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  1. #1
    Join Date
    Sep 2015
    Location
    Berkshire
    Posts
    29

    Rear end geometry

    I had a rolling chassis delivered by AK. It's been on axle stands for the last few months while I have been doing bits and pieces.

    Today I put a set of ordinary XJ40 wheels on it, lowered it off the stands and pushed it out of the garage. Something was squeeking.

    It turned out to be the rear offside tyre (225 width) rubbing on the right hand roll hoop mount. On the left hand side (near side wheel) there was approx 10mm clearance between the tyre and the roll hoop mount. So the positioning of the rear wheels appears to be offset to the left of the chassis.

    Now I know that the wheels I have will not have the correct offsets, but I assume (maybe wrongly) that when I buy my wheels, both rears will have the same offsets. I also assume that the roll hoops are mounted equi-distant from the centre line of the car on both sides (maybe wrongly again!!), but if that is the case it suggests that the rear wheels are not eqi-distant from the centre line.

    I don't know whether that matters from a handling perspective or whether from an aesthetic perspective, the left hand wheel will fill more of the wheel arch that the right hand.

    Has anyone else found this issue??. Is it an issue?? Or is it standard for an AK and makes no difference to the finished car. Does anyone have any thoughts.??

    Many thanks

    Nigel


    I suppose one explanation is that the XJ40 wheels have different offsets front and rear (is that likely....???) and I've mixed them up. The offset maybe marked on the inside of the wheel. I'll check tomorrow.................
    Last edited by NigelB; 09-03-19 at 09:27 PM. Reason: Possible explanation
    AK Gen 3 with LS3. Build start January 2019

    www.flickr.com/photos/marlinbuild/

  2. #2
    Join Date
    May 2008
    Location
    Costa del Newcastle upon tyne
    Posts
    1,975
    I would show my naked rear end in Harrods window if the chassis was at fault from AK.... especialy it it was a rolling chassis purchase. So i would say that your donor wheels are the issue here.

    Try fitting the wheel backwards. So put the face of the wheel agaist the hub and this should offset the wheel enough to roll about. I did this myself many years ago, but i was Gen1 chassis.

  3. #3
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    390
    What happens if you swap the wheels side to side? If the gap and interference swaps with the wheels then they have different offsets and you don't have a problem.

  4. #4
    Join Date
    Jan 2014
    Location
    High Wycombe
    Age
    55
    Posts
    533
    Pick one!

    Attached Images Attached Images
    AK gen 1 delivered 05/05/17, on the road shortly!

  5. #5
    Join Date
    May 2008
    Location
    Costa del Newcastle upon tyne
    Posts
    1,975
    Middle looks good to me!! ๐Ÿ˜†

  6. #6
    Join Date
    Sep 2015
    Location
    Berkshire
    Posts
    29
    I've now swapped the wheels over left to right and the right hand wheel (offside) is still rubbing on the roll hoop mount.

    So I got the tape measure out and started measuring. The first thing I wanted to check was the rear wheel positions in relation to the chassis. So I measured between the chassis and brake disc on each side and the measurements were within 0.5mm of one another. Phew. That's good. So left / right symmetry is maintained. I then found the centre line of the chassis and measured to the outboard roll hoop mounts on each side. The offside mount turned out to be 10mm further from the centre line than the right one. So that would account for the discrepancy. And by eye, I can clearly see that right hand outboard roll hoop mount overhangs the edge of the chassis a lot more than the left hand outboard one. I then measured the distance between the two mounts for each roll hoop. Both measurements were the same. So what I have got is a RHS roll hoop that is 10mm further from the centre line than the LHS. I'm not sure why but I don't see it will matter a great deal and I'm relieved it is nothing handling or safety related.

    So it's good to be aware of it. Whether it is significant enough to be noticeable when the car is complete is a 'wait and see'................
    AK Gen 3 with LS3. Build start January 2019

    www.flickr.com/photos/marlinbuild/

  7. #7
    Join Date
    Apr 2004
    Location
    East Leake, Nottinghamshire, England.
    Age
    54
    Posts
    9,451
    You might find the discrepancy is due to the body not being cimetric. Which won't effect the geometry of the car.

  8. #8
    Join Date
    May 2008
    Location
    Costa del Newcastle upon tyne
    Posts
    1,975
    Did you try flipping your wheels round Nigel. As this will put the deeper offset of the wheel to the outside face as opposed to the internal face. It will/should stop it rubbing during the build process. It depends if you have alloys or steels i belive and what nuts you have, but as said it worked for me during my build.

    Tommy

    Ps looks like the Harrords window is safe then eh!! Lol

  9. #9
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    390
    Quote Originally Posted by TINKA View Post
    You might find the discrepancy is due to the body not being cimetric. Which won't effect the geometry of the car.
    I'll second that, I know mine (not AK) has differnces side to side and I've heared many are similar. Probably due to inaccuacies in the original car the body was splashed from.

  10. #10
    Join Date
    Jul 2014
    Location
    North Wales
    Posts
    239
    My body has a slight miss alignment
    It appears to be when the inner tub was bonded to the tub
    It now shows up with the gaps between wheels and arches on the rear being different one side to the other
    About 5mm
    Maybe the tub is slightly out, I bet itโ€™s still probably better than the original hand made ACs

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