"I Wish I Knew This Before Purchasing The BMW 430i/440i And After Giving My Lexus IS250 To My Son"

What insider tips do BMW 4 Series owners have, for someone upgrading to the 430i or 440i, from a Lexus IS250?

When you want a two-door compact BMW sportscar with reasonable rear seat and trunk space, the 4 Series is an excellent choice. 

The appeal of either BMW’s 430- or 440i is obvious, but what about some features that first-time owners might not know? That’s the issue discussed on the BMW M340i/440 and M Cars Facebook group, after one of the group members posed a reasonable question:

I just gave my Lexus IS250 to my son, and I'm looking at getting a 430i/440i xDrive coupe or convertible. What do you wish you knew before you made your purchase? What do I need to look for and what do I need to be aware of?

Fellow forum members responded with their driving and ownership experiences, highlighting things worth knowing about 4 Series ownership before buying. 

Rissy San is rated as a top contributor on the BMW M340i/440 and M Cars Facebook group group. He’s also an M440i Grand Coupe owner and had this to say about the difference between driving an IS250 and 4 Series. 

You’ll notice how bumpy the ride is. But of course, there are bad roads where I live. Getting used to it and switched out the run flats. It definitely will not be as smooth as the IS, but it sure will be more fun and better handling.

Another BMW M340i/440 and M Cars Facebook group member, Sebastian Soroka, was clear about what made BMW’s 4 Series cars so great. 

I have had the BMW M440ix coupe for a year now. The worst part is getting out of the car because I’ve reached my destination. Car is a blast to drive, and so far, zero issues in the first year of ownership. Had the M440ix convertible as a loaner for a couple days and thought it was great, too. That car looks excellent in convertible form, with top down and up. I don’t think you can go wrong with either.

BMW and Lexus are both luxury car brands, but the former focuses more on driving dynamics than the latter. That’s something worth remembering if you give someone in the family your trusted IS 250, and upgrade to either a BMW 430- or 440i. 

But what about the ride quality and run flats? Why is that an issue, and does it really matter? In principle, run flats are a good idea, there’s a sensible reason why BMW uses them. It’s all about keeping you mobile, even when road debris or badly surfaced roads, damage your low-profile tires. 

The good and bad of run flats

Run flat tires have the advantage of getting you home, even if you puncture, instead of leaving you stranded with the hassle of changing a flat. If you live in an area with heavy industry and a lot of construction activity, there’s the risk of fasteners, bolts, and nails falling off trucks and littering the road, just waiting to cause a flat. You'll always get to your destination in a 430- or 440i with run flats, even if your tire is punctured. 

The compromise with run flat tires is that they have much sturdier sidewalls to keep the tyre shape and driveability, even if it does puncture and start losing air. Those stiffer, reinforced sidewalls mean less compliance and harsher road quality. Compared to a Lexus IS250 on standard tyres, any 430- or 440i on run flats will feel harsher on roads with poor surface quality. 

You don’t have to keep your 4 Series on run flats, though. If the roads in your area are degrading, you can always fit conventional low-profile tires, with run flat technology. For a less harsh ride. 

However, if you’re noticing unusual behavior in your 4 Series, like shaking during startup or anomalies in fuel consumption readings, it’s worth exploring whether these are normal quirks or signs of a deeper issue—here’s one owner’s experience with their BMW M440i dealing with a similar concern.

The driving dynamics remain great

For any buyer changing from a Lexus IS250 to one of BMW’s 4 Series two-door cars the ride quality on run flats might feel less comfortable, but there are many other benefits. Like BMW’s legendary driving dynamics, steering feel and chassis feedback. Exactly what you want from a two-door car. 

Replies to the post about upgrading from an IS250 to either BMW’s 430- or 440i, mention the value of the 4 Series driving dynamics. It’s not marketing. Remember that the 4 Series platform is also used for the M4, one of BMW’s most lauded performance cars. That means that even less powerful versions, like the 430- or 440i, have excellent chassis balance, suspension set-up and driving dynamics, way beyond the ability of an IS250.

The cornering and dynamic stability on offer with BMW’s 430i or 440i will quickly make you forget about the slightly harsh ride quality across bad road surfaces. 

What’s your experience been with BMW run flat tires? Especially on the performance models? Have they gotten you home safely in an emergency?

What insider tips do BMW 4 Series owners have, for someone upgrading to the 430i or 440i, from a Lexus IS250? 

Lance Branquinho has 20 years of reporting experience working with various carmakers and OEMs. His work at Torque News focuses on covering BMW news and opinion about the latest BMW vehicles and their development Follow Lance at LinkedIn and X for the latest BMW-related news.