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Thread: Tarmac Rally Stratos Build begins

  1. #221
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    Re: Tarmac Rally Stratos Build begins

    Quote Originally Posted by sean999r View Post
    Good video, Porsche 911's similar weight distribution typically have rear RC 12-15" above ground.

    Really, That sounds very high?


    Quote Originally Posted by rutthenut View Post
    Interesting video.


    For the rear wishbones, do you have alternative inner mounts?


    One thing to watch when setting up the rear suspension is to ensure you still have enough clearance for plunge on the driveshaft/CV joints. Playing with camber of wishbone angle can affect that. Though given your other attention to detail, I doubt you would have issues with that.


    The short wheelbase certainly contributes to fore-and-aft weight transfer, and the strut-type rear means camber change happens in roll, so nothing is ever ideal. The high C-of-G with the V6 doesn't help either, can certainly feel that weight sitting just behind your shoulders

    Yea Rear Wishbone Inner Mounts are a nolathane Bush from a Holden Commodore Pan Hard Rod, Its just a good sized bush, easy to get, used them for a long time on the Alfa


    All good on the plunge of the driveshaft, but good point


    Yea the Short Wheelbase definitely makes the vehicle far more sensitive to this sort of stuff, and as you say there are a lot of compromises with Strut Type suspension, Roll Centre Migration is a big issue, particularly with such short bottom arms

  2. #222

    Re: Tarmac Rally Stratos Build begins

    Quote Originally Posted by ByrneEngineering View Post
    Yea Rear Wishbone Inner Mounts are a nolathane Bush from a Holden Commodore Pan Hard Rod, Its just a good sized bush, easy to get, used them for a long time on the Alfa
    Sorry, I meant to ask if you had alternative mounting points on the chassis.
    My car, which I think is a later one, has two points for the inner wishbone, and for the long rear track control arm.

    So rather than extend the hub carrier downwards, can choose higher or lower inner mounting point for the wishbone to change the angle.

    Also, mine has spherical joints on the chassis end, with some hard poly-style bushes on the outer, fwiw.
    Did have to replace some recently as there was some slight play and it allowed a bit of rear-wheel steer, with angles changing under throttle and brakes, which is not ideal

  3. #223
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    Re: Tarmac Rally Stratos Build begins

    Yea my chassis mounting points are in the same spot, I have made the rear mount removable, it was an attempt to get more camber adjustment, but limited by drive shaft length. My first idea was to move that point up, as you suggest, but quickly run into the drive shaft CV

  4. #224
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    Re: Tarmac Rally Stratos Build begins

    Thanks for all your great videos. This one is especially excellent. They are very helpful in getting the Hawk running.


    If only we could fabricate longer driveshafts, we could use longer lower arms to reduce the detrimental geometry change itself.


    If we can make it into a Group 4 fender, we can extend it by about 60mm on each side.


    Does Hawk have any extended lower arms for Group 4 fenders as a retrofit part? Maybe I just don't know.


    I'm sure you could make a lower arm with a beer in your hand. ��


    Wishing you all the best for the future!

  5. #225
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    Re: Tarmac Rally Stratos Build begins

    Cheers mate, glad the vids are useful to you.

    Yea longer arms would be great, I've made new bottom arms and got them as long as I could, longer than the original Hawk, The limiting factor for me was the Wheel offset, brake calliper and disc i'm running, rather than the driveshafts as I've got some custom ones

  6. #226

    Re: Tarmac Rally Stratos Build begins

    Quote Originally Posted by tommy View Post
    If only we could fabricate longer driveshafts, we could use longer lower arms to reduce the detrimental geometry change itself.

    Does Hawk have any extended lower arms for Group 4 fenders as a retrofit part? Maybe I just don't know.
    Moving the hub carrier out into a wider wheelarch wouldn't be a great solution, especially when considering this is a strut-type suspension setup. Smaller changes possible with some rework, but hard to quantify the returns.

    Hawk have made some chassis with the lower rails closer together around the engine bay in the past, but only as a special for a Ferrari-engined kit. That allowed for longer wishbones (and driveshafts), with inner pivot point closer to the CV joint of the driveshaft which reduces plunge as shaft and wishbone nearer to being parallel to each other.

    That's definitely not a retrofit part and would be a lot of work, with less scope under and around the Alfa sump to get a lot of benefit.

    In most cases, drivers would never be able to tell the difference. With 'less than ideal' suspension geometry, the Stratos replica has better handling than many (most) drivers are capable of using. And even with changes to improve the theoretical behaviour of the suspension angles, the character of the car itself will - and should - remain as something that can change direction quickly and rapidly. It was designed for rallying, which required low polar moments of inertia and great responsiveness. It's not supposed to be an understeer-heavy fwd-style chassis designed to save drivers from themselves...

    That's not to say making changes won't be worthwhile and all kudos to Colin for working this stuff out and applying great engineering to modify things in his desire to improve the car to his liking and for his needs.

    (After all, it may be a twitchy car, but getting that more predictable and controllable at the limit has to be a good target)

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