understeer question

[jacabean]

I am finding that my newly acquired 3.6 Boxster understeers much more than my 2.7
My 2.7 would give a nice mid-engine drift , very controlled . The 3.6 with the coilovers just tends to understeer . I know these same twisties are a lot faster in the 3.6 but i want that mid-engine sliding feeling . does anybody have a remedy for this ?

[CJ_Boxster]

Brake alittle harder before accelrating, also, upgrading the rear sway bar can transfer the understeer into oversteer

[Adam]

What kind of alignment specs are you running? What kind and size of tires and air pressures?

[blue2000s]

Increase oversteer=stiffen rear suspension

[jacabean]

The car is still running the original Roock set up . the car is lowered way down . would actually like to lift the suspension a 1/2" or so. this will probably not help the handling situation. the roads in Mass. are really bad and the height adjustment will help a lot. What is the optimum ride height for the boxster suspension?

[Adam]

Lower is better. The ideal height is as low as you can get without scraping too badly. What kind of tires are you running? If you're losing front grip maybe try some grippier tires and if you want more oversteer then stiffen the rear like CJ and Blue said.

[kabel]

someone mentioned it alrady, but I'll echo experimenting with tire pressures first (it free!).

[blue2000s]

Originally Posted by Adam

Lower is better. The ideal height is as low as you can get without scraping too badly. What kind of tires are you running? If you're losing front grip maybe try some grippier tires and if you want more oversteer then stiffen the rear like CJ and Blue said.

I have to slightly disagree with lower is always better. Handling suffers alot if the suspension runs out of travel over bumps and in corners. You can also end up with so much camber that you're wearing the heck out of the inside of the tires and not using the full tire's grip.

[Adam]

Originally Posted by blue2000s

I have to slightly disagree with lower is always better. Handling suffers alot if the suspension runs out of travel over bumps and in corners. You can also end up with so much camber that you're wearing the heck out of the inside of the tires and not using the full tire's grip.

That's a good point, the surface being driven on has to be considered. The optimum setup for a smooth track or circuit wouldn't the same as a street driven vehicle or vise versa.

[stephen wilson]

Ride height isn't going to change the handling balance, though added rake may help turn-in. As has been mentioned, try a wider front tire relative to the rear, larger rear anti-roll bar ( preferrably adjustable), or stiffer rear springs (or softer front springs). More agressive front alignment may help a little. Stiffer struts would only help with transient balance, not mid-corner "steady state" handling.
Steve

[jacabean]

what would happen if I raise the front suspension about a 1/2" . this would also soften the springs a little and increase travel . would softening the front give more of and oversteer feel?

[blue2000s]

Originally Posted by stephen wilson

Ride height isn't going to change the handling balance,
Steve

Lowering the car lowers the center of gravity and moves the car's roll center. Both changes work together to alter the car's handling.

[blue2000s]

Originally Posted by jacabean

what would happen if I raise the front suspension about a 1/2" . this would also soften the springs a little and increase travel . would softening the front give more of and oversteer feel?

Assuming your car was originally set up by a competant tuner, your best bet is to either get new tires and/or a set of adjustable sway bars, as has already been noted.

[stephen wilson]

Raising the front ( say by adjusting a coil spring perch ) won't change the spring rate, you have to physically replace the spring to do that. Does this car have coil-overs? If so, experimenting with ride height would be much easier, though the alignment will have to be adjusted after each change. If anything, you'd want the front lower, relative to the rear, not higher.

As far as lowering changing the balance, I'm not a Boxster expert, but in general:
The C.G. will drop, and the roll center will drop by a similar amount, so the front roll couple, and therefore the handling balance, remains essentially unchanged.

Lowering will also lessen front weight transfer by a small amount, increasing the available traction of the front tires, but the magnitude would be small.

The only way to quantify the results would be to try and see.

Steve

[blue2000s]

Originally Posted by stephen wilson

As far as lowering changing the balance, I'm not a Boxster expert, but in general:
The C.G. will drop, and the roll center will drop by a similar amount, so the front roll couple, and therefore the handling balance, remains essentially unchanged.
Steve

As the suspension arms rotate the roll center moves relative to the CG. In a car with a strut suspension it's typically more pronounced than with wishbones or multilink.

[Sboxin]

Originally Posted by Adam

What kind of alignment specs are you running? What kind and size of tires and air pressures?

Agree with Adam - tires and alignment are your friend - on the track we ran 245 on front and 285 on rear=good balance for cornering and catching those GT3s

[jacabean]

Ok , I got pirelli p-zero asimmetrico tires , 225-40 front 285-30 rear 18" . the car has a set of H&R coilovers and the factory M030 package. So if I lift the entire car a 1/2" or so how will this change the handling? I do not have the alignment specs. what do you guys think is the simplest way to adjust the car for street use. I do not track this car. just some crazy back road blasts .

[Adam]

Originally Posted by jacabean

Ok , I got pirelli p-zero asimmetrico tires , 225-40 front 285-30 rear 18" . the car has a set of H&R coilovers and the factory M030 package , built to Roocks specs. So if I lift the entire car a 1/2" or so how will this change the handling? I do not have the alignment specs. what do you guys think is the simplest way to adjust the car for street use. I do not track this car. just some crazy back road blasts .

At least part of your understeer problem has to do with the extra wide tires you have on the rear. You need wider tires up front as well, like a 245 to balance out the back. The Pirelli's you have are ok, but there are better street tires out there for ultimate grip. Look into Kuhmo XS, Bridgestone RE-11, or Dunlop Star Specs. On a well set up car you'd have to have a death wish to overwhelm those tires on the street.

[stephen wilson]

Yeah, the factory 18" set-up on the 987 is 235/265 widths, and understeer. Your narrower fronts/wider rears will magnify the understeer. Try 245/265's ? That's probably what I'll do when my tires wear out.

[Sboxin]

"So if I lift the entire car a 1/2" or so how will this change the handling?"

OK -- so you want to raise the car because of the poor street conditions -- that's all good.
When you raise the H&R's you will want to find a very good Porsche alignment shop/tech to reset both front and rear. If you can find a guy in Mass with a Biesbarth German alignment machine they may be your best bet to tune out some (but not all) of the understeer during your twisty road runs. If you keep the same tires - sound like good rubber - then you will always have some understeer (and that is a 'safe' thing).
You may not like the same alignment for the normal street/road driving. If you put a little front toe out in the alignment the car will turn into turns quicker but will not be very steady down the straight roads at high speed -- this is all a trade off

IMHO of course...

Edit: Also, if you put a GT3 front sway bar in the Boxster that may help also -- some folks do this for Ax, etc.