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      05-05-2018, 03:05 PM   #1
Vetracr
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Tire Edge feathering

I have an E89 Z4 that I run on track days. I have a complete monoball front suspension, no bushing deflection. I run Zero front toe as measured by toe plates. I have had feathering on the outside edge of the passenger side front tire using two different brand of tires. Never on the driver side, only on the passenger side. It does not make sense to me. Slip angle for tires is same going left or right. Only thing I can think of is that BMW uses some form of anti ackerman or pro ackerman steering. Not likely but possible. Anyone have any ideas or suggestions??

Larry
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      05-05-2018, 04:10 PM   #2
impulsE89
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Feathering

There are a lot of variables. It probably has pro-ackerman for understeer. Maybe bad combination of caster and toe is happening. Could the bushings be shot? Maybe worn out from dirt?
Not a lot of track guys on here but you know where to look.
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      05-05-2018, 09:10 PM   #3
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Quote:
Originally Posted by impulsE89 View Post
There are a lot of variables. It probably has pro-ackerman for understeer. Maybe bad combination of caster and toe is happening. Could the bushings be shot? Maybe worn out from dirt?
Not a lot of track guys on here but you know where to look.
Looking at position of steering arms it looks like there is no apparent anti or pro ackerman. Suspension parts are all new so no wear. I think feathering may be due to Palm Beach Raceway layout with mostly high speed right turns. Ackerman steering is turning passenger wheel to a tighter radius causing feathering. Unloaded passenger side tire also has much less slip angle. Need to run again at Sebring to get more equal left and right turns. I added a little bit of toe in for this weeks session at PBIR to see if it helps.
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