[Biturbos4] Wet Handling Questions

[Quincy Chiang]

Hi all,

I went to test drive the new '06 WRX with the new 2.5t engine yesterday, I was quite impressed.  It's raining pretty hard , great to put the WRX's awd system to the test.  Aside from the bigger engine and inside/outside cosmetic changes, apparently a rear LSD is now standard, as are bigger brakes with 4-piston front and rear 2-piston calipers all finished in red, from the older WRX and STi in Japan and Europe, all for the same price as last year's model, not bad at all.

So anyway, the test drive route was short but sweet, in particular it had a nice right and left hand 90 degree turns combo.  The Subie understeered a little, I could feel the tires (Bridgestone RE92, same as my S4 nearly bald stock tires!) slipping when pushed hard but I was able to put the power down and shoot out of that corner combo quite nicely.

So after the test drive, I drove my S4 on the same test route to see how the 2 cars compare.  As mentioned above, conditions were very wet, and ESP was off. As expected, my car immediately felt heavier, not too bad though. However something weird happened in that turn combo, I turned in sharply, the car responded, but as the tires were struggling to find traction, the entire car started to shake, so bad that even the speedometer needle was vibrating!  I've never had that before, it felt like the tires were slipping and gripping at the same time, causing the wheels to hop and make that awful shaking and sound. 

Has anyone ever experienced this?  I know my tires are nearly at the end of their life, but they are the same ones as on the WRX, could that be the cause of the vibration?  Or could it be EDL or ESP doing something funky to stop the wheels from spinning/slipping?  When I drive very hard in the dry, say on a freeway cover-leaf entrance with no one around, I push until the tires start the squeal slightly, never had I pushed beyond that point though. Even at the ACNA driving school, I never got this sensation.

I'd appreciate if you can chip in your experiences or theories on what could have happened to cause that vibration/wheel hop, thanks!!

Quincy
'01.5 S4 - Stasis Tracksport (500f/600r/sport), AWE center-vent boost gauge, ecodes, stock everything else
'90 CQ - mostly stock.