The stock size tires for the 2003 M45 is 235 45 18. Will size 235 50 18 fit? Thank you.

ire32 wrote:The stock size tires for the 2003 M45 is 235 45 18. Will size 235 50 18 fit? Thank you.

Hi!

Yes, a 235/50-18 tire will fit. However, its rev/mile is off from stock, of course, so your speedo will be off a small amount.

So, I would recommend 245/45-18 as a better fit for your car - slightly less speedo error and still give you excellent performance! I use this size on my 2003 M45 and am very happy with it (the tire selection in this size is way better than 235/45-18 and a bit better than 235/50 too).

See my Basic Specifications sticky thread for available tires ... make sure to get at least 95 load index tires, by the way. Most of the 235/50-18 are above this, so that issue is at least good for the size ... but I would still consider 245/45-18 as a better fit.

Z

Thank you for the information. Will the 235/50 give a taller sidewall? Can I go with a 245/50?

You might want to look here:

http://www.miata.net/garage/tirecalc.html

ire32 wrote:Thank you for the information. Will the 235/50 give a taller sidewall? Can I go with a 245/50?

The 235/50 will definitely fit and it will give you a taller sidewall than a 235/45 and bit more than a 245/45. The 245/50 will also give you a yet taller sidewall (it should also fit, I would think), but the speedo error has now become a bit more off.

Here are approximate diameters (I tried to find a single tire model available in each of the following sizes to get a consistent comparison, but could not, so this information is necessarily approximate):

235/45-18 : 26.5" Bridgestone Turanza ER-33245/45-18 : 27.0" Goodyear Eagle F1 GS-D3235/50-18 : 27.3" Goodyear Eagle F1 GS-D3245/50-18 : 27.7" Goodyear Eagle F1 GS-D3

As you can see, the differences are relatively small, but will affect your speedometer reading and the handling characteristics of the car. Taller sidewalls will feel different on the road too.

So, my question to you: what are you trying to achieve per se? We might be able to offer better advice if we knew that. For example, if you are trying to fill out the wheel well a bit, then you may find that lowering the car (and also with larger diameter wheels for example) and using similar diameter tires to stock, may give you better results.

Z

SilverShadow wrote:You might want to look here:

http://www.miata.net/garage/tirecalc.html

This is a good starting point for sure. There are other good calculators like this on the web too, but this one seems better than most!

However, as you can tell from my tire spreadsheet in the Basic Specifications sticky thread in this forum, the actual results will vary a bit for the "same tire size"! The tire manufacturer, the model, the sidewall stiffness, the tread and section widths all have an impact of the actual final dimensions of the tire.

Even the diameter is not a sufficient indicator for speedo error for example - the rolling diameter is different under load. The only way to get a good comparison to stock is to look at the actual manufacturer specs, particularly the revs/mile info.

So, everybody's final check ought to be the actual tire specs (for example, the ones provided at Tire Rack for almost all the tires they sell).

Z