Mazda has a habit of supplying OEM tires in unusual sizes (215/50/17 Mazda6, 225/45/18 RX-8). Upon reviewing the specs for the BF Goodrich KDW-2 at tirerack, the tire is offered in the stock 225/45/18, as well as 235/40/18 and 245/40/18, the latter being closest in overall diameter to the stock size (25.9" stock vs. 25.7" for the 245/40/18). http://www.tirerack.com/tires/Spec.j...omCompare1=yes

Are there any disadvantages to going to the 245/40/18, other than an optimistic speedometer? Is it significant that the MINIMUM recommended wheel width for the 245/40/18 is 8 inches?

Along those lines, will the ODOMETER reading also be incorrect, showing more miles than actually traveled, ending the warranty earlier? I seem to recall a car dealer once telling me that there is a separate box recording miles driven, other than the display, to avoid odometer fraud. I don't know how the "box" could measure miles driven differently than the odometer, but it doesn't hurt to ask.

 

245s will fit fine on an eight inch wheel. If you drive a full 40,000 miles with the 245/40x18 tire showing a 1% odometer error, you would loose a whole 400 miles off of your warrenty. Up to you but I wouldn't sweat 400 miles.

 

I'm buying 245/40/18 KDW2's at COSTCO soon... Price is more than Tire Rack, but I get balancing, installation, lifetime rotation, and I think road hazard thrown in for a sweet deal.

Who cares about 400 miles - life is too short to not enjoy your 8.

 

Hey, it's a Mazda! I don't need no steenking warranty. :D

 

For your information, I e-mailed BF Goodrich regarding the weight of the BF Goodrich KDW-2 in 225/45/18. The answer is 22.51 lbs. They replied:

"Mitchell,

Regarding your email: I'm considering replacing the stock tires on my RX-8
manual with 225/45/18 g-Force T/A? KDW-2 new tread. How much do they weigh
in that size?

Thank you for your email Mitchell. The KDW in this size weighs 22.51 lbs.

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I am interested in what the advantages would be to change the tire width from 225 to 245. Besides the cosmetic value, would the performance increase?

Have you seen any tests of the same tire in different widths?

 

A search will turn up several threads on this subject... The short answer is yes it will increase grip to go to a larger size. And a 275 fits on an 8" rim too

If you are going for BFGs, go with the KD (no w)... Much grippier (is that a word?)

consider also the Kumho and Falken tires. Just as good (maybe better) for less money

 

For my needs, quicker acceleration is more important than greater grip, so I'll probably go with the 22.5 pound 225's, rather than the 26.3 pound 245's.
I'm sure it will handle just fine in the stock size.

 

Wow,,, almost 4 pounds is a lot. That probably makes it my choice as well, and puts the KDW above other tires I was also considering. I guess I will have to check the weight of all of them.

 

For us that live in the Pacific Northwest, we need the wet weather option for our tires, so the "W" is a must if I elect to go with this tire. But I still have not finalized my purchase yet....

 

Well, then the Toyo T1S is a pretty good all around tire, and it is usually lighter than some other brands...

...BTW, I live in Miami. You don't get much wetter (how many Hurricanes was that again?)

 

Thanks Alex - I'll look at the Toyo T1S also.

 

www.treadepot.com lists both the Toyo T1 and Toyo Proxes 4 at 24 lbs for 245/40/18. I have the Proxes 4 and am quite happy with them.

I combined the 245/40/18's with lighter Enkei 18x8 rims and ended up 3 or 4 lbs. lighter per corner than OE rims w/225 tires.

Regardless, my butt-dyno is too numb to detect any of this lightness of tiredom in normal driving conditions.

 

Toyo T1S is an excellent tire. My friend has an SLK with mods and he loves 'em. Only problem is he gets about 12k miles on a set, but I guess that's the trade-off.

 

I sure like the comments on the KDs on Tirerack and called BFGoodrich to get some weights on the following:

-------------------KD--------------KDW
225/45/18......22.5
225/40/18......24.56..............22.89

225/45/17......23.46..............23.77
245/40/17......25.31..............24.6

more food for thought, I'm suprised our 225/45/18 are the lightest of the bunch?

 

Ned M, do you find that the proxed 4 compared to the RE040's are:
1) the same handling
2) slightly worse handling
3) slightly better handling

I am trying to decide if all-season tires are ok for my non-winter use (I have Toyo Garitt HT's for the winter), or if I should go for pure summer tires (like the T1-S or KDW NT).

 

Go with the summer tires if you have winter tires. Summer tires will outperform all-seasons even in the wet, as long as the temp is above 40 or 50 degrees and there is enough tread to resist hydroplaning. The T1-Ss is a great three season tire (had 'em on my Miata) if you don't mind the soft turn-in.

No reason to compromise in the spring, summer and fall if you already have winter tires.