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Discussion Starter · #1 ·
K2 \"pogoes/swirls\" under hard braking

Took my K2 for a afternoon ride and decided to test out some really hard braking from speeds @ +200 km/h and the bike pogoes or moves like a snake at the front like slow swirling movement.
I have seen the 600 supersport bikes do similar coming hard on the brakes before a certain corner at last race in Monza, but this feels like it is different.
I am going to check it out tomorrow, but could it be that i have different settings on each forkleg? I hardly doubt it.

The bike doesn't hop under hard braking and I tried coming onto the rear brak a tad before the front, but it didn't help settling the bike much.

It isn't like I am loosing control over it, but something tells me it shouldn't be like this.
My K5 does not behave likewise.

Any ideas what could cause this?

FYI I am running Ohlins suspension front/rear, newly balanced rims with Rennsport tires, and as the settings are now the bike handles very good.

basic setting front are:

- one turn less preload from stock Ohlins
- stiffened up the comp 2 clicks
- stiffened up the rebound 4 clicks

Rear:
- all settings are at stock Ohlins but stiffened the comp 2 clicks
 

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Re: K2 \"pogoes/swirls\" under hard braking

I'm not exactly sure what you mean by swirling or 'moving like a snake' especially since, in my mind, that would be contradictory to 'pogo-ing'. could you explain what the bike's doing better?

Have you just switched over to the renns, or is that what you've always run?
Have you ever done this braking exercise before for comparision purposes?
 

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Discussion Starter · #3 ·
Re: K2 unstable under hard braking

I'm not exactly sure what you mean by swirling or 'moving like a snake' especially since, in my mind, that would be contradictory to 'pogo-ing'. could you explain what the bike's doing better?

Have you just switched over to the renns, or is that what you've always run?
Have you ever done this braking exercise before for comparision purposes?
Sorry for the spelling/wording, my english not always that good


What I mean is I have this slalom unstable movement alsmost like a very very slow slapper without having the feeling of loosing control.

I just swithced to the Renns and I cannot recall having this feeling with my other tires, but then again I never tried as hard braking as today.

Could it be that the Renns do sacrifice a little stability in exhange for the enormously good grip the offer?
 

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Re: K2 unstable under hard braking

my initial thought would be the tires, though I don't have any significant experience on rennsports. it may just be a characteristic of the tire. working with tire pressures and suspension setting may help - but make sure you don't have any mechanical issues first.

what brand of tires were you running before?
 

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Discussion Starter · #5 ·
Re: K2 unstable under hard braking

my initial thought would be the tires, though I don't have any significant experience on rennsports. it may just be a characteristic of the tire. working with tire pressures and suspension setting may help - but make sure you don't have any mechanical issues first.

what brand of tires were you running before?
3 sets of M-1's, 1 set BT-012ss and the stockers BT-010's
 

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Re: K2 unstable under hard braking

I don't know man - since you never put your old tires through this test, you're kind of shooting in the dark looking for answers. I suppose if you were really curious, you could slap the old bridgestones or m-1s back on & see if you get the same results.

regardless, I'd first check your steering head play - make sure you don't have too much slop in the head bearings. If that pans out, see if dialing in more rebound up front helps. and make sure your tire pressures are within a reasonable range (not just the front - check the rear also).

Is there any possibility that the front tire is sliding? How's your chassis set up... have you increased the ride height in the rear; are your springs good for your weight?
 

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Re: K2 unstable under hard braking

LACK OF COMPRESSION DAMPING (FORK)

Front end dive while on the brakes becomes excessive.
The rear end of the motorcycle wants to "come around" when using the front brakes aggressively.
The front suspension "bottoms out" with a solid hit under heavy braking and after hitting bumps.
The front end has a mushy and semi-vague feeling--similar to lack of rebound damping.

*Not sure if that's what you were talking about...but I got it straight off the Sportrider website.

Here are the numbers for the stock settings, maybe you can compare it with your own to see if anything is drastically different....(disregard the rider sag, as this pertains to my weight)

forks set 6mm above clamp
90mm oil L01(10w est.)
fork spring rate .876kg/mm (85mm internal spacer)
fork external preload - setting 4 (3 lines showing)
fork comp - 10 clicks out
fork rebound - 6 clicks out
front rider sag (160 lb rider w/o gear) - L1 225, L2 182, L3 194 = 37mm
front free sag - L1 225, L2 197, L3 204 = 24.5mm

L01 oil (10w est.) and nitrogen
shock spring rate 7.7kg/mm
spring preload - 177mm
comp - 8 clicks out
rebound - 7 clicks out
rear rider sag (160 lb rider w/o gear) - L1 515, L2 490, L3 489 = 25.5mm
rear free sag - L1 515, L2 505, L3 507 = 9mm

*trail is approx 250mm
 

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Discussion Starter · #8 ·
Re: K2 unstable under hard braking

Thanks for your response


Leanangle,
I am running stock tirepressure and no increased rideheight. Springs are good for my weight.

Gixxervan,

I am running Ohlins forks and I don't know if the settings would apply for me. I have learned that the Ohlins are supersensitive to adjustments.

I highly doubt that I am running too little comp, cause the bike handles well under all other circumstances.............and actually I stiffened up the rebound quite a bit just before yesterdays ride.
However I'm going to try out your ideas today and I'll let you all know.
 

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Re: K2 unstable under hard braking

Thanks for your response


Leanangle,
I am running stock tirepressure and no increased rideheight. Springs are good for my weight.

.
What do you mean by Stock Tire Pressure...?

Rennsports are to be run...31 front, and 29 rear...those are cold tire pressures..
 

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Discussion Starter · #10 ·
Re: K2 unstable under hard braking

Thanks for your response


Leanangle,
I am running stock tirepressure and no increased rideheight. Springs are good for my weight.

.
What do you mean by Stock Tire Pressure...?

Rennsports are to be run...31 front, and 29 rear...those are cold tire pressures..
From Metzeler website:

Front 120/70ZR17TL(58W) RENSPT - 2.50 BAR = 36 psi
Rear 190/50ZR17TL(73W) RENSPT - 2.90 BAR = 42 psi

I think you mean what pressure they should be run at the track right?

I agree those tires are suitable for lower pressure than the recommended, but they give me plenty of grip at "stock" pressure for street riding.

In any case thanks for those numbers Hammer

I'll try them out and they should make for quite a diffrence in grip I would assume.

 

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Re: K2 unstable under hard braking

Bro, the pressures I posted are for the Rennsport DOT race tires, they are almost the same as the Pirelli Supercorsa's, which also use the same pressure as the Rennsports do...I think maybe you have to much air in them..???
 

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Discussion Starter · #12 ·
Re: K2 unstable under hard braking

Bro, the pressures I posted are for the Rennsport DOT race tires, they are almost the same as the Pirelli Supercorsa's, which also use the same pressure as the Rennsports do...I think maybe you have to much air in them..???
..............maybe exept that I do not have the DOT race tires


...........btw you say 31 front and 29 rear.

More pressure up front? Is that correct?
 

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Re: K2 unstable under hard braking

there are rennsport RACE tires, and rennsport STREET compounds. same with the supercorsas. I'm pretty sure comeback's running the street versions, hammer - not the race.

btw - comeback, back in the day I ran the supercorsa street tires (which were excellent)... unless you're riding 2-up, 42 is a bit much in the back. I don't think it has anything to do with your problems, but may help a bit with grip. 36/36 might work better.
 

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Discussion Starter · #14 ·
Re: K2 unstable under hard braking

there are rennsport RACE tires, and rennsport STREET compounds. same with the supercorsas. I'm pretty sure comeback's running the street versions, hammer - not the race.

btw - comeback, back in the day I ran the supercorsa street tires (which were excellent)... unless you're riding 2-up, 42 is a bit much in the back. I don't think it has anything to do with your problems, but may help a bit with grip. 36/36 might work better.
Yup street compound it is.

And now to my problem..and this is almost a little funny if not embarrasing.

I checked all my settings before todays ride and found that the right forkleg had 3 turns less preload than left......................let the flaming begin

I was like WTF...how come I didn't notice this when riding the bike through the very bumpy twisties here. Still puzzles me that one
Seriously the bike was just fine yesterday besides this weaving thing at the front....believe me or not.

I had a look at the rear end, actually I inspected the whole bike and when lubing the chain I found the rear brake was dragging heavily. It turns out that the spring on the brakelever (Harris rear sets using OEM spring) is not strong enough to bring back the lever to resting position and therefore were still pushing on the mc. Fixing the lever in a more lower position fixed that.

Anyway, I dialled in the correct sag (preload) and the other settings and to no surprise the weaving effect is gone. Feels fine now, only some normal weaving when the rear is just skidding over the asfalt.

No wonder I had some moments yesterday, with an uneven preload and a rear brake that was dragging quite a lot .

I also set the pressure to 32 front and 36 rear which seems to be good for the tires. Could feel the increased grip, though not very noticable. I think I'll settle for a bit higher.

Again thanks for beeing with me on this one guys.

 

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Re: K2 unstable under hard braking

That's awesome, comeback!


Now, could you PLEASE do me a favor - 'cuz I <u>have to know</u>....

change the preload back to it being the way it was - all hoaky - and do your hard-braking drills. I'm VERY curious to see if your problem was caused by the rear brake dragging or the forks. I'm thinking that the problem won't reappear by dialing in different preload settings up front.

If I had to guess, I'd think that the fork preload actually had very little to do with it... the rear brake sounds like the culprit. Usually, your rear end will want to run up the front under hard braking (as it's doing now). But if it was dragging - I'm thinking this is what caused the front end to misbehave... alot like what happens to the front when you get a rear tire flat.

could you PLEASE, PLEASE, PLEASE run this little experiment for me?
 

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Discussion Starter · #16 ·
Re: K2 unstable under hard braking

That's awesome, comeback!


Now, could you PLEASE do me a favor - 'cuz I <u>have to know</u>....

change the preload back to it being the way it was - all hoaky - and do your hard-braking drills. I'm VERY curious to see if your problem was caused by the rear brake dragging or the forks. I'm thinking that the problem won't reappear by dialing in different preload settings up front.

If I had to guess, I'd think that the fork preload actually had very little to do with it... the rear brake sounds like the culprit. Usually, your rear end will want to run up the front under hard braking (as it's doing now). But if it was dragging - I'm thinking this is what caused the front end to misbehave... alot like what happens to the front when you get a rear tire flat.

could you PLEASE, PLEASE, PLEASE run this little experiment for me?
Sure thing

I'll see if I can do it tomorrow. I'm off to Busan today with the K5 to put on some Pilot Powers. I'm in Korea and you have to go 120 km's to get to nearest motorcycle tire dealer...........can you believe that


Anyway I agree with you that the rear wheel dragging is probably what caused it, because I just can figure out why I didn't feel the "offset preload" during other circumstances.

I'll keep you posted.


 
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