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Suspension And Chicanes Question


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Hi all,

 

I ride a ZX6R. At my last track day, a suspension guy suggested to me that we add some preload in the front, to make it easier to flick the bike from side to side in a quick transition. He observed that my bike was low in front during the first turn and transitioning slowly to the second turn. He added a couple of turns of preload, and lo and behold, it was in fact MUCH easier and faster to flick the bike from one side to the other.

 

I'm not quite clear on WHY this helped. My normal thinking is that when the front suspension is compressed, the bike is easier and quicker to turn - but in this case, when going quickly from one side to the other, Suspension Guy said it was diving too much and therefore had to come UP and over, which was slow. I'd love a little help in understanding this better, if anyone has a more detailed explanation.

 

Incidentally, we tried another couple of turns of preload and OMG the front was suddenly really bouncy and now I have a whole new appreciation for the term "tankslapper". So needless to say those extra two turns came back out. Surprisingly, I never really noticed a difference in the intitial turn-in rate - I though more preload would make the bike a little harder/slower to turn.

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A mini reply: if the front suspension moves less, that would make a more solid pivot (with less preload),wouldn't that make it easier to turn?

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A mini reply: if the front suspension moves less, that would make a more solid pivot (with less preload),wouldn't that make it easier to turn?

 

Yes - but I guess it had not occurred to me that the bike front suspension would move during a hard left-right transition. Wouldn't it just stay compressed?

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Incidentally, we tried another couple of turns of preload and OMG the front was suddenly really bouncy and now I have a whole new appreciation for the term "tankslapper". So needless to say those extra two turns came back out. Surprisingly, I never really noticed a difference in the intitial turn-in rate - I though more preload would make the bike a little harder/slower to turn.

 

The reason the bike became bouncy here, is probably because there wasn't enough rebound and compression damping to control the return of the spring up and down as you transitioned across the bike. Certainly having a couple of turns more pre-load would change the height of the front a little, (though not enormously), and would typically make the steering slightly slower, but I think Cobie has covered that off for you?

 

Certainly there is much improvement to be had with a good suspension setup. Was your bike running standard settings for example? Or had you had it been tweaked previously?

 

Bullet

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A mini reply: if the front suspension moves less, that would make a more solid pivot (with less preload),wouldn't that make it easier to turn?

 

Yes - but I guess it had not occurred to me that the bike front suspension would move during a hard left-right transition. Wouldn't it just stay compressed?

 

What state is the suspension in midway through a turn Hotfoot? What position is the suspension in when the bike is stood upright (say going in a straight line)?

 

Bullet

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A mini reply: if the front suspension moves less, that would make a more solid pivot (with less preload),wouldn't that make it easier to turn?

 

Yes - but I guess it had not occurred to me that the bike front suspension would move during a hard left-right transition. Wouldn't it just stay compressed?

 

What state is the suspension in midway through a turn Hotfoot? What position is the suspension in when the bike is stood upright (say going in a straight line)?

 

Bullet

 

This might get long, sorry... To answer your prior question, the bike was set up by In House suspension, when they did the Ohlins internals on the front, and it has an Elka rear shock. Will Eikenberry from CSS has tweaked it as well, and the bike is set a bit higher in the back than stock, per Will's recommendation. It is set up for me, but we were doing a little fine tuning with it and tweaked the pre-load based on Suspension Guy's observation that my transitions through a particular tight chicane were pretty slow. The change in preload (two turns) made a dramatic difference, the transition was way easier and quicker. We did go on to adjust compression and rebound to get rid of the bouncing. When we tried adding more preload the bike got unstable under acceleration, nasty headshake, so we went back to where it was. I can give you exact sag setting measurements as taken that day if that would be useful.

 

Not sure if you are asking a general question above about how it should be, or about how mine specifically is behaving - but I'll answer about mine. The suspension midway through a sweeping turn is nicely mid range and the bike handles great. I am running a zip tie in front and under the hardest braking or cornering it goes to about 1" above the bottom. In a straight line, how it sits in the front depends on throttle - when WFO, it feels like it's up pretty high and under braking and entering the chicane Suspension Guy is telling me it dives noticeably, which is what he was trying to fix with preload. I did notice with a LOT of preload (2 more turns)the bike felt more balanced and did not dive under braking, but I preferred the braking dive over the acceleration headshake!

 

In all other areas of the track the bike handles very well, and in fact I didn't KNOW there was a problem in the transitions, until we changed it and it got so much easier! So I guess I'm confused about what happens in a quick chicane - this one is a left-right and here is what I do: I brake hard with three downshifts coming in, release the brake as I make the left flick, then flick it back to the right as quickly as I can, then roll on the gas. I am off the throttle and off the brake between the turns.

 

So, under those conditions, does the bike spring back up in between turns? Is it supposed to? Or wouldn't it just stay compressed? If you added a ton of rebound damping, would it stay down, and if so, would that make it easier to turn, or harder? Presumably with more preload added the bike doesn't dive as far in front, but doesn't having it down in the front normally make it EASIER to turn? Maybe I am missing something obvious. I guess I'd like to see a graph of, or close-up video of, a front shock through a chicane to see what it does.

 

I hope you can make this more clear to me, it bothers me not to understand it.

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Hotfoot--we talked a little about this on the phone, and an area I mentioned but didn't talk about more later is: how does the bike handle in the fast turns? What speed is this section/2 turns? And is this the only turn you are trying to improve?

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