In talking to the local Nissan dealer they are suggesting that if I go 225/40 18 on the back, I should go 245/40 18 on the rear.

Essentially I would have "40s" all around instead of "45s".

Is this a good idea? Will the 40s have any negative effects on the various sysstems; e.g. VDC or handling. To say it another way is there a downside to going 40s?

Appreciate the help, guys.

 

I am not sure of the stock size there.

As long as the ouside diameter of each tire is within 3% of stock size, you should be ok.

Google the "miata tire calculator" and input the stock size vs. the sizes they are suggesting, that will help.

-ps - the gsd3 tires are great

 

Stock sizes are 225/45 18 and 245/45 18.

Yeah, it looks like the GSD3 are the cream of the crop; thats why I'm screwing around with this sizing issue.

 

I would go with 245/40 front, 245/45 rear. It still keeps the overall diameter stagger and will reduce understeer.

 

+1 Thats what I have on my track wheels now and it handles good, no VDC issues.

 

Wanna try 235-40-18front 255-40-18rear :lighter,less sidewall flex,but your speedo will be a bit off
No VDC-TCS problem, stagger=0.6

 

The only downside of going from 45 section tires to 40 section tires is that for every mile traveled, the wheels turn around 4% more revolutions than before, with a fractional impact on highway cruising mpg. The VDC and handling won't be affected.

 

With less tire sidewall you increase the chance you could damage/dent your wheel. It also will increase wheel gap and not look right, IMO.