Let's talk about tire sizes for 18" wheels

[gtman]

After a whole lot of research, I've decided to upgrade my stock 17" wheels to 18's. I think that size offers the best overall combination of looks, handling and price. Now the question is tire size. Tire Rack recommends 215/45-18 for 18" wheels. At 25.6" diameter it's very close to stock 25.5". But, IMO it's kind of narrow for an 8" wide wheel. Most members here are going with the wider 235/40-18. And I understand why. It's much wider and at 25.4" just slightly shorter than stock.

Here's my situation...

The roads around here are a potholed, frost heaved mess. The higher profile stock tires give me a decent ride (with mediocre handling). I'm just concerned that 235/40 might be a bit harsh. My idea is to go 225/45-18. That size would be wider than stock and have more sidewall than the 235/40. The only thing is, they would be 1/2" taller than stock. Great for filling the fender gap but my speedometer will read a couple mph slow.

Is anybody here running 225/45-18's? Your thoughts...

Sponsored

 

[jred721]

Glad to hear you're going for the 18" wheels! Did you pick which ones you're getting yet? As far as tire size goes, there will not be much difference in the sidewall of a 225 tire vs a 235 tire. As far as I know, 235 just means it's a wider tire but the sidewall stays pretty much the same. Go to this website: https://tiresize.com/calculator/ and you'll see that the sidewall is actually more on 235 tire rather than less. It shows you the comparison between the tires visually to give you a better idea too. 235 has 3.7" sidewall versus 3.54" sidewall on the 225 tire.

 

[gtman]

jred, your numbers are a bit off.

Stock has a 4.4" sidewall just to give you a base line.

Tire #1 in the pic (235/40-18) has a 3.7" sidewall like you said.

But, Tire #2 (225/45-18) has a 4.0" sidewall.

For comparison, the stock 215/50-17's are 25.5" and 8.5" wide.

 

[Overeazy]

245mm wide / 40% of 245mm tall / 18 inner diameter this is the best tire to run in my opinion.

the 2nd number is an aspect ratio so yes going wider also increases the sidewall height

 

[jred721]

jred, your numbers are a bit off.

Stock has a 4.4" sidewall just to give you a base line.

Tire #1 in the pic (235/40-18) has a 3.7" sidewall like you said.

But, Tire #2 (225/45-18) has a 4.0" sidewall.

For comparison, the stock 215/50-17's are 25.5" and 8.5" wide.

My bad! Accidentally put it in as 225/40/R18 instead of 225/45/R18 into the calculator. Yeah that makes sense then. But for what it's worth, I have a lot of potholes around where I live because of what salt did to our roads and the tires have been handling them great. The roads aren't that bad though but there are areas where it's horrible. If where you live is horrible in road condition though, then yeah stick with the 225 tires.

 

[TypeSiR]

I think rim width is also important. Not sure if you're going with 18x8 (same as Si wheels) or 18x8.5. Si tires are 235/40/18 for reference. I think for 18x8 rims, 235/40 is about perfect. In short, if your selected wheels are 8"-8.5" wide, go 235/40 or 245/40, whichever provides more selections on tirerack or discounttiredirect. The ride on 235/40/18 isn't bad at all, not nearly as cringe-worthy as 30 profile on the CTR. Are Si guys reporting tire or wheel damages?

 

[gtman]

I'm going 8". For me, it's about practicality as well as handling. The roads around here suck and I deal with snow from time to time (I use one tire year round). So too wide and too low won't be ideal for me.

 

[TypeSiR]

I'm going 8". For me, it's about practicality as well as handling. The roads around here suck and I deal with snow from time to time (I use one tire year round). So too wide and too low won't be ideal for me.

Totally understandable. For practicality and better traction in snow, I'd stick with 17x7 OE wheels and go one size wider and better tires (225/50/17). The EX-L wheels aren't much to look at but they're virtually indestructible.

 

[racer]

After a whole lot of research, I've decided to upgrade my stock 17" wheels to 18's. I think that size offers the best overall combination of looks, handling and price. Now the question is tire size. Tire Rack recommends 215/45-18 for 18" wheels. At 25.6" diameter it's very close to stock 25.5". But, IMO it's kind of narrow for an 8" wide wheel. Most members here are going with the wider 235/40-18. And I understand why. It's much wider and at 25.4" just slightly shorter than stock.

Here's my situation...

The roads around here are a potholed, frost heaved mess. The higher profile stock tires give me a decent ride (with mediocre handling). I'm just concerned that 235/40 might be a bit harsh. My idea is to go 225/45-18. That size would be wider than stock and have more sidewall than the 235/40. The only thing is, they would be 1/2" taller than stock. Great for filling the fender gap but my speedometer will read a couple mph slow.

Is anybody here running 225/45-18's? Your thoughts...

I have a stock Si and travel in the DMV area. There have been many times this later winter (early?) spring where potholes have caught me by suprise. The stock Si wheels with 235/40-18s sometimes make me feel like my teeth will fall out. Then, on a nice smooth curvy road? mmm wonderful!

Brand and construction can have as much impact as a slight aspect ratio change. Since a /45 would impact, imho, gearing negatively, I would not pursue that route.

Also, given the "used" value of your stock wheels, you might consider holding onto them and run "winter" tires on them. That would allow you to run 8 or 8.5 x 18s as your other set.

If really worried, try to meet up with someone with "stock" 18's from a Sport or Si or whatever has them these days and try it out to know for sure.

 

[gtman]

I have a stock Si and travel in the DMV area. There have been many times this later winter (early?) spring where potholes have caught me by suprise. The stock Si wheels with 235/40-18s sometimes make me feel like my teeth will fall out. Then, on a nice smooth curvy road? mmm wonderful!

Brand and construction can have as much impact as a slight aspect ratio change. Since a /45 would impact, imho, gearing negatively, I would not pursue that route.

Also, given the "used" value of your stock wheels, you might consider holding onto them and run "winter" tires on them. That would allow you to run 8 or 8.5 x 18s as your other set.

If really worried, try to meet up with someone with "stock" 18's from a Sport or Si or whatever has them these days and try it out to know for sure.

I definitely plan on keeping the stock wheels and might wind up putting dedicated snow tires on them. I wouldn't sell them either way for resale value reasons.

The reason I mentioned the 225/45/18's was for a bit more cushioning. Plus the slightly taller height would fill the wheel gap a bit. I have no plans to lower my ride. But it would throw my speedometer off by 2% slow.

Right now, my car is a tuned non-Si turbo. It comes with crappy Firestone FT140's in 215/50-17's on 7" wheels. I've added a UR front strut bar and will be installing an Si rear sway and UR rear cross member brace this spring.

My original plan was just to get grippier tires using the stock wheels.

Along the way, I realized that if I was to upgrade, 18's would look much better. I mostly just commute in my car but love having some fun on ramps and the occasional back road, too.

So for me and how I drive, the 9.5" wide, 40 profile tires aren't a necessity. Ultimately, I may just go for UHP tires, 18x7.5 rims and the conservative Tire Rack recommended 215/45-18 tires. I'll have the better looks and somewhat better handling with similar ride quality.

 

[HexSosa1]

I have been looking into wheels for the spring when winter is over and after so many different reads on forums and videos I think I will be going with 18X8 235/40/18 tires. From what I have researched this will be the best blend for me to preserve the speedo reading, fill the wheel well gap (planning on lowering it) and preserve comfort somewhat while adding more grip in accelerating, braking and cornering. Similar to gtman mine is a CVT sedan, not yet tuned, but plan on doing it soon. I have already ordered my Strut Tower Bar (Megan Racing), I have dedicated winter tires and was thinking of eventually mounting my winters on the stock 17" Touring rims (Currently on 17" steel wheels) but if I could sell them and get an ok price for them with the stock rubber (Driven for 2000km) I would prefer to do that as I don't mind the look of the black steel rims in winter (looks rugged to me anyways).

I am hoping to find a buyer for my stock wheels and tires and was thinking of asking for $800.00-$1000.00CDN which I think is fair.

 

[gtman]

Hex, since you're lowering, I think the slightly shorter but wider 235/40-18's are perfect for you. Me, I find the wheel gap on my sedan to be too large but won't lower because I have a bad back and bad roads and want a smooth ride. So getting slightly taller diameter tires that are grippier will probably solve my problem. I think 225/45-18 will work best for my situation. My speedo will read a bit less than 2% slow which I guess also means my gearing will be slightly lower on the highway for less rpm's.

 

[HexSosa1]

Hex, since you're lowering, I think the slightly shorter but wider 235/40-18's are perfect for you. Me, I find the wheel gap on my sedan to be too large but won't lower because I have a bad back and bad roads and want a smooth ride. So getting slightly taller diameter tires that are grippier will probably solve my problem. I think 225/45-18 will work best for my situation. My speedo will read a bit less than 2% slow which I guess also means my gearing will be slightly lower on the highway for less rpm's.

I guess that makes sense for your needs, and the whole 2% slower shouldn't be too much of an adjustment over time seeing as it is a daily driven vehicle more for quick zips here and there and not a track monster.

 

[BlueLdr]

I'm in the same boat, planning on getting 225/45s over 18x8s to minimize the road noise increase from 215/55r16s.
My question here is why everyone insists on keeping the same diameter to prevent speedo error, even if a different size would better suit your needs. Recalibrating the speedo is possible, obviously. Are there unwanted side effects from doing so? Is it overly difficult to have a dealer or shop perform the service, or to do it yourself? I'm genuinely curious if there's something I'm missing here.

 

[racer]

I've run with oversized and undersized years on various cars. A slight % is hardly noticable imho. heck, I've run with such a drop that the speedo was 10%= off at 60mph. Just do simple math.. its not hard.. I guess its just an OCD thing

Sponsored