18" CX-9 Wheels on CX-5 and Changing to Smaller Sidewall Tire?

What I don't know about tires would fill several books so I'm asking the smart people here for some help/ideas.

Backstory...2014 CX-5 Touring with stock OEM 17" wheels. Want to move up to 18" wheels. Found some 18" CX-9 wheels nearby that the owner will practically give away. Pretty sure the wheels are going to be okay on my CX-5 But...can I go to a slightly smaller sidewall size than the stock 65...maybe 55 or even 45 when I put tires on the CX-9 wheels? Just 'cause I'd like a little less sidewall height for looks and to get the tire diameter back close to the stock set up to keep speedo close to correct.

Am I able to do this or is it not a good idea? Thx for any info!
Bill

PS Just found out that the CX-9 wheels have 245/60r18 tires on them already. Slightly wider and almost as tall as my P225/65r17stock tires. Can I go 245/45r18 and be okay? I'm okay with a little harsher ride with the shorter sidewalls. I can literally bring the new wheels with tires home and slap them on the CX-5 to see how they look/perform. Will post pics.

Hey Bill, l guess I'll give you my 2 cents on this. First, to mirror what Mazda has done on their OE tires (P225/65R17 or P225/55R19) for an 18" wheel the choice would be P225/60R18. The 245/60R18 tires will be larger than OE and give a 3.7% speed error (60 mph indicated will be 62.2 mph). The 245/45R18 will be too small by 6.5% (60 mph will be 56.1 mph). If you want a 245 width, a 245/55r18 would be the closest to the OE size (0.3% difference).

One other thing I would watch for in any scenario is weight. If your not careful, going to a wider tire is going to add weight and you may lose a little bit of zoom from your zoom-zoom.

Hope this helps. Paul

P.S. I forgot, to check size numbers yourself try this site:
https://rimsntires.com/specspro.jsp

The 245/45R18 isn't going to be the best size tire to run on 18's for the CX-5. You want to think of tires and rims like two circles, one inside of the other. The outer circle is the tire diameter and the inner circle is the wheel diameter. You can change the inner circle diameter but you need to keep the outer circle as close to stock as possible which is 28.5" for the 225/65R17. A 245/55R18 is 28.6" which is acceptable. think of placing a quarter on the table then putting a dime on top of it in the center. The dime is the rim, the quarter is the tire. You can change the top coin (rim) to what ever you want within reason and not have an issue as long as the quarter remains. The dime would be 17" rims, a penny, 18" rims and a nickel 19" rims. Make sense?

Thanks for the replies!

I went and got the wheels today. Couldn't pass them up at that price. The tires look like the middle tread areas are worn more than the outer areas. Maybe over inflated and driven a lot that way? The tires are Yokohama YK580s. Pics...mostly to see the CX-9 18" wheels in relation to the CX-5 17" wheels...attached...I think/hope.

Understood about keeping the outer diameter close to stock to keep speedo accurate. I'm not concerned if I go with a little shorter sidewall and end up with a speedo that's off a little bit. We'll see how it works out when I buy tires. Also understand I will have more weight at each corner of the CX-5. The CX-9 wheels will probably be a temporary thing until I can get some decent lightweight wheels. 90% of my driving nowadays is in the city so the weight penalty won't be felt too much...I hope.

Two new questions:
1. The CX-9 wheels (off of a 2008 CX-9) have tires that are a 245 width. Can I use 225 width tires on the CX-9 wheels to match stock tire width? Maybe a 225/55 (or 45)R18? Not sure if a 225 width tire will work on the CX-9 wheels.

2. What happens to TPMS if I use the CX-9 wheels on a 2014 CX-5? Looks like the valves on the CX-9 wheels is for a TPMS system with a sensor inside the wheel. The 2014 CX-5 does not have sensors in the wheels as far as I know. So maybe the sensors can go away?

Thx so much for your thoughts and recommendations!
Bill

Hey Bill, good job getting the CX-9 wheels. As for your new questions:

1. Look at the inside of the wheel and on one of the spokes you should see something like this, 18X7J 50, cast into the wheel. That means an 18" dia., 7" width and a 50mm offset. A 225 wide tire will fit on a wheel from 6-8" wide, so as long as you're within that range you'll be okay. Personally I'd put a 225/60R18 on them.

2. Yes, with a '14 you don't need TPMS sensors so the old ones can go away and be replaced with normal valves.

Thx Paul!

Found the marking inside the wheel...18X7 1/2J. Curious...what does the J signify? With it being 7 1/2 wide can I still put 225 width tires on these wheels? I see that there are also 235 width tires on Tire Rack. Are those an option? Obviously 245 is okay because that's what are on the wheels right now.

Separate marking says offset 45. Isn't the stock 17" wheel on a CX-5 something like a 50 offset? I guess the 45 offset is not going to be a problem as long as I don't get a really wide tire?

Glad to know that the TPMS sensors are not needed.
Appreciate the educational info you all have provided!
Bill

The J is the bead profile (the area where the tire and wheel join together). J is by far the most common for cars today.

Since you have a 7-1/2" wide wheel and a 225 width tire will work on a wheel between 6 and 8", you will be fine. Personally I would put a 225/60R18 on them.

Yes, the offset for your OE wheel is 50. Offset is measure in millimeters (mm) so an offset of 45 is 5 mm less (0.2") so the wheel will stick out that much further. No big deal.

Happy to help. Paul

Bill, are you looking to get winter tires for the 18" rims? or run all seasons on the larger rims? If you are looking to get winter tires for the 18's I would recommend staying with the 225/60R18 which you can get the IceX3i's in that size, great winter tires.

If you are going to get all seasons on the 18's you should weight your options on what it is you want out of a tire. I would get some 245/55R18 tires for those rims in a high performance all season and then get winter tires for the stock 17's. There is some truth in the fact that the wider tire will be slightly heavier but I think the grip of a wider tire, 225mm vs 245mm is a welcome trade off to go with the wider size. You will have better corning and lateral control with the wider tire. if it were me I'd be looking at either the the General G-Maxx GS-05 or the Kumho Ecsta PA31 tires for the larger wheels. I think the 225 is a tad narrow for he CX-5. It was done because of weight and MPG results rather then handling. I prefer handling over mpg. It won't take a huge hit, maybe 1 mpg if even that.

the current tires on the 18" rim are the correct sidewall for your car. you can perhaps go down to 55 in the future but no more.

GJ-Molestor said:

the current tires on the 18" rim are the correct sidewall for your car. you can perhaps go down to 55 in the future but no more.

Click to expand...

You are wrong, once again! Just because a sidewall is 60 series does not mean that it's the correct sidewall for any given vehicle. Sidewalls are given as a ratio to the tread width. The 65 series sidewall on the stock 17's is 146.25mm or 65% of the 225 tread width of the tire. You cant just take a tire with the same sidewall ratio and apply to any car. What your saying is that if a tire has a 60 sidewall it will fit. a 255/60R17 will not be the right tire for the 17's that would be a sidewall of 165.75mm for the 255/60R17 which is way to large a tire, it's almost an inch larger in diameter and your speedo will be off by almost 3mph.

The correct tire size for an 18" wheel on the CX-5 is going to be 245/55R18 or 225/60R18. Both of those are .1mm difference in overall diameter which will not matter.

I have 18" wheels on mine with the 225/60's and they are absolutely fantastic. I wouldn't ever have 19's on a Mazda again. They ride much smoother and the speedo is exactly on. Love them!

Hi all!
Didn't realize this thread was still alive so I haven't been checking lately.

Ride92: Just looking to move up to an 18" wheel from the stock 17" wheel. I'm in S Texas so winter tires are not a factor. I simply don't like the stock wheels with their different sized spokes and I want to go to 18" so this is a chance to do that short term. Nicer wheels will be bought eventually. Agreed about maybe going wider than the stock 225 tires. Maybe a slight jump up to 235? The weight difference looks like 6 pounds heavier for the 235 tire...25 pounds for the 225 and 31 pounds for the 235. Might end up with 235/60R18.

shronemann: Glad the 18" wheels are good for you! What tires are you using?

I cleaned the "new" 18" wheels this afternoon and put them on the CX-5. All seems good and no rubbing or trouble with the 245 tires that are on the wheels. Not sure I can tell any difference in the ride feel but I've only driven about 8 miles so far. I need to double check tire pressures tomorrow. I like a couple of PSI over what Mazda recommends and I think the tires are currently right at spec. Might need to add just a couple of PSI...not enough to cause wear issues.

Hopefully the pictures (if I've added them correctly) will show the before and after...stock 17" wheels versus "new" 18" wheels. I can tell the difference but most folks wouldn't even notice.
Thx!
Bill