edx1
I suggest you google and find out exactly what the tyre sizes mean.
http://www.gonebush.org/t213-tyre-si...d-letters-mean
Don't worry about understeer. That is just wannabe racers talking you have been reading. Seriously unless you track the car (or autocross in the US) it won't make a difference. On the road you should be nowhere near the limit of the car for that to be a factor.
And even if it is understeer is safer/more predictable/more controllable than oversteer.