17" wheels - tyres - handling

I have 17" wheels on a TF and 215x40x17 tyres front & rear. I read that the fronts should be narrower as the TF is highly susceptible to tyre size. EG Should the fronts be 195? This week I came off a roundabout in the wet a bit too quickly and ended up facing the wrong way on the roundabout which doesn't seem right, so I thought it might be an idea to get a bit of expert advice - if there is any around, someone who really knows what they are talking about, I would be most grateful for advice - before I embarrass myself further.

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