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Thread: Tracking

  1. #11
    Join Date
    Oct 2006
    Location
    Toton, Nottinghamshire
    Age
    45
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    811
    Quote Originally Posted by 1dayiwill View Post
    Here’s what Dax suggest.
    That was the page of the build manual I was thinking of. Saved me going up in the loft to find it

    Russ.
    Joint Area Rep - East Midlands Region
    1984 DAX Cobra
    Rover 3.5 V8 with Holley carburetor.

  2. #12
    Join Date
    Jan 2017
    Location
    Mansfield, Notts
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    58
    Quote Originally Posted by Outcast View Post
    I think you could be right Clive. The car drives beautifully and handles really well, I find that on ordinary roads there's no problem whatsoever, but if you get up to high speed on an undulating road or one that has quite an uneven surface, it tends to become very twitchy and feels too precise as it then only takes slight movement of the steering wheel to make it "move" unnecessarily. It has a Fiesta rack fitted, but haven't a clue what it's set to regarding geometry as I've never had it checked since I bought it.
    Cheers...NIge
    Sounds like you might be suffering from bump steer possibly?
    https://www.youtube.com/watch?v=LO07qmJ9zkk

  3. #13
    Join Date
    Oct 2005
    Location
    Cape Town, RSA
    Age
    55
    Posts
    127
    Why don't you let the suspension shop set everything as discussed, but have them dial in 0 deg for front toe.
    Then let them turn the spanner 1/4 turn on each tie rod (in) and get a new reading. Same for out. Now you know what difference a 1/4 turn makes.

    Drive. Try toe-in versus toes out. One of my customers likes 1/16" toe out in front because she lives in the mountains and prefers cornering versus straight line stability.

    On the bum steer issue:
    As your car is still on the chassis machine, let the mechanic raise the car by 30 mm from ride height and drop, while watching the change in toe.
    Last edited by dominik; 16-11-18 at 06:14 AM.
    Nothing is as it seems...

  4. #14
    Join Date
    Jul 2012
    Location
    NW England
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    368
    Quote Originally Posted by Legendary 427 View Post
    Sounds like you might be suffering from bump steer possibly?
    https://www.youtube.com/watch?v=LO07qmJ9zkk
    Interesting video. Like the way he's eliminated the outward movement of the wheel from the reading by reflecting back onto the bit that's moving. Interesting what he says about being better with toe out in bump due to the effects of body roll, not sure I completely agree though as I suspect the bump steer will alter when the rack is moved from central as the tie rod pivot point moved away from a line drawn betwen the upper and lower wishbone inner pivots.

  5. #15
    Join Date
    Dec 2008
    Location
    Exeter
    Posts
    124
    Quite few years ago a forum member recommended the following process for checking bump steer on Sumos. Attach a laser level to the front wheel. Loosen the large nuts under the spring so that the spring is not engaged. Jack up the wheel so its just off the ground and level the laser which was then pointed to a white card or nearby wall. Clamp the wheel to stop it rotating. Mark where the beam hits the card. Then keep jacking the wheel up and marking the track the beam follows. Ideally the beam should track as close to vertical a possible. In my case it changed through quite a large angle originally but after adjusting the steering rack height it varied from a very small toe out to a small toe in over the normal range of wheel movement. With the wheel jacked up to the limit the 'toe in' increased a lot more but in real world use the spring would probably be close to fully compressed and you would have other problems. Checking and adjusting the bump steer on my Sumo changed the juddering steering wheel, on a bumpy road, to a smooth more like a tin top feel. Note: to cover the full vertical range of wheel movement one would need to mount the laser beam on the front hub instead of the wheel but I found just using it on the wheel was sufficient as the toe out did not change much at the bottom end of the range of movement. Road use would usually range between normal ride height and bump up and recovery.

  6. #16
    Join Date
    Jul 2012
    Location
    NW England
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    368
    Quote Originally Posted by johnpen View Post
    Quite few years ago a forum member recommended the following process for checking bump steer on Sumos. Attach a laser level to the front wheel. Loosen the large nuts under the spring so that the spring is not engaged. Jack up the wheel so its just off the ground and level the laser which was then pointed to a white card or nearby wall. Clamp the wheel to stop it rotating. Mark where the beam hits the card. Then keep jacking the wheel up and marking the track the beam follows. Ideally the beam should track as close to vertical a possible. In my case it changed through quite a large angle originally but after adjusting the steering rack height it varied from a very small toe out to a small toe in over the normal range of wheel movement. With the wheel jacked up to the limit the 'toe in' increased a lot more but in real world use the spring would probably be close to fully compressed and you would have other problems. Checking and adjusting the bump steer on my Sumo changed the juddering steering wheel, on a bumpy road, to a smooth more like a tin top feel. Note: to cover the full vertical range of wheel movement one would need to mount the laser beam on the front hub instead of the wheel but I found just using it on the wheel was sufficient as the toe out did not change much at the bottom end of the range of movement. Road use would usually range between normal ride height and bump up and recovery.
    Did you point the laser forwards or sideways?

  7. #17
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    612
    If mount the laser pointer on the front wheel you would point it forwards and mark on a white card the points of travel of the suspension . Marking the points as the suspension travel through the non-compressed and compressed state . You should have a straight line or as close as possible which will show no bump steer.

  8. #18
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    368
    Quote Originally Posted by jon1d View Post
    If mount the laser pointer on the front wheel you would point it forwards and mark on a white card the points of travel of the suspension . Marking the points as the suspension travel through the non-compressed and compressed state . You should have a straight line or as close as possible which will show no bump steer.
    Unfortunatelyi that does not work. As the suspension moves from full droop to full bump the hub will move in and out (sideways) due to the arcs of the wishbones, if you simply piont the laser forwards you won't be able to determine if a sideways shift is due to changes in toe or changs in track, hence the reason for using a mirror in the video link above and reflecting the laser back to the target which is also moving in/out. when I did mine I pointed the laser sideways (my level has a prism to do this) so any movement was indicating change in toe.

  9. #19
    Join Date
    Dec 2008
    Location
    Exeter
    Posts
    124
    I started from the baseline of correct tracking. Plotting the movement from full droop to full compression passing through the existing ride height gave me a reference point to judge the effect on toe in/tracking. Moving the rack up to approach a vertical symmetry in the curve either side of the known ride height definitely can be easily seen to minimises the effects of bump steer. Repeating the same process for the opposite wheel completes the bump steer process. Finally just to make sure I had the tracking checked professionally to see if there had been any change due to my adjustments. Tracking was then -0 degrees 15 minutes. Re-tracked to 0 degrees which for a Sierra based Sumo is recommended and certainly I have had no odd wear on the tyres over some 15k miles.

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