I plan on putting either the 215/45/17 or 215/40/17 tires on my 04 MCS stock 17" S-lite rims. I currently have factory run flats (only 2k miles) and stock suspension. After reading many post on tire size, I am still confused. Why would it be better to use one size over another?

I am thinking about using the new Azenis RT-615 tires in one of these sizes.
My driving is agressive street (not a daily driver) with a few club type autocross schools and hopefully track days this year.

Am I heading in the wright direction with this size tire choice and with the Azenis?

Thanks for the info. in advance.

 

I'll let someone else go into technical details, but basically it changes the tire height, which in turn can affect your speedometer, ABS system and possibly even handling. (atleast that's what I went through on my corvette )

 

Well, I put a 215/40-17 on my Kosei's and it did throw off the speedo a bit but the handling went up a notch. I say that about the handling but I went from a 215/45-17 Yoko AVS ES100 to a 215/40-17 Goodyear F1 GS D3


(Love the goodyears, don't like the price though)

No problems so far and technically you are over the load rating on a 40-17.

 

To make your decision easier, the 215/45/17 RT615s won't be available until thrid quarter..

 

I would suggest given your stock suspension and for street use-
Try the 215/45-17 tires if you can find them in the tire of your choice.
It's aggressive enough without being too harsh for daily driving. The 40 series tires are good for performance but have a lower load rating than recommended for a MINI (applies when you have 3 passengers).

If you feel that you don't drive much on the street and mostly use it for autocross or track then the 40 series tires will also work- mostly for one or two persons in your car. The 40 series tires can be a bit more expensive compared to the same tire in 45 series.

 

Based on the calibration of the stock performance runflats

Stock:
205/45-17: 60 mph on the speedometer

Aftermarket:
215/45-17: 59.1 mph on the speedometer
215/40-17: 61.2 mph on the speedometer

Note that there is a built-in 2-3 mpg exageration in speed on the stock tires.

Also, your ABS will not be affected by tire size as the system compares the difference in rotational rate among the tires, not the actual rotational rate compared with some absolute calibration.

Finally, if the condition of the roads in your area is anything like it is here in the Northeast, you may find the 45s will protect your rims better.

FWIW,

Theo

 

215/40-17 - performance choice
215/45-17 - comfort choice

Based on your application - I'd recommend 215/40-17

 

I have both and there is a major difference in comfort and side wall cushioning on the rims

If you don't care about a harsh ride, and want "track use" tires, go for the 40s, but you can use the 45s on the track as well.

 

According to the Falken Web site, both size tires have an 87 load rating