When you widen the front tire width it'll decrease understeer (or increase oversteer). When you widen the rear tires it'll decrease oversteer (or increase understeer). You widened the front by 20mm and widened the rear by 30mm over stock so in effect you've widened the rear more than the front. What you can try is play with the tire pressures. Try increasing the pressure in your front tires and/or decreasing pressure in your rears. Here's a few other corrections you can try....
John Yim (Houston) 91 ZTT Stage...stages are confusing. Just read the mods. :) SM2, Houston Region SCCA "...Just as they're about to catch me... Twin... Turbos... Kick... In..."