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Discussion Starter · #1 ·
Got an 09 CS with the base OE 18's, was hoping to fit those wheels with either MPSCs or R888s for track days but the sizes don't work out.

OE is 235/40 and 265/40.

Both MPSC and R888 come in 235/40 and 265/35.

Any concerns with the lower ratio in the rear, is that ok or any other thoughts or recommendations?

Thanks in advance!
 

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There is a Word Document in the files section:

Track Tire Size and Price Chart

It pretty much covers all your options, though last time I checked there were no 'track' tires in the stock 18" sizes. The doc gives diameters, so you can see that the percentage difference using non-standard tire sizes isn't that great if you choose carefully. I went with Nitto NT-01 tires.

18-235/40 Front
18-275/40 Rear

Have a look at your options and decide.

Chuck
 

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If you go with the MPSCs you're only choice in the rear is the 265/35. A lot of people, including me have run them with the 235/40 in front and it works great. No problems with ABS or PSM.

The Nitto NT01s and the Toyo R888s also come in a 275/40, which a lot of people also use with much success.

brad
 

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Discussion Starter · #4 ·
Great link Chuck, thanks!

Brad, good to hear on the 888's they are my first choice. So installing 275/40 on the stock 9" rim is fine for track use? (showing my ignorance on this topic)
 

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Yes - they'd be optimal on a 9.5" rim, but will work fine on a 9" rim - I see it all the time, and never seen a problem.

brad
 

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Great link Chuck, thanks!

Brad, good to hear on the 888's they are my first choice. So installing 275/40 on the stock 9" rim is fine for track use? (showing my ignorance on this topic)
Yes - they'd be optimal on a 9.5" rim, but will work fine on a 9" rim - I see it all the time, and never seen a problem.

brad
RQ_GT3,
Like Brad said above, the 275/40ZR18 Toyo Proxes R888 will mount to a 9" rim without issues, but if I may make a suggestion, I always check the manufacturer's web site before 'pulling the trigger' on tire purchases. Here is the Toyo page:

Toyo Proxes R888

If you click on the "SIZES AND SPECIFICATIONS" tab, and scroll down to 275/40ZR18, you will see that the "Approved Rim Width Range (inch)" is listed as:

9.0-9.5-11.0

The BOLD 9.5 indicates the ideal width rim, but the tire is approved for rims between the range of 9.0 to 11.0 inches.

As a side note, the 275/40-18 is nominally closer in size to the OE 265/40-18 than a 265/35-18 tire is. Here is a cool calculator to keep you from having to do maths:

Miata.net Tire Size Calculator

Nominally the 275/40-18 is 1.2% too big, and the 265/35-18 is 4.0% too small. I keep saying "nominally" because actual tire sizes may vary slightly from what their nominal size would indicate, for instance the 265/35-18 R888 is listed as 25.4" diameter whereas pure math yields 25.3", a small difference (and closer to OE) in this case, but still worth checking in my opinion, and once again a good reason to check the manufacturer's specs before 'pulling the trigger'.

And finally, Tire Rack unfortunately doesn't currently sell the Toyos, or the Nittos I bought, but keep them in mind for future purchases, they are a sponsor, and support this site by using the Planet-9 link to Tire Rack.

Best of luck with your tire purchase,
Chuck
 

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Discussion Starter · #7 · (Edited)
Wow, really appreciative to the time taken to educate me on this!

I'm staying away from slicks or Hoosiers because this is only a backup car that will not get trailered. Liked the MPSCs from the GT3 days but the R888s are great on my current track only Exige.

Chuck, after reading many links intrigued about the Nittos, so right now planning on just ordering 235/40 - 275/40 and putting them on the OEM rims for the time being.

Next adventure will be finding the right wheels but that is probably another thread.

Thanks again,

Ralph

P.s.: yes long time TireRack fan use them whenever possible and mind the links. A bit surprised that with their participation across brands and audiences they dont cater more to track type needs but I am sure they are smart and know what they are doing.
 

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Wow, really appreciative to the time taken to educate me on this!

I'm staying away from slicks or Hoosiers because this is only a backup car that will not get trailered. Liked the MPSCs from the GT3 days but the R888s are great on my current track only Exige.

Chuck, after reading many links intrigued about the Nittos, so right now planning on just ordering 235/40 - 275/40 and putting them on the OEM rims for the time being.

Next adventure will be finding the right wheels but that is probably another thread.

Thanks again,

Ralph

P.s.: yes long time TireRack fan use them whenever possible and mind the links. A bit surprised that with their participation across brands and audiences they dont cater more to track type needs but I am sure they are smart and know what they are doing.
I think you'll like the NT01s. I do. I use the 245/40/front, and 275/40/rear on 8.5/9.5" BBS RS-GT 18" wheels. It's a good set up, and works for me.

brad
 

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Discussion Starter · #9 ·
Hmm, just when I thought I knew what to do <g>

Nittos on the OEM wheels at 275/40 Rear

BUT 235 or 245 Front?
 

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Wow, really appreciative to the time taken to educate me on this!

I'm staying away from slicks or Hoosiers because this is only a backup car that will not get trailered. Liked the MPSCs from the GT3 days but the R888s are great on my current track only Exige.

Chuck, after reading many links intrigued about the Nittos, so right now planning on just ordering 235/40 - 275/40 and putting them on the OEM rims for the time being.

Next adventure will be finding the right wheels but that is probably another thread.

Thanks again,

Ralph

P.s.: yes long time TireRack fan use them whenever possible and mind the links. A bit surprised that with their participation across brands and audiences they dont cater more to track type needs but I am sure they are smart and know what they are doing.
Ralph,
My pleasure, absolutely. Geez, I am like a kid opening presents at Christmas whenever I think about new tires, even if they will belong to somebody else.

I have previously used Kumho Ecsta V700, Pirelli PZero Corsa, Michelin MPSC, and Nitto NT-01 tires at the track, on various vehicles. I don't have any first hand experience with the Toyo Proxes R888, but I've seen them run, and I haven't heard any complaints about them. I can give a fairly hearty recommendation for the Nittos, once you get the pressures dialed in they are pretty grippy, close to MPSC performance for a good bit less money (and closer to OE sizes).

You are right about aftermarket wheels being like opening a whole other can of worms, I just assumed you were using OE wheels. Plenty of time to think about wheel sizes as you wear through your new set of tires.

Cheers,
Chuck
 

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Hmm, just when I thought I knew what to do <g>

Nittos on the OEM wheels at 275/40 Rear

BUT 235 or 245 Front?
Good question. I went with the 235/40-18 fronts because I had never been on the track with this car before, and I wanted to play it safe and lean towards a little understeer while learning how it handled. The car does in fact understeer at the limit on tighter corners, and I will probably switch to 245/40-18 fronts when I am ready for a new set of tires.

The % change in sizes match well with the stock sizes, and I have read reports here of people using those sizes on OE wheels without any fitment issues.

Use your best judgment, but I'm leaning towards recommending the 245/40-18 size.

Cheers,
Chuck
 
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