Different ride height same springs and wheel size
 

Car 1: Sport wheels stock tire size, swift springs, stock shocks
Car 2: F14 (255/35/19) (305/30/19) wheels, swift springs, koni yellow shocks

why does car 2 ride 1 inch lower then car 1?

before you tell me that tire size is different, i measured from the top of the rim to the bottom of the fender. Dealer mechanic told that custom wheels (regardless that they're also 19s) will make ride height different but that doesn't make sense to me.

My only thought would be koni yellows

Wheel width can also affect ride height. 1" seems like a lot though. If you know the details, go HERE and it will give you a good idea of what to expect when changing wheels and tires.

The over all diameter from stock tires to the 255/305 combo mentioned is very close. It would have to be the shocks, and/or maybe a different part number on the spring?

It's my understanding that shocks do not affect ride height, and swift makes sport and spec r but both have same ride height

What are the differences in offsets?

Spring rate or overall length must be different if tyre OD is the same

What i have are the standard deep concave f14s
19x9.5 +20 - 255 35
19x11 +15 - 305 30

according to willtheyfit.com my ride heigh should be about an inch lower (5/8s) so it matches up to what i measure, but that is due to the tire being lower profile, but when i measure from the bottom of the fender to the top of the rim, i'd expect it to be the same as my 09 unless what BGTV8 is saying is true...either way i guess i need to get some coilovers

Remembering reading that someone else who had installed the Koni shocks had a lower ride height. Something about the shock length/how the spring perch on the front was mounted. If you search, you may fine it. Can't remember all the details.

Swift springs only lower the car about 1 inch. There is no way there is one inch difference due to the same diameter wheels.

Have you compared car one with another stock Z? Perhaps car one has the stock springs?

The differences in offsets (the Forgestar set has lower numbers) create a longer leverage arm on the springs. The result is like loading the springs with more weight, thus compressing them further. In order to drop the ride height by 5/8", the springs only need to compress a fraction of that due to the suspension design.

I say it's to be expected.

you sir know your stuff, thanks, i think the dealer was trying to say this but didn't know how. rep point for you

they're both in my garage....i think pos vet is right, its the only explanation