #17 · Jul 14, 2010

Jim Moore said:
I wasn't trying to give you a hard time, lol. When the suspension guru set mine (with OEM springs), he set them right at 7.5 turns out from full hard. I weigh about 165 geared up, so based on that I think you need significantly more preload than 7.5 out.

Here's an interesting tidbit on compression damping. If you get down and turn your adjuster, you will find that you have about 5 turns of adjustment. OK, fine, yours is set roughly in the middle. Well, not really. The way the plunger is designed, your orifice is essentially fully open after two turns or so. Basically your range of adjustment is from fully closed to about 2 turns open. So at your current settings you are significantly too soft on your preload and you have virtually no compression damping.

Whatever the case, play around with it some and let us know how it works out.

I was aware that I was right on the edge of compression adjustment...Right on the edge of noticeable adjustment. I will probable work my way down to 1.5 turns and maybe further.

I find it quite interesting that everybody talks about most bikes being built for 140-160lb riders...yet this one has what most would consider too MUCH spring in the front.

What do you all think about the back...is the Shock sprung for a heavy weight? or is the bike sold "unbalanced"?

-PB

pbcrisp

Discussion Starter · #18 · Jul 14, 2010

OveRReV said:
have you tried removing the oil lock valves on the rod? they could also be causing your problem.

I have read a little about removing the oil-locks, again on PVD's web site about 05-06 forks. Are they the same on the 07-08's? What about the consequences? Only bad if you go off-roading, or hit a monster pothole, or stunt?
Opinions?
-PB

[email protected]

· #19 · Jul 15, 2010

max600racing said:
I'm also having the similar chattering problem. I thought that the chattering was caused by fork bottoming. But after I put a cam to see how does the front fork look during chattering, I found that it happens before the fork bottom out. In the vid, the zip tie is about 106mm and it is close to its maximum travel (110mm). The front starts to chatter before touching the zip tie. This kind of chattering happens at various locations. Any idea to sort out this problem?

The front fork is Ohlins 30mm cartridges so it doesn't have the oil lock. Now the sag is 20mm and rider sag is 32mm. The compression/rebound are set to the recommended setting by Ohlins.

http://www.youtube.com/watch?v=J8X1xLCc_bY

Chatter can be caused buy a few things, If I was to take a pot shot, I would say dial 2 or 4 clicks out on rebound and try that, Is it better? if not go the other way 6 - 8 clicks. (2-4 clicks past recommended settings) any better ?

[email protected]

· #20 · Jul 15, 2010

pbcrisp said:
I have read a little about removing the oil-locks, again on PVD's web site about 05-06 forks. Are they the same on the 07-08's? What about the consequences? Only bad if you go off-roading, or hit a monster pothole, or stunt?
Opinions?
-PB

There's pro's and con's for removing the oil locks, It all depends which way you look at it. You can leave them in place for the peace of mind ect but reduce the way they work and from when they start to work by drilling bled holes in the cartridge caps.

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