2008 Lexus ISF
Recently I replaced my wheels to 2011 OEM wheels from aftermarket rohana wheels
When I had the Rohana rc10 (19inch) I was running the regular ISF tire specs on Michelin PSS
When I installed the new wheels I upsized the tires with 245/35/19 275/35/19
When I now drive on the freeway at any speed over 80mph the car feels super unstable and floaty, feels outrageously dangerous to be very honest. The wheel feels super soft and not as stiff as it did before. Prior to doing all this my car felt stuck to the ground 150mph+ no problem.
what can cause this issue are the tires too big? Do I have to do an alignment? (last done last summer)
many thanks for the help until then I am seriously going to limit how much I drive… yes that’s how bad it was.

 

What width were the Rohanas and what tire model are you running in the OEM wheels?

 

The Rohanas were 19x8.5 front and 19x9.5 I was running 225 40 19 / 255 35 19 (The oem specs) with Michelin Super sports

Now with the new wheels it’s the 2011 model year wheel, and I’m running 245 35 19 / 275 35 19 Bridgestone RE980 AS. Before installing the wheels I did balance them. No vibrations on the wheels so I would assume I balanced them correctly.

When I drive slow the car seems to pull to the right <40mph but when I pick up the speed it feels like I’m constantly adjusting both ways? Steering wheel feels soft now at higher speeds, almost feels like the winds are pushing my car around.

Im getting a wheel alignment today hopefully to see what I can find.

could it be because 2011 wheels don’t fit properly on earlier years?

 

No. I am running those same wheels with Michelin PS4S in the same sizes you are and I have no stability issues at all.

What tire pressures are you running? Factory 36 psi cold in all four corners?

 

Im currently at 35psi each tire. It’s weird because I was so used to the stable feeling of the F before going well over 120mph the wheel felt LOCKED IN now it’s like a 2000 Toyota Camry haha

Also wanted to mention that on my old wheels the rear tires had very very bad uneven wear on the inside, could it be possible that I didn’t feel the bad alignment because the wheels kinda went down a certain way from driving with a off alignment?
My thought is that my alignment was always off but since the tires wore down with that alignment it would feel good - and now that I put fresh tires I’m starting to feel the affects of it.
Could I be safe to eliminate the wheels as a problem and say it’s tire or suspension related?

Previous work done to suspension was the shocks, replaced it with bilstein oem height shocks and used the old springs since they were pretty much very good.

 

In my opinion it's safe to say it's not a wheel problem. You went to wider tires on narrower wheels and from worn summer tires to all seasons with deep tread and lots of sipes. It's no surprise it now feels disconnected at high speeds with all that extra tread squirm and reduced sidewall support.
Sounds like you may also have an alignment issue that was masked by the old tires.

 

That’s a bummer kinda wished I went didn’t get these wheels now… I’m going to get an alignment tomorrow hopefully pops shop was busy and couldn’t do it today unfortunately. I bought these wheels with the tires for a good price if I knew the sidewalls were soft wouldn’t have got the tire with it tbh. Looks like I’m going to have to burn through these quick to get some Pilots sports again haha.

If I was to replace the rear tires with the same size but Pilot sports and keep the Bridgestones on the front would that make a difference? I still have my front Michelins but they are 225 40 19 but I assume I can’t put that on since the rear would've 275 30 19

I ask this because I’m going to install headers and tune my car soon and want to make sure my car will be able to handle all the extra power.

 

Also another question for you guys, are the tires supposed to be at 35psi all around? I thought the rear was supposed to be higher around 37 compared to the front

 

The sticker on the driver's side B pillar says 36 psi on all four corners.

It sounds like there's an issue with toe in at the back of the car. Might even be slightly toed out which really makes the car unhappy.

My wife's GS F runs those same Bridgestones in the exact same sizes. Her car is 100% stable at any speed. If it's tires, it's your specific tires, not the brand and model.

 

When you do an alignment does the toe in the back get adjusted? I’ve never done one myself but we have the equipment at the shop. What do I tell my guy when I bring the car to him tomorrow?
Also I believe my cars sticker says 35 front and 37 rear psi? I would have to double check

 

The only adjustments from the factory are toe front and rear. Everything else is replace parts until you are good. This sticker is on every IS F I have seen.

 

You know I realized that I replaced all 4 shocks about 7 months ago and never did a alignment….
will tell them to adjust the front and rear toe to factory specifications and see how it rides. Hopefully that resolves my issue because I don’t think that going with this wheel and tire setup would make the car feel this sloppy, a little bit I would understand but not like this.

Not sure exactly what I was talking about with the tire psi sticker haha thank you so much for your input!

Im also looking into doing some suspension upgrades slowly to establish a more sticky planted feel, what should I start off with aside from spring/shocks (want to keep oem height)

 

Factory specs have a range of "acceptable" values which may not necessarily give you the best performance or high speed stability. Many of us use 0 toe at the front and middle of the spec range for the rear.

 

Whats the middle range for the rear if you don’t mind brother

 

All alignment shops will know the factory spec range. I just ask them to set it as close as possible to the middle of the range for each side so that it's balanced left to right. Many people here have posted alignment sheets if you want to know the numbers.