Hi, as many have, I'm considering replacing my 17" alloys to some fancy 18 or 19" ones (I've got an LS430 with the boring 17" ones).
My question is what differences should I expect?

I've heard that the handling might become more sportier but at the same time harder (the new LS430 has 18" as standard so I think maybe increasing to 19" won't be too much?).
In the past, some guy in my local Halfords told me that bigger wheels actually increase fuel consumption and also worsen acceleration(!) . If that is the case why do so many people want big wheels?

Any comments from your own experiences are appreciated.

if you fit bigger wheels, then usually you need to fit tyres with a lower profile to compensate, maybe because using a a bigger tyre wouldnt fit under the arch etc, and thats where the lack of comfort comes in as they are usually stiffer, so you feel the bumps more, but this also means the tyre is not deforming as much when you corner so you get better handling.

im not sure about the fuel consumption, but bigger wheels can change how accurate your speedo and satnav become, most people put on bigger wheels with low profile tyres so that the rolling radius of the whole wheel+tyre is around the same as the original wheel+tyre.

smaller rims = smaller diameter = quicker accel.
bigger rims = bigger rolling radii = higher top speed

unless you get the exact rolling radius from what brett said.

personally I wouldn't go too big as price of tyres would be higher.... go for a wider rim and bring the car closer to the floor for a decent ride.

Tyresave have a useful wheel size calculator, so you can go for bigger alloys and see what tyres would give you the same rolling radius.
Click here.
(If the link doesn't work go to the main Tyresave site, click "Please click here to visit", click "Site Index" on the right below the phone, then click "Tyre Size Calculator" halfway through the TYRES section.)

They're pretty keen on their prices, too - I bought a set of Mille Miglias & tyres from them just before Christmas.

Heres what i noticed going from 17s to 19s...

Road stability went up alot
Handling was improved (could be to do with the awesome tyres)
Road noise went up
Suspension felt firmer
Felt little slower building up speed
Traction around corners was MUCH better (super wide rear wheels!)
Oh, they look alot nicer than stock 17s!

There are for me alot more Pros than Cons.

some of those plus points are due to the wide rims as opposed to the bigger diameter.

if you aren't going to drop it super low then yes a bigger rim does look a lot better as they help fill the arch.

if you go for an awesome deck then I would think 17's or 18s would look uber cool as well.

nah sod it if you got the money go for mahoosive rims!!

Rolling radius on the 19s is only 10mm more than stock 17s...

I wound the coil'ys down more when i fitted the 19s... it sits about the same as when it was dumped silly on the 17s!

Have a read through some of the LS400 posts about the wheel offset,on the LS400 models the wheel offset is not a common one.My mk1 LS had a 50 offset which makes it difficult to find aftermarket alloys that will fit.
The standard size wheels on my car were 15s,i put 18s on and like above found the car felt more stable and had alot more grip because i went wider with the tyre size.There was more road noise but not enough to worry about.
I prefered the way my car drove with the bigger wheels.

Cheers chips.

mpg will increase and acceleration decrease if the wheel+tyre weight increases (as it normally would do with larger wheels). Normally the bigger the wheel the wider it is too which also increases the weight and increases rolling resistance.

People put in larger wheels for looks rather than performance.

If you want total performance then you could use some 13" magnesium formula one wheels.

^^

didnt the worlds fastest GS have them?

LS on 20"s