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I've been trying to brainstorm what size of tires to get next time they need replaced and I could use some advice. My car is a G37 sedan RWD. It's lowered about 0.75" front and rear. Just a mild drop. But part of the issue I'm having is because my CURRENT tire diameters are already smaller than stock, therefore lowering the car a bit more, and I'm not sure if I want it to go lower. I like my current size because the stock sidewall sizes were too large. I also get a tire gearing advantage with the current tires.
I don't mind lowering the car A LITTLE more if I choose smaller diameter tires again, but I don't really want tires that put me back close to stock sizes as far as diameter / sidewall is concerned.
So my wheels are 18x8.5 +35 in the front and the rears are 18x9.5 +38. I will post below some tire size comparisons that I've made:
New 1: ......245/45/18........... 756........................................... 678mm................ 110mm
..................275/40/18........... 756...........................................677m m................ 110mm
New 2: ......255/40/18........... 775........................................... 661mm................ 102mm
..................275/35/18........... 788...........................................650m m.................. 96mm
New 3: ......245/40/18........... 784........................................... 653mm.................. 98mm
..................275/35/18........... 788...........................................650m m.................. 96mm
Obviously from this chart, the "New 1" option are the best matching sizes. But I'm a little afraid to increase the diameter from my current setup because I remember when I got bigger diameter tires on a previous vehicle, and I could feel the difference. It felt .... slower and more sloppy. I like the increased tire gearing that I currently have over stock sizes. Looking at the New 2 and 3 options, the diameter does get even smaller than my current setup, so that means the car will sit even lower than it currently does. I also don't know how 255's in the front would feel compared to 245's. Would it be too sloppy?
Even though I have some pre-disposed thoughts and opinions, please share with me what your advice is! I'm open to all suggestions. I don't track the car, just some spirited driving sometimes and possibly taking it to the drag strip occasionally. The car has about 330whp with the current setup.
Last edited by backman_66; Jan 6, 2021 at 02:39 PM.
Im not sure on the size, this was just a quick search to have a visual idea. I assume that all of the wheels posted are between 8-10 inches which the variation can backfire with the pics.
Another important factor is that the sidewall height is subjective to manufacturers depending on tire wear. Some will be a bit higher than others.
Also 35s can be rough on you disks and overall feel of the car.
I like new 3. You'll just have to deal with some hotdog size sidewalls when they wear and possibly go lower
Maybe a 245/40 for the front and whatever fits in the rear. I would concentrate more in the front because you can always tinker with the rear unlike the front.
We seem to have very similar ideas as far how low we want to be and what tire set ups are the best fit/looks for the car at a minimal drop.
With that said, I don’t think the front 245/40/18 size on option 3 will look good at all at your current drop. You would need to drop the ride height much lower for them look like they belong.
Here is my car at stock height when I was test fitting the my wheels with the current 245/40/18’s on 18x8.5 wheels.
They just look too small in my opinion even with a minor drop such as yours. Reason why I’ve got a set of 245/45’s ready to go on the wheels once I refinish them. Speaking of which I should probably update my own build thread. Anyway just my 2 cents.
That's kinda why I'm afraid to reduce the diameter even further.. at least in the front. Because my drop is only 0.75" and the gap will look bigger again if I make the front tires any smaller with option 2 or 3. Maybe I'm just gonna have to be forced to put 245/45/18's on the front and 275/40/18 on the rears, which is still SLIGHTLY smaller than stock diameters. The car will feel slower though because I'm losing a little bit of tire gearing. I really don't like the stock 3.7 gear and eventually I plan to put 4.08's in.
Is your chart in #1 based on calculated sidewall height or is a function of revs/mile? I would think the latter would be more accurate in terms of overall tread diameter. IOW, you can have two tires exactly the same size (225/50/18 for example) but different revs/mile.
I could feel a difference going from a 26.3inch tall tire to a 26.7inch (stock). I've since gone back to 26.7inch tall, mostly to keep the OEM tire height and speedo reading. You can mitigate the sluggishness by finding a lighter wheel/tire combo. What's on the car currently?
This is an 18x9.5+30 with a 275/40R18 all around. 18 inch tires tend to be less expensive (and have better options) than 19s, although the selection problems are becoming less as cars move towards larger wheels.
I could feel a difference going from a 26.3inch tall tire to a 26.7inch (stock). I've since gone back to 26.7inch tall, mostly to keep the OEM tire height and speedo reading. You can mitigate the sluggishness by finding a lighter wheel/tire combo. What's on the car currently?
This is an 18x9.5+30 with a 275/40R18 all around. 18 inch tires tend to be less expensive (and have better options) than 19s, although the selection problems are becoming less as cars move towards larger wheels.
Your setup looks really nice! I currently have 18lb wheels on it already and pilot sport a/s 3+
The wheels are 18x8.5 +35 and 18x9.5 +38
I got some specs on the actual tires that I'm using instead of using a tire size calculator, and then I compared it to the specs of the tires I'll be purchasing next time (Michelin Pilot Sport A/S 4) so I can get more accurate measurements
Here's what it looks like:
Soooo judging from these specific tires, I really don't want to use the 275/35 in the rear because it's way too small, like one of you mentioned earlier!
That leaves me with upsizing to the 275/40 option or going with the 265/40 which is in the middle. I am really liking the 265/40 option and it's not really much thinner in tread width than the 275/40!
As for the fronts, I'm actually leaning toward the 255/40. I know it's not as big of a stagger as stock specs, BUT will that matter very much? I don't understand the dynamics behind a staggered setup very much and how it relates to handling etc. Looking at the section and tread width, it's definitely smaller than the 265/40 though, so it's still staggered a bit.
The 245/45 option for the front is a bit smaller in section and tread width, with a larger diameter. How would this impact my ride quality, handling, and steering feel compared to the 255/40 up front?
Once again, I appreciate all of the feedback! I love brainstorming about these things.
Note, the rpm (revs/mile) is all encompassing, it takes into account wheel diameter, sidewall height, tread thickness, etc.
You can put this to a test by accurately measuring your current wheel diameter and comparing it to diameter based on published spec for that tire/size combo.
