Quote:
Originally Posted by kwayne
New to autocross (have only done it twice, on stock tires) so pardon my ignorance
1) what is in the Z0k GXP pkg?
2) sway bars-FE2, FE3, Saner? bushings, what is stock urethane or rubber? Can bushings alone make a difference like in offroad trucks?
3) tires: can a rim height increase of less than 3mm really make that much of a difference?
245x.35=85.75mm
295x.30=88.50mm
I was under the impression that a shorter stiffer sidewall was preferred? 
4) tire pressures: is it better to have higher pressure in the steering wheels or driving wheels? and at what ratio difference in PSI?
Thanx from all us newbies. |
Hoo boy --- here we go!!
1) There are two versions of the Kappa platform - Pontiac Solstice and Saturn Sky. Each has a "base" version in the 2.4 FI (port injected fuel injection engine) and the base (FE2) suspension. However, Pontiac has an "sport" version of the 2.4 with option code Z0K. Saturn does not. The GXP is a bare bones Solstice with no upgrades except the Z0K package which includes posi, ABS, and the same FE3 suspension on the turbo Kappas except the front springs are shorted than stock. The turbo Kappas are the Solstice GXP and Saturn Sky Redline. This car has the newest Ecotec engine (2.0 direct injected) and turbocharger. The GXP/RL both have the regular FE3 suspension which is firmer shocks, springs, sway bars. Recently Pontiac rolled out a Z0K suspension package for the GXP, but again not available for Redlines. This package has different springs, sway bars and a replacement rear frame member. Again this is a "club sport" version. And it is about 1.5" lower. And it's pretty stiff.
2) FE2 and FE3 refers to GM parts codes for factory assembly. As above the FE2 and FE3 packages are model specific, although completed interchangeable across all Kappa versions. I think that the FE3 bushings may be firmer rubber than the FE2, but not sure. Polyurethane bushings are a WONDERFUL thing to have for off road or dedicated sport use on road cars. But they can hammer you senseless on a newer street car. I have them everywhere on a Triumph TR8 and they do tighten up what is otherwise a very loose car. The Kappas are very stout, stiff cars and poly bushings might not be a good idea except for a dedicated track car that gets trailered. A Saner sway bar is an aftermarket adjustable sway bar made by Saner Fabrication in Florida.
3) For purposes of properly addressing this question, the rim is the metal thingy and the tire is the rubber doodad that goes on the metal thingy.
The example you gave was the 245/35X18 vs. the 295/30X18. The interior diameter is the rim diameter, the first number is the "section" WIDTH, and the middle number is the aspect ratio (section vs. the measured difference of rim diameter and overall tire diameter. The larger the FIRST number they wider the tire. The small the middle number the "shorter" the sidewall. Low aspect ratio tires tend to have firmer ride because they flex less, which is an advantage in hard driving. The 295 you cited is taller than the 245 (despite a shorter side wall) because although it is the same rim application, it is a bigger tire overall. If it were a 295/
35, it would be larger in o/a diameter because of the aspect ratio I explained. Confused yet? I wouldn't recommend anything less than a 40 series on the Kappas for a) overall ride quality, and b) taller sidewalls are better at protecting the rims from curbs and chuckholes. Short stiffer sidewalls are GREAT for racing. Oh, and they LOOK good, too.
4) Tire pressures. I think GM hit the 10 ring when they recommended 29 psi front and rear for the Goodyears. Any less and the car gets "mushy" (high tech term there, huh?), and much more and the handling and ride get "edgy". Also, excessive are pressure for road use may crown the tread and increase wear. For racing purposes just erase the previous two sentences. If you want to start a free for all, just drop a case of beer in a room full of race car/autocross drivers and ask what proper tire pressure should be for XYZ track/course.
. Then GET OUT. There were at least 10 entries in Kappas in A/Stock at the Nationals last week. Not only was there not a consensus of tire SIZE (let alone brand) but if any two cars were running the same pressures it was a coincidence. It is a matter of "feel". Street and track are very different, so the tire demands are different. I have run anywhere from 43/39 (earlier alignments and 245/35x18 Hoosiers) all the way down to 33/31 (more aggressive alignment and 295/30X18 Hoosiers) at the last day of Nationals. It just "depends". Loose rule of thumb for autocross is lower traction = lower pressures and greater traction = higher pressures.
So. now that your hair may be on fire, I certainly hope some of that helped.