I needed your opinions on a little issue I ran into. I want to put 225/45 size tires on my stock TL-S rims. From what I was told, if I put that size (225/45) it can actually cause the speedometer to read incorrectly. What they mean by that is the speedometer will be off by 1 - 2 mph. Another issue is that I can not have my tires be wider than my rim. It may effect my handling and cornering. Are these true? Your opinions are greatly appreciated! Thanks

 

If you put on 225/45, yes ur speedometer will be off. NOT by 1-2 MPH, it's 1%-2% error, ur speed will be 2% higher then what you see on the speedometer. TLS rims are 17x6.5, you can fit 225 on them, 225 are wider then stock, so i think in that area you will get better handling.

 

Regarding the speedo, the only thing that can cause a discrepancy is changing the overall circumference of the tire. So, a number of things could do that: going to an 18 inch wheel might do it. Changing the aspect ratio of the tire could do it; that is, going from the stock tire's 50 aspect ratio to a 45 aspect ratio will make the tire have a smaller circumference, I believe.
I'm not exactly sure how a change in aspect ratio will change tire circumference, since I haven't done that math, but there will be an effect on the speedo.

Making the tire wider (from 215 to 225 or 245) will have no affect on the speedo.

regarding the wider tire, I don't necessarily think that putting a 245 tire on the stock TL-S rims will improve handling. In fact, it could make handling worse since that tire is too wide for our rims. See below:

Copied from previous thread:

I've always heard that the width of the tire should NOT exceed 1.25 times the wheel width. Or, conversely, the width of the wheel should be WITHIN 80% the width of the tire. There are obvious reasons for this, including sidewall support during hard cornering.

So, in the case of the TLS, we have a 215 mounted on a 6.5 inch wheel. According to the formula above, the maximum wheel width that should be mounted on a 6.5 inch wheel is: 6.5 inches * 1.25 = 8.125 inches * 25.4mm/inch = 206mm. So, the 215 tire actually exceeds this rule of thumb by just a little.

Ideally, I think the TL-S should have been developed with at least a 225, or possibly a 245 tire (see BMW 330: 245 on 8.0 wheels). This would mean the wheel needs to be at least 7 inches wide (for the 225), probably 7.5 or 8.0 (for the 245).

 

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

 

The correct sizes for the TLS are:

205/16/16 25.7 inches - what the original tl was designed for
215/50/17 25.5 inches - stock tls, close enough
225/50/17 25.9 inches - close enough
235/45/17 25.3 inches - close enough
245/45/17 25.7 inches - perfect

FWIW I have 245/45/17 on my stock wheels with NO difficulty. I think manufacturer recommendations for minimum wheel width are extremely conservative.

225/45/17 24.97 inches will cause the speedometer/odometer to be off by about 3% (ie. you will be going slower and not as far as u think you are)

 

245/45/17?? Man those are big. I was looking into getting a set of 19" rims and most post said no bigger than 225. Some said 235 but 245. that pretty big and still have no problems. nice. Where'd you get your info from?

 

The tire dealer had the same car and guaranteed that it would work.

I guess my own car is my info now

I am not lowered btw, that may be a factor why others dissuede you.

 

Thanks for the replies! I might just stick to the stock tire size. I was hoping to put 225/45 but i don't want my speedo to start reading wrong. I'm hoping to get them today.