'04 G35 coupe 6MT
my current winter setup is separate FRD 17" rims with Blizzak LM-22's;
225/50/17 - Fronts and 235/50/17 - Rears.
My rear tires only need replacing.

I'm located up in Western Canada and am having a real problem trying to find a reasonable deal on a used pair of replacement LM-22's.
New pricing will cost me roughly $700 Cdn and about as much if I import from the US and pay all the taxes, duties, border charges, etc. etc.
I'm only going to have the car for another 3 months, but, I'm uncomfortable driving the car in the ice and snow here with my current rear tires.

I've located a pair of Blizzak LM-22's that I think can be bought for a reasonable price that are almost new (2500 miles wear).

Here is the problem: size is 235/45/17.
I've done the Miata calculator and it suggests it will induce a 5.1% speedo differential on the rear axle. My 17" winter fronts are virtually a perfect match for the 18" summer fronts.
Rear axle: [summer (245/45/18) - winter (235/45/17) ]
Rev/mi summer = 756; winter = 796

How big of an issue is this really? I won't consider it if I'm going to screw up the skid control or cause issues with the LSD or induce other problems.
TPMS isn't an issue because the sensors are on my summer wheels and I just monitor the pressures manually on the winter setup.
I am really tempted because it's been such a headache trying to find a decent pair of LM22's in the 235/50/17 size for anything close to a reasonable price.

I should also mention that I'm at the point now where I'm considering any brand of winter tire to put on the rear axle providing its either a 225/55/17 or 235/50/17 size. I realize mixing front and rear winter tires isn't ideal, but, I need the rear traction. I should also mention I do not drive the car hard and I'm considerably easier during winter time because of road conditions.

I'm hoping some of you people here, familiar with this issue, can give me some sound, thoughtful advice either for or against doing this, given my situation.
Thanks for your help.

 

I'll guess that you could just about get away with it.
I do know Nissan recommends only a 3% difference in circumference, but there must be some safety and error built in.
If it were me, I'd try it.
G/L
C.