BUMP STEER AND AFTERMARKET WHEELS. | FerrariChat

BUMP STEER AND AFTERMARKET WHEELS.

Discussion in '308/328' started by Skindiver, Dec 7, 2013.

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  1. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
    Full Name:
    Greg
    Hi.

    Can anyone say under which conditions with aftermarket wheels
    is one most likely to get bump steer ?
    I understand bump steer to be felt by the steering wheel twisting
    by itself in your hands as you drive over uneven surfaces. The car feels
    twitchy and unplanted and wanders on the road.

    Would wider wheels contribute because they are simply wider -besides tramlining-
    or does it depend where they are wider. i.e. increasing the track ?
    What of offset ? What is offset actually ?

    Do wider aftermarket wheels use the same wheel alignment numbers
    as the stock wheels ?

    Thanks
    Greg
     
  2. hardtop

    hardtop F1 World Champ

    Jan 31, 2002
    11,293
    Colorado
    Full Name:
    Dave
    Wider tires in the front will cause more bump steer and wandering on the road surface. If the wheel/tire combo is also heavier, you will feel more bounce from the wheels as well. This, I know from experience. You may get a little more ultimate grip from wider tires but there are tradeoffs. There is so much body roll in stock 308/328 suspensions, you will find there is little benefit in handling anyway.

    Dave
     
  3. ztarum

    ztarum Formula 3

    Mar 30, 2008
    1,302
    South Jersey, USA
    I may be off base here, but I thought that bump steer usually occurs when a car's ride height has been altered significantly such that the suspension geometry is no longer as designed and travel up and down results in a change in steering input even if the position of the steering wheel does not change.

    If the wheel outside diameter does not change, then there would be no more or less bump steer than before. That said, there would be more steering feedback for irregularities in the road, but I don't think that is technically bump steer.
     
  4. GordonC

    GordonC F1 Rookie
    Owner Rossa Subscribed

    Aug 28, 2005
    4,158
    Calgary, AB, Canada
    Full Name:
    Gordon
    Correct - bump steer occurs when the suspension geometry is such that when a front wheel hits a bump, the upward motion of the wheel causes the steering to turn the orientation of the wheel in one direction.

    Properly designed suspension and steering geometry requires that the steering angle of a wheel does not change noticeably as the wheel moves up and down in normal travel. A poorly designed suspension, or altered factory suspension by lowering, can result in bump steer with normal movement of the wheels over bumps.

    Changing offset of the wheels can affect bump steer feel if there is a bit of bump steer to start with. Tugging and pulling of the steering wheel as you drive is not bump steer, it's more commonly referred to as tramlining, where the tires have a greater tendency to follow imperfections in the road surface. Changing offset, or changing to lower profile tires or wider tires, will usually increase tramlining.
     

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