Mirage - Still lifting a front tire

[twistedwankel]

But, let's start with going back to basics. Slam it to the ground.

Yes that is where I start too. Bitch slap. Slam...down bitch down. 30-40* Whoa. Drone. Actually, I rarely lowered a car. Only did it once with professional advice and springs. Learned about not planting a tire the hard way when it wouldn't plant anymore cause it had no travel.

[Loren]

Yeah, I'm a big fan of suspension travel. I presently don't have a lot of it. Only about 1.5" of compression and about the same rebound. Fortunately, I can lower the car without affecting the travel. Just shortening the shock body.

[aw614]

___

[Loren]

Someone's not reading.

As I said just above, I can and will easily shorten the shock body length without losing any of my suspension travel. Don't need any more trick parts to make that happen.

[CaptainSquirts]

If it was me I would've revisited the helper springs/tender spring dual spring setup route. I just use the helper spring for more droop travel but would've liked to try a dual spring setup for comfort for regular driving and stiffness when load is being on one end. Might be the easier route but seems like you aren't keen on revisiting that.

[Loren]

I really don't think going with a stiffer spring (using a progressive stacked arrangement or not) would help the fundamental problem that the car is top-heavy. Weight is still going to transfer, the body is still going to roll, and the inside tires are still going to lift. Dangerously so.

Stiffer springs won't change that, they might slow it down a little, but ultimately, the CG is too high... still going want to roll over.

Raising the roll center also didn't change that. It changed the way things felt, and made the car FEEL more stable, and maybe "geometrically" resisted body roll a bit more, but ultimately, the CG is too high... still going to want to roll over.

Need to lower the CG. Removing 28 pounds of battery weight and the back seat probably helped bring the CG down a little bit. Lowering the car another 3 inches should help a lot more.

[Loren]

Alright, got the front of the car down.

I was going to shift the spring perch height a little bit to get less compression travel and more rebound, but I found that I was already at the limit. Lowering the spring perch any further causes the spring to go slack. It's got zero preload on it as it is. This is less than ideal with the car super-low because I presently have a measured 1.5" (maybe 1.75-2.0" if the shocks were fully settled) of droop travel. With a 4.5" stroke, that means I have 3" of compression travel... and maybe last 3/4" is unreachable due to bump stop compression. But, I still have a good 2-2.25" or more of compression travel. And if I'm going to be this low, I can't have that much compression.

And while I could have lowered it a solid 3", I stopped right at 2.5". Where it's at now, the static ride height is right at where the "full-tilt, max G" wheel tuck was on the outside wheel before. As mentioned, I have a good 2" of compression travel. That's a lot to be trying to tuck up into that fender!

Drove the car around a little bit. First test run, I had the shocks on full soft to ensure that I was getting the full range of travel easily. No problems with bottoming out the frame (4") or even the muffler (3"), but the fender liners rub on every little bump, and with the slightest turn of the wheel. Freakin' Cadillac ride quality, though! Wow! I haven't had the front shocks softer than about 3/4 in a very long time.

Went over to Dunedin for dinner. Set the front shocks at 1/2. The rubbing improved some (partly due to getting some wear on the fender liners... partly due to stiffer shocks, but still made Cathy cringe a lot. I'll at least be able to pop the wheels off and see exactly where it's rubbing and decide what I want to do about it, if anything. As long as it's just rubbing plastic, I'm not too worried about it. It will clearance itself. I might help it along, though. The angle grinder would make quick work of it.

So, I'm going to see what springs I have on the shelf. If I have some stiffer springs that are just a little shorter than what's on the car now, I should be able to set it up with a little less compression travel, more droop travel. A little more front stiffness wouldn't be a bad thing for handling... and as long as I keep it under 350# or so, I don't think the ride quality will be horrible.

I need to get under the rear of the car and bring it down to match the front, too. That's easy enough to do. Just run the spring perches down, and then shorten the shock bodies to match. I'll probably leave the rear spring rates alone. Softer rear springs are good for ride quality, and I'm getting all the weight transfer that I need back there due to the added rear swaybar.

[Loren]

BTW, Philip's photos from the past few months (the past year, really) have been instrumental in helping me figure out what my setup is doing and how to adjust and improve it. Thanks, Philip!

[Loren]

I've got a 6" 450# pair of springs on the shelf.

My brain is going into overload trying to figure out if it's going to work or not. I'm in a "try it" kind of mood, so that's what I'm going to do.

The spring is 6" long and has 3-1/8" of compression.

The 450# rate with current weight of the car should compress less than 1.35" under the weight of the car, and another 1.35" at 1G. That's 2.7" total spring compression, so that can work.

Will find out for sure tomorrow.

[Loren]

Epiphany:

Droop travel is determined by spring rate.

If you're at full droop, shock is fully extended. You run the spring perch up to contact the spring, and maybe add a tiny bit of preload.

At this point, you have your full shock stroke available. You set the weight of the car on it. The spring rate determines how far the shock compresses. That IS your droop travel.

So, the 1.35" that I have calculated that my 450# spring will compress... is my droop travel. The remaining travel MUST be compression travel.

So, I have 3.15" of compression travel. But, the spring is only going to allow me to get 1.35" into it at 1G, and it's going to coil bind 2".

This setup should have me completely OFF of the bump stop, which I think was 1.5" tall, soft and progressive.

To get back onto the bump stop, I'll need to put some kind of bump stop spacer/packer in there. And I won't be using more than a total of 2.7" of my 4.5" of shock stroke.

Interesting. Will be fun to see how it all works out in reality.

[twistedwankel]

Interesting. Will be fun to see how it all works out in reality.

I wonder how they set up the Mirage Rally Cars I've seen pix of? I assume they are still FWD not AWD? They stay flat on turns and leap hills but then have enough power/torque to pull out of corners and not just roll around them yelling whee. I assume the car is more stabile with a passenger weighing it evenly or maybe not? Rally cars have passengers for the most part giving directions. Ask Dan to point left and right? Note puddles where Philip's passengers wet themselves ahead of you? Or where my AC dumped when I forgot to turn it off?

Anyhow this remains a very interesting read. Hope for all young guys with high insurance rates for sure. I did see two guys doing wheelies all the way up a steep hill on supped up Mopeds in Greece. The ONLY gas they sold was 95octane @ 2 euros/liter. Hmmmm.

[Loren]

Rally cars tend to have very specialized suspension with dual-rate spring stacks. (not unlike what Dan ended up doing on his Evo, but a lot more extreme) They'll have a pretty tall long spring that is fully compressed at static ride height, and only comes into play when the suspension droops. It keeps the spring stack in place, and provides a softer, more progressive "landing" when the suspension comes out of droop. (which might very well be coming down from being airborne) When that spring is fully compressed, the stiffer main spring fully takes over and gives them a stiff setup for cornering and such. But, even that has a LOT more suspension travel than you'd think. From there, it gets into shock magic. The shocks need to be able to handle coming down from a jump, in addition to the usual "digressive valving" that a good shock should have, anyway.

Glad I'm "just" building an autocross car.

[Loren]

Did a lot of work this afternoon. I've had it all apart enough times now that it really didn't take long. (I've also had it apart enough times, and been over-torquing the lower strut bolts enough that I destroyed the threads on them and had to replace them... but, I saw it coming. I had replacements on hand when one of them finally seized today! Actually, one on each side. The first one I cut off, the second one I was able to hammer off with the impact. The frustrating part? OE bolts are 17mm nut and bolt. Replacements are 16mm bolt and 18mm nut! Two wrench sizes that I *never* use and had a hard time finding!)

So, I lowered the rear to match the front. I set it a half-inch from as low as it would go. (I like to leave a little on the table) I've got some rattles back there now, I need to go back and look and see if I can figure out why.

And then I took the front apart and stuffed my 450# springs in there while raising it up about an inch. (half inch with coilover height adjustments, the rest due to the springs being stiffer and compressing much less than the old springs) Quite proud of myself, too. I did all the math last night, so I knew that the replacement springs would compress 1.3" under the weight of the car... and another 1.3" at 1G cornering load. So, I knew exactly where I needed to be in my shock stroke. I was able to set things up perfectly the first time! And I was able to trim a custom bump stop so that it is right about a half inch from making contact at static ride height. It all fell together perfectly! There's something to be said for experience and understanding what you're doing.

Here's today's gratuitous "moar low" photo. All nice and level.



Raising the front up and making it stiffer so that it can't compress too low took care of the rubbing problem, which was worse than it sounded. I was actually hitting metal in two places, one of them was sharp!

Feels pretty good, and no tire rub so far. I was running around over damped and under sprung before. Now I have enough spring, so I can run proper damping and the ride is actually smoother. As I used to say with my first Miata, "firm, but not harsh".

I need to touch up some rubbed bare metal under the front, and reset the front toe. And I need to figure out what the rattly and squeaky noises are in the rear suspension.

The steering feel is different, and I haven't quite come to terms with it. There's definitely more body roll per amount of steering input, which I expected. But, the stiffer springs brought some of that back. My first "yank the wheel left and right" move with this setup was downright startling! Even with the shocks set pretty soft, the response was very quick. I liked that. Overall, it feels very settled. I had the shocks so stiff before that it felt borderline twitchy.

Can't wait to see what it does at Sunday's autocross. Will it behave?

Oh, for the bumpstop/spacer setup, I used the NB Miata front bump stop that was already in there (and already trimmed) as a supplement to the very hard poly bump stop that came with the coilover kit. I further trimmed the NB stop so that it has about 1/2" of slack at static ride height. So, I've got 1/2" of 450# spring rate, then it gets into a fairly soft progressive bump stop before going into the really hard bump stop.

That first 1/2" of travel on a 450# spring is about 0.4G. So, things start firming up right as you turn in. The remaining Miata bump stop part is only about 1.25" long, and will probably give another 3/4" before maxing out and yielding to the harder bump stop. The 450# spring rate alone only compresses 1.3" at 1G, so with the progressive bump stop adding to it, it will compress even less at 1G. So, basically, unless I'm REALLY hammering it, I should be working within about the first 1.25" of compression travel, and I can't imagine it's going to go past 1.5" ever.

Will all of this tame the inside wheel lift? Tune in next week...

[Loren]

Fun fact:

That 1.3" of compression travel at 1G = 2.7 degrees of body roll.

That sounds promising.

[Loren]

Alignment checked out. Was less than 1/16" toed in up front. I adjusted the right side to bring the steering wheel to straight. 2/3 of a turn on the tie rod brought it to right about 1/8" total toe out. Close enough. (unless it wanders too much... then I'll bring it back to zero)

Checked the rear toe. It's not as bad as I thought. 1/4" total toe in. Not ideal, but not horrible.

Also found that my anti-fouler adapter on my O2 sensor had loosened. That was one of my rattles. Another one was a little plastic clip holding a fuel vapor line wasn't quite tight. And lastly, the whole rear twist beam freakin' RINGS like a bell! I zip-tied a piece of stiff foam to it to deaden it a little bit. The springs are still creaky.

Ready for a shake-down.

[Native]

[twistedwankel]

Certainly the best looking newer Mirage out there Tasteful stance staying inside the fenders.

[Loren]

Uh... about that rattle in the back of the car.

Gave things a final once-over before the autocross. The left lower shock bolt wasn't tight. That'll do it!

[Loren]

Okay, the 450# spring rate setup passed the autocross test. Feels good. Doesn't seem to be lifting the front tire. (though it is "almost")

I've decided that 450# was not at all "too much" spring rate for either street or autocross, and a little more wouldn't hurt. I have a pair of 4" 500# springs on the shelf. I bought them as "tender" springs, but in this case... I can actually use them as main spring.

I do want to install a tender spring to allow for more droop travel, and I can't fit a spring stack taller than about 6" without raising the front of the car. So, I found a 2" tall 100# tender spring. It allows .94" of travel. It's 100# rate will be completely compressed at static load, so it will basically act like a spacer until the inside wheel unloads. Then, instead of lifting the tire up... it can droop for another inch.

This setup should give me a little better turn-in due to the stiffer rate, and it might reduce the wheelspin that I'm getting coming out of tight turns due to holding that wheel down with at least a little bit of force.

The short springs were like $65 shipped, and I already have the 500# springs (that I paid about $40 for). So, not an expensive experiment.

What I needed on this Sunday's course was more power.

[Loren]

Oh, and I'm not bottoming out the front now... which means that with a slightly stiffer front spring, I should be able to lower the car maybe as much as another half inch.

Baby steps.