REAR TIRE WINTER RUBBER OE SPECS

[xugo1kpr]

Stock OE Specs for rear G37S call for 245/40/19 summer rubber. I just had Blizzaks put on my G37S, but they put on 245/45/19s. Will this mess up my mileage or have any other adverse consequences?

[Kendahl]

As you already know, the correct size is 245/40-19. According to Bridgestone's web site, the 45 series tire will have a 3.3% larger diameter. This will marginally reduce acceleration and make your speedometer read low. At an indicated 60 mph, you will actually be going 62 mph. It will also raise the back end of your car about half an inch.

Bridgestone makes Blizzaks in both sizes. Either your dealer didn't pay attention or they had some 45 series tires to get rid of. You will have to decide if a 3.3% difference is big enough to return them and insist on the proper size.

[xugo1kpr]

Thanks for the info. How does that impact the odometer, as the computer is programmed to measure mileage from the rotation of 245/40/19 tire? We "tested" the mileage last night on the highway via mile markers, and 1 mile driven appeared to equal 1 mile on the odometer.

[Kendahl]

The bigger tires will result in a 3.3% lower odometer reading over a given distance. This is only a third of a mile in 10 miles. Since the trip odometer only reads down to tenths, you would need a rather long test (50 to 100 miles) to get a good measurement.

You should also be aware that highway mile markers may not be exactly one mile apart. Sometimes, that would require placing them in the middle of a ramp or on a bridge. Then, they are put in the best available location. That's fine for general purposes but not for a quantitative distance measurement.

If 45 series tires were your only option, you could get by with them. The best argument for taking them back is that the correct size is available and should have been installed to begin with. Why should you make do with the tire dealer's mistake?

[Q45tech]

Unfortunately different brand or even model tires are not uniform inthat a size is only an approximation.

All that counts is the as mounted with vehicle weight on the tires ...loaded radius.

[xugo1kpr]

Understood, but both the performance and winter tires are Bridgestone brand, so I would think the overall OD would be different from the OE 245/40 than the winter tires' 245/45.

[RedG37SNC]

Tirerack recommneds a 225 width all around judging by the site tool. Also wouldn't you want thinner tires to better cut through the snow.. seems to make sense.

[Kendahl]

Tirerack recommneds a 225 width all around

Not all G37s come with the same size tires. The base model has 225/50-18s all round. The Sport model has 225/45-19s in front and 245/40-19s in back. The 19 inchers are optional on the Journey. I suspect the tire dealer missed the change in aspect ratio from front to back.