I don't think the i3 (well not mine at least) comes with lane assist. My one has traffic jam assist which i've not actually used yet, apparently you can use it up to about 35mph and it will self drive as long as there's a car in front of you.
I had a read online, a lot of things are pointing to the tyres which are obviously the thinnest wheels i've ever seen on a car. According to someone on one of the i3 forums, the front and rear wheels are not the same size and if you have taken your car to a tyre place and got them all done it could be easy for them to not put them on the right way. Something to do with the one i have specifically (Range Extender) because it has a small petrol engine at the rear, the wheels are wider so the tyres are wider too. I know my car had the wheels taken off so they could be refurbished before i got the car, it was on stilts when i first saw it so i think this might be a fair assumption.