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Thread: Scrub radius, and offset importance

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    Quote Originally Posted by smudge View Post
    The amount of adjustment you have at the top will not make much of a dent to the positive the extreme 0ET will create.
    True. Im going to add another half inch adjustment to it. Also my very low ride height and in turn the shorter strut length will help also.

    If I can tell any negitave effects of the wheels I may try to machine down the wheel mating face to get some more offset.

  2. #102
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    If you are after a wider track it's much better to use wider wishbones to create this because they move the KPI with the lower ball joint, a man of your talents and resources could easily make a pair up and then have sensible scrub, maybe even negative scrub and average ET wheels. It would save you having to further modify your top mounts that look great btw.

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    Quote Originally Posted by smudge View Post
    If you are after a wider track it's much better to use wider wishbones to create this because they move the KPI with the lower ball joint, a man of your talents and resources could easily make a pair up and then have sensible scrub, maybe even negative scrub and average ET wheels. It would save you having to further modify your top mounts that look great btw.
    Well I plan on making a tubular subframe and chromoly a arms. Ill be raising the motor up slightly so ill have to widen the track width slightly to keep the stock cv joints in their optimum range.

    what other benifits - drawbacks would moving the upper strut mounts inboard have?

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    I guess I could also make some offset ball joint spacers that move the balljoints outward while keeping the knuckle in the same position. Not sure how much I could gain before I start running into rotor clearance issues. I plan on using spherical bearigs instead of ball joints also.

    maybe thats what you meant in your last post and im just now understanding it.

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    Here you are Mike. All dimensions relative to the Ball Joint!

    NB. The change in the dimension of the Upright holes relative to the wheel bearing. This was where my initial measuring error was!



    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    That's just amazing.

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    x2

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    Fantastic detail Daved. Trully an epic acheivment that is very time consuming - well done.

    I may update my drawings with all this detail and then take some readings in a sweep of my setup to see how the scrub changes as the supenion compresses.

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    Quote Originally Posted by smudge View Post
    Fantastic detail Daved. Trully an epic acheivment that is very time consuming - well done.

    I may update my drawings with all this detail and then take some readings in a sweep of my setup to see how the scrub changes as the supenion compresses.
    Thanks Tom, LCT n' sparrow.

    Quite right Tom it is time consuming, especially when dimensional errors and machine failures require re-draws, but I want to do it both for myself and CGTI members like yourselves. I only wish than I could be 100% sure that the numbers are perfect. I am 99% sure, but if anyone wants to point out errors, then please do. I believe most on here realise by now what a pedant I am so must also realise that I will not be upset at all to get things spot on.

    Many times in the past I have been accused of being a perfectionist!

    Not true! I just try to get everything exactly right.


    (except speeling of course)
    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    Default 30mm wide track - #1

    Alex (sparrow)

    As requested I have sketched out the set-up with wishbones extended 30mm.

    If you can supply me with details of your wheels and tyres, IE:

    Dia, Rim Width and ET, plus a dynamic rolling radius, I'll draw the details in.

    If you can put your car on a really flat surface, and measure the height under the subframe at 'X', I'll be able to draw your exact set-up!

    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    Daved, any chance you could send me that design info on the mk2 front suspension? I really need some for a mk2/corrado project I'm working on and haven't been able to find it anywhere!

    Is it in some form of CAD?

    Cheers,

    Jon.
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    Quote Originally Posted by daved View Post
    Alex (sparrow)

    As requested I have sketched out the set-up with wishbones extended 30mm.

    If you can supply me with details of your wheels and tyres, IE:

    Dia, Rim Width and ET, plus a dynamic rolling radius, I'll draw the details in.

    If you can put your car on a really flat surface, and measure the height under the subframe at 'X', I'll be able to draw your exact set-up!
    Brilliant, thanks Dave.
    Wheel details are OZ Superleggera, 15" diameter, 7" wide, et 35.
    The car is in pieces now, so I don't have the dynamic rolling radius (or x), but I'll be using Toyo R888s which have a nominal diameter of 22.6".

    When the car's back together I'll measure x. Don't hold your breath. Unless you like the colour blue.

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    Quote Originally Posted by sparrow View Post
    Brilliant, thanks Dave.
    Wheel details are OZ Superleggera, 15" diameter, 7" wide, et 35.
    The car is in pieces now, so I don't have the dynamic rolling radius (or x), but I'll be using Toyo R888s which have a nominal diameter of 22.6".

    When the car's back together I'll measure x. Don't hold your breath. Unless you like the colour blue.
    Alex.

    What is the section and aspect ratio of the Toyos?

    There is a really good web page, if I can find it again, which works out dynamic radii for wheels using full data.

    Dave.
    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    Quote Originally Posted by jonlikescad View Post
    Daved, any chance you could send me that design info on the mk2 front suspension? I really need some for a mk2/corrado project I'm working on and haven't been able to find it anywhere!

    Is it in some form of CAD?

    Cheers,

    Jon.
    Jon.

    Read the posts below. Can't remember which?

    You are not the first to ask, and if I can I will.

    Dave.
    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    Epic drawings, thank you!

    Started revising my spreadsheet and hope it will allow changes to wishbone lengths, adjustable top mounts, ride height and camber too.

    Trying out changes in suspension travel, shows that for a 40mm change in travel up and down scrub can go +- 2mm.

    Sound on track (excuse the lame pun)
    If it ain't broke ... can we make it go any faster

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    Quote Originally Posted by daved View Post
    Alex.

    What is the section and aspect ratio of the Toyos?

    There is a really good web page, if I can find it again, which works out dynamic radii for wheels using full data.

    Dave.
    195/50/15s is what I ran before.

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    Quote Originally Posted by daved View Post
    There is a really good web page, if I can find it again, which works out dynamic radii for wheels using full data.
    This one?

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    Quote Originally Posted by sparrow View Post
    No.

    This one.

    http://bndtechsource.ucoz.com/index/...alculator/0-20
    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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    Quote Originally Posted by daved View Post

  22. #120
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    Hi Dave. ....... All the best, Jer (1/3)

    If it ain't broke I will re-design, manufacture parts, uprate, then perform preventative maintenance, so it never breaks!

    When it's really broke I will make it better. Much, much, much better

    "Facts alone are wanted" - Mr Gradgrind ('Hard Times' by Charles Dickens)

    "They do not know what they do not know" - Wagner: US Sniper Vietnam ('Out of Nowhere' by Martin Pegler)

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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.

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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.

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    Quote Originally Posted by Truckinduc View Post
    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.
    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?

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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.

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    Some excellent info here if a little bit over my head but I am trying

    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, I’m guessing this set up is pretty similar to that of Sparrow’s kindly drawn by Daved unless the vr hubs and wishbones will alter things?

    I’m 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:


    Using Sparrow’s 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

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