I need new tires on the 400H and I now have 235/55R18 size and the tire shop suggested a "better" tire that he has in 235/60R18. It looks like the speedo will show 67mph when in fact I'm driving 65 so not enough of a difference to cause any problems with that. Question is will it effect anything else that I'm not aware of?

 

Contacted Lexus and the engineer said he would not do it as the computer would be thinking something is wrong with the system and giving off a check engine light. So I ordered the original size tires.

 

Even without doing the math, if you fit tires with a larger diameter it must be the other way round, surely?

 

Your correct, my writing it backwards.

 

Weighit : I believe i have an answer with your questions on changing tire size from the factory recommended size. Recently i just upgraded my 07 RX400h from 235/55/18 -> 255/55/18 for my personal preference. In the years of owning many different cars I have not triggered any CEL from changing the size of my tires or rims. Not saying it will not happen on other cars. I have increase the diameter to raise the ground clearance, and decrease the diameter to lower my car. I have some experience with this setup. One rule of thumb I used is not to exceed 5% increase or decrease from the original size and you should be fine. The computer of the car itself is intelligent enough to adjust for a small change.

My current setup of 255/55/18 actually rides a little smoother "personal opinion" then the factory size. My own goal was to increase more ground clearance for the vehicle itself which it did.

On your conversation with the Lexus about the change. They will read everything by the books because it will void your warranty. Ultimately they do not want to be liable for the recommendation. I hope this helps.

Sam

 

What I did do was lower the speed rating to a lower speed, which gives a softer sidewall and hence a softer ride. I did not think I needed a 130 mph tire speed as about 80 is all I ever get to. We did notice the ride is nicer for us with the new Michelin tires over the Bridgestones.

 

but I'd REALLY like to know if you confirmed that the 235/60s would fit?? I have the 255/55s on my mine now, they're pretty tight next to the rear strut. The 255/55s are 29" tall. The 235/60s are 29.1" tall. Anyone...will the 235/60s fit?

 

I ended up with the 235/55-18's and the lower speed rating and the tires have been great. Ride improved and wet weather driving has been fine. Don't know if the larger size will clear and fit.

 

Hi Sam
I am thinking of doing the exact same with my lexus. 2009 rx350. I want a larger diameter tire to make for a smoother ride.
If I go with a 255/55/18 is the width still the same as the original? I currently have 235/55/18. Its been a few years, do you have any regrets or issues when you made the tires bigger? Also what are your thoughts on the smoothest riding tire for the lexus rx? Thank you for your time
you can email me at golferguy@hotmail.com if possible.
Bruce

 

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