ARB Handling

[m3215]

My Suspension setup is as follows

HR Coilover unsure of spring rates, does any body know how you can tell? They came with the kit
HR ARBS
15" BBS, Dunlop sp9000 brand new,
Mounts are new, front and rear, front are Crash/Ecentric Mounts.

ARBS setting - Front Stiff
Rear soft,
Height setting not to low sorry cant be more precise.

you wouldve thought with all this fancy hr bits the car would've handled like its on rails but wrong, there is a mixture of understeer on fast bend entries (even at med sized r/about at about 30mph) and as you exit it tends want to overstear. There is no grip at all and its like driving on skates!

Im thinking and have been told there is to much stifness from the ARBS, and revert back to stock roll bars would improve the handling from what it is.

the diameter for stock ARBS are 19mm front 14.5mm rear but as i havent got them any more i can get hold of the 20mm from the 325i sport/Touring with 14.5mm rear.

quetion would this 1mm make a huge difference or would it be just best to stick to 19mm standard front intended for the e30 m3?

does this sound about right because or the ARBs or should i be looking at something else?

any input about my suspension setup, why and hows and criticism (be gentle and stay on topic) is welcome.
Thanks

[monzon]

Just checking, but did you get the car's alignment checked or set after installing all those parts?

[Mmark]

My Suspension setup is as follows

HR Coilover unsure of spring rates, does any body know how you can tell? They came with the kit
HR ARBS
15" BBS, Dunlop sp9000 brand new,
Mounts are new, front and rear, front are Crash/Ecentric Mounts.

ARBS setting - Front Stiff
Rear soft,
Height setting not to low sorry cant be more precise.

you wouldve thought with all this fancy hr bits the car would've handled like its on rails but wrong, there is a mixture of understeer on fast bend entries (even at med sized r/about at about 30mph) and as you exit it tends want to overstear. There is no grip at all and its like driving on skates!

Im thinking and have been told there is to much stifness from the ARBS, and revert back to stock roll bars would improve the handling from what it is.

the diameter for stock ARBS are 19mm front 14.5mm rear but as i havent got them any more i can get hold of the 20mm from the 325i sport/Touring with 14.5mm rear.

quetion would this 1mm make a huge difference or would it be just best to stick to 19mm standard front intended for the e30 m3?

does this sound about right because or the ARBs or should i be looking at something else?

any input about my suspension setup, why and hows and criticism (be gentle and stay on topic) is welcome.
Thanks

The tyres are brand new. The tread blocks are at full height and will deflect and overheat(if used in track day millieu). This is partly responsible for some of the understeer.
The tendency in the USA for track days in BMW is to keep the rear ARB small or delete it, in order to allow more rear end grip or earlier throttle, and stability on corner exit.
The Rear ARB may or may not be planting the rear so much better than the front and contributing to some of the corner entry understeer.

How much front neg camber do you have at the front? For hooning around, you want at least 1 and 3/4 degree neg on the road, and probably 2.5 for the track.

Once the tyres are well scuffed in, you can adjust tyre pressures front Vs rear in order to shift the relative degree of grip between the two ends.

you may also need to adjust your driving style to suit the suspension if it is all brand new to you.

The front bar, I'd leave alone for a bit, until you find out what tyre pressures the car/tyres want.

If you have very little camber neg in the front, then get some camber plates, play with tyre pressures, and technique but leave the bars alone.

m

m

[m3215]

thanks for replies. hope you can contribute more.

well the parts have been on the car for about 2 years. It was aligned after fitting the parts on.

this is the story....

the same setup as above I was running with type 5 alloys with 15mm spacers equating to about et5 and it was suberb! took it to silversone and the balanace and the grip was really impressive, you can really chuck it in the corners and it will hold. To describe it the car felt like an M3, poise balance and grip. perfect.

since then i changed the alloys to the stock 15" bbs minus the spacers and the handling effect has been described as above.

Mmark i also did a search and read a few people removing the rear bar but i dont really want to do that as its not a track holigan car but enjoyable for the road and 1 2 track session a year.

Stupid question does the coilover height effect the handling of the car, by only adjusting height does the spring rate change or not??

my level of knowledge for suspension is very basic so be kind. :-)

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just a note the tyres have about 500miles on them

[UK215M3]

If you have the H&R coilovers with the progressive springs they are in the range of:

270-375 lb front
340-400 lb rear

Are your bars H&R ?

If they are I had exactly the same problem as you, it seemed to me as if the bars and the suspension were 'fighting' each other. I reinstalled standard bars and it was excellent. I think the springs do not match the H&R bars at all.
However the H&R RSS or Nurburgring version of the kit is very different and they work very well. This has 630lb Fronts and 680lb rears, non progressive.

[Hoofty]

Other members have had similar stories regarding the combination of H+R coilovers and H+R bars, though with what spring rates I'm not sure. By swapping back to OE alloys from the type 5s, you will have decreased the track by about 40mm (what ET are the BBS 15s?), so this will have increased the load transfer seen by the tyres. In that instance, it's possible that there's just too much roll stiffness for that amount of track width (though roll stiffness is dependent on track width). The experience I've heard of suggests that stock bars with H+R coilovers is a good combination - see http://www.s14.net/forums/showthread.php?t=32405 , esp post #6.

Changing ride height doesn't change the spring rate - only the geometry. The spring remains the same rate, even if you preload it (i.e. the spring is compressed by the strut, even with zero load on it). Preloading isn't particularly useful in my opinion - all that happens is that the spring won't deflect until the load on it exceeds the preload.

Losing suspension travel has no real advantages, so don't run it on the floor. If you are using 15" wheels, you won't be able to use 'roll centre spacers' between the strut and the knuckle to 'correct' the wishbone geometry, so that's another reason to not go too low.

Regarding the 325i bar, I don't think it will fit. All other E30 ARB's (except the M3 cabrio) had different mounting points for the drop links - I don't believe that they're compatible with the direct acting M3 drop links.

Oh, and remember - there are no such things as stupid questions, only stupid answers. And most of those are from me.

Nick

Edit - This chap (previous post) is the one I've been referring to! :drive:

[UweM3]

all E30 bars will fit, it's just the drop link which is different. The standard E30 drop link is attached to the wishbone, not to the strut but can be used as well.
But beware of the different diameters of the bar, the E30 drop link reduces the effect of the roll bar and some E30 roll bars are thicker than M3 to compensate.
All the diameters can be found in the EPC

[Jake]

the same setup as above I was running with type 5 alloys with 15mm spacers equating to about et5 and it was suberb! took it to silversone and the balanace and the grip was really impressive, you can really chuck it in the corners and it will hold. To describe it the car felt like an M3, poise balance and grip. perfect.

since then i changed the alloys to the stock 15" bbs minus the spacers and the handling effect has been described as above.

If it was perfect before, and a change in wheels/tires made it perform poorly, odds are the problem is associated with the new wheel/tire set up.

I suggest you play with different tire pressures before making suspension adjustments.

There are a lot of theories out there and to be honest it takes serious testing to pinpoint specific problems. It's just that there are so many variables that there is no way any of us keyboard jockeys can really tell you want the problem is. At best they're just guesses (including mine).

Personally, I wouldn't remove the rear ARB. I ran larger bars (16mm rear) and loved the handling. But I spent a fair amount of time with damper settings, tire pressures, ARB adjustments etc... In the end I was running higher tire pressures than suggested but it worked for me and the car.

Jake

[m3215]

hi

thank you guys for your input, its is much appreciated, have a virtual bear on me. ;-)

like dave mentioned its the balance between the spring rate and the bars. the bars are HR. I had a wider track, more coverage on the road, so there was more wide spread load transfer.mmhh...

personally i dont want to lower it any more as i like the height, no scrapes and looks decent.

im going to find out my spring rate from the dealer i bought it off and ill post back and as soon as i get hold of the orginal bars ill test the theroy out.

Tire pressures? Im currently running 32 all over (the last time i checked ouch) but how would one determine what tyre pressure are correct?

because if you run to high pressure the inner thread wears out considerably quicker than the outer. ill pump them up and have a go.

thanks again. :-)