[Chubbiejones]

Curious to know everyone's perspective on my decision dilemma. Recently purchased a slight used 2020 M340i (non EDC) and I'm at a cross roads as to whether I should install a set of aftermarket 20in wheels with a set of PS4S and H&R springs including Dinan handling kit or keep the stock 19in wheels with run flats and install a set of KW V3 coilovers??

The car will never see the track and will only be a DD.

If you could let me know your thoughts I would greatly appreciate it.

[jlapicki]

Ditch the run flats....

[Chubbiejones]

Originally Posted by jlapicki

Ditch the run flats....

Fully agree - run flats are definitely not my cup of tea! I know the car will handle and ride soo much better with a set of new tires.

[1WickedE90]

I would do 19" (lighter wheels & PS4S tires) & Dinan springs w/ handling kit.

[Chubbiejones]

Originally Posted by 1WickedE90

I would do 19" (lighter wheels & PS4S tires) & Dinan springs w/ handling kit.

I like the way you think! What is the average amount of weight saving between a set of 19s vs 20s?

[1WickedE90]

Originally Posted by Chubbiejones

I like the way you think! What is the average amount of weight saving between a set of 19s vs 20s?

A lot - you can see for yourself here:

https://www.tirerack.com/wheels/resu...&package=false

https://www.tirerack.com/wheels/tech/index.jsp

[Chubbiejones]

Originally Posted by 1WickedE90

A lot - you can see for yourself here:

https://www.tirerack.com/wheels/resu...;package=false

https://www.tirerack.com/wheels/tech/index.jsp

Appreciate the links my friend - I know some of the aftermarket wheels (i.e. HRE) can have a 20in wheel that is lighter than the factory 19in wheels.

[Ikester19]

I'd do 19" OEM wheels with a staggered setup and PS4S tyres. Apart from aesthetics there is no upside in installing lowering springs, in fact in my experience I found that making changes to the OEM suspension setup adds to vagueness in steering feel and upsets the ride quality and overall suspension geometry.

[thakid22]

Originally Posted by Ikester19

I'd do 19" OEM wheels with a staggered setup and PS4S tyres. Apart from aesthetics there is no upside in installing lowering springs, in fact in my experience I found that making changes to the OEM suspension setup adds to vagueness in steering feel and upsets the ride quality and overall suspension geometry.

Lowering springs can significantly reduce body roll, brake dive, and squat.
They can also reduce understeer. They can also increase slalom speeds and boost grip.

The downside is that they often make the ride harsher, more jiggly, and less well controlled.

They have their ups and downs.
The key is to not go too low.

I personally will only go .50 to .75 inches lower.
Like you, I feel big drops compromise suspension geometry.

But done in moderation, you can carefully balance the pros/cons. Even factory sport suspensions lower the car a tad.

[Ikester19]

Originally Posted by thakid22

Lowering springs can significantly reduce body roll, brake dive, and squat.
They can also reduce understeer. They can also increase slalom speeds and boost grip.

The downside is that they often make the ride harsher, more jiggly, and less well controlled.

They have their ups and downs.
The key is to not go too low.

I personally will only go .50 to .75 inches lower.
Like you, I feel big drops compromise suspension geometry.

But done in moderation, you can carefully balance the pros/cons. Even factory sport suspensions lower the car a tad.

I had ACS lowering springs fitted to my M340i and reverted back to the OEM springs after 3months. The ACS springs resulted in a moderate drop of 20mm in all four corners. Although there was a slight (not significant) reduction in body roll, brake dive, and squat, the trade off was an unsettled ride, vagueness in steering feel and the chassis balance felt off. BMW engineers spend years designing and optimising suspension geometry and to say that slapping on after market springs will improve performance such as reduce understeer and boost grip is simply not true. If you looking to reduce understeer and increase grip you will need a good set of coilovers and wider rims/tyres. Aftermarket lowering springs won't do much apart from aesthetics. Just my 2c worth but to each their own.

[SoCalM340i]

Originally Posted by Ikester19

I'd do 19" OEM wheels with a staggered setup and PS4S tyres. Apart from aesthetics there is no upside in installing lowering springs, in fact in my experience I found that making changes to the OEM suspension setup adds to vagueness in steering feel and upsets the ride quality and overall suspension geometry.

I was thinking the same thing once these OEM run flats wear out. It's the reason I opted for the spare in the trunk, to get PS4S tires and not worry about a flat while out and about

[SoCalM340i]

Originally Posted by Ikester19

I had ACS lowering springs fitted to my M340i and reverted back to the OEM springs after 3months. The ACS springs resulted in a moderate drop of 20mm in all four corners. Although there was a slight (not significant) reduction in body roll, brake dive, and squat, the trade off was an unsettled ride, vagueness in steering feel and the chassis balance felt off. BMW engineers spend years designing and optimising suspension geometry and to say that slapping on after market springs will improve performance such as reduce understeer and boost grip is simply not true. If you looking to reduce understeer and increase grip you will need a good set of coilovers and wider rims/tyres. Aftermarket lowering springs won't do much apart from aesthetics. Just my 2c worth but to each their own.

Thanks for the honest feedback on the ACS springs. I was considering them, but given the potholes, tall concrete parking lot carriers, steep driveways and what not, it doesn't sound like a good payoff for the limited amount of better handling, if any. I agree that BMW engineers have applied years of knowledge, testing and engineering expertise into our cars, no need to overthink the process.