What is the easiest way to lower the car a few centimeters?

Your car seems to me to have the perfect height!

 

I have a yellow Konis in another car that can be adjusted in hardness (not in height), but in the reds from the 308 I do not think it is possible neither one nor the other.

 

+1 for Superformance springs. Just installed a set about a year ago on a friend's car. They set the height absolutely perfect looking, and are a bit stiffer.

 

Well, my setup is all stock, but for the springs, so I figure it's attributable to them. Just a heads-up, and this likely applies to replacing shocks - as opposed to springs only - but it did take the car a few drives to "settle" down when I installed the new suspension bits. The gap started out about an inch bigger upon install, so don't be alarmed if you observe this.

But for $400 and some labor (be CAREFUL if you're going to do your own work, lest a spring blow off in your face), it seems the "easiest" way to lower the car a few cm.

 

Buy a set of 'run flat tires'.

 

Can you use the stock Koni's with the Superformance springs?

 

I couldn't get a definitive answer to this question but at £65 + Delivery + VAT (at 20%) for each spring it's an expensive guessing game.
You can get fully adjustable set ups for around £500 and they include the springs!

But if you are hell bent on keeping with the original Konis, at about one third of the price I would be tempted to work out the spec myself and source the springs from here (or the equivalent supplier in your country):
http://www.dfaulknersprings.com/

 

Take air out of the tires.

 

YES. The pics you see of my car are stock Konis with Superformance springs.

 

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Here's the proof. Had to dig these up from my restoration archive. Fresh OEM-spec Konis with Superformance springs. The ride is fantastic!

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I changed the spring perches on the front end which lowered the front still using the original shocks. With 16" wheels the car looks perfect.

 

Thanks for the information everyone.

 

I really (really) despise that "slammed" look that's so trendy these days. But I agree - your car's gap is perfectly proportioned to the tire, rim, and curve of the well. Nicely done!