Now under heavey braking or downhill cornering the rear end becomes very light and unstable. Would stiffer shocks, EG Koni Yellow single adjustable, cure this. This is a major problem especially at Sears Point. It is very unstable in the downhill braking sections

 

Is this a perception, or are you having real controllability issues under braking? What brakes, and tires are you running. Changing to the H-Sport springs, and especially the wimpy sport rear bar, isn't a big enough change to quantify the behavior you're experiencing.

 

Toyo Proxes RA1 215/40-16. Brakes are crossdrilled rotors, SS lines, Super Blue, and the first set of Porterfield R4S ever made for the MIni

I also have a set of victoracers for auto-x and track use. 225 width on 15's.

And yes, this really is an issue. I am thinking the bump in rear spring rate compared to the front is what is responsible for this. Hopefully I can cure it with some koni's in the rear? Yes?

 

It's mainly during the quick wieght transfer during initial hard breaking but after that sudden jump it settles to an ok level but it should be more planted.

I hope that helps some

 

Wait, isn't this known as trail braking??

 

If it is indeed trailbraking, your thicker rear sway would be contributing to rotating the car under heavy braking. That's the idea behind a thicker rear sway bar! It shouldn't be unstable or unpredictable, though. What are your camber adjustments like? What setting is the sway bar on?

 

You're basically experiencing too much dive and weight transfer to the front.
Stiffer shocks will maintain getter stance at hard braking before turn-in.

The stock shocks are a bit too soft for the H-sports when taken to
the limit. It just does not have enough damping capacity. Im going to try
some Koni's over my H-sports or do KW's V1. I only street my car so it
does not need to be super firm, but I want it a tad firmer than this to
settle the undulation at high speed cornering.

 

minispilot,

You just added H-sport springs and rear swaybar (22mm??). You didn't mention if you have rear lower adjustable control arms, if you don't then you cannot set rear camber. If you did not do alignment after installing the springs then you might be like me.

I had added H-sport springs and madness rear swaybar on soft setting. Without alignment I had -0.5 degrees camber in the front and -2.4 degrees camber in the rear. My handling during hard braking in a straight line was horrible, difficult to control and my ride on rough roads was super jarring as it rattled everything on my dash like I was in the space shuttle on take off.

Then I did a four wheel alignment using the rear lower adjustable control arms (H-sport and RDR make them among others) and used -0.5 degrees camber for the front (stock front is -0.1 to -0.9 degrees) and -0.7 degrees for the rear (stock rear is -1.0 to -2.0) and everything was very smooth. Toe was set to stock settings.

Since then I have changed the rear swaybar to firmest setting and added front camber plates so my alignment for autocross and street is now -2.2 degrees camber in the front (toe 1/16" out) and -1.2 degrees camber in the rear with 1/16" in. And all is good for both autocross and street driving ( a little rougher than stock settings but OK).

 

I would tend to think your car has an alignment issue. With all my auto-x, track, and Dragon driving, my car brakes stable and straight.

--->minihune - read the thread title! he says he has the NON-Comp H-Sport bar, which is the hollow 19mm.

To answer minispilot's question - yes, firmer rear rebound and firmer front compression on the shocks will quicken weight transfer to the front and create more predictable and consistent braking. I would sort the alignment before going any further with your setup, however.

 

I have the alignment under control with RDR camber plates and four adjustable rear links. I have 2.5* fr and 1.5* r camber. 1/8" toe out FR and 0 toe in rear.

No that is not trail braking because this is in a straight line instead of a turn.

The rear bar is set to full stiff. It is needed for auto-x because it pretty much cures all of the understeer.

I think more rebound dampenning is needed in the rear.....

 

I still think its your bound that is too soft in the front.

:smile:

 

did you check the rear trailng arm bushing bolts to the chassis? if they are loose (a few have reported this) your rear toe will wander. rear toe out will definitely feel unstable

 

Nope the bolts are not loose. I am having the car aligned today. I have a theory that when the car settled on the new springs the rear toe changed (bumpsteer). It was set at 0 before and I will probly go to 3/32" toe in just to be sure.

 

dump the sport sway bar!!


get the comp!!!

the car becomes much more stable. I had the same set up.. had the entire hsport sport suspension.. front and rear sways front and rear camber adj springs..

i found that the rear end was very "light" at any settings..

i got the comp bar in the back .. and the car just feels and drives better..

It's harder to swing the back around so it is a bit more controllable...

a

 

I really don't understand how that could be possible, Andy. Rolling = increased grip on the outside tire. Reduced roll = more of a tendency to break loose. It just seems really counterintuitive that it would become more stable with a competition rear sway. *shrug*

 

I wish i could explain it.. Not smart enough.. just know what the butt dyno tells me.. maybe it's all smoke and mirrors..



dont harsh my mellow...

 

I have H-Sport springs and H-Sport comp rear bar. In the tight hole the rear swings nice for AutoX but it gets real loose and squirrelly at higher speeds. For everything except AutoX I run the middle hole. Nice and stable and predictable.

 

Interesting surprise this weekend. I changed street tires from ES 100's to Sumitomo HTR Z's. They're considerably stickier. I inadvertantly left my rear sway in the tightest hole after an AutoX and didn't feel like pulling the wheels again to adjust it (I know you don't have to, it's easier on me) so I drove home with it in the tight hole. Wasn't looking especially forward to that from past experience, it was so twitchy. Now it handles very well on the street in the tight hole. Maybe just a tad twitchy but not enough to make it worth changing back and forth. Does it make sense a tire swap would effect this sort of change?

 

A larger rear sway will make the car oversteer more. What hole is the new bar on and what hole was the old one on.

I would think going to a larger bar would INCREASE this erratic handling............

 

Tires make a world of difference, so between your ES100's and HTRZ's
I am sure this can happen. ES100's were never really that responsive
in terms of initial turn-in feedback. It tramlines so we would assume
that the sidewall is stiff and would get an instant feedback, but it
comes short... but being slower on the response makes it much easier
to control straightline especially at high speeds.

Ive tried S03's and currently on GS-D3's. The GS-D3's have much softer
initial turn in than the S03's and make straight line very easy to control,
so I am going to stick with the softer tires for my MCS.

 

Same bar, different,(stickier) tires.

 

I was replying to this..........

 

a year or so ago, i did a fairly thorough suspension check: took off the springs, put the springless shocks back on and measured camber and toe front and rear for the full suspension movement. (the post is somwhere on mini2). found that camber changed very little (.5 degree max, as I recall), over the entire range for the front, but got increasing negative at the rear with compression, up to 1-1/2 degrees more negative. Toe stayed almost constant front and rear (no bump steer!)


The effect of lowering your car is that you gain negative camber in the rear only.

One report has it that as you change front camber (with plates) toe will change, so a camber change will require a toe check.

 

Right?! That's what I keep saying, but the man insists it just isn't true.

 

Andy...ivan is right

22mm is too much for the Cooper which is lighter than the S's that all run 22s. I've got the 19mm on my cooper and anything stiffer than the stiffest setting would be overkill.