Wobble at 250Km/h

[Zug]

I went to The Ridge Motorsports Park this weekend, had a blast except for one thing:

Just about every time I went down the straight at about 250Km/h or so, when I changed into 5th gear the front would wobble.

I asked the tire guy there adjusted the rear spring, which helped a little.

Info:
Stock suspension. Had the sag set before I went. I am 215 and 6'

Any suggstions?

[usrodeo4]

Mine has the factory settings and is rock solid at 182 mph (293 kmh)...I am 5'7" and weigh 140 lbs

[Zug]

Originally Posted by usrodeo4

Mine has the factory settings and is rock solid at 182 mph (293 kmh)...I am 5'7" and weigh 140 lbs

That is great for you, does not really help me at all......But glad you don't have the problem.

[Alterego]

What tires and presure? And are you talking fear of tank slapper or just unstablitiy?

[Zug]

Originally Posted by Alterego

What tires and presure? And are you talking fear of tank slapper or just unstablitiy?

Running Pirelli Diablo Rosso Corsa. Had the tire guy check the pressure as soon as I got off the track, I think it was 34 in the back and 32 in the rear.

I had it at 28 in the rear and 30 in the front COLD.

I am running a 180 in the back instead of the 190

No it was not close to a tank slapper just a bit of a wobble.

[Alterego]

Not sure why running a 180 in rear??, its smaller circumference will likely load the front differently especialy at high speed under full power front becomes light. My guess is the 180 tire is the problem.

If not that check steering head nuts for proper torque, also replace damper with ohlins.

QUOTE=Zug;132033]Running Pirelli Diablo Rosso Corsa. Had the tire guy check the pressure as soon as I got off the track, I think it was 34 in the back and 32 in the rear.

I had it at 28 in the rear and 30 in the front COLD.

I am running a 180 in the back instead of the 190

No it was not close to a tank slapper just a bit of a wobble.[/QUOTE]

[MilleR Time]

Originally Posted by Alterego

Not sure why running a 180 in rear??, its smaller circumference will likely load the front differently especialy at high speed under full power front becomes light. My guess is the 180 tire is the problem.

I don't know why this would have anything to do with it, and I would have to respectfully disagree. I've switched down to 180's on all bikes I've owned and will likely do so on the S1k as well.

I think your tire pressure was too low, personally. Typically in my experience I've found that high speed wobbles are a result of the tire deforming at high speeds, but being low on pressure the bike wobbles from side to side as the "stickier," sides basically pitch back and forth when they contact the ground. At those speeds they shouldn't be. Try stepping up to maybe a few psi front rear and see if your luck changes. It's much like the wobbles when you're doing high speed wheelies. Especially on the stickier tire with the even softer and larger super-sticky compounds than pure road tires.

Try letting the TC do your 'hooking up,' for you if things get feisty. I've not had my S1k on track yet, but I've gotten on the throttle pretty hard, pretty early in the corner on the street with much less grip and have had it hold pretty good on the stock tire at 36-38psi.

FWIW I'm 6'2 and 225ish, mine has no wobble up to 180.

[Alterego]

I'm sure that many people go from a 190 to a 180 without any problems.
Also, I know that when making changes like that you need to go thru and set up the bike to handle that change.

What specificaly do you gain from this? Not sure here.
Some might say the contact patch is larger?? Some say smaller?
Some might say the profile of the tire will changes regardless of tire pressure??
Some say the tire is smaller lighter faster??

Several tire guys I know advise to use tire that the rim width was designed for for optimal performance.

His specific problem indicates all he did was go from 190 to a 180 rear, sure he should try different things to try and figure out what works best. Why go to a 180 tire in the first place?

FWIW 165 lbs, 5'9'' Busa wobbled at 195mph lowered tire pressure, 210+, no wobble.

Originally Posted by MilleR Time

I don't know why this would have anything to do with it, and I would have to respectfully disagree. I've switched down to 180's on all bikes I've owned and will likely do so on the S1k as well.

I think your tire pressure was too low, personally. Typically in my experience I've found that high speed wobbles are a result of the tire deforming at high speeds, but being low on pressure the bike wobbles from side to side as the "stickier," sides basically pitch back and forth when they contact the ground. At those speeds they shouldn't be. Try stepping up to maybe a few psi front rear and see if your luck changes. It's much like the wobbles when you're doing high speed wheelies. Especially on the stickier tire with the even softer and larger super-sticky compounds than pure road tires.

Try letting the TC do your 'hooking up,' for you if things get feisty. I've not had my S1k on track yet, but I've gotten on the throttle pretty hard, pretty early in the corner on the street with much less grip and have had it hold pretty good on the stock tire at 36-38psi.

FWIW I'm 6'2 and 225ish, mine has no wobble up to 180.

[DanQ]

What is happening when you shift to 5th gear? How aggressively are you turning the throttle? How firmly are you gripping the bars?

Before I'd consider buying parts, I'd inventory what is happening technique-wise. A lot of times we're doing something to upset the machine, more than the machine doing something to upset us. Overly simplified, but with proper baseline suspension setup and a careful watch on riding principles we can avoid wobble and front end shakes more often than not.

[Stang10189]

For the guy that said tire pressure was to low, are u talking about track pressure? If so i would have to disagree with you I actually believe his tire pressure was too high. all tire brands have a different pressure for the track but I have noticed with the conti that a lower pressure 28 front 26 pack is a good starting point. if you are excelerating hard in fifth gear and gripping the bars tightly you might be causing it yourself the front tire will barely be touching the surface of the track well under hard acceleration . as for the 180 to each his own I guess