G-Spyder 18" Alloys from GS300 to IS250 RWD?

OS-IS250 · May 30, 2023

I have a set of G-Spyder 18" alloys from a GS300 that I want to transfer to my 06 RWD IS250. All 4 alloys currently have 245/40/R18 tyres on them.

I currently have the basic 17" running on Front 225/45R/17W and Rear 245/45R/17W tyres.

If someone could kindly recommended RWD tyre setup for these 18" G-Spyder alloys even though this new set may not be staggered🤷🏻‍♂️

Thanks

OS-IS250 · May 30, 2023

Images for reference..

Linas.P · May 31, 2023

The correct sizes for IS250 are 225/40/18 and 255/40/18.

That said 255 is massive overkill on IS250, so I personally went for 245/40 in the rear. So basically just pick two best tyres of what you have and put them in the rear and just order fronts. I don't believe you can run 245s in the front without rubbing, I think the widest you can get are 235s... but as you have the wheels already then you can simply fit them and see if they are not rubbing. Sure 245 square would be overkill, but if they fit then why not use them?

Not sure what you mean by "this set may not be staggered"? On GS the tyres are square, but usually G-Spider set is in itself staggered (i.e. alloys themselves are 8JJ and 8.5JJ). Now sure it is possible somebody swapped the set and have all 8JJ for example. If that is the case, then I personally would go full square on IS250... like 225x4 or 235x4. Honestly, 225 is plenty for 200hp (something like 160hp to the wheels) and then you get benefit of being able to rotate the tyres.

In short - if you have staggered set of alloys, then get pair of 225/40/18 and use 245s you already have. If it is indeed square set, then try to fit it as is... if not then replace fronts (or all tyres) to 225s or 235s.

OS-IS250 · May 31, 2023

What I meant by staggered is the rear wheel size being wider to the front. I assumed all rwd cars have a staggered setup?

But these came off a RWD GS300 sport and all 4 alloys are 8j's

Thats why I wanted to know the ideal tyre setup for all 4x8j alloys on my RWD IS250

Linas.P · May 31, 2023

There are many RWD cars with square set-up, Lexus IS250 cam with ridiculous 255s on the back almost as if it has 400HP. It depends what you mean by "ideal" - cars came from the factory with 225/40R18 and 255/40R18 as I have said. If you just want factory set-up then those are your sizes.

However, that is far from "ideal" by my own definition... 225/255 feels almost FWD with a lot of understeer - that is considered "safe", but it really handles poorly and balance is poor in the corners. If you want more neutral balance where the car grips well, but isn't much "fun" to drive, then you can go for 225/235 or 225/245. Finally, if you have all 8J wheels you can go for square 225 or square 235. This will make car like it should, with rear bias and little bit of oversteer if you really push it, and then as well you get benefit of rotating the tyres and you will get better fuel economy.

OS-IS250 · May 31, 2023

Thank you Linas, now I have a better understanding of the type of set up to go for. Appreciate you taking the time to respond to my query. Thank you again!