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Bike Sitting Up Under Braking


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Now that I've added my 2 cents worth on the rising suspension whatsit, I'm looking for an easy answer as to why my bike wants to situp under front wheel braking into corners.

I had a 2000 model ZX6 that didn't do this but now riding the wife's 2002 ZX636, it nearly sends you onto the wrong side of the road, it wants to sit up so badly.

The bikes run identical fork oil and level and similar suspension settings.

The ZX6 runs a Michelin Pilot Sport 60 profile and the ZX636 runs a Pilot Sport 65 profile. Could it be the different tyres that is causing the difference do you think?

Thanks for any input

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Now that I've added my 2 cents worth on the rising suspension whatsit, I'm looking for an easy answer as to why my bike wants to situp under front wheel braking into corners.

I had a 2000 model ZX6 that didn't do this but now riding the wife's 2002 ZX636, it nearly sends you onto the wrong side of the road, it wants to sit up so badly.

The bikes run identical fork oil and level and similar suspension settings.

The ZX6 runs a Michelin Pilot Sport 60 profile and the ZX636 runs a Pilot Sport 65 profile. Could it be the different tyres that is causing the difference do you think?

Thanks for any input

The tyre profile will certain affect the steering but I'd expect a more direct response from the 65 and more push and resistance from a 60 which is more likely to make the bike run wide.The thing about a bike standing up on the brakes is it's usually the rider who instigates it and by that I don't mean you are to blame.I'm guessing you sense there isn't enough grip/steering to continue braking and turning in so one has to go and the uncomfortable feeling makes you choose slowing the bike rather than letting off the brakes and taking your chances with more entry speed.You mentioned the 636 is your wife's and it's running similar settings ,is that just for the forks or both ends?Your basic problem is either not enough weight transfer to the front or it's returning too quickly.I'm guessing here but have you by any chance lowered the rear on the 636 to make your wife more comfortable to reach the floor?If you haven't then try letting some preload off the forks(mabye 2-3mm)at a time and go for a test

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The bike is basically trying to counter-steer itself back up. I think the braking force causes the slowing front wheel to become an anchor point and the steering head behaves like a hinge with the momentum of the mass behind it applying force there that turns the wheel inward. The fork becomes a lever or moment arm with the fulcrum at the contact patch and outward force being applied at the steering head torquing the front wheel inward, hence, the bike comes up.

 

I'll try to edit that for clarity later.

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The tyre profile will certain affect the steering but I'd expect a more direct response from the 65 and more push and resistance from a 60 which is more likely to make the bike run wide.The thing about a bike standing up on the brakes is it's usually the rider who instigates it and by that I don't mean you are to blame.I'm guessing you sense there isn't enough grip/steering to continue braking and turning in so one has to go and the uncomfortable feeling makes you choose slowing the bike rather than letting off the brakes and taking your chances with more entry speed.You mentioned the 636 is your wife's and it's running similar settings ,is that just for the forks or both ends?Your basic problem is either not enough weight transfer to the front or it's returning too quickly.I'm guessing here but have you by any chance lowered the rear on the 636 to make your wife more comfortable to reach the floor?If you haven't then try letting some preload off the forks(mabye 2-3mm)at a time and go for a test

 

Thanks for your input Toly.

 

Just for the record, my ZX6 sold 2 weeks ago and the 636 is now mine. I've given the rear spring 2 turns tighter last night (from standard). I had previously played with front compression and rebound and also taken preload off but to no avail. I'm thinking that if it's not the tyre, then maybe it's a case of the forks running out of movement. I'm going to try maximum preload today and see how that goes.

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The bike is basically trying to counter-steer itself back up. I think the braking force causes the slowing front wheel to become an anchor point and the steering head behaves like a hinge with the momentum of the mass behind it applying force there that turns the wheel inward. The fork becomes a lever or moment arm with the fulcrum at the contact patch and outward force being applied at the steering head torquing the front wheel inward, hence, the bike comes up.

 

I'll try to edit that for clarity later.

I understand what you are saying (I think I do).

My old ZX6 was wonderfully neutral when braking into corners and I'm surprised that the 636 is totally the opposite. They are basically the same bike (in typical Kwaka fashion). I'm on the point of ditching a perfectly good 65 profile tyre in favour of the 60.

I wouldn't imagine rear tyres would affect things too much but I could see rear rebound having some sort of effect.

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This subject was discussed here a long while back and I seem to recall Keith weighing in and saying something to the effect that the bike is basically trying to counter-steer itself up, but, it was a long time ago. I may be mistaken. I will try to search for the thread when I have more time.

 

That said, I think a taller tire might amplify the effect.

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After playing with preloads, compression and rebounds, the thing that alleviated much of the problem was more compression on the forks.

 

From what I can gather, the bike was diving so forcibly when applying the front brake that the steering angle would alter considerably and all at once.

 

Am now happy once again.

 

Cheers for your input fellas

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