Scrub radius, and offset importance

Discussion in 'Chassis' started by Brian.G, Jan 6, 2011.

  1. sparrow Paid Member Paid Member

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    Blimey, at standard ride height that's about as good as it's going to get!!
    Will see what happens when I measure X.

    Thanks for all the hard work Dave.
     
  2. Truckinduc Forum Member

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    Im going to turn my brand new wheels on the lathe tomorrow to modify the back spacing. I hope I dont destroy them.

    They are 15 x 8.25" et 0. Im going to remove as much as I can from the hub.
     
  3. Hilux Forum Member

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    I`m sure you know what you are doing and its not a critique but I would have thought the wheels will have been stress tested as they are so how much do you know you can actually remove without them failing catastrophically?
     
  4. Truckinduc Forum Member

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    Well realistically I can only remove around 3mm from the hub mating surface. Its not even really worth it.

    Ive modified quite a few wheels before. I usually dont touch the spokes unless they are very thick. The hub though you can almost always remove material between the lugs as long as you have a nice radius on everything as well as a nice surface finish. If I was worried I could draw them up and run stress analysis on them.

    That being said I have some nissan titan offroad 17" wheels which Im planning on removeing around 3 to 4lbs from each wheel. The truck Ill be using them on only has half the gross weight that the wheels were intended for.
     
  5. Gazhatt Forum Member

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    Some excellent info here if a little bit over my head but I am trying[:s]

    My Mk2 is lowered on koni coilovers not stupid low- and runs mk3 vr hubs (more caster) and wishbones with 7*15 et35 with 195/50 tyres at the moment, Im guessing this set up is pretty similar to that of Sparrows kindly drawn by Daved unless the vr hubs and wishbones will alter things?

    Im trying to decide on what offset for new 17*8 wheels running 215/40 tyres, these should fit as the arches have been adjusted a little, a 225/45R17 on an et28 fitted but fouled the inner wing on full lock and was getting close to the spring platforms,pic:
    [​IMG]

    Using Sparrows drawing as a datum I believe the scrub radius will be increased by approx 3mm more ve by a 14mm increase in tyre radius, good? But if I reduced the offset to say 25 this would give a 7mm swing into +ve scrub radius, not good?

    In the real world is this going to have much effect or should I just run a 25et and push all the extra width out widening the track further?

    One thing I do notice is that at high speed, at the strip for example, when approaching peak torque at 7500rpm the car will want to snake a little, could the scrub radius have an effect on this? or could this be down to the characteristics of the quaife atb and unequal driveshaft lengths fighting each other? Could a plate diff improve this?

    Any thoughts much appreciated
    Gary
     
  6. Truckinduc Forum Member

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    Hey guys I have a few questions regarding front suspension. I'm currently designing new tubular control arms and a tubular subframe.

    The stock control arms are parallel to the ground when viewed from the side of the car. Obviously this effects the amount of dive and lift when the car accelerates and brakes. Being flat the car is setup very neutral from the factory. My pickup points will also be parallel to the ground from a side view to retain a neutral setup.

    This is the part I'm unsure about.

    When viewed from above the front control arm pivots are more toward the center while the rear pivots are wider. I'm guessing this is to maintain the caster settings. If the pivots were parallel then you would gain more caster as the front end compresses. The stock setup has the balljoint moving rearward under compression. My question is how important is this?

    My pickup points will have height adjustability so I can tune my camber gain under roll. Right now I'm just planning on different holes for the heim's. They will be on an arc with the center being the balljoint so the trackwidth wont change between adjustments.

    I hope this made some sense.
     
  7. Admin Guest

    Stuck. :thumbup:
     
  8. Nige

    Nige Paid Member Paid Member

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    Just bumping this very useful thread. Many thanks to the contributors who spent a lot of time and effort collating and sharing this information. I`m finding it very useful for my brake setup calculations :thumbup:
     
  9. bobby_ New Member

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    great thread
    thanks a lot of those people!!!
    i found so many answers ...... and they build new questions :)

    in a few months i will take a measurmen of my car.... couse in the moment ive build it like a Lego :)

    vw golf 2 ....
    mk2 king pin
    mk3 gti arms
    ..... camber plates (castor plates in my car)
    5,5 castor
    2,3 camber
    KPI ?
    scrub radius ?

    for now (4years).... i dont have any problems.... but....
     

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