Help!! is all the bump steer normal
09-26-2002, 02:38 AM
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Help!! is all the bump steer normal
let's say for instence my car was perfect no play in the rack or bearing and it's aligned and everything, should I still have alittle bump steer or should it feel like my 97 honda civic where I could let go of the wheel no matter how un even the road or bumps and it would not pull to either side. can anyone tell me ?
DrJeremyb 84S
DrJeremyb 84S
09-26-2002, 03:08 AM
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Both of my 928s will follow bumps and gooves in the road a little bit if I were to take my hands off the wheel. How much they do it has varied depending on tires and tie rods. Both of my cars came w/ thier original tie rods, at 85k miles for the 82 and ~120k for the 84. The 84's were so badly worn that it was challanging to keep it in the lane on badly paved freeway stretches. New rods, cv boot, and an alignment later and its straight as an arrow.
09-26-2002, 10:04 AM
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A little clarification:
Bump steer - a condition where the wheels change direction with suspension travel. Caused by the steering rods not swinging the same arc as their attachment steering arm. Can be caused by lowering the car beyond the expectations of the designer.
Trolley-tracking or tram-lining - a condition where the wheels change direction with surface irregularities. Caused by wide tires, made worse by misalignment or looseness.
Wide tires are the root cause of trolley-tracking. Its a simple matter of leverage - the amount of tire that you have inside and outside of the steering center.
If you put very wide tires on the Honda, there would be more trolley-tracking. (Not as much as the 928, because the front-wheel drive cars normally have very little steering offset.)
If you visualize the front suspension from the front, and draw an imaginary line thru the ball joints, the point where that line hits the pavement is the steering center. Then visualize how much tire you have outside and inside of that point, and estimate the leverage that can pull the steering. That is the steering offset (not the same as the wheel offset).
Trolley-tracking can be influenced by tire width, wheel offset, tire pressures, suspension looseness, and alignment.
Bump steer - a condition where the wheels change direction with suspension travel. Caused by the steering rods not swinging the same arc as their attachment steering arm. Can be caused by lowering the car beyond the expectations of the designer.
Trolley-tracking or tram-lining - a condition where the wheels change direction with surface irregularities. Caused by wide tires, made worse by misalignment or looseness.
Wide tires are the root cause of trolley-tracking. Its a simple matter of leverage - the amount of tire that you have inside and outside of the steering center.
If you put very wide tires on the Honda, there would be more trolley-tracking. (Not as much as the 928, because the front-wheel drive cars normally have very little steering offset.)
If you visualize the front suspension from the front, and draw an imaginary line thru the ball joints, the point where that line hits the pavement is the steering center. Then visualize how much tire you have outside and inside of that point, and estimate the leverage that can pull the steering. That is the steering offset (not the same as the wheel offset).
Trolley-tracking can be influenced by tire width, wheel offset, tire pressures, suspension looseness, and alignment.
09-26-2002, 11:34 AM
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Great explantion Wally (we would never expect less from you <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> ). I had the awful symptoms of both "trolly tracking" and "bump steer" as I had wider tires and my 928 was lowered. I corrected most of the problems buy doing some minor tweeks to the suspension- like the ride height, four wheel alignment, and repair of s few failing suspension parts. I could not tell you which made the biggest contribution to correcting (or minimizing) those problems because I completed them all simultaneously but I can say with confidence that the problems seemed to almost disappear. <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />
09-26-2002, 01:28 PM
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Wally said:
Trolley-tracking can be influenced by tire width, wheel offset, tire pressures, suspension looseness, and alignment.
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One addition to this statement. I have found that if the alignment is out but everthing else is correct and then you do a proper alignment, you seem to feel more trolley-tracking.
This is caused by the effect that if the alignment is out, then the car has a numb feel. After the proper alignment, you can feel the road better so it is more sensitive to the trolley-tracking feel.
Trolley-tracking can be influenced by tire width, wheel offset, tire pressures, suspension looseness, and alignment.
--------------------
One addition to this statement. I have found that if the alignment is out but everthing else is correct and then you do a proper alignment, you seem to feel more trolley-tracking.
This is caused by the effect that if the alignment is out, then the car has a numb feel. After the proper alignment, you can feel the road better so it is more sensitive to the trolley-tracking feel.
