Buttoning down the rear end

[redux]

My boy John took the M out to the track for it's first test and tune of my street tire set-up while I was out of town.

Video from behind:

1:26 is damn good SOW (CCW) time for a stock horsepower car running MPSS tires, PFC brake kit, and Motons. But, as the videos show, driving it still seems to be a point and shoot ordeal unless you want to deal with the cars harsh transition into oversteer. With a base line set-up now out of the way, it's time to start working methods to button down the rear end of the car.

The set-up for the car for the trackday was:
Front and Rear PFC BBK (street pads)
Moton Club Sport (rear coil-over conversion)
No Rear Sway Bay Bar

The set-up for the next test and tune is going to get a little more extreme:
Full TCK mono-ball kit
Rear Seat delete
Tuner Motorsport solid sub frame bushing
New springs and removal of the helper springs from the rear suspension
AMS intercooler
18" wheels
Hankook RS3's
Race pads
*os giken LSD

Since the stock corner entry understeer issue has been resolved, it's time to play with the camber, tire pressure, and such to find a suitable solution to add some predictability/progressiveness to the rear of the car. Do any of you track junkies have ideas on stabilizing the back end?

[robertm]

If it were me I'd go to an 18" square setup, add the Vorshlag camber plates and reattach the rear sway. I bet that will fix your snap oversteer.

[redux]

The 18" setup is already in the works and the camber plates are already on the car. A rear bar may go back on for fine tuning the balance of the car once the back end is close to where I want it. But, it's also on one of the things that makes the car rotate so abruptly.

[MDORPHN]

What size tires were you running?

Also, why are you considering replacing the very trick E9x M3-derived diff?

Neil

[redux]

265's up front and 295's out back (275's and 285's weren't available at the time of purchase). When I go to 18's, I'll most likely be running 265's squared or something in the 265 front/285 rear range.

Why replace the stock LSD with another LSD? Because an aftermarket solution is another way to fine tune the balance the car. The stock LSD is designed to work in a wide variety of situations, and since to my car is nothing more than a weekend play thing, daily driver versatility is not a requirement. With the aftermarket unit, I'll be able to tailor the handling dynamics and ability to put down the power of the 1 to my specific tastes.

[RimasRS]

No rear sway bar. What does that mean?

[redux]

Roll bar, anti-roll bar, anti-sway bar, the black tube in the picture below. It has many names, and it's been removed from the rear of my car.



Springs will be used to compensate for loss in roll stiffness.

[MDORPHN]

Originally Posted by redux

265's up front and 295's out back (275's and 285's weren't available at the time of purchase). When I go to 18's, I'll most likely be running 265's squared or something in the 265 front/285 rear range.

Why replace the stock LSD with another LSD? Because an aftermarket solution is another way to fine tune the balance the car. The stock LSD is designed to work in a wide variety of situations, and since to my car is nothing more than a weekend play thing, daily driver versatility is not a requirement. With the aftermarket unit, I'll be able to tailor the handling dynamics and ability to put down the power of the 1 to my specific tastes.

Yes, I understand. I went through three limted slips (including a Quaiffe) on my previous car (a highly modified M Coupe) before I had it where I wanted with a custom 3 clutch variable ramp set-up built by Dan Fitzgerald (diffsonline).

However, I'm very pleased with the diff in my 1M and have no plans to change it.

As has been discussed ad nauseum, the 1M is not an easy car to drive on the edge, although steps can be taken to tame it just a bit.

Among other things, I'm running camber plates, JRZ dampers and a stiffer E93 M3 front sway. Car still requires quick hands (and feet), but I really dig how it handles.

Neil

[redux]

The M is not drive is not an easy car to drive fast. Unfortunately, dancing on the edge in this thing is somewhat of an addiction. I'm pretty nifty behind the wheel, but I have no delusions of having Leob like abilities. I would have eventually run out of talent if the car kept it's stock handling traits. Slides at near triple digit speeds are fun, but you can only get away with that for so long.....

[HP Autosport]

In our experience, larger anti roll bar will only add to the oversteer especially a snap oversteer.

If the main springs don't stay loaded in the inside rear corner during a turn, a snap oversteer may also occur.

What spring rates are you running?

[bdaddylo]

Originally Posted by redux

Roll bar, anti-roll bar, anti-sway bar, the black tube in the picture below. It has many names, and it's been removed from the rear of my car.



Springs will be used to compensate for loss in roll stiffness.

You said you already removed the rear roll bar and that didn't help reduce oversteer, so why would you go with stiffer springs? That would help roll stiffness but also reduce rear weight transfer. Maybe a small roll bar and softer springs would do the trick.

[MDORPHN]

Originally Posted by HP Autowerks

In our experience, larger anti roll bar will only add to the oversteer especially a snap oversteer.

If the main springs don't stay loaded in the inside rear corner during a turn, a snap oversteer may also occur.

What spring rates are you running?

Harold -

I'm running Swift springs. 7" 392# front/10" 672# rear.

Neil

[HP Autosport]

Originally Posted by MDORPHN

Harold -

I'm running Swift springs. 7" 392# front/10" 672# rear.

Neil

Neil,

I remember the rates you run. My question was directed at the OP.

Harold

[Pete_vB]

I'm a bit surprised with your decision to pull the rear bar. Where are you getting this advice from?

I run one of my Porsches without the rear bar, but I wouldn't expect it to help stabilize the rear in your situation.

Running no rear bar means running stiffer rear springs to maintain overall roll compliance. Stiffer rear springs mean you can't put power down as well, causing the back end to step under power.

The other thing I could imagine contributing to instability is mismatched shocks. How have you tuned the shocks so far? Have you used principles like these to guide your shock tuning?
http://www.ozebiz.com.au/racetech/th...hocktune1.html

[redux]

Originally Posted by bdaddylo

You said you already removed the rear roll bar and that didn't help reduce oversteer, so why would you go with stiffer springs? That would help roll stiffness but also reduce rear weight transfer. Maybe a small roll bar and softer springs would do the trick.

I not try to reduce the amount of oversteer, I actually find that one of the more endearing features of the car. I'm just trying to make the break away characteristics more progressive and predictable. I would love to get a smaller bar, but finding one is proving to be somewhat of a challenge.

Originally Posted by HP Autowerks

In our experience, larger anti roll bar will only add to the oversteer especially a snap oversteer.

If the main springs don't stay loaded in the inside rear corner during a turn, a snap oversteer may also occur.

What spring rates are you running?

I can't remember the rates off the top of my head, but they are relativity soft. I'm going stiffer and getting rid of the helper springs to better control the loads on the wheels. As it stands, removing the rear bar provided a decent boost in traction and made the rear end more predictable, but it not were I want it yet.

Originally Posted by Pete_vB

I'm a bit surprised with your decision to pull the rear bar. Where are you getting this advice from?

I run one of my Porsches without the rear bar, but I wouldn't expect it to help stabilize the rear in your situation.

Running no rear bar means running stiffer rear springs to maintain overall roll compliance. Stiffer rear springs mean you can't put power down as well, causing the back end to step under power.

The other thing I could imagine contributing to instability is mismatched shocks. How have you tuned the shocks so far? Have you used principles like these to guide your shock tuning?
http://www.ozebiz.com.au/racetech/th...hocktune1.html

I have no problem with the back end stepping out on me, it's the rate of the transition that worries me. This was just an initial test of the baseline setup to get some numbers with the data logger. The dampers will go back on the shock dyno, valving may be changed, spring will be adjusted to suit, and the package will be track tested again. I have a long way to go with the street tire setup (at least 9 more test sessions) before I call it good enough to move on to things like R-comps and more horse power. By the time I done, every angle will have been investigated, and also tested by people that are much better behind the wheel than I am.

[Pete_vB]

Originally Posted by redux

I have no problem with the back end stepping out on me, it's the rate of the transition that worries me. This was just an initial test of the baseline setup to get some numbers with the data logger. The dampers will go back on the shock dyno, valving may be changed, spring will be adjusted to suit, and the package will be track tested again. I have a long way to go with the street tire setup (at least 9 more test sessions) before I call it good enough to move on to things like R-comps and more horse power. By the time I done, every angle will have been investigated, and also tested by people that are much better behind the wheel than I am.

Not sure if you've missed the point. Stiffening the back springs as you've done as well as presumably stiffening the shocks has been the cause of the increased twitchiness you've experienced. Going stiffer with the mains is unlikely to help.

Find a good setup guy to test the car, not just a good driver.

[robertm]

One thing you might consider doing now is switching to r-comps. Lots of little adjustments needed when you switch and if you are at the level of playing with valving and spring rates then it seems a wasted effort to do so on street tires only to redo everything again once on a proper track tire.

Removing the rear sway seems a blunt way to fix a problem that's likely not solely related. When are you getting the sudden loss of grip? Spring rates and high or low speed valve adj are usually the best avenue of adjustment. Possibly initial static alignment could be an issue too? Changing out factory bushings may help as well. Another source of information would be the M3 track guys; dynamically a bit different but still very similar geometry and hardware. I'm just spit balling here but let us know what you end up with!

[HP Autosport]

Originally Posted by redux

I can't remember the rates off the top of my head, but they are relativity soft. I'm going stiffer and getting rid of the helper springs to better control the loads on the wheels. As it stands, removing the rear bar provided a decent boost in traction and made the rear end more predictable, but it not were I want it yet.

Yes, removing the rear bar will help with traction when putting the power down. Back in the Redline Time Attack days we would run without the rear bar for better corner exiting speed and traction.

Main and helper combo if not done correctly can certainly hurt traction.

[redux]

Originally Posted by Pete_vB

Not sure if you've missed the point. Stiffening the back springs as you've done as well as presumably stiffening the shocks has been the cause of the increased twitchiness you've experienced. Going stiffer with the mains is unlikely to help.

Find a good setup guy to test the car, not just a good driver.

I get what you're saying, but I also know that general guidelines are just general guidelines. There are many exceptions to those rules. I chose to avoid directly answering some of your questions because of the possible of ensuing internet argument; I despise internet arguments. The truth is, I know which direction the setup is going to go. And yes, I do have professionals working on it.

The 1M forum seems to be all about HP figures, selling crap, stupid ass "exclusive" polo shirts. So, I made this post just to stir up some actual suspension talk. The transition to oversteer in my car is actually better than it was stock, but not as progressive as an m3. So it's not bad, it's just not where I want it.

Originally Posted by robertm

One thing you might consider doing now is switching to r-comps. Lots of little adjustments needed when you switch and if you are at the level of playing with valving and spring rates then it seems a wasted effort to do so on street tires only to redo everything again once on a proper track tire.

Removing the rear sway seems a blunt way to fix a problem that's likely not solely related. When are you getting the sudden loss of grip? Spring rates and high or low speed valve adj are usually the best avenue of adjustment. Possibly initial static alignment could be an issue too? Changing out factory bushings may help as well. Another source of information would be the M3 track guys; dynamically a bit different but still very similar geometry and hardware. I'm just spit balling here but let us know what you end up with!

Because it's a street car that will mainly be used with street tires. I'm not racing, nor do I care about lap times, so ultimate speed on R-comps isn't something I plan on chasing. They'll just be applied whenever I feel the itch and put back on the shelf once the rash is gone.

[MDORPHN]

Originally Posted by redux

The transition to oversteer in my car is actually better than it was stock, but not as progressive as an m3.

That's primarily the result of the 1M's shorter wheelbase and is exacerbated by its greater torque.

Neil

[HP Autosport]

Originally Posted by MDORPHN

That's primarily the result of the 1M's shorter wheelbase and is exacerbated by its greater torque.

Neil

That is correct!

[bdaddylo]

[quote=redux]
The 1M forum seems to be all about HP figures, selling crap, stupid ass "exclusive" polo shirts. So, I made this post just to stir up some actual suspension talk. The transition to oversteer in my car is actually better than it was stock, but not as progressive as an m3. So it's not bad, it's just not where I want it.
[quote]

Well said. HP is worthless if you can't utilize it. The 1M's biggest weakness is how abrubtly it transitions to oversteer. Thanks for sharing your quest to resolve this characteristic.