Unstable as in understeer?

Not sure if the your new tires in the rear are more grippy than the stockers but if they are, it is common to encounter more understeer since the rear end sticks more. But then again, you would rather want understeer over oversteer for public roads because it is easily corrected.

Andre

 

My rear tires are a lot gripper. Come to think of it it is understeer. I figured I would need new front tires..... Any recommendations on uping the tire size?

 

If you kept the 245 size in the rear, then I would suggest just buying the same brand tire as the rear for the front and keeping the 215 size. If you go up to 225 in front with the 245 in the rear, then you might get a lot more oversteer, which is corrected from VSA but if you do any tracking or Auto-X, you will see it more.

The usual is...

215 front/245 rear
225 front/255 rear

Andre

 

There you go!
Looks like you have found the limits of the VSA system.
More rear end grip than it anticipates I guess fooling it in to thinking you oversteering.
Hence it cuts in one side of the front ABS

 

I'm running the original size 245 in the rear so I'll go 215 front. Initially thinking about this whole ordeal I started leaning towards hating VSA. I thought it needed a lot of work and bugs cleaned out, but looking back on it now I think it is doing exactly what it should. I mean the car is off balance right now and if it weren't for the VSA I probably wouldn't have noticed until a lot later when I got into more spirited driving. I probably would have discovered it in a dangerious environment too. So thank you VSA for discovering the balance issue between tires.

 

Yeah, thinking about it, I would guess that mixing tire types front to rear is a much bigger No-No when VSA comes in to the picture.

 

That's why VSA is great. No one is perfect, I don't care if you're even a track instructor. People make mistakes and when the person does make that mistake, VSA will be there to protect yourself, your investment, and everyone else around you.

Andre

 

Yep spot on
I had this issue in my 330D sport when I change rears for a different type.
I now stick to the same tyre on all four corners