Can I run this set up attached front 19x8.5 +30 , rear 19x9.5+40. Front 235/35 rear 265/30

 

Also if I decide to go with lowering spring, could I still put them ON? You suggested an r3down spring that would drop 1 inch

 

Yes you can run this setup no problem.
You could run the above setup at any height, stock or lowered.
The RSR Half Downs will drop the car about 1 inch in the front and half inch in the rear. Some that installed them feel the drop isn't enough, but it really comes down to personal preference and road quality.
A lot of folks go with the RSR Downs as it's just over an inch drop in the front and an inch in the rear...but once again, personal preference.

 

No chance of doing 19x8.5 +30 fromt and 19x9.5 +30 Rear. I am struggling finding wheels.

 

To give you an idea of what the boundaries are for the rear, with 19x9.5 an offset of +35 is the borderline. Depending on the specific vehicle, ride height, size of tire, brand of tire, you could have rubbing or it could fit...it's literally hit or miss.
As soon as you move to 19x9.5 +38, this opens the door to eliminate rubbing and have appropriate tire sizes, and not be locked to specific brands of tires.
When you get to 19x9.5 +42 you can put a bigger/beefier tire and not worry.
At 19x9.5 +45 you could install tractor tires and not worry lol! Ok, you really can't but you get the idea.

And yes, finding rims is a little challenging as you go wider because the offset shrinks as to what will fit or not fit.
Another way to go is using spacers...example, if the rim you wanted came in 19x9.5 +45, you could get that with a 265/30/19 tire and add a 5mm drop-in spacer. It's a win win win scenario...once you're ok with spacers.
With spacers you can reduce a larger offset for a better fitment. Up to 5mm the spacer just fits between the rotor and rim and you don't need to do anything else...and they are fairly inexpensive.
After 5mm usually the next size is 10mm which typically is a bolt-on spacer...and the price reflects the increased complexity of the spacer.

 

Newbie here and I don't know much about cars. I have a Lexus is200t with staggered 18inch wheels. I've spend tons of money on tires because I can't rotate them. Am I able to install a different pair of wheels to be able to have all wheels same size and be able to rotate them? I assume that's what a square set up is.

 

Of course you can. I run staggered in the summer and square in the winter.

 

So what is it about my tires that are different and I can't rotate them? I have
225 /40 R18
255 /35 R18
Do I have to change my rims? Should I do all 4 the 35 part or the 40 part? Will that affect my speedometer?

Thanks for the help. I want to be able to buy 4 tires the same size and be able to rotate them.

 

Your current rear tires are 3cm (little over an inch) wider than the front, and your rear rims are probably 1/2 inch wider than the front (at least my OEM rims are). (Why Lexus bothered with a 1/2 inch stagger is beyond me.)
Physically you could rotate your current setup (I swapped the front and rear wheels with no problem while tracking down a vibration issue), but probably not recommended for the long term.
Simplest solutions:
A. If you like your OEM wheel design, you could get another pair, the same size as the fronts with matching tires, and run them on the rear. Or,
B. Get 4 aftermarket wheels, same size as your current fronts, reusing your current front tires plus 2 matching new tires, or buy 4 new tires for the new rims.

 

That answers all my questions. Thanks for your help.

 

If you have an F Sport (or F Sport wheels), the rear wheels won't fit in the front, it hits the calipers.
Saying this so you know that you'll have to mount/unmount your tires to do this rotation.

 

Good to know, but mine is not an F sport.

 

I think you have the staggered wheels, no? So your rear wheels will probably not fit.

Besides that, you absolutely don't want to run wider wheels up front. It will make the car handle in a way that is probably unpredictable, particularly in the rain.

I don't think you should even try to rotate the tires as they are. I'd personally just swap to a set of wheels that are the same size front and rear, like it was suggested before, and use the same size tires front and rear as well.

 

You won’t know until you try. Mine did.
I agree, and said before, not the way you’d want to normally run it. But came in useful when I was tracking down a vibration issue (result: a front tire was defective and not round).

 

Your rear F Sport wheel fit in the front without touching the caliper?
Mine hits the caliper (I tried it a few years ago).

Unless you have aftermarket wheels, then forget what I said haha!