Mirage - Still lifting a front tire

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Mirage - Still lifting a front tire

Postby Loren » Tue Jan 08, 2019 10:12 pm

New front tender springs are due in Thursday. Anybody wanna help me put them in on Friday? I'll probably do it with or without help, but I've been putting off bleeding my brakes since the Enduro... would be nice to get that done, too.

In other news, I've been reading/re-reading a lot of stuff about FWD car setup. They seem to use REALLY stiff springs in the rear for autocross. I generally don't because it REALLY wrecks the ride quality. But, not I'm wondering if I should at least try to stiffen up the rear "some". I used to do it with rear shock adjustment, but there's a difference between jacking the damping into the stratosphere and actually adding spring rate.

The beam axle in the rear of my car has the springs between it and the body, rather than the alternative coilover spring setup on the shock. Not at all uncommon, the Yaris was the same way. The problem with this setup is that the the axle is pivoting on a point that's a foot or so forward of the spring such that the spring isn't compressed "straight". It's not a problem with soft spring that has enough tension to keep it in it's perches and can easily adapt to the changing angles. But, when you go really stiff with the springs, it takes a lot of preload tension to flatten the ends of the spring against the perches because the upper perch is level, the lower perch is angled... and the spring quite stubbornly wants to be straight. I actually did a tender spring setup on my Yaris that worked "okay", but it was clunky because at full droop, the spring stack wanted to bend... it was just a sloppy solution.

I could maybe find a spring to get a LITTLE bit stiffer in the rear without issue. But, what's back there now is 3kg... and with 9k in the front... conventional wisdom says that the rear should probably be somewhere around 7-11k! I wouldn't go that far with a spring, it would suck on the street. But, clearly, more than 3k would be a good thing.

Soooo... the ideal, as in the front, would be a dual-rate setup that's stiff when it needs to be stiff, but soft under droop both to allow more droop (keep the tire on the ground longer), make the "landing" smoother, and generally make street driving more comfortable and less clunky.

What I'm thinking is, rather than changing my 3k rear springs, I just leave them in there as the "soft" spring. Ideally, even softer would be better, would allow more droop travel. And then, to get the stiffness under compression, instead of relying solely on the swaybar (again, going too far with that WRECKS street comfort), I put a secondary spring at the shock. And that could be done in the form of a "bump spring". But, given that my rear corner weights are around 400 pounds, I'm thinking I could get by with some really stiff bump stops. Set them up so they're nearly making contact at static ride height.

A project for another day. But, very likely the next stage.
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Mirage - Still lifting a front tire

Postby CaptainSquirts » Wed Jan 09, 2019 3:02 pm

Bumpstop idea seems pretty straight forward. Wonder if the gap being too close for the bump stop to be active under small inperfections/bumps in the road would cause it to have the nice soft spring feeling, then to a huge hike uncomfortable feeling when there is a little compression from the bump stops. Then if they smack too often would they start losing rates and then just fall apart over time?(now that's a run on sentence)
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Mirage - Still lifting a front tire

Postby Loren » Wed Jan 09, 2019 3:19 pm

Oh, bumpstops in a "high use" situation will definitely be a wear item.

What I was reminded of when I put the stiffer springs on the front of the car is this:

Stiff springs... considerably stiffer than you think would make sense... don't ride as harsh as trying to jack up shock stiffness to compensate for springs that are too soft.

To put it another way:

Being under-sprung and over-damped is a harsh ride. Every little bump you hit rattles your teeth.

Being stiffly-sprung and mildly-damped is a MUCH smoother ride. You still feel the bumps, but the're a lot smoother than they are with overly-stiff damping.

I expect the same sort of thing from using bump stops to get the "spring rate". The trick is to make the bump stops progressive enough. If you go from being off the stops to being ON a hard bump stop, you'll feel that and it will be somewhere between uncomfortable to just disconcerting or distracting. But, if the stops have a smooth and progressive engagement, you don't notice so much.

Where the rear of my car is right now, it has 5" of shock travel. It has only about an INCH of droop travel. Maybe 1.5". The bump stops are STIFF, and they're 1-5/8" long. That means I have about 2" of compression before they engage, then they engage HARD.

Thinking of it that way... I really don't need to get too crazy. I can do exactly what I did with the front bump stops... add a softer bump stop on top of the stiff 1-5/8" long bump stop. That will make it engage earlier and go pretty stiff after the first inch of travel.

I think what I (and a lot of other people) are catching onto is something that manufacturer's like Mazda knew in the late 80's when they designed the Miata. Softer springs are required to allow the suspension to work and ride properly, and proper progressive bump stops are the answer to getting the "spring rates" stiff in a turn.
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Mirage - Still lifting a front tire

Postby CaptainSquirts » Wed Jan 09, 2019 3:55 pm

Would be cool to get a bumpstop, measure the hardness with a durometer, run it for a while and retest the hardness to see how much it degrades.
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Mirage - Still lifting a front tire

Postby Loren » Wed Jan 09, 2019 4:04 pm

You should do that. :thought:
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Mirage - Still lifting a front tire

Postby CaptainSquirts » Wed Jan 09, 2019 4:12 pm

Pfff, I dont roll with bumpstops. They add too much unsprung weight from those.
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Mirage - Still lifting a front tire

Postby mymomswagon » Wed Jan 09, 2019 9:16 pm

I have the bump spring setup and it definitely can change the balance and can be adjusted with ease.

I went into the concept wanting something that could be 'turned on' for events and turned off for the street.

The spring is not loaded but has about an inch of travel before it becomes loaded. The travel can be packed with bump rubber or nylon packers...whatever to cause earlier engagement. All can be adjusted without removing a wheel or wrenching on anything.

On the street, the setup is friendly and the only real downside has been hitting high speed dips on the Vets: The car will bounce just enough to engage the bump springs in a rather non-linear way (bouncy).

I think I succeeded, though my choice of spring rate (300#) was a guess.

As far as I know, my car has never tri-podded though it's not sprung that much to begin with and the rear sway is modest compared to most aftermarket options.
Image
Last edited by mymomswagon on Wed Jan 09, 2019 9:16 pm, edited 1 time in total.
Critical damping ??? We don't need no stinking critical damping !
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Mirage - Still lifting a front tire

Postby Loren » Wed Jan 09, 2019 9:22 pm

A VW that won't tripod? That just seems wrong. I thought they invented the concept!
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Mirage - Still lifting a front tire

Postby mymomswagon » Wed Jan 09, 2019 9:32 pm

not even Uncle Steve can make it happen.

Not sure why it's that way...but it has independent rear suspension these days, maybe that helps? I think I have a lot more droop as well.
Loren wrote:A VW that won't tripod? That just seems wrong. I thought they invented the concept!
Critical damping ??? We don't need no stinking critical damping !
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Mirage - Still lifting a front tire

Postby Loren » Wed Jan 09, 2019 9:41 pm

mymomswagon wrote:not even Uncle Steve can make it happen.

Not sure why it's that way...but it has independent rear suspension these days, maybe that helps? I think I have a lot more droop as well.
Loren wrote:A VW that won't tripod? That just seems wrong. I thought they invented the concept!
Yeah, all of that. Bigger rear bar would make it happen. But, if you've got the car oversteering without a big bar... you're set!
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Mirage - Still lifting a front tire

Postby mymomswagon » Thu Jan 10, 2019 9:12 am

One of my low priority experiments is to see how difficult it is to disconnect the rear bar at the end links and zip-tie it out of the way, then replace its tension with a stiffer bump spring.

Sounds like your problem is solved, but maybe another area of flexibility.
Loren wrote:
mymomswagon wrote:not even Uncle Steve can make it happen.

Not sure why it's that way...but it has independent rear suspension these days, maybe that helps? I think I have a lot more droop as well.
Loren wrote:A VW that won't tripod? That just seems wrong. I thought they invented the concept!
Yeah, all of that. Bigger rear bar would make it happen. But, if you've got the car oversteering without a big bar... you're set!
Critical damping ??? We don't need no stinking critical damping !
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Mirage - Still lifting a front tire

Postby Loren » Thu Jan 10, 2019 9:56 am

It's getting there. I think (hope) the "safety" issue is taken care of. Just trying to improve the drivability and comfort aspects of it now.
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Mirage - Still lifting a front tire

Postby Jamie » Thu Jan 10, 2019 5:36 pm

Loren wrote:I think (hope) the "safety" issue is taken care of.
You should hope...another one of those, and we're going to have to put outriggers on it....
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Mirage - Still lifting a front tire

Postby Loren » Thu Jan 10, 2019 6:18 pm

Retro rockets would be cool.

So, the tender springs showed up today. Decided to go ahead and install the right side this afternoon. That went quickly enough, and Cathy was late getting home... ended up doing both sides.

Current spring stack looks like this:

Image

I set the ride height exactly 1/4" lower. I haven't measured it, but it should have at least a half inch more droop, total of about 2-2.5". At static load, it's firmly touching the bump stops, which are a stack of really stiff 1-5/8" hard poly and a soft poly foam about 1.5". Feels pretty good. I may play with setting the shocks softer and see what it does.

That 1/4" was enough to get me rubbing a tire again, though. I thought the added firmness of 50# more spring rate, plus being on the bump stop would keep that from happening, but I guess it was just that close before. I'm going to see if I can adjust the one little metal tab that I think it's contacting. If not, I'll have to raise it back up.

I really think I want to go ahead and play with the rear. Softer springs to allow more droop travel, taller & stiffer bump stops to catch the compression travel. I don't know that it will make the car handle any better, but it should make it ride smoother. There's something to be said for refinement.
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Suck Less - Drive something resembling a proper racing line.
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Mirage - Still lifting a front tire

Postby jbrannon7 » Thu Jan 10, 2019 6:32 pm

Have you named your car? Maybe it should be called "Tinker Toy".
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Mirage - Still lifting a front tire

Postby Loren » Fri Jan 11, 2019 4:42 pm

I have measurements in my head that I didn't write down. Need to put them somewhere before I forget them.

Rear spring ID = 3.2", actually 80mm. Kind of an odd size. If I'm going to replace it, I'll probably need to go ahead and replace the adjustable perch with a 2.5" piece and go with 2.5" springs.

Rear spring free length = 7.5" (again, metric, whatever)

Rear height is set max low. I could go lower by removing the adjuster, but I really don't think it needs to be any lower.

Rear droop travel is 2.25". Front is 1.75". I'm okay with that. It's a little less than half the shock stroke for each of them.

Added more bump stop in the rear. It's still a good half inch from contacting the bump stop at static load, but it was well over 2" from it before! This effectively gives me more rear spring rate as the body starts to roll. And I could amplify it by reducing that gap with some poly spacers pretty easily.

The car is now as low as it reasonably can be. Slightly scraping the front fender liners when pressed VERY hard (and I bent the one metal tab that could do damage to a tire out of the way). Initial driving impression is that it's a flat-cornering BEAST! But, you really have to temper throttle input on the exit of the turn. It will flat out light up the inside tire if you try to get on it too early. It feels bouncy when there are bumps in a turn, but otherwise okay.

Dampers are set at 6/16 front and 10/16 rear. I'm lazy, I'd like to leave them there. But, if I can't come up with a good setting that works for both autocross and street... maybe I'll add shock adjustment to my "event prep".

Dan hasn't driven the car since the Enduro. Will be fun to get his perspective tomorrow.
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Mirage - Still lifting a front tire

Postby CaptainSquirts » Fri Jan 11, 2019 7:03 pm

Mmmmm, I like me some dual spring setups. :cool:
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Mirage - Still lifting a front tire

Postby twistedwankel » Fri Jan 11, 2019 7:07 pm

Dan cornering a totally morphed car flat out 180 BLIND :lust: Make sure he runs in the PM heat please.

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