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Thread: Adjusting ride height - thoughts needed on methods

  1. #1
    Electron Lane's Avatar
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    Adjusting ride height - thoughts needed on methods

    I currently have Hoosier A4 tires on the car for track use. The 295-45-17 size I have in the rear appear to have raised the ride height by what looks like 3/4" to 1" over the preferred ride height as stated in the manual. Switching to my 275-40-17 Toyo R888 in the rear even raises it a bit more. Since the fronts are closer to the factory-sized tire for circumference/diameter, there hasn't been much change to ride height on the front end of the car so I'm mainly focusing on the rear for now.

    Brammo's owner's manual for the USA Atom 2 states the following: VEHICLE RIDE HEIGHT ADJUSTMENT "If the vehicle ride height must be adjusted, you must use the spring platform/perch on the shock body instead of the suspension pushrod. This is also the proper method for adjusting corner weighting during suspension set-up. Adjusting ride height with the pushrod will negatively affect your vehicle's suspension and bellcrank geometry."

    In the past, I've had problems with the rear suspension not having enough travel, especially under compression. I wrote about the details on the other forum here: http://www.atomclub.com/forum/index....html#msg210831 . At that time, I shortened my pushrods as much as possible by adjusting the rod ends inward while I lowered the bottom spring perch on the shock to increase compression travel. This worked extremely well and I couldn't be more pleased with the results.

    If I follow Brammo's instructions for adjusting the ride height, I would be undoing all of that effort and would likely be reducing the rear compression travel even worse than it was when I received the car from the factory. I do not want to do that, so at this point, I'm pondering why Brammo said it was bad to adjust the length of the pushrods, and really can't visualize how geometry would be negatively affected. If I shortened the pushrods, what changes is the angle relationship between the A-arms and the frame. The bellcrank at-rest position and angle would not change, and available compression travel on the shock would not change. Conversely, adjusting ride height by moving the bottom spring perch changes compression travel, at-rest bellcrank angle, rear suspension pre-load, AND the angle relationship between the A-arms and the frame. So that actually affects more components than shortening the pushrods would.

    If anyone can see something I'm not seeing would support Brammo's method, please let me know. The way it looks right now, I'm almost certain I'm going to go the shorter pushrod route. Since I currently have the rod ends screwed into my existing pushrods as far as I can, I'm going to have my local race fab shop make some new pushrods that are a bit shorter. I still have to do the math though to determine how much shorter. Since they're on an angle, I realize that pulling 1" out of them would not equal 1" of ride height (rod end adjustment being equal)...

    The shop has offered to do a quantity of these pushrods when they put mine together and the price should be pretty low as there isn't too much for parts and labor in them. They'd be Chromoly, powdercoated satin black, and the same diameter/tubing thickness as the factory pieces and take the same rod ends. If anyone else has potential interest, let me know and I'll figure the end cost with the shop based on quantity and will consider posting a group buy thread or something similar.

    Thanks,
    Lane
    Last edited by Lane; April 10, 2012 at 11:16 PM.
    Ariel Atom 2, Ecotec 300, owner since 2007. Drive, Detail, Improve, Repeat. Visit my website.

  2. #2
    Lepton
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    Quote Originally Posted by Lane View Post
    I currently have Hoosier A4 tires on the car for track use. The 295-45-17 size I have in the rear appear to have raised the ride height by what looks like 3/4" to 1" over the preferred ride height as stated in the manual. Switching to my 275-40-17 Toyo R888 in the rear even raises it a bit more. Since the fronts are closer to the factory-sized tire for circumference/diameter, there hasn't been much change to ride height on the front end of the car so I'm mainly focusing on the rear for now.
    I might shoot dp35 a PM. He's done a lot of work on dialing in the setup on his AA2 and is very fast.I don't know a lot about suspension setups, so I have a stupid question - is ride height the correct metric to use when using drastically different tire sizes? Wouldn't hub to a given reference point on the frame be a better metric that ignores tire diameter? One last thought - A4s are getting old enough that you might want to consider putting them out to pasture. What's the date code on your set? You'll be way faster on a new (or even used) set of A6s, but more importantly you'll be safer on the limit.
    2011 Ariel Atom Not Supercharged
    2006 Range Rover Sport Supercharged

  3. #3
    Electron Lane's Avatar
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    Quote Originally Posted by Payne View Post
    A4s are getting old enough that you might want to consider putting them out to pasture.
    Oops - meant to say A6. Must have Audi on my mind when I typed that.
    Ariel Atom 2, Ecotec 300, owner since 2007. Drive, Detail, Improve, Repeat. Visit my website.

  4. #4
    Proton Terry Kennedy's Avatar
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    Quote Originally Posted by Lane View Post
    If I follow Brammo's instructions for adjusting the ride height, I would be undoing all of that effort and would likely be reducing the rear compression travel even worse than it was when I received the car from the factory. I do not want to do that, so at this point, I'm pondering why Brammo said it was bad to adjust the length of the pushrods, and really can't visualize how geometry would be negatively affected. If I shortened the pushrods, what changes is the angle relationship between the A-arms and the frame. The bellcrank at-rest position and angle would not change, and available compression travel on the shock would not change. Conversely, adjusting ride height by moving the bottom spring perch changes compression travel, at-rest bellcrank angle, rear suspension pre-load, AND the angle relationship between the A-arms and the frame. So that actually affects more components than shortening the pushrods would.
    I seem to recall TMI being adamant that Brammo was wrong about this and ride height adjustment should be done with the pushrods. You could check with them to make sure I'm remembering correctly.

  5. #5
    Lepton Positron's Avatar
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    I've not had much luck with their ride heights. My assumption it was their poor attempt to recreate a corner weight position.

    I think your best bet is to get it corner weighted. My car was much more controllable and didn't seem to want to swap ends at the drop of a hat.

    Larger rear tires could possible help tranfer some needed weight to the front. A large piece of it is on the left rear.

    Corner weighting is a black magic unto itself with as many opinions as those doing it.
    AtomII #73 for sale, PM for details.

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  6. #6
    Electron Lane's Avatar
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    I have corner weighed the car without issue in the past with tire sizes close to stock, and will do so again with the newer sizes shortly. But that is not my concern at this time. It's the fact that the ride height is now significantly different than the reccommended spec and I would like to get that closer.
    Ariel Atom 2, Ecotec 300, owner since 2007. Drive, Detail, Improve, Repeat. Visit my website.

  7. #7
    Lepton Positron's Avatar
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    I think to raise it with tire size an then to lower will alter suspension geometry. I am of the option to retain suspension geometry over frame height to ground.

    But I reserve the right to be wrong.
    AtomII #73 for sale, PM for details.

    Turning money into smoke and noise since 2006.
    Member "I drove the Brammo mule with Tom S." club.


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