Unofficial Honda FIT Forums - Weird tire handling problem

Hi guys, I'm new to the forums so I hope you guys can help out. I have a 2002 Honda Fit/Jazz Vti CVT.

Recently I've replaced the stock rims with 5Zigen MK-5 ones. When I bought them they had really cheap, reconstituted, bold, 10 year old tires on them. The wheel dimensions are 205/40x17. I immediately went to order Toyo Proxes 4 to replace them with, however I had to wait rougly a week until they would arrive. So in the mean time I decided to go to Pedders and get some new springs. They replaced the stock ones with their Sports Ryder Coil Springs which gave me a 40mm drop. Obviously being very excited I decided to test out handling around the area. I took a few corners and the car was very level and flat. The handling was greatly improved even with the $20 tires on the car. One particular corner I took a bit too fast, oversteered and span out (I was a bit confused as to why it didn't understeer?). To the point, the car handled A LOT better.

When the Toyos came I was even more excited, being better tires one would expect them to handle even better. After they were put on I went again to the same corners for another handling test. The car handles horribly; Massive understeer. I would go as far as to say the stock wheels handle better. I was really confused so I called Ian Diffen (who supplied the toyos) and asked them whats going on. The guy had no idea and assured me the new tires are about 100x better then what I had on previously. Therefore I went to Pedders and asked them if they had any idea. The guys there think Ian Diffen may have mucked something up. I now have to pay more for them to take another look at it and maybe do another wheel alignment or whatever needs to be done.

Has anyone here got any idea as to what could of happened? Could they have screwed up something? When Pedders finished replacing the springs, the setup was perfect. When replaced with better tires the car handles significantly worse. I'm stumped.