Getting Softer Ride: Downsize Rim, Raise Tire Profile>>>Pr

[dave_k]

Just bought a used 2011 IS 250 - Nav, and the 18"X40 profile tires are too rough.

Can I avoid buying new rims and just go to a 18"X45 or 18"X50 without hitting the wheelwell or messing up the trac control/ABS computers? I know the speedometer will be off a little with a different circumference. The one Lexus service manager I spoke to was very concerned about the effect on the trac control and ABS.

Or do I have to go with new rims ($$$!) and use the 17"X45's that come with the non-Nav model?

Or maybe do 17"X50's?

Many thanks!

[clubfoot]

Is your IS250 a sport package model? If it is you may have better results installing the "standard" model shock and spring package. If you can take a test drive in the same model year IS with the standard spring/shock setup then you will be able to compare.

[dave_k]

Thanks, Edward. My IS 250 is a standard model with the navigation system, not a sport model (F?). So, I think I'm back to the rim and tire size.

I do know that if I add more air between me and the road (higher profile), the ride will be softer. I did it with my old SC 300 by 10 or 15 profile units. So, it's the limitations of wheelwell and computers on the IS that concern me.

[clubfoot]

Then I would say the 17" wheel package for your model would be a very good compromise as it would have the smallest speedometer effect. The dealer may even offer you a straight swap as the 18" are more expensive.

[dave_k]

Thanks. So far, the dealer is not interested in a swap. They sold me the car at an "internet price" and seem to want to be done with it. But, I'll keep nudging.

Is it unwise to go to a 45 profile on an 18" rim with this car? Or a 50 with a 17" rim?

I understand the speedometer problem. It's the wheelwell and computer part that's a concern.

[clubfoot]

The 50/17 combo will give you the smoothest ride. don't worrry too much about the speedometer as it will not be too far off.

[LEX-SV]

I would not recommend going to higher profile tire on the IS250. Speedo error and slower acceleration will be be significant on the modest horsepower IS.

My preference would to go to the correct-sized comfort-oriented all season tire such as Continental ExtremeContact DWS. I've been running those on a Mercedes C300 for 13K+ miles with good comfort, low noise and little wear so far. This scenario is a lot cheaper than replacing both tires and wheels, and sizing will be correct for optimal performance.

[clubfoot]

I don't think the OP is interested in acceleration and a slight speedo error but more with ride "softness". Come to think of it he probably should have gotten an ES,...but that's another thread. He may gain some quietness from an all season but he indicated the ride was too rough. So you're saying an 18X40 all season is allot quieter than an 18X40 summer tire! Did you change brands of tires in your conversion?

[LEX-SV]

Yes, we know OPs primary concern is ride quality, I'm not convinced OP will tolerate large speedo error and significant deterioration in acceleration. Yes, the ES might be a better choice...

Yes, but going up over 1" in tire diameter impacts too many things including acceleration. Not recommended going from 40 series to 50 series (as mentioned by OP in post #1), speedo error is significant, not to mention making 2.5L acceleration really sluggish.

Yes, going from certain summer tires to certain all-seasons can make a big difference in ride comfort/softness and quietness.

Example: (as done on Mercedes C300 with stock sizing) Hankook Ventus V12 (summer) vs the Continental DWS (all season). Changing brands is not the issue, changing specific tires is the bigger issue, even with identical sizing.

[dave_k]

To clarify, I understand about speedometer error. I'm aiming to go down an inch in wheel size and up in tire profile to match, so the wheel circumference stays about the same.

[LEX-SV]

dave_k - Thanks for clarification, that makes more sense sticking with Lexus tire sizing per specs for 17" or 18" wheel as equipped. And if you stick with the tire sizing that Lexus specifies for the wheel, tire diameter will be nearly identical.

Seems like a lot of money (to replace both wheels and tires) to get minimal impact on ride softness, especially if you are the one that has to pay for it (not the dealership). My suggestion is careful selection of tires (all season versus UHP summer tires). What tires are on the 18" wheels now?

Notes:

f 225/45/17 versus 225/40/18

r 245/45/17 versus 245/45/18

[dave_k]

Bridgestone Potenzas.

[LEX-SV]

Bridgestone Potenzas are known for noise and hard ride. Standard equipment due to low cost to the automaker(s).

Do the tires have a lot of miles on them?

Are they over 1/2 worn?

[LEX-SV]

Did you change tires?