Ride height and handling balance

[Piledriver]

Since playing with my new elcheapo DIY coil over setup (Bilstein S6Ms modded up front, rear Fox 2.0 truck shocks w/custom ends and valving) and being able to play with ride height without it being a major project unto itself, I found something interesting

73 square, stock front end (other than the coil overs, bars are also active) early 944 turbo out back, with 16" Fuch manhole covers from same. Spring rate is ~ 3x stock F&R. Doesn't ride much if any worse, oddly, probably due to having ~correct damping. (front digressives, initial is a bit stiff but those are also becoming take-aparts with lighter oil as soon as I get a free dry day, the redline likewater shock oil should take some of the edge off by itself)

A ~1/2" ride height change out back takes the car from handling like a boxer on his tippy toes (in a good way---very tossable) to ungodly understeer with very heavy steering input, but it feels like velcro rear traction, it feels like I lowered the rear 3".

I know there is a slight but measurable camber change, but it seems odd to totally change the dynamics of the car with what would seem to be a minor adjustment...
What one would assume it would have a gradual effect, feels more like a step function.

I'm running 1.5 degrees neg camber out back, zero toe with relatively sticky Cooper RS3-As all around, 205/55-16 on 6s F and 245/50-16 on 8s out back. Rears are ~stock vw diameter, fronts a little less, running about stock ride height maybe 1" drop, (but level) as a T3s front suspension geometry goes to hell dropped.
Rear tire wear is amazingly uniform, esp. considering 95% of my driving is down a freeway at 75 MPH..

Is the camber setting moving around some critical point when running wider tires? Or is it something else?
I could see that as they stay up all by themselves off the car even if you give them a roll.
Thoughts?

[Marc]

Does seem strange. Are the rear t'bars still present and carrying some of the weight? If so, could be that they're starting to pick up the load and you've had to back the coilovers off to the point that they're ineffective and you're relying solely on the t'bar spring rate. I presume you've checked that the shocks aren't running out of travel...

Stock IRS Type III bars are 23.5mm (Beetle are 22mm).

[Piledriver]

Does seem strange. Are the rear t'bars still present and carrying some of the weight? If so, could be that they're starting to pick up the load and you've had to back the coilovers off to the point that they're ineffective and you're relying solely on the t'bar spring rate. I presume you've checked that the shocks aren't running out of travel...

Stock IRS Type III bars are 23.5mm (Beetle are 22mm).

Front bars about 20% loaded, rear bars are neutral in either setup, as I free up the porsches spring plate adjustment and lock it down again at target height, so they work ~like the "4-way" coil over snubbers but much more robust, and with really decent tunable shocks rather than having to use Monroes. I can also preload them up or down against the coil overs.

It has the 23.5mm bars out back, I put the lighter early sway bar in the front, as the Tbars themselves act as sway bars to some extent now--- it moves a bit in corners as it must, but no significant dive or squat on braking or accel.

Have been trying to sort out the "why" but I will probably just raise it back up a bit in the morning, it just seems to have a LOT more effect that I expected. (saw it before but didn't think about it too hard)

It has plenty of travel left, shock length/modded mounts and relocated the bump stops to suit new setup.
I would probably not do the 944 alloy arms again on a T3 due to having to flare the fenders, but it does work very well... but so did the steel arms.

[Jadewombat]

That does seem pretty drastic. Sounds like the dampening is just right at the edge of the sweet spot where the car handles well if such a small adjustment makes such a large difference. I agree with Marc, it sounds like something in the suspension components is working against something else. I.e. a full tank of gas vs. an empty one is not going to make night and day difference of the way a car handles.

I got my bug the way you described it originally, very neutral. It wasn't ideal for everything, but I liked the predictability of it vs. surprises.

[Piledriver]

Drove it today as-is, at speed its nice, its at low speed it seems to make the bigger difference.
I haven't had the shocks dyno'd yet, figure I'd see if the valving's in the right zip code first. (it is)
If I could get the front to eat expansion joints and such like the back (but still firm) it would be bordering on awesome.

I did try something weird with the valving, linear compression and digressive rebound. (Linear pistons with a ring shim setup, may move it to compression side for more initial weight transfer)

[PhillipM]

Running out of droop travel on the inside wheel when the car is higher?

[Piledriver]

Running out of droop travel on the inside wheel when the car is higher?

Its actually short on compression travel front and rear, has tons of extension, but the rear rides smooth and feels planted,.

The front damping's a bit too stiff. it has S6M-4020s on there, digressive, the right valving is probably more like ~2005 (Bilstein Reb/comp order) based on the autocrosstowin.com calculator...

One of these days I'll pull the S6Ms off and turn them into take-aparts and fix, need to put std bearing eyes on anyway to shorten them another inch or so, I ordered 12mm ones but the OD is larger than the typical 1/2" ID ones, which has reduced the effectiveness/put me off doing the mod so far, as they ~work as-is with the shortened factory eyes welded on.
I originally was going to use the ($20 on clearance) S6Ms out back, but they were too long, the Fox 2.0s are about right for the rear @~15" extended, the fronts were 17", down to ~15.7 now, fronts should give up another ~inch with spherical bearings/cups welded on, without altering the shock travel.

The rear revalve on the converted Fox truck shocks seems to be ~in the ballpark to the point of they feel OK, still haven't gotten around to have them dyno'd as its roundy-round racing season and there is a waiting list, I'd basically have to drop them off and pick up the following week.
They feel weird (compressing by hand) with no bleeds and almost don't self-extend even with 200 PSI on the IFP, but they are actually reasonably cushy, and were not that hard to bleed even by hand, they just have a lot of "nose" with no bleeds.

Out back, I suspect its the "unloaded" torsion bars, there is a tiny bit of give in the urethane bushings, so right around static ride height they don't contribute much to spring rate, I probably need a bit of preload one way or another to get the instant action. I should probably set the fronts up ~the way the rear is, but they run in needle bearings it may not help very much.

I do have some super hard but poorly cast (ID is concave) urethane SACO bushings, I guess I could bore those out and put delrin or bronze bushings in them for less suspension pivot point give, its just hard to find bronze or delrin in that tubing size.

[PhillipM]

Yeah, I run low bleed but fluttered on the compression to give me linear comp/digressive rebound pretty much the same on the rears, ride well like that, stop it nose diving over jumps too.
I'd try a touch of preload on the rear bars if that the case with yours - a sudden rate change is usually what causes that kind of behaviour, which is why I wondered if it was hitting the droop stops.

To be honest one of the best things I ever did on the rail was ditch the bushings for rose joints, taking the slack out there made the rear so much more stable on the power out of corners and under braking into them it felt like someone had swapped the M/T's for road tyres.

[Ol'fogasaurus]

I had to look up the term "Rose Joint" as I had never heard the term used before. For those who don't know what they are: here in the US we call them Heim Joints or Spherical Rod Ends while the rest of the world calls them Rose Joints.

I am cautious about their use as quite often they are used either undersized or miss-applicated in their use.

I still don't know the use of the word "fluttered" in this case.

If I remember correctly nose dives on landing (jumps) is usually caused by too much reduction of power when in the air. Like wise landing tail first is not reducing power enough or too late when in the air. I try to not do jumps in either case as with a short wheel base that power things gets exacerbated quicker and I have seen some things I did't want to see also; e.g., toys towed in in pieces, tires dismounted or in a couple of cases people damaged.

[PhillipM]

To be honest the stuff we hit even if you're hard on the throttle they'll pitch the car, they're usually 45* transitions or ruts made by tanks on the training ground so they're pretty brutal, plenty of low-speed rear rebound helps to stop the chassis kicking up off the bumpstops. It doesn't help that they usually have a dip before them. If you don't have the right approach, throttle control, and valving all combined....well, this happens*

oops1.jpg

oops2.jpg

oops3.jpg

oops4.jpg

oops5.jpg

Flutter stacks are actually a term from your side of the pond - running a single face shim spaced away from the rest of the valve stack to allow you to effectively have different low speed/bleed transitions with pistons that use the same bleed for both rebound/compression.

There are no issues with using a rose joint/rod end in place of the torsion bar bushings, the loadings are almost purely radial there.

*Not guilty, local club event I went to watch the other weekend!

[Ol'fogasaurus]

Since my suspension travel isn't that long nor that critical... just close so I have been able to live with what I could order predone. I have never had to re-valve a shock so the term was new to me.

Hitting "tank tracks" as you have shown would do that to pretty much to everything. I wouldn't call that a jump more like an Aw $#it!

From your pictures the term "rail" is different than we use the term rail here which really confused me after seeing your post. Here that would be some kind of "buggy" as a rail here is usually open tubes with maybe some "skin" on the sides and/or top.

When it comes to Rose ends so many of the uses I have seen are not aligned or even close to being straight forward which is what the spherical end it is for... miss-alignment... somewhat. My first do with spherical rod ends'rose joints was with numerious triangulated supports/mounts of a 200" long ladder beam to support stowage bins. In 200" the support, bins and open doors had to be less than 0.01 from straight the full length of the structure as you can see a ragged looking installation at 0.01. A laser beam was used to check alignment along the entire length of the bin system, outboard and center. When you pay that much for something you expect it to be perfect.

English, world wide, is sure complicated isn't it?

Lee

[Piledriver]

In diving that's a "full gainer", or at least it would have been if all done in the air.

Ditching the spring plates would be easy, but then I lose the ability to preload and use the torsions as I do. That works pretty good from past experiments, so I'll play with that the coming weekend.

Right now it just makes for heavy steering at low speed, once over ~30MPH its fine.
It just weirded me out as I only messed with the rear.

[Ol'fogasaurus]

Philip, the 4th picture down: I just noticed the suspension in the picture; I have never seen a rear suspension hung like that before. Very interesting to say the least!

Pile, I was a diver in high school, that is until I started to grow taller. A gainer is leaving the board forward then flipping backwards towards the board. Now if you are in clown diving competition that is another matter and the dives and scoring is different.

What he had done there is a good approach to the dive follwed by a face plant to face plant in the open position. Awkward but the degree of dificulty is very low so a score of "0" is likely (I've done a couple of them so I know for certain). Since the twists were after the landing they can't be counted for scoring but are of entertaining (and dangerous) value.

Diving: score "0"

Trampoline: A forward face plant to face plant with two half twists. Score again zero but a broken neck or scrubbing your nose off on the canvas on the "tramp" might give some enjoyment to some.

In tumbling the the ability to come out of the second face plant and do the twists might get you some "style" points but most likely some gritting of teeth and sympethic groans of support as they carry you off the floor.

(sorry, I couldn't help it!)

[Marc]

Philip, the 4th picture down: I just noticed the suspension in the picture; I have never seen a rear suspension hung like that before...

K70: http://www.ttguy.com/scot/vw/vwk70/k70rear.jpg
411/412 has similar geometry.

[PhillipM]

From your pictures the term "rail" is different than we use the term rail here which really confused me after seeing your post. Here that would be some kind of "buggy" as a rail here is usually open tubes with maybe some "skin" on the sides and/or top.

That's not mine, that's a 4wd buggy that was originally based on Land Rover bits then later adapted to independent suspension (that car's about 30 years old), it was just an example.

Mine is a rail:

New Suspension Trail Run Small.jpg

With the right valving ours will actually jump even those things almost flat - or flat enough to land happily anyway - with some careful use of the throttle on the upramp, it's all in the bleed and low speed setup. Just have to be careful as you can make the rear twitchy in the wet if you go too far.