Tire size advice

[Lost]

I am a total wheel/tire purchasing newb. I've never purchased aftermarket wheels for any of my vehicles. So I'm looking for some advice for tires. I've looked at all the fitment/size calculators on the planet, but I really would like some real-world input from people that have done this stuff before.

I've picked out some 18x8 rims for my BRZ. Tirerack's web site is recommending 235/35 tires. I have some reservations about daily-driving 35 series tires and also curious if I need all that width. I like that this setup is slightly smaller diameter than stock, but that seems to be the biggest plus. I am not planning on tracking or autocrossing.

I started looking at some 225/40's and while those are a touch bigger in diameter (~.5"), it's a bit easier to get some tires that save a pound or so over the 235's. Plus, I am expecting the 40 series to ride a bit better. This setup still gives me an inch over the wheel width. Is the weight savings going to help offset the extra height (performance-ly speaking & new wheels are lighter than stock as well)? I have seen a few pics of people running this setup, has it worked well for you?

Am I on the right track here? Am I totally off track? Any and all input is appreciated.

[MTeator]

You won't notice the difference in the height at all, I say go with the 225/40's. They'll be a pretty short sidewall even in that size, but better than the 35's.

At 60mph your speedo could be off by about 1mph. No biggie.

[rice_classic]

Tire manufacturers will have their tire specs for each tire listed. Look at the rolling diameter of the tires you're planning on and try to retain the factory rolling diameter.

OEM tire has a 24.7" diameter (according to Michelin).

[ZDan]

MUCH greater tire selection in 225/40-18 (Tire Rack shows 110) than in 235/35-18 (Tire Rack shows *2*). Slightly larger in diameter, but you'll never feel the 1.6% difference.
Weird, Tire Rack shows 235/35-18 as the "recommended" size when you're looking at wheels, but recommends 225/40-18 as the recommended size when looking at tires...

Personally, I'd sooner go with 17x8 wheels (cheaper, lighter weight, stock brakes won't look "lost" inside them) and 235/40-17 tires (cheaper, wider, same weight, slightly shorter than stock rather than slightly taller).

Anyway, choosing the best specific make/model tire for your specific wants/needs/usage is the most important thing. Very easy to buy crap tires, when EXCELLENT tires are available for short money. What are your priorities?
Tire life
Dry grip
wet grip
autoX or track usage
snow/ice usage a possibility
etc.

[Lost]

Yeah, the increased selection is another big plus for the 225/40's.

[MF_DEUCE]

Originally Posted by ZDan

What are your priorities?

Tire life
Dry grip
wet grip
autoX or track usage

ALL OF THE ABOVE

[mines13]

I went with 225/40-18, as stated they are pretty close to the stock tire height (.5" taller). The NT05 in this size which I have coming, is within a pound of the stock tire's weight.

[Mitch]

If you haven't purchased the wheels yet, I'd think long and hard about going with a 17x8. The tire selection is much, much better.

[Lost]

Originally Posted by Mitch

If you haven't purchased the wheels yet, I'd think long and hard about going with a 17x8. The tire selection is much, much better.

I haven't (I don't even have the car yet, but should come this month). 17's are still on the table, but aesthetically I prefer the 18's. So the final decision is still a month off probably, but trying to get my budget set.

[s2kdrew]

People please read the rim's width carefully!! We are talking 8" width rim and the suggested tire width would be 235 tire. If you install 225 then the tire will stretch (stretch tire look) and you will also loose the little extra height from 225/40. No matter what as soon as you upgrade to 18" there is no way the rolling diameter will still be the same as stock. If you really want 225/40/18, the proper size for the rim would be 18x7.5.

[ZDan]

Originally Posted by s2kdrew

People please read the rim's width carefully!! We are talking 8" width rim and the suggested tire width would be 235 tire.

Depends on aspect ratio. For sure 225 width is OK on 8" wide wheels for a broad range of wheel diameters (15", 16", 17", 18", 19") and aspect ratios (50, 45, 40, 35).

If you install 225 then the tire will stretch (stretch tire look) and you will also loose the little extra height from 225/40.

No you won't. The sidewall is not a perfectly rigid wall, it is designed to allow a pretty broad range of wheel widths for a given tire size without affecting diameter/rolling radius.
BTW, 8" is right in the middle of range, and is the "measuring rim width" for a 225/40-18 tire.

No matter what as soon as you upgrade to 18" there is no way the rolling diameter will still be the same as stock. If you really want 225/40/18, the proper size for the rim would be 18x7.5.

That would be a bit on the narrow side, but acceptable. 225/40-18 will fit fine on widths from 7.5" minimum to 9" max. 8" is the "best fit", but anything in that range = A-OK.

225/40-18 will be slightly taller than stock, 25.1" vs. 24.7", but no big deal, really, +1.6%. 215/40-18 is almost identical to stock diameter.

Personally, I prefer to run the minimum wheel diameter I can get away with, though. 18"s are generally heavier, with an even higher (relatively) polar moment of inertia, more expensive, and tires cost more as well.

[s2kdrew]

I am talking about the measure rim width. Not rim width range, go to Hankook USA website then you can see two different column for rim width. The measure rim width is ideal rim width. The rim width range means it could go on the these width. So I am not saying you are wrong on that part, but for performance and how long they would last. I would go with ideal width. That's why you never see an OE rim width is 8" wide and having 215/225 tires on. At least for what I have seen on the cars I worked at in the shop. From Japanese to European.

[s2kdrew]

And according to that website 225/45/17 measure rim width is 7.5". 235/245 tires measure rim width is 8". It would fit for sure, since 225/45/17 indicate could go on 8.5" rim too but the side wall won't flex the way they are suppose to. My friend also not listening to me at the end he is also regret on his setup too.

[ZDan]

Originally Posted by s2kdrew

And according to that website 225/45/17 measure rim width is 7.5".

Most manufacturers give a rim width range from 7" to 8.5" for a 225/45-17 (should always go with the specific tire make/model recommendation, they are usually consistent but can be different). 7.5" is the rim width used for measurement data for most 225/45-17. The 7" to 8.5" width range is *conservative*, so no worries whatsoever running a 225/45-17 with the widths in that range.

But that wasn't the tire size we were talking about. Here's what you said previously:

If you really want 225/40/18, the proper size for the rim would be 18x7.5.

Again, 7.5" is OK, but it is the minimum end of the recommended range of 7.5" to 9" for a 225/40-18 tire. If you really wanted to be anal about it and run the "measuring rim width", that would be 8".

235/245 tires measure rim width is 8".

NOT ALWAYS. It depends on the aspect ratio. For most 245/40-17 tires (similar to stock FR-S diameter), the measuring rim width is 8.5". Also for 235/40 tires, measuring rim width is 8.5".
for most 245/45 and 235/45, the measuring rim width is 8".

The lower the aspect ratio, the wider the rim you'll want to use for a given tire width.

It would fit for sure, since 225/45/17 indicate could go on 8.5" rim too but the side wall won't flex the way they are suppose to. My friend also not listening to me at the end he is also regret on his setup too.

In general, if you go with the wider end of the acceptable rim width range (or wider than that), you'll effectively get stiffer sidewalls than if you go with the narrow end of the rim width range. But this effect (within reason) will be smaller than the tire choice. I.e., a Hoosier R6/A6 of a given size on the narrowest rim will be stiffer than a Continental all-season tire of the same size on the widest recommended rim width.

But mainly, my point is that you are wrong in your assumptions about what rim widths are appropriate for lower-aspect ratio tires. Rim width range and measuring rim width for a 45-series tire of a given width are generally .5" narrower than for a 40-series.