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  1. #1
    Join Date
    Mar 2015
    West TN

    Default Questions/Thoughts on GM triangulated W suspension

    I'm building my first coil car ever. I have a software and engineering background and 10 years experience running leaf cars and I enjoy fabrication. I love building not buying. The class I am building for is the 2021 CRUSA Street Stock. This class allows re-engineering of the front upper control arms, corrections for bump & Ackerman, you can swap out nova lowers for metric lowers as well, and yeah pretty much whatever is needed to correct the front end on any of the frames. That's just the background not the question. Here's the question: When we tie a coil car down onto a bump spring on the RF is it just so that we can get more angle into the left rear lower to induce more roll steer? Is it roll steer at all costs even if it might hurt you on some tracks you travel to? Is there some other tangible benefit such as being able to run a softer left rear spring and have it stay loaded longer during the extension travel time period? Would you still do a soft LR spring but have a plan to avoid the roll steer on a hooked up track or a big oval with sweeping turns? Do we always want to run as short a bar as possible just to get more roll steer and is this why I don't see any of the GM frames with the 22 inch lowers such as the 68-72s or 73-77s or is it just the 112" wheelbase that has killed these cars off for a class like this? Is the 112" why the 1980's big metrics are not built? I believe a 3200lb car is fairly easy to build so I'm not thinking its just a frame weight saving issue alone.What's the deal with the mono-balls and heim joints on the rear bars? I see so much conflicting data. One person argues you MUST have the mono-balls or it binds up. Another argues that with all heims or mono-balls the rear-end is locked up even tighter because the geometry is imperfect and the rubber being pushed/pulled/squeezed it what lets it work. How do you get a free suspension that is completely bolted up (not putting loose undersize bolts) and allows for drive? Is it best to put a mono-ball or heim on one end and a factory rubber on the other as a way to achieve this balance?I realize this board has very limited interaction but looking at the list of users who still frequent it, I see some real heavy hitters and guys with serious design/engineering skill so if you don't mind I would sure appreciate some thought or even a PM if that is your style. And thank you.
    Last edited by SuperDuke; 11-20-2020 at 04:24 PM.

  2. #2


    In my own experience, I felt more hooked up with bushings than monoballs. Today , you basically go around in dynamic all the time (car up on LR , on RF , ) so why do you need all this free movement with heims for? I run Medeval and x Factor bushings.
    I never had luck with the soft lr spring deal, I went back to a standard. LR 225 - RR 150-175 setup.

  3. #3
    Join Date
    Jul 2007


    The big frame cars are wider and in dirt racing wider is not better, the longer wheel base also reacts much slower to changes of direction etc.

    I built a nova when I moved to iowa to race dirt, then a big chevelle then a metric like everyone else. The metric was like a go kart compared to the big chevelle, if not for everything I learned about jigging rearends on the big chevelle I would look back at those couple of years as wasted time.

  4. #4
    Join Date
    Dec 2012


    Keeping the rf pinned and the lr up in the air does at least two things: 1) this makes the car more consistent and it makes things more repeatable. This is due largely to the fact that the chassis does not move as much , and their is less weight transfer involved, also, on corner entry, the left rear does not move as much, so the rear steer does not change much at all. With an older setup, the rear steer changed alot when the car rolled into the corner. 2) this setup keeps the body up in the air, the spoiler is more effective, it also turns the entire upper deck into one giant spoiler. Do not under estimate the effects of aero on a dirt car. Aero starts to become a factor at around 45 mph.

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