I've had this one since my 3, but it's been working so much better with the 4: https://www.amazon.com/iOttie-Touch-Wireless-Charge-Mount/dp/B0754NDNT8/

The Iottie wireless Qi car charger indicates it can do upto 3.5". https://www.amazon.com/iOttie-Touch-Wireless-Charge-Mount/dp/B0754NDNT8

https://www.amazon.com/iOttie-Wireless-Samsung-Standard-Charger/dp/B0754NDNT8/ref=sr_1_6?keywords=Iottie+car+mount&qid=1550682743&s=gateway&sr=8-6

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Yup, I adore this thing. I almost shelled out for a wireless-charging magnetic solution, but this mount is so smooth and intuitive that I've convinced half my friends to buy them. The charging version is pricey, but the fact that it means I almost never have to look at my battery level on a normal workday makes it worth it.

I have this one and love it.

iOttie Easy One Touch Qi Wireless Fast Charge Car Mount for Samsung Galaxy S8, S7/S7 Edge, Note 8 5 & Standard Charge for iPhone X, 8/8 Plus & Qi Enabled Devices https://www.amazon.com/dp/B0754NDNT8/ref=cm_sw_r_cp_api_AWZlAbP97QVZX

Loved this when I had it but it was windshield mount.

https://www.amazon.com/iOttie-Touch-Wireless-Charge-Mount/dp/B0754NDNT8

Personally I don't think a vent mount will ever work great because you're mounting to something that is not solid in a bouncing vehicle.