The problem you get fitting a 22mm front bar and 25mm rear is the lack of droop on the front inside wheel under cornering, this induces the wheel to spin up when pushing on "hard". 8/10ths its fine and not noticable, 10/10ths it becomes an issue having to back off to stop wheelspin! Mainly in 2nd and 3rd gear.

Yeah there are good gains to be had but i'm not sure where to go next?

Apparently it is a known problem talking to the rally boys.

 

Soft? - do you mean still too much roll?

 

wow, this thread has been very informative and given me lost to think about. Thanks!

 

We normally run a 24mm rear, not a 25mm. But the problem you are referring to is solved by increasing caster and a change in low speed bump damping......

 

Yup just a bit too much roll, even with everything stiff, but it's so rarely on track it isn't worth chasing thicker bars F&R, or yet more struts/springs.

IMHO

dunx

 

You don't alter arb stiffness for a track day?

 

You change the caster by the usual means?

ie Whiteline or Perrin rear bottom arm mounts?
http://ep.yimg.com/ca/I/fastwrx_2071_240719259

 

I use Whiteline Caster bushes or WALK (the others on the market seem to be copies of Whiteline's design, perhaps with some measurement mistakes in them), off set top mounts as well as some other tweaks to get as much caster as possible. On the Impreza you want at least 6 degrees. For motorsport you might want considerably more............ But I'll leave other chassis dynamics engineers to make their own decisions.

When I use normal mono tube dampers, I run a fairly agressive pre-tension on the bump stack. If using multi stacked pistons or other trickery like g-force compensation, it is a different story again. On semi mono tube I also use a fair bit of 'nose' on bump.

 

No, I have a neutral road car that just edges into oversteer on track, as I like it.

I find that chasing my friends 450/500 bhp Evos around has made me want a "safe" set-up.

When I was running 340 bhp, I had a more aggressive set-up and "she" was a bit lively on fast B-roads....

dunx

P.S. I may go for a stiffer rear bar after having mine powder coated, as it looks cr*p all rusty....

 

I may try the 20mm packers I've made then.

I need to do something and I suppose it is fun developing the old trackcar.

 

If you mean packers for the dampers, to fine tune bump travel and run rising rate, it could work. Just monitor tyre temps as they might just shoot up when the suspension frequency rises abrubtly.

If you mean packers for caster increase, sounds good :-)

 

Yeah for the caster increase

 

If you use 20mm packers, make sure you use decent strength, longer bolts :-)

Oh, and re-fresh the power steering fluid with some synthetic atf as with very high caster angles, the power steering will get a bit hotter...........

I forgot, make sure you have enough drive shaft plunge as well.


Cheers

 

Who is that masked man ?

And who'd have thought about the poor old PS fluid ? As it lasts forever....

LOL

dunx

 

If you referring to me, just an old git, with a tiny bit of chassis dynamics experience

 

Enlighten us oh wise one....

LOL

dunx

 

Looks like he doesn't want fame?

 

Quick note on the rear Whiteline 24mm arb recently fitted on my 96 Sti.

Car feels totally sorted now.

Handling has gone from soft in the corners with rear wallow and a feeling of quite a bit of overall roll, to feeling tighter, flatter, more precise on the steering, with a huge increase in the amount of overall grip. I would say the car's balance is neutral. The arb is on the middle setting.

Handles like a true Scooby now

I reckon the rear arb has got to be must upgrade. On a bang for buck basis you get a massive improvement for your money. Highly recommended...