Tires

[T dawg]

I just joined and have a question about tires. I want to go up to 18 inch rims and know that the tire size I should run is 225/40. My question is could I run 225/45 and if so what would I have to be concerned about. I know the speedo would be off slightly and I'm ok with that. I'm trying to buy a used set of tires and rims on kijiji and many of the tires are 245/45 on 18's.

Thanks

 

[j3nsmz5]

Here's a reference for you http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=25#.

 

[T dawg]

Thanks. Lots of good info there. Sounds like the safe bet is to be patient and find the right size tire.

 

[Davicho]

I know all tires are not created equal. But I had that size 225/45-18 and I rubbed on full compression upfront and at rear. If you want to play it safe stick to the recommended size of 225/40-18

 

[MarkVII88]

I think to some extent, whether or not you get rubbing with 225/45/18 depends on the offset of your rims. Stock Mazda OEM rims in 16, 17 ,or 18 inches have +52mm offset I believe. Maybe the RX-8 rims have slightly less positive offset. Anyway, if your rims have less than +52mm offset, you may be able to run 225/45/18s without rubbing. Your speedo will only be off by about 2%, reading slightly slower than your actual speed.

 

[phunky.buddha]

I think to some extent, whether or not you get rubbing with 225/45/18 depends on the offset of your rims. Stock Mazda OEM rims in 16, 17 ,or 18 inches have +52mm offset I believe. Maybe the RX-8 rims have slightly less positive offset. Anyway, if your rims have less than +52mm offset, you may be able to run 225/45/18s without rubbing. Your speedo will only be off by about 2%, reading slightly slower than your actual speed.

I know all tires are not created equal. But I had that size 225/45-18 and I rubbed on full compression upfront and at rear. If you want to play it safe stick to the recommended size of 225/40-18

Exactly- offset matters a LOT. The rear has a 17mm lip that extends straight into the wheel well. I fit 235/45-17 tires on +55mm offset wheels with about 2mm to spare. Offset means EVERYTHING for tire fitment in the back. If you don't roll your fenders and you run an 18 at a non-Mazda friendly offset, you'll rub the lip and chew your sidewalls to hell. If you fold the lip all the way you in can gain another 10-15mm of space depending on how aggressive you are with the roller. The RX-8 wheels are 18x8 +50mm, so you're going to be pretty close to the lip depending on how wide your chosen tire manufacturer decided to actually make the tire from sidewall to sidewall.

As far as the larger diameter, I know at least one person on here is running a 26" tall tire setup (225/45-18 also I believe) with no rubbing. Here: http://www.mazdas247.com/forum/show...0-lift-kit-to-my-Mazda5&p=6374465#post6374465 . Everybody runs 215/50-17 (25.5" diameter) with no problems, and 26" just takes you a quarter inch farther into the wheelwell.

Now with my fenders where they are, I have room for 255s all around on my 5 if I get aggressive with the front camber- like an extra degree negative compared to where I am now. Maybe I'll rotate tires from the S2000 over to the 5.

 

[loosenut]

Exactly- offset matters a LOT. The rear has a 17mm lip that extends straight into the wheel well. I fit 235/45-17 tires on +55mm offset wheels with about 2mm to spare. Offset means EVERYTHING for tire fitment in the back. If you don't roll your fenders and you run an 18 at a non-Mazda friendly offset, you'll rub the lip and chew your sidewalls to hell. If you fold the lip all the way you in can gain another 10-15mm of space depending on how aggressive you are with the roller. The RX-8 wheels are 18x8 +50mm, so you're going to be pretty close to the lip depending on how wide your chosen tire manufacturer decided to actually make the tire from sidewall to sidewall.

Phunky is right, I have the above mentioned RX8 wheels with 235/40 and rubbed ever so slightly on the right rear when I had my rear camber set at -1.2 degrees. I have since changed the camber to -2 degrees for a track day and don't rub at all. I left the camber there and with my rear toe set to near 0 I don't have any tire wear issues.

 

[phunky.buddha]

Phunky is right, I have the above mentioned RX8 wheels with 235/40 and rubbed ever so slightly on the right rear when I had my rear camber set at -1.2 degrees. I have since changed the camber to -2 degrees for a track day and don't rub at all. I left the camber there and with my rear toe set to near 0 I don't have any tire wear issues.

My rear camber is -1.8 degrees right now, but I'm going to raise the car up a bit since it looks like the springs have settled some, so I'll probably end up back around -1.4 degrees rear and -1.0 degrees in front. Hopefully I'll be able to do my own alignments soon so I don't have to wait forever on the rack at NTB... then I can experiment all I want.