I'd find a pressure you're willing to live with, and just run that in both sets.
Unless it's an MOT issue, you are allowed to run a pressure in those wheels to help you maintain control of the vehicle at all times and in all conditions.
Most of the time though, it's the type of tire, it's size in sidewall, and the width of the rim, that makes the ride either, very pleasant and have the looks like; balloon-y tires, or that stiff ride and makes you feel every bump and heave in the road and in the meantime you and your passengers are rocking right along with it.
- So if you are in an area of smooth, well-maintained roads, you're fine.
- IF you live your life in gravel or backwoods roads, the issues of cut sidewalls are going to leave you stranded.
- Between the two extremes, you will have struts, shocks, rims, tires and the undercarriage and the essence of "Road rash" that can occur during any moment in time you have to cross curbs with steep slope driveways - where many a front bumper nose and the front valence shows scarring - you will be recognized upon arrival by the characteristic SCRA-A-APE noise emanating from your direction.
Your 205/40 R18 ties give you a 24.5" diameter already - and you have little room for bounce and road rock give - so that sends a red flag up with my own desire to have a comfortable ride - not a bone-jarring experience just trying to get to the store.
So you know, your Spare tire (Service tire) is a 175/65R14 - which is a 23" diameter (smaller by 1.5 inches) and you drive a hybrid correct? 2012 Year I am thinking - so that means; in using those rims those tires and one goes flat, you might have to have your ride flat bedded to a shop to fix the tire and or rim, versus just changing the tire and rolling it to the shop yourself.
So if Curb weight is an issue, those tighter sidewall tires are VERY dependent on the type of roads you use and limits your ability to roll on a wide range of surfaces other Fiesta with a different Rim and tire size can otherwise roll along on and not have issues with bumps and potholes as much.
It looks good, but it can cost you.
You can get simple dents and run outs in some rims repaired, but these rims I see in your photo - are rare enough. You may not be able to recover the rim from accidents to make it so it's serviceable again. Including, with Ford's bulldozer attitude about moving forward, not many of those rims are around - at least ones you can buy new - for everyone else using that style is pretty much determined to keep theirs.
![[?|]](/images/smilies/icon_smile_banghead.gif "Bang Head [?|]")
I myself live in an area where road conditions and potholes are crevasses into an underworld that some vehicles have fallen into - never to be recovered. Around here, we watch our step and some seasons, it will cost more in repairs than in others...
IMHO - I run with tire widths of 185/65/R15 (Winter) and 195/50/R16(Summer) which may be narrower, but if you search around for some tricks about the Drive By Wire and the Electronic Rack steering controls - you'll find that a narrower tire might be easier on you and your wallet - don't quite understand Ford's deisre to make everything in the RIM size to huge that it encumbers your ability to find better choices for ride, height and rolling resistance.
(Those differences in Tyre pressure are due to the weight distribution - since it's a Hybrid, the battery is in the back and is where all the weight is at - which is why you feel the ride the way it is. The rear tire to rear bumper and Front tyre to Front bumper distances are not exactly "equal" so there is an asymmetry to the performance when you're on the roads you're on now. Ford set up Fiestas for weight in the front engine area - so the stiffness you feel is the rear suspension design handling all that weight and mass from those batteries)
