Hey all!

I'm due for new tires soon and am planning to add a little more meat onto the car to help with handling/traction. Right now, I have a square setup - General G-max AS05 (I hate them) 245/45R18's on 18x9 +35 Konig Oversteer's - but want to go a little wider on the tire. My biggest concern though is I don't want handling feel to suffer. I already feel like the tires I've got currently feel too squishy for me on turn in, despite being responsive, and I feel like the side wall flexes too much under braking which causes some undesired trammelling/pulling on certain surfaces. I've already ruled out brakes/suspension/alignment as the cause here, but when I brake, the car wants to dart right at completely random times. It's not consistent, and I'm thinking it is partly due to the tire I'm running. I'd really like to avoid making any characteristics like that worse, or more prevalent.

Here are my goals for the car:
It will occasionally see autox events, maybe a track day or two, but will mostly be a backroad driver. Steering feel, responsiveness, and predictability are my #1 wants when it comes to tire size selection. I do not want any major sidewall buldge that'd cause the steering to be slower or feel lazy, and I don't want the tire rolling over on itself more often than not due to tire width being too much for the wheel.

I know I can technically fit a 265/40R18 on my wheels, but I think that'd probably have a bit of sidewall bulge. I am also adamant about a square setup since I need treadlife warranty and daily the car, so a staggered setup is not in the cards.

For those that have done it, can anyone weigh in on what a 265/40R18 squared setup handles like and how your steering inputs were impacted? Any negative aspects of how the tire handled on a 9" wide wheel since that's basically the max width that wheel can handle?



The other thing I'm considering is one of two options that still keep the rolling diameter under a 3% difference from stock (I'm RWD not AWD) is running either a 255/45R18 or a 255/40R18. I know the 255/40 will be about 3/4" shorter in overall tire height than my current setup, so I'm curious if that would look goofy with the fender gap it may create. The flip side of going to a 255/45 means I'm adding MORE sidewall overall as it's slightly taller than my setup, and again more sidewall generally means more flex. Has anyone ran either of these two sizes, and if so, how was your steering response, feel, and predictability compared to a 245/45R18, or even the stock 225 front tire size if you were running a stock staggered/Journey size setup?

Again, my main want is more control over the front end of the car, a stable and predictable ride, less squish/roll feel in the tire, and of course something that fits my wheels perfectly.

 

Realistically 245 is a little narrow for a 9" wheel. I ran it for years, but its on the verge of stretching. You shouldn't be getting any sidewall bulge with that set up.

255/45 vs 245/45 is a difference of .354" (a little under 3/8") of overall height. The sidewall height changes by .177 ( a little under 3/16")

 

Yeah, it's the rear tire size for the RWD G37's with the sport package. I'm sure the engineers chose this size for a reason. Probably rolling resistance, snow traction, weight, ect. I do notice the stretched look too. It looks odd to be honest.

 

Aside from focusing on size you could research specific tire models, too. I just ordered some new wheels and tires and the tires are reviewed as having a very noticably stiff sidewall compared to others in the class. Check out the Kumho Ecsta PA51 tires.

Whole video is worth the watch but here's an example of the sidewall stiffness at the linked time:



Also regarding width of tire vs width of wheel, check this out:

https://motoiq.com/how-to-properly-s...performance/2/

According to that 0.5" "rule of thumb" if you run a 245/45/18 on 18x8.5 and 275/40/18 on an 18x9.5 with the PA51 tire you'll be within the rule. This spec is also only 0.7% larger diameter in front and identical diameter in rear when talking about OEM spec. Tire Rack has tread width specs on each tire, so you can look up something that would work with the width of your wheels.

 

Things to consider is that each tire model has it's own tire dimensions, overall width and diameter. So not all 265/40R18 will measure out the same, making the fitment on the rim width different also. Most are relatively close to each other, but there are some tire models that can be on either the narrower side or wider side relative to the nominal size.

Going down to in section height for the 265/40 will naturally make the tire more responsive than a 245/45.

It'll be very difficult to compare one person's experience on 265/40R18 to another person's on the same size if the tires are different due to tire compound, construction, tread pattern. only true comparison would have to be the same tires.

I have ran 255/40 on a 9.5, Toyo Proxes AS. I personally would prefer the 255/40 over the 255/45.

I currently have 265/40 on my 9.5 with Maxxis VR-2 on my track set, but havne't ran on them yet.

 

Thanks for the responses all!

I've been doing some pretty extensive research on the actual tires (and my nerdy *** made a literal spreadsheet comparing tread depth, UTQG ratings, weight, measured rim width, section width, tread width, and true diameter per tire) so I am definitely factoring that into my overall decision. I just really was hoping to see some pictures of a 255/40r18 on an 18x9 compared to a 255/45r18 to get a visual of the sidewall height. I know it'll vary slightly by tire brand, but before I pull the trigger on buying anything I like visuals. And of course every pic I find online is a 9.5" wide wheel vs a 9" like mine are haha.

 

Check customoffsets, fitmentindustries, tyrestretch.com, threepiece.us