Secrets of the Mirage

[Loren]

Swaybar maths...

According to my trusty swaybar calculation spreadsheet for a 36" bar with 6" arms:
1" Hollow (.188 wall) = 753 lbs/in
1" Hollow (.095 wall) = 505 lbs/in
1" Hollow (.083 wall) = 458 lbs/in
7/8" Hollow (.095 wall) = 325 lbs/in
7/8" Hollow (.120 wall) = 376 lbs/in
19mm (Solid) = 278 lbs/in

Soooo... the above is an approximation. But, it does give a good indication of relative stiffness between different options.

The knowns:
- Commonly available (in the Phillipines) aftermarket rear bar is 19mm solid. Probably "not bad", but I always like a lot of rear bar on a FWD car, so I want more than that... enough more that I can actually tell the difference.
- What's on the car now is a 1" hollow .188 wall bar with very rigid arms. It's nearly 3x as stiff as the 19mm. I opted for this size because I didn't want to end up with a bar that would be fragile and easily dented, and I just plain wasn't sure how "thin" something like a .120 wall would be. As it turns out, .188 is REALLY thick, and I think I could get by with running something around half as thick... like .095... maaaaybe even .083.

The extrapolation:
I don't think I'll get where I want to be with a 1" bar. Not willing to go thinner than .083. So, we go down to a 7/8" bar. The .120 wall gives stiffness that is 35% more than the 19mm bar (nice), and 50% less than what I have now (certainly an improvement in ride quality). Cutting my bar rate in half should allow me to run the rear shocks a bit softer, and smooth out the ride even more.

And a 3' chunk of 7/8 x .120 runs right about $34 plus shipping. Not bad.

Where'd I put that credit card...

[JasonS]

I absolutely love reading this stuff. Keep it coming!

[twistedwankel]

Loren you really need a disclaimer on your site: "Do not try this at home."

[Jamie]

Loren you really need a disclaimer on your site: "Do not try this at home."

Or at least, "Do not try this with your own credit card...."

[Loren]

Just in case we have to bug-out for the hurricane, I thought I'd better get my alignment sorted. So, camber is set at around -1.9 degrees. (half inch tip-in over 15") Relatively even side-to-side. Toe is set to near zero, steering wheel is straight. Good to go!

Went ahead and removed the rear swaybar to improve the right for now. (and it will be interesting to see how much that affects the handling... I haven't driven it that way yet)

Also ordered that thinner hollow bar stock to redo the rear bar. So, I'll probably get that done before reinstalling the bar.

[Loren]

Since the last update, I got the rear swaybar reworked (thanks, Joe!), painted and reinstalled. Didn't mess with anything else.

Put it on the scales while it was at Joes:
Front: 573/648
Rear: 362/474
Total: 2057

Front-Rear bias is actually less than 60%. Pretty good for FWD. Of course, that changes a little bit with the driver in the car. The left-right balance improves, though. (didn't bother documenting those numbers... should have)

And finally got in an autocross yesterday. Not a great "shake-down" because it was very wet. But, the car seemed to handle well enough. No particular understeer problems, and the back end stayed put. Can't complain too much. Steve also drove a few runs in it, and almost matched my time... that either means we're both awesome, or the car is easy to drive. (maybe both?)

One bad habit the car has is wheel hop. It was really bad in the rain. Maybe it won't be as bad on a dry course? If it is, I'll need to do something about it. Not sure what's causing it. Springs too soft? Shocks too stiff? Engine mounts allowing too much motion?

Will be playing with shock settings and tire pressures first to see if that helps.

[Loren]

I changed my mind, and actually decided to go ahead and fit an engine torque damper (I have one on the shelf from a Miata that I can adapt to fit) to help with the wheel hop. And then I promptly did NOT make any effort to fabricate the mounts and fit it to the car last week.

In the end, all I did between events was check the engine oil and adjust the front shocks. I learned that I had the fronts set at 7 from soft (of 16). For the ride up to Dunnellon, I set them at 2/16. That made for a comfortable ride. But, it made the car a little too snap-happy. I almost spun on my second run (or not). Then I set them back up to 6/16 and they seeemed pretty happy there. This car slaloms like a boss!

I need to get wild at a Classic event and TRY to spin this car. I'm starting to think that it's almost impossible to actually do. The traction control can be turned off, but I feel like whenever a little slide starts, it still corrects (with braking) and cuts power. Stability control is still there.

One of these days, I need to check my tire pressures.

[Native]

One of these days, I need to check my tire pressures.

You won't.

[twistedwankel]

One of these days, I need to check my tire pressures.

Like the man said. I'll check them for you on my own car and we'll race them both. Trick car vs race car.

[Loren]

Oh, ye of little faith.

[Loren]

Today, the stars aligned, and I found Time and Motivation at the same time and managed to finish a mod that didn't require Money! I modified the brackets for my engine torque damper and got it on the car.

Things aren't aligned just right, so the rod ends on the damper are near the limit of their articulation. This causes a buzz in certain situations. (like when you're just letting out the clutch) Otherwise, it's not creating any significant NVH that I noticed. I'll need to take the brackets off of the car and give them a little twist to align things a little better.

It's really hard to say how much it helped with the wheel hop. It didn't totally eliminate it, but I guess that's just inherent with FWD. It did make the throttle response feel sharper. Off-on throttle transitions don't have to take up all that slack in the engine mounts. So, even if it didn't kill the wheel hop, I think I still like it.

While I was playing, I went ahead and stiffened the shocks. Thinking that I didn't need to go too stiff on the stock springs, I never put them at even fully 50%. Most I'd ever done was 6 or 7/16. So, I bumped them up from 6 front, 2 rear to 10 front and 8 rear. That feels pretty nice! And, I think it had some effect on the wheel hop, as well, which makes sense.

I think one thing that makes this car particularly susceptible to wheel hop is that it has a 3-cylinder engine. 3 cylinders, and they have to cover the full 720 degrees of rotation required for a 4-stroke engine. That means one cylinder fires every 240 degrees of rotation. Makes for an inherently rough running engine, especially at lower RPM. So, if I'm digging out of a corner at 2400 rpm (ugh!), the little cylinders (same size as the cylinders in a 1.6 liter 4-banger) have enough pop to at least rock... well... everything (engine mounts, suspension mounts, shocks, etc) if not cause a momentary lapse in traction. And then nothing... for another 240 degrees. The car has a VERY heavy flywheel to help compensate for this. Keep the revs over 4k and it feels pretty smooth.

Anyhow... the experiment continues. And I still haven't checked my tire pressures.

[Loren]

Did a little driving around on wet roads this evening. The changes I made today DEFINITELY improved the car. Wheel hop still happens with a hard full-throttle first-gear turn, but it's much more controllable. The engine strut makes it easier to feel that the car is actually responding to the throttle, making it easier to effectively modulate the throttle and control the hop.

I'm starting to think about how hard/expensive it would be to do some tuning of the drive-by-wire throttle on this car.

[CaptainSquirts]

From watching the car in action on the course, it looked like the inside front tire when cornering was almost or was hopping a bunch.

[Loren]

Yeah. I experimented with some more shock settings today. Tried going softer. Seemed to help. So, my last run was full soft in the front, and 2 clicks from soft in the rear.

Aside from the pogoing (which the shock adjustments helped), the car feels really good.

I did check tire pressures. They were at 30 cold... 32ish warm. I set them to 38 warm. Figured I could bleed them down from there if I needed to. The fronts seem happy. A little less rollover, no grip issues. The rear... it's along for the ride. It's staying put. I'm okay with it.

So, I'll probably leave tire pressures alone for a while. Probably leave the shocks alone, too... maybe tweak the rear shocks for "surface". (I could have gone stiffer in the rear today... on asphalt, I think it could initiate oversteer)

I'm aaaaaalmost off the fence about staying in S5. I think the car would be a lot happier on stiffer springs and sitting a couple inches lower in M4. But, it's REALLY fun to be running competitively in S5. So, I'll probably stick with S5 this season and make the move to M4 next season.

The setup is coming together. Oh, and I've still got the spare and tools in the back, jack under the front seat. Could shed probably another 40 pounds by pulling that stuff out.

[aw614]

would disconnecting the front bar lessen the pogo'ing?

[Loren]

would disconnecting the front bar lessen the pogo'ing?

It might. But, that would probably make the steering feel very sloppy, and bring back a lot of body roll.

I've been thinking... Here's my latest theory:

The shocks are designed for a much lower ride height, with much less suspension travel. I set things up as best I could to give as much upward travel as I could. By default, with only about 4"of travel, and set 2" higher than intended, it has nearly no extension travel.

So, what I'm getting is simply the inside front tire getting light, almost lifting due to not having any more extension travel available. Add a bump to the mix, and that tire just dribbles like a basketball.

Having the front shocks stiffer just made it worse. Abrupt steering or throttle inputs would lift that inside corner quicker than the shocks would allow the suspension to move... Lifting the tire, causing the lack of traction, initiating the pogo.

Softening the shocks allowed the light inside front tire to maintain contact with the pavement better. Less loss of traction. Less pogo.

So... I don't think the added engine torque strut helped the hop. But, it did improve feel greatly so that I can better feel what the car/throttle is doing.

I think the real solution is to try to get a little more front shocks extension travel.

How? The only thing I can think of is to figure out how much extra stuff length I have on the upper strut mounts (or get longer studs). Then lower the spring perch by... Maybe a half inch? The put a half inch spacer above the upper shock mount to get the ride height back.

I guess I could also try what I did in the rear. Washers under the upper shock mount as much as the extra threaded length of the shaft will allow the top nut to still engage. Effectively making the shaft longer and allowing more extension travel with no change in static height. But, as I recall, there's not enough shock shaft length to do that method.

[mymomswagon]

maybe there's something like this out there? might be hard to find fitment to both your shaft and your camber plate:
https://www.summitracing.com/parts/afc- ... urEALw_wcB

[Loren]

Something like that could work. But, yeah, it would need to have the correct OD to fit the fancy pillow ball upper bearing.

[twistedwankel]

Pondering why they would put the 30# lead acid battery on the driver's side of the car? OH, in Japan they drive on the right side. Bet that messes up your corner weights. What if you borrowed Steve's ski doo battery or get a MC battery which weighs zip to try it out. Would have to help?

[Loren]

Well, I took my meager bit of motivation out to the garage. Dialed the rear shocks up to 14/16 and took it for a drive.

Ride quality didn't seem to change much. (It already had a rough ride due to the rear bar and firmer front shocks... And RE-71s)

Curiously, there wasn't a night and day change on handling, either. First thing I felt was... Like the front end rolled a lot more on turn-in. It wasn't, of course... Just that the rear was much slower to roll.

Once I adapted to that, I could tell that maybe there's a little less wheel hop. It will still do it on a hard launch right turn, but it's much easier to avoid. So, probably some improvement. Will need to autocross it to be sure.

Still no hint of oversteer or instability... Or that the rear tire is lifting. Though, I did feel stability control kick in once (forgot to turn it off... Again), that could have been wheel lift while LFB at turn-in.

Baby steps. Might experiment with disconnecting the front swaybar this week and see how much I hate it.