I just am curious if anybody has actually ever seen that malfunction or read an experience about it happening.

I have read about the 3% rule a few times on different platform forums. In my experience, I’ve never had any issues, but I have never ran over a 3% differentiation between front and rear. I have ran way over 3% taller OD than stock, but it was always on a square set-up.

A down side of text is that you can’t hear tone. No aggression here, but it does seem a little silly to pass a rule as gospel when we haven’t found anybody that has even seen this as an issue in real life.

For the sake of experimenting, I may swap some wheels around. I’ll dig through my wheels and see if I have any that differentiate over 3%.

I don’t personally think it’ll throw any lights or behave oddly from past experience, but maybe I’m wrong.

Edit- technically, my is350 runs a 3.6% differential front to rear stock, so Lexus has already proven that it doesn’t matter. If they tuned it for that differential somehow, then it would have acted up now that I’m running square, which the car would see as a differential (if the car is supposed to run a 3.6% differential as normal, now it’s running a 0% differential, which would still be a 3.6% variance).

 

^^^^OK - Let's keep this going The electronics and mechanical componentry in an IS350, or any non ISF IS, is set up differently than the ISF. Unlike the ISF there is a factory stagger front to rear (rear tires are taller). Same for the RCF and GSF. On the RCF, GSF it's 2.3%. On the 2IS it's it's 3.5%. On the iSF it's zero. Again, the factory sets up the vehicle to run with the stock wheel and tire sizes.

I am not saying there will be a massive malfunction or the world will end in a cloud of dust and mankind as we know it will disappear. All I'm saying is that it's not optimal because the vehicle was designed and engineered with certain components having a specified dimension. (Electronics, axle ratio, transmission ratios - and to a lesser extent bearings, brakes and etc). Changeing the wheel/tire OD or stagger to a great extent will throw all that engineering out the window.

Lou

 

There's a whole lot of wiggle room between I can drive the car and the car performs well. Changing the diameter of the tire impacts roll center, center of gravity, instant center, potentially roll couple and a few other things important to getting the most out of the tires. Just like changing ride height and wheel offset for fashion, there ARE consequences. Will you notice this driving down the street to get groceries? Probably not. Will you notice it in an autocross? Definitely.

There's a whole lot to getting the most from your tires. It's all about how important it is to you. Deviating from factory will impact how the car performs and if you don't understand why you are changing something the likelihood of it being positive is pretty small.

 

^^^I wasn't even thinking of the dynamics, guess I should have been

Lou

 

In short, no.
I trust the guy I was talking to about it, otherwise I wouldn't have bothered involving myself in some internet forum debate, because beyond that I don't have the background to sufficiently defend it.

Flowrider already covered all the potential reasons floating around in my head. Just add me to the group that is pushing caution and research before adding 6-7% circumference, for comfort/aesthetics.

 

So I did a thing:
Front: 225/45/19
Rear: 255/40/19



i did this purely to reduce harness. There is no rubbing, as expected. I feel like it fills the wheel wells better, and I don't notice the car sitting any higher (I know it is).

For people that are just DD and don't want to mess with suspension changes, this is a viable improvement.

My plan has been to track with a different set of wheels/tires anyway, but I've not noticed any significant degradation in turn in when ridin' my on-ramps :P

 

That looks great.

I have some PS4S in 245/35-19 - 275/30-19 combo on order.. you are making me what to cancel now.

I thought for sure a 27” diameter tire would rub in the front.

 

2014 IS350 AWD F Sport, running tires 3" taller than OEM for 55k miles. No rubbing, no added noise, negligible 0-60 (~5.6 seconds), 19.7mpg city/highway. Taller tires were needed due to serious potholes on the NE. Just make sure if you"re AWD to keep same/close diameter. The 3% rule...I dunno. There is presumably a light that comes on if you"re running tires front to back with excessive diameter differences, mine are at exactly 3%, so no warning lights yet.

Some aspects of this debate are akin to the number of lawyers and MDs that come out of the woodwork with their FB/LI degree to debate Constitutional law or virology/infectious disease issues surrounding COVID. SMDH

[img]blob:https://www.clublexus.com/208a242b-3775-4991-ad18-4e26a5ef35bb[/img]

 

^^^^How do you know your 0-60 time? Your speedometer is off

Lou

 

So you never drive much outside the envelope of the average driver and it works for you. Good on you. I wouldn't suggest this to someone autocrossing or using some other timed course to measure performance. It's an epic fail for a multitude of reasons in those venues.

And I have direct experience with chassis tuning for performance. Not an armchair quarterback.

Given your chosen platform, you would have been way ahead to fit 17" wheels for the additional sidewall cushioning while retaining the OEM suspension geometry.

 

Was that small increase a noticeable difference on the ride confort at all? Was debating on doing that or getting 18s but I don't really want to have my 19s just sitting in the garage since I like the stock wheels.

 

I think it feels a bit better. Didn’t rub at all. I might go wider next time too. It was a challenge getting a flat replaced.

 

How much wider can you go? Why was it a problem getting a flat replaced?

 

The size isn’t common and I had to wait for one to show up.

I’m not sure how wide. it will be a while before I get to that point, but it seems based on other setups width is the problem, so how that interacts with height is uncharted. This is a subtle difference in height though.

 

Hi lou, hope all is well!
I think you had 255/35-19 and 295/30-19 on RC-F wheels for a while, correct? How did you like the performance with that size? I'm thinking about going with that sizing on my 9"/10.5" wheels since you seemed happy with it.