Sorry in advance for the long winded post...
I'm not a novice in autocross, but my past four seasons have been in SM with cars that were more capable that I am as a driver. As a result, I felt like I was always just trying to figure out how to drive the car, since it had enough grip and power to cover up my mistakes. This year, due to a growing family, I sold the engine swapped e30, and bought a more practical, more modern car. The weekend before my wife gave birth to our first child, I bought an 04 Matrix XRS with a blown clutch for a steal from CL.
The change from RWD to FWD was interesting, as I was afraid I would find it lacking in comparison to my prior experiences, but I quickly found out that unlike with my previous overbuilt cars, I could easily find the limits of the car. As a result, I improved my driving more in the last season of autocross than all my previous seasons combined. At the same time, however, I quickly pinpointed the weaknesses in the cars setup. While my prior cars might have masked any mistakes, the Matrix was holding me back.
The car had 167k miles when I bought it, but aside from the worn clutch and sticky rear calipers and e-brake cables, was in good shape. I immediately started researching suspension options, and while lowering springs were readily available to reduce it's crossover ride height, there seemed to be an absence of quality shock options. Both Bilstein and Koni lacked any part listings for the front struts of a first gen Matrix, and Tokico seemed to be on galactic backorder. I bought Tein springs while they were on sale, and installed them on stock struts. I also installed crash bolts to adjust camber, and got an alignment, set to 2.5 degrees negative camber and stock toe. It felt good on the road, but during the first autocross, I found I was plagued by wheel hop every time I went WOT.
Before the next event I replaced the worn out control arm bushings with polyurethane, and installed polyurethane engine mount inserts, and tackled the front shocks. Even though no one lists quality shocks for the Matrix, I learned that the 1st gen Matrix, and 9th gen Corolla have essentially the same suspension design, with the only major difference being the Matrix is a a bit more heavy duty, with larger hardware holding it together. While Koni doesn't list a front strut for the Matrix, they do sell a cut-a-strut insert for the 9th gen Corolla. Without being positive it would fit the Matrix housing, I ordered a pair, and figured that even if they wouldn't fit into the cut open Matrix strut housing, I could snag a set of used Corolla struts to hack up, and just drill out the bolt holes to fit the Matrix knuckle. Fortunately, the inserts fit perfectly, and between the Koni's and the poly bushings, the wheel hop was cured.
The next event revealed another problem, however. Even with the lower, stiffer springs, there was just too much body roll, and the rear sway bar was too weak to keep the car balanced. Exiting every corner, or even traveling into a corner, if I didn't wait until I straightened, the wheel and the weight had settled, the inside front wheel would spin as soon as I got on the gas. No amount of tire pressure changes or modifying my line through the corners could make up for having to wait until I had completely exited a corner before being able to touch the throttle.
A 24mm rear sway bar cured the body roll problem, and once I dialed in the tire pressure, I could predictably rotate the car through corners, and even induce slight oversteer with trail breaking, and keep the front tires planted well enough to hammer on the throttle out of corners. I was able to get a good feel for the car, and put down times that were within .8 seconds of each other over an events worth of runs. I had experienced drivers ride along, and offer their input, including the reigning FWD driver in our region, and he agreed with my sentiment, the car needed stickier tires to be faster. I ran the whole season on the Mastercraft tires the previous owner had installed right before the clutch wore out and he sold the car to me.
I snagged a set of relatively ugly 16x7 Motegi's that come in at about 18lbs each for $25 a piece from CL, which brings me to the point of my post: Now I need to pick rubber. Since I'm in STF, I know I need to stay 225mm width or less.
I am wondering if there is much to be gained by running 225, vs the factory 215?
I see some other FWD cars running wider tires up front than in rear. Should I be considering a staggered setup? Maybe 225 front / 205 rear?
Would I be better off running 225 all around to get as much possible grip available, and then dial in the grip bias by changing tire pressure spring rates?
