2004 to 2020 Mazda 3 Forum and Mazdaspeed 3 Forums banner

Wheel fitment advice please?

1 reading
10K views 10 replies 3 participants last post by  arathol  
#1 ·
Hello everyone, first post so bear with me. I'm looking at getting some summer wheels/tires in a few months after winter. I've mainly been a truck/suv guy my whole life and haven't had to worry much about wheel fitment as much as tire size so I'm a tad lost on this.

I've looked at a couple websites and think I have a basic grasp on what the dimensions mean. With that said I'd like to ask the more knowledgeable about the wheels I'm looking at should clear.

I'm looking at some Motegi MR145 in a 18x8.5 with a +42mm offset. Would like to wrap them in a 235/40 tire. From what I can see the wheel will be 16mm(.6") closer to the suspension and I'd gain 22mm(.86") of width towards the fender.

I dont currently have access to my car as I'm out of town for work, but I assume these should fit? I think an 8" wide wheel would be ideal but that one isn't able in that size unfortunately.

Thanks for any input.
 
#2 ·
Assuming you have a Gen 4 car, the OEM rims are +45 offset.
Offset - the distance from the hub mounting face to the center of the rim.
Image

If you have OEM 205/60-16s, you will be increasing the tire width by 30mm overall, 15mm on each side (235mm - 205mm = 30mm, 30mm Ă· 2 =15mm). Change to a +42 offset and you move the wheel out by 3mm. So, you'll have a 12mm increase on the inside and an 18mm increase on the outside.
The same math applies to the larger rim and tire sizes.
 
#3 ·
You can put original and replacement wheel/tires at this calculator and see how they will fit. 16mm is significant but you might try a different offset to correct it.
Rim & Tire Size Calculator. Custom Offsets
 
#5 ·

Attachments

#6 ·
According the site Aegean posted its showing the same stats as will they fit.

 

Attachments

#7 ·
How did you arrive at those numbers? The first one has the tire 16.1mm wider on the inside and 22.1mm wider on the outside. Thats a 38.2mm increase in width. If you are going from a 205 to a 235, that is a total of 30mm increase. You can't have a 22mm increase on one side and a 16mm increase on the other.
The second one has the tire at 7mm closer but the rim 16mm closer? That would mean the rim is 9mm wider than the tire on each side.....which would indicate a tire that is too small for the rim. A 235 should fit an 8.5" rim just fine without stretching it 18mm.
Either the math on those sites is wrong or you are not understanding the tire and rim specifications.
What size tires are actually on your car?
 
#9 ·
How did you arrive at those numbers? The first one has the tire 16.1mm wider on the inside and 22.1mm wider on the outside. Thats a 38.2mm increase in width. If you are going from a 205 to a 235, that is a total of 30mm increase. You can't have a 22mm increase on one side and a 16mm increase on the other.
The second one has the tire at 7mm closer but the rim 16mm closer? That would mean the rim is 9mm wider than the tire on each side.....which would indicate a tire that is too small for the rim. A 235 should fit an 8.5" rim just fine without stretching it 18mm.
Either the math on those sites is wrong or you are not understanding the tire and rim specifications.
What size tires are actually on your car?
Because the stock rim is 7" wide which is a shade under 178mm, the wheel I'm looking at is 8.5" wide which is about 216mm.

I dont have access to my car right now, but they're the OEM wheels and tires for a turbo 3 hatch, which from googling appear to be a 215/45/18
 
#8 ·
I am not convinced you need 8.5” width. What about changing your existing 215/45R18 on 7jx18 ET45 to 235/40R18 on 7.5jx18 ET45?