I noticed that cars always seemed to pass me when I was going the speed limit on backroads (35mph) or highway (55-65mph). I just tried a GPS app on my phone and found that when the car read 35mph, I am actually going 29-30mph! At highway speeds when the car shows 65mph I am going 57mph. How is it so far off? I did get rims but they are only 18's and the OD of the tire (lo pro) is actually the exact same as the stock tires and rims. Is there anything I can do to adjust this? My miles will be going up quicker on the car than I am actually driving too, won't they?

 

Yup, the OD mileage will be going up. Was the speedo off prior to the wheel change? Your speedo is off more than 3% if you matched the 225/60-16 with 245/45-18. (2LS)

 

I'm not sure if it was off with the stock wheels, I never checked. My speed felt the same though. Like I said, the OD of both tires is almost exact.

My rims are Motegi MR107
http://www.sfxperformance.com/parts/...0728542342.htm

The tires are Falken Ziex ZE512 225/40ZR18

I actually want to get some bigger tires to help fill in the wheel well better.

 

225/40-18 is the wrong size technically, your speedo will be ~5.8% off. if your speedo was indicating 60MPH you would be actually travelling ~56.5mph.

with 245/45-18 the difference is only 0.2%

 

Oh, is it a different OD then that is doing this? Do you know if that size tire would fit on my existing rims? I'd like to get something that I can use during the winter here in MN too.

The first # is tire width and the second is sidewall height, correct?

 

first is tire with second is percentage of tire width which makes the sidewall height.

I have 245/45 on my 18x9.5 15mm offset

 

1LS (205/65-15 1990-'92) the 225/40-18 is ok
2LS (225/60-16) the 245/45-18 is correct.

 

You can always use this tool to calculate your tire size choices

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

Personally, my next set of tires, I will be going with a 225 65 16, and for winter I was thinking about a 215 70 16, not sure about rubbing yet, for the winter tire.

 

^ been using that link for years with great results!

 

So how can I tell if 245/45 will fit my rims? 245 is 20mm wider that 225, correct? I believe the rims are 8" wide.

 

you should be alright. you can always check the specs of the tire.

 

Any opinions on a good all season tire? My Falken's were pretty poor last winter. Price is of course important, same with longevity.

 

Just check this out... with stock and now your replacement... just input the information..

http://www.anycalculator.com/tiresize.htm

 

Our own wheels and brakes forum sponsored by Tire Rack
https://www.clublexus.com/forums/the...akes-forum-76/

Pick a category:
http://www.tirerack.com/tires/surveyresults/index.jsp

 

Zero survey results for 245/45/18.
Maybe I'll make a new thread in the Tire Rack section.
Thanks for all the help.