First track day. Front end bounces on when braking - 600RR.net
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post #1 of 31 (permalink) Old 08-04-2014, 04:51 PM Thread Starter
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First track day. Front end bounces on when braking

Ok so had my first evening on track. There was a long straight before a big right hander. When hard on the brakes the front end of my bike was bouncing and clattering resulting in a feeling of no brakes.
Anyone know how I can resolve this issue and what is actually happening so I understand it?
I have only set the sag on my bike to 31mm front and 28mm rear. I'm around 80kg fully geared up. Haven't touched any other settings
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post #2 of 31 (permalink) Old 08-04-2014, 08:53 PM
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Sounds like your bottoming out on the fork.

Put a cable tie on the fork and see how much travel it goes; if it goes all the way to the bottom that means you're bottoming out.

Either add some fork oil, increase compression damping or you'll need a harder spring.

Or do this to put more weight towards the back while braking
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post #3 of 31 (permalink) Old 08-04-2014, 10:35 PM
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+1 for Rinon response. Exactly what you should do. Make sure your rebound isn't too much either


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post #4 of 31 (permalink) Old 08-04-2014, 11:23 PM
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You've set your sag numbers at 31mm front, i'm expecting you aren't bottoming out but YES first thing you should try is the zip tie on the fork trick.

Second thing is check your rebound. You might be too hard on the rebound so the valving is too slow at pushing back. If you aren't bottoming out your forks i would suggest softening the front rebound.

One other HUGE thing could be how you apply your brakes, if you spike them it doesn't matter what your rebound or preload or sag is at, you will reach the bottom of your forks and any bumps will be transferred into your arms and become very aggressive. Proper braking technique is to apply slowly and set the forks and squeeze the brake lever smoothly. Doing this (all in a quick and smooth motion) will allow your forks to set, then absorb the bumps as braking forces increase. Smooth is the key to being fast. Let us know what you discover next time on track.

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post #5 of 31 (permalink) Old 08-05-2014, 12:26 AM
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Also how bumpy is the track around the end of the braking zone?

in the video above, there is a join on the track near the end and a lot of people bottom out when they hit the bump and ended up having quite a hairy braking moment (can be seen on the other videos in my youtube channel)
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post #6 of 31 (permalink) Old 08-05-2014, 02:05 AM Thread Starter
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I already have a zip tie on and it it's not right at the bottom. Maybe a couple of cm up from bottom. Yes there were some bumps in the braking zone. I thought I was being quite steady on the brakes also not aggressive and grabbing them hard.
I might have to get someone who knows what they're doing to set them up for me as I don't have a clue and don't want to make them worse.
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post #7 of 31 (permalink) Old 08-05-2014, 02:43 AM
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keep in mind, the mechanical bottom on a 600RR is not the bottom of the actual inner tube. its about 1/2" off the bottom IIRC. Can someone clarify that for me? so if your zip tie is 1/2" off the base you could be bottoming out.

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post #8 of 31 (permalink) Old 08-05-2014, 07:37 AM Thread Starter
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Yeah I did read that somewhere too. Maybe on a guide on this forum somewhere?? Did feel like it was bottoming out and front wheel was bouncing up and down.
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post #9 of 31 (permalink) Old 08-05-2014, 05:35 PM
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You can zoom this picture to be quite large and should be able to see the front fork marking

The top of the yellow label on the front fork is the end of the fork travel. i.e. when the zip tie touched it = the fork bottoms out.

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post #10 of 31 (permalink) Old 08-06-2014, 11:58 AM Thread Starter
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Ah yeah then I'm definitely bottoming out. My zip tie is in exact position so I've been using all my travel even on the road.
I put all settings back to standard yesterday then had compression half a turn from full and rebound 1 and a half turns. I think that might be fine for track but a tad aggressive for the road so I put 1 turn from full and 2 and half turns on rebound. Still feels like it dives when braking hard and that it would bottom out on track.

Would adjusting preload improve anything?? That's still set at standard 5 turns from hard.
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post #11 of 31 (permalink) Old 08-06-2014, 01:20 PM
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First track day. Front end bounces on when braking

Probably gonna need different springs if that's the case, or different fork oil.


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post #12 of 31 (permalink) Old 08-06-2014, 02:18 PM Thread Starter
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Really?? I thought at 80kg I'd be perfect weight for a sportsbike so optimum setup wouldn't be hard to achieve. It's just gone over 12k miles so would of thought oil was spot on still.
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post #13 of 31 (permalink) Old 08-06-2014, 03:00 PM
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You're only halfway into your preload.

You can certainly add a few turns to help with bottoming
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post #14 of 31 (permalink) Old 08-06-2014, 03:07 PM Thread Starter
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Quote:
Originally Posted by wibbly View Post
You're only halfway into your preload.

You can certainly add a few turns to help with bottoming
Am I right in thinking that adding preload would increase ride height? So more compression and preload would theoretically stop the bottoming out.
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post #15 of 31 (permalink) Old 08-06-2014, 03:42 PM
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Kind of but not really. It will reduce static sag (how far the bike alone will compress the suspension). If you want to call that ride height I suppose you could but that's not the point. What it will do is decrease the overall travel of your front suspension under load.

The simplest way to think of it is that preload will change stroke length and compression and rebound damping adjust the rate of change of the suspension in compression and extension respectively.

Because these are dynamic systems, the way that load is applied to the suspension will change how much travel is used. Stiffer compression valving will reduce travel in high impulse loads (bumps etc) but very much less so in low impulse loads (long braking zones etc).

To get a setup that works for you isn't as simple as applying settings that you read on the internet (though many will offer you their input, its not that simple)

If I were you I would first add a couple turns of preload and monitor your total fork travel. After you have managed to use as much of the stroke as you can you can focus on setting your valving to tune out some of the characteristics that will cause you grief (chattering, excessive diving, limited traction mid corner, ugly tire wear etc)
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post #16 of 31 (permalink) Old 08-06-2014, 03:46 PM
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I should add that you want to use as much travel WITHOUT aggressively bottoming. Its not a sin to use the full travel of the fork. The way a fork will work at full travel is determined by the oil level in the fork. This will affect the stiffness of the fork at the bottom of the stroke. More fluid means a stiffer air spring, less fluid means a softer one.

But we aren't there yet. Focus on preload first.
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post #17 of 31 (permalink) Old 08-06-2014, 04:05 PM Thread Starter
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So what if by adding preload I don't get an ideal sag measurement say 30mm. Does it matter or is there a range of say 30-40mm of sag will work?
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post #18 of 31 (permalink) Old 08-06-2014, 04:11 PM
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Sag means very little. There is no 'ideal'. Get these internet numbers out of your head

Its just a simple baseline measurement to get an idea if your springs are suitable for your weight, they offer very little as to how the suspension will work for you in your specific circumstances.

How did you measure the sag? Did you fully unload the bike and get that initial measurement? Or are you only measuring the displacement of the suspension without and then with you on it?

Total sag and rider sag are two different things. So you may be referencing numbers that dont correspond to your measurements. At the end of the day, The best way to set your preload is to monitor total fork travel. Sag numbers are far less meaningful than people seem to think.
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post #19 of 31 (permalink) Old 08-06-2014, 04:27 PM Thread Starter
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I measured everything from lifting the bike off the ground then again when on the ground then again with me on in gear. I went from a youtube video called 2 clicks out. He seemed to know what he was talking about.
But I never touched the compression at all it was totally standard when on track at 2 1/2 turns from hard I think is standard iirc.
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post #20 of 31 (permalink) Old 08-06-2014, 04:34 PM
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Well you know where to start now.

And YouTube isn't going to set up your bike, there are way too many people who think that suspension is cut and dry and even more who try to push that theory. It isn't. You watched a YouTube video and your setup sucks. So maybe you need to try something else.

There's been a lot of good advice here. You aren't going to get the answer served on a platter. You'll have to ride the bike, make small adjustments, ride it some more, make more small adjustments and keep going from there.
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post #21 of 31 (permalink) Old 08-06-2014, 04:42 PM Thread Starter
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Yeah I have been out doing that as said. I'm surprised the frequent track goers haven't had this same issue as me. I know compression stops the dive at 1/2 a turn from hard but was too much for roads I thought. The more I talk to people and read about it I'm starting to get an idea of how the adjustments effect the bike. Thanks for the advice.
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post #22 of 31 (permalink) Old 08-07-2014, 06:59 AM
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If the bike handles well and the only issue is bottoming out at very hard braking then adding fork oil @ 5ml increment may help.

but this is the last step.

The general rule of adjustment steps is preload then rebound then compression then play around with fork oil level.

I can't comment on how to get the correct spring rate and/or valving; I've given that task to the suspension tech, they have some fancy formula to work it out based on bike, your weight and the total weight.
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post #23 of 31 (permalink) Old 08-07-2014, 10:00 AM
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Kev, you sound like a DIY'er who has a good idea of where to start but if you're doing track days usually there will be 1 or 2 vendors there that do this for a living. Paying 40 to 50 dollars to get your bike setup to its best potential in one day is worth it's weight in gold and saves a lot of frustration on trial and error. Just a thought.
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post #24 of 31 (permalink) Old 08-07-2014, 11:52 AM Thread Starter
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Thanks and yeah getting my suspension set up is on the to do list but I wanted to learn for myself which adjustments do what and what effects they have on the bike first. My friend just had his r1 setup by a guy and says it's transformed the bike but doesn't know anything about what he adjusted and why.
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post #25 of 31 (permalink) Old 08-07-2014, 09:41 PM
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Well, another way to learn these things if you're interested in doing so is just to talk to the suspension vendors at the track. They should be more than willing to talk you through all the adjustments they're making and why. A great crash course for you and a properly setup bike.
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post #26 of 31 (permalink) Old 08-08-2014, 03:28 PM
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Quote:
Originally Posted by roach954 View Post
Kev, you sound like a DIY'er who has a good idea of where to start but if you're doing track days usually there will be 1 or 2 vendors there that do this for a living. Paying 40 to 50 dollars to get your bike setup to its best potential in one day is worth it's weight in gold and saves a lot of frustration on trial and error. Just a thought.
I have been very happy doing this, and I'm a person who wants to basically learn everything about bikes. I leave it in their hands and just try to understand the underlying dynamics. It will be interesting, next TD I'm doing I'll be on a new aftermarket shock and redone forks that are both taller than stock. Seeing the suspension guy first thing fo sho.
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post #27 of 31 (permalink) Old 09-02-2014, 10:33 AM
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Just a little input...

I experienced the exact same thing you did my first few track days @ Hallett this year... As soon as I did MSR Cresson with Ridesmart, I had Roger setup my suspension for $40 and it was a completely different bike. I was bottoming out the front forks before he adjusted the suspension for me. Best/cheapest investment i've made so far. I'm not sure if the stock setup is that "soft" because i'm the second owner, but it's very different when you have it setup "stiffer" for the track...

-Starfish
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post #28 of 31 (permalink) Old 09-10-2014, 12:00 AM
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Originally Posted by DirtyStarfish31 View Post
Just a little input...

I experienced the exact same thing you did my first few track days @ Hallett this year... As soon as I did MSR Cresson with Ridesmart, I had Roger setup my suspension for $40 and it was a completely different bike. I was bottoming out the front forks before he adjusted the suspension for me. Best/cheapest investment i've made so far. I'm not sure if the stock setup is that "soft" because i'm the second owner, but it's very different when you have it setup "stiffer" for the track...

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post #29 of 31 (permalink) Old 09-15-2014, 03:12 AM Thread Starter
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I had my suspension setup last week and as said its handling awesome but haven't tried it on track yet. The guy Ian 'pixie' Patterson who set it up is a TT racer and has actually came 8th in the senior TT so he's an absolute legend.
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post #30 of 31 (permalink) Old 09-15-2014, 04:07 AM
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it sounds obvious that you're mechanically bottoming out your forks during hard braking, you also mentioned you haven't touched the compression damping on your forks, i assume teh forks are still stock internally so here's my suggestion, start with turning the compression adjusters to 1.5 turns from full hard & 1 turn on the rebound adjusters, that's where my baseline setup is for 600RR forks, if you still experience bouncing under hard braking you can increase compression damping by 1/4 turn but never go under 3/4 turn, for rebound anything under 1/2 turn means you have to revalve your forks.

hope this helps.


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