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Thread: Autocrossing a Mirage

  1. #21
    Administrator Daox's Avatar
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    Sounds like a good idea.

    How do the springs get installed? Do they have some sleeve that keeps them concentric with the other spring?


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.5 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.8 mpg (Imp)


  2. #22
    Still Plays With Cars Loren's Avatar
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    Yeah, they make little adapter/spacer sleeves for that. They just fit between the two springs to keep them centered on each other.
    Simplify and add lightness.

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  4. #23
    Administrator Daox's Avatar
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    Have you tried out the tender springs yet?
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.5 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.8 mpg (Imp)


  5. #24
    Still Plays With Cars Loren's Avatar
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    Indeed, I have!

    So, the league of minions has been keeping an eye on my car lately (that's a good thing), and some of them are photographers. That means I have both anecdotal and photographic evidence of most of the goofy things my car does. They didn't catch the "oh s#it" moment on 12/29 where my co-driver got 2 feet of air under the front tire, but I had the luxury of seeing that one for myself.

    Anyway, the general vibe on 1/6 after lowering the car more and putting the 450's on the front was that the car cornered a LOT flatter, but was still lifting a front tire slightly on occasion. See first attachment.

    For 1/12, I lowered the car another half inch, and fitted the 500# springs with tenders on the front. Also fitted some additional foam bump stops in the rear to stiffen it up. Net result: it's on the bump stops both front and rear at rest. Just barely touching the fronts, pretty hard on the rears. This totally wrecked the ride quality. Made it very bouncy.

    But, the handling was good, and I don't think anyone saw the front tire lift at the 1/12 event. See second attachment.

    I picked up an annoying suspension rattle in the rear this week, so I checked that out this afternoon. The locking ring on one of my rear shocks had come loose. So, I tightened that up. While I was in there, I cut 3/4" off of the rear bump stop to give the rear at least a little bit of "free travel" (on it's 3kg springs). That helped the ride quality quite a bit. And, of course, getting rid of random rattles is always good.
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    Simplify and add lightness.

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  7. #25
    Still Plays With Cars Loren's Avatar
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    So, where I'm at now:

    The car is as low is it can practically be.

    There's not much I can do to improve the roll center further without getting into modifying the lower control arm pick-up points on the subframe, which I don't really want to do... and, I don't think it would help all that much. It would make the car feel better, but it's not going to change the fundamental physics of having a high CG.

    Spring rates are as high as I'm willing to go with them. Conventional wisdom for purpose-built FWD autocross suspension says "really stiff" springs in the front, and "even stiffer" in the rear. But, I'm not willing to go stiffer in the rear because I do daily drive the car (and drive it over an hour to and from autocross events). The reason for the greater rear spring stiffness is to be able to induce oversteer at will... which is rapidly corrected with a jab of the throttle. This is how FWD cars can be ReallyFast on an autocross course.

    I'm sure "magical" shock valving could improve things a lot, but I'm not willing to spend that kind of money, so that's not even on the table. My shocks are "adequate". They have enough adjustment range that I can make them "too stiff", and I'm finding good performance in the middle range. At least in the front. The rears I tend to set to full stiff for autocross just to add some additional rear stiffness, at least on turn-in.

    I've got about 3 degrees of negative camber in the front, and a tiny bit of toe-out. Rear alignment is what it is. Tire wear is generally pretty even, so that's all good enough.

    All that, and the car (still) feels quite good. And it's got enough grip to try to turn itself over if you get overly aggressive with a "one-two" maneuver. It's a lot better than it was a month ago, but I'm not kidding myself, I know it could still do it, so I make it a point to NOT give it that one-two punch without really having my wits about me. "I'm gonna ease out of this if I feel it going up!"

    What the car "needs" is a little bit more oversteer bias. It actually "needs" the rear end to let go at some point rather than to continue inducing chassis roll. I've done all that I can to optimize the front grip, but even when the front gets so loaded up that it pitches up on 2 wheels... the rear end stays planted on that one rear wheel! This is causing me to step back and consider doing something that goes against my grain.

    There are two ways to deal with handling balance. You either give the end that's not gripping MORE grip, or you give the opposite end LESS grip. My philosophy is to always try to improve grip rather than give it up, so that's what I've done. Now, I need to accept that it's time to try to GIVE UP some rear grip. How do I do that?

    Well, as I've said, shocks and springs are off the table. Rear swaybar... well, I've already done that, and it's already lifting the inside rear tire. A bigger rear bar might make that tire lift SOONER, but it's really not going to have any other effect. Once the rear tire lift, all roll stiffness goes to the front suspension.

    Alignment isn't an easy option on the Mirage. Nothing is impossible, but it's not adjustable, and thus not "easy". If it were easy, then I could maybe play with rear camber, and definitely play with rear toe-out. But, can't do any of that.

    About the only thing that leaves is the tires. The rear tires are already 195 (vs 205 in the front). Next time I buy tires, I'll probably look for a set of 185's and try that. But, in the mean time... tire pressure. Yep, I can play games with tire pressures, just like stock class autocrossers do. I can either raise or lower the rear tire pressures outside of their optimal range, and get the rear tire to grip less. With the tires that I have, and the lack of weight on the rear of the car, I'm not sure I could get the tire pressure low enough to make a difference. But, if I increase the tire pressure past a certain point, the tread face will crown and make the contact patch smaller. That might be just the thing.

    That's my experiment for next weekend. Autocross on 1/27.
    Simplify and add lightness.

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  9. #26
    Administrator Daox's Avatar
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    I really enjoy hearing your explanation of suspension stuff Loren. I know a little, but not nearly as much as you! Thanks for sharing with us.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.5 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.8 mpg (Imp)


  10. #27
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    Outside of adding a rear sway bar, I sort of like the Mirage as is. I still enjoy reading about what others are doing with their Mirages! Pushing this little car to its limit is interesting stuff! I also appreciate everything you share!

  11. #28
    Still Plays With Cars Loren's Avatar
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    Thanks!

    If I were just street driving the car, I'd have been pretty happy with just the base coilover kit and a good set of tires. The inherent weaknesses of the chassis don't really become apparent until you're really pushing the limits. I guess the same is true of any car, the weaknesses are just a lot more relevant when you're talking about a cheap economy car.. especially one that is as top-heavy as the Mirage.

    Oh, and I just remembered another thing I could do that would probably help keep the car "settled". That would be to widen the track. Could easily do that with wheel spacers, but I don't have fender clearance. Maybe if I decide to put flares on the car...
    Simplify and add lightness.

  12. #29
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    Thanks Loren, I have always been looking forward to your updates with your auto-x mirage.

    To tell you the truth, I'm a young and inexperienced driver whose passion in the technical aspects of racing started from playing sim games. Now I'm giving myself a favor to try-out auto-x this weekend with my almost stock mirage with a few minor suspension improvements.

    I loved watching your auto-cross videos but I never have seen you do a handbrake turn. What do you think about this technique on 180-degree or 360-degree turns? Is it just that you seldom do it or you just prefer to rely on mechanical grip?

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  14. #30
    Moderator Eggman's Avatar
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    Quote Originally Posted by bloodehunter View Post
    Thanks Loren, I have always been looking forward to your updates with your auto-x mirage.

    To tell you the truth, I'm a young and inexperienced driver whose passion in the technical aspects of racing started from playing sim games. Now I'm giving myself a favor to try-out auto-x this weekend with my almost stock mirage with a few minor suspension improvements.

    I loved watching your auto-cross videos but I never have seen you do a handbrake turn. What do you think about this technique on 180-degree or 360-degree turns? Is it just that you seldom do it or you just prefer to rely on mechanical grip?
    The handbrake technique is somewhat advanced, bloodehunter. I would suggest you get some experience in and enjoy the experience as it is before trying to coordinate deceleration, rear braking and cornering.

    I'm wondering if you have taken any training or courses in performance driving dynamics?


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.9 mpg (US) ... 21.2 km/L ... 4.7 L/100 km ... 59.9 mpg (Imp)


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