05RollaXRS

I have mentioned sporadically about the RCF version of MPSS tires as to my disappointment. It stemmed from my gripe with the car rolling over the sidewalls especially in slow corners in normal, ECO mode when VGRS "softens" the steering response and quickness. This is very important for those who want the car to feel highly responsive to steering inputs, light on its feet and agile even in slow turns. I had done chalk tests on the sidewall and it proved at 34 - 35 psi, the sidewalls tend to get used excessively unless you are going fast, sport+ mode when the steering has super quick turn in. I don't care much for being able to drive over crappy roads since this is driven only on nice, smooth roads.

I found a band aid solution to this by inflating the fronts to about 36.5 psi and rears to 38 psi so that it can stiffen the sidewalls to the point where it can resist side-to-side weight shift. Fronts are a bit lower to maintain feedback from steering.

As it turns out after much research, the RCF spec MPSS tires as per spec'ed by Lexus, were non-XL rated tires. The BMW M3/M4 version of the exact 255/275 is different and rated XL (see snapshot below). The only rational explanation common sense tells me, is Lexus wanted to make the car easily daily drivable without harshness. This must have been due to complaints by the press of the ISF version of the PS2 tires, which were XL rated and press complained, it was too harsh on non-perfect roads.

What are XL rated tires?

As per tirerack:

https://blog.tirerack.com/blog/miles...at-should-i-do

"This is accomplished in the manufacturing process by adding additional material to the shoulder of a tire for extra strength. These reinforcements (usually accomplished with polyamide belting found where the sidewall and tread meet) are designed to minimize any tire deflection and reduce potential damage due to road impact. These strong tires will be branded with an "XL" or "RF" in their descriptions."

Benefits in handling of XL rated tires:

"if more feedback from the tire is desired. Drivers seeking a firmer ride and enhanced car control would not need to be concerned with the XL warning when comparing different tires to match their driving expectations. As a matter of fact, this type tire will enhance the overall vehicle stability and handling. Also, the selection of a more aggressive tread compound will increase grip in the wet and dry."

Who should not consider the XL version of RCF tires:

"For drivers desiring a softer feel and are willing to forgo the car’s stability in cornering, the standard load tire will be a more appropriate choice."

RCF-Spec MPSS tires (non-XL):




BMW M3/M4 version of the MPSS (Same 255/275 size) XL rated:



New MPS4S tires for RCF are only available in XL version:



Conclusion:

Essentially, if you would like less side-to-side weight shift and if are going to be looking for new tires, then going with the MPS4S is the best option as they are the latest and greatest. Otherwise, you can opt to order the M4/M3 version of the MPSS and it will give you the reinforced sidewalls. I still have 6/10th tread on OEM left so for now I am keeping the rear pressure at 38 psi and fronts at 36.5 psi and it gives me the rigidity in sidewalls I really want while maintaining feedback through the steering from front wheels until these tires run out and then I will either go for MPS4S or MPSS (XL).

flowrider

iTrader: (9)

Yes, this has been mentioned before, in threads you were a part of. Here's one:

https://www.clublexus.com/forums/rc-...bber-time.html

Lou

LXSDO

Thanks for doing all the research and consolidating it in this post. Definitely some things to consider when j need new tires.

TOPHER9425

I recently ditched the Michelins and went with Continental Extreme Sports in 275/35 front and 305/30 rears.....happy with my choice thus far

05RollaXRS

Just curious, how is the steering response and feedback from the road through the steering on those 275mm on the front? Do you get any "spongy' feeling at all? Is 275 not too wide for OEM front wheels? From past experience of experimenting with various sizes, it may cause tires to bulge out from the sides if all of the tire width does not sit completely across the wheel width, which gives a bit of a "spongy" feeling.

flowrider

iTrader: (9)

^^^^Per manufacturer's specs, a 275/35/19 tire is the max width you can mount on a 9" wheel:

However 305/30/19 is too wide for a 10" wheel.:



Lou

05RollaXRS

Yeah, I would say 265 max on the front for OEM wheels and 295 max on the rear wheels in order to retain balanced handling.

flowrider

iTrader: (9)

^^^^^I'm running 255/35, 295/30 on my ISF with RCF wheels. Luv the combo.

Lou

05RollaXRS

Yeah, that is definitely a very good setup Does not compromise on the steering response and feedback.

GunnyFitz

Interesting. I'm currently running 37 lbs all the way around right now.

Curious to hear what the "Normal" range is to retain longevity and performance on these tires.
Debated going a Conti's, Nexxen's - but changed my mind at last min to stay w tried & true (IMHO)

245/30/20
275/30/20

05RollaXRS

36 psi all around is what Lexus recommended on OEM MPSS (written on the door jamb). I typically like running 33 - 34 psi, but these MPSS become marshmallows at that air pressure. So, I run 38 psi rear and 36.5 psi fronts since stiffening the front tires too much results in loss of feedback in the turns of how the steering is loading up, which is important to accelerate out of the car (psychologically).

TOPHER9425

Honestly brother....I can't feel anything spongy about the set up, she holds corners great, and I travel Hwy and residential roads daily. I run 36 front and 37.5 rear PSI. Now this feeling is great to me, due to coming from the stances scene running 245/35 stretched on a 11.5" wheel back in the day LOL

05RollaXRS

yeah, I was just wondering since to me the stock 9 inch wheels seem too narrow for 275 mm wide tires and my theory was, they cause the tires to bulge out on the sides. But, great you like the setup. Thanks for clarifying.

bob67

I have been running 37.5 all the way around. So... Which is better? Non-XL version with higher than Lexus recommended psi, or go XL rated with Lexus recommended psi?

05RollaXRS

Definitely, XL rated tires would be better. Increasing tire pressure somewhat mitigates the issue of softer sidewalls, but still can flex under certain circumstances. An XL rated tire has proper reinforcements in the sidewall that will offer crisp response under all load conditions.