For some reason my rear tires still have at least 15-20k miles on them according to my mechanic, but my front ones need replacing soon. This isn't an alignment issue or anything like that, the tires are are worn evenly, just worn differently front and rear. Why is this?
If I want to replace my front tires only with a different brand is that okay or should I just replace all four at the same time?
What tires would you recommend for wet conditions? I am on some Toyos and they are great when its dry, but absolutely horrible when it rains.
My car also just hit 70k miles, should I replace the spark plugs?

 

I'm at 54K miles. I had to change my front tires twice:
Bridgestone Turanza (OEM) (25K miles worn out) -> Michelin A/S 3+ (50K worn out) (still had Turanza rears) -> Pirelli (cheap tires) (current)

Rears:
Bridgestone Turanza (OEM) (33K worn out) -> Michelin A/S 3+ (current / 54K worn out) - need to be replaced but still have them on.

I read this somewhere that these sports sedans (including 3 series and other cars in the class) front wears faster than rear. I've noticed that as well because my steel wire was showing on the front of my tires which forced me to replace them, they still handled good in wet conditions. My recommendation is just change the fronts for now, try to use the same tire brand / spec if you can. The cheap Pirellis I have on the front don't have as good as grip as my rears and it shows when doing hard driving. I changed them as needed, not all 4 together. If you do that, it's almost $1000 each time you change tires, I don't think that's necessary.

 

Without knowing what year, engine, and drivetrain you have it's a little hard to answer some of the questions you posed.
Assuming that you have some form of the V6 engine, then you don't need plugs yet...if you have the 4-cyl. turbo then the answer would be different.
If you have a RWD IS, then you can replace the front tires only...try to stick with the same category of tire as the rear...i.e. if the rears are all-season, then get all-seasons in the front
If the car is AWD, which I'm guessing not, then you want to have the front and rear tire diameters relatively the same...meaning you don't want almost worn out tires on one axle and brand new tires on the other axle...it could cause the AWD to function unexpectedly which could result in a driving issue.

 

If AWD, I'd say no, it's best to replace all of them especially if tread depth has more than a 2/32" difference across any two tires. RWD is more flexible since the front and rear wheels don't have the same level of sensitivity as AWD cars.

What tire pressure do you run?

 

I presently have Yokohama Avid Envigor 225/40R18 run flat tires on the front and Turanza EL400 255/35R18 run flat on the rear. Both all season tires, both run-flat tires. I believe this is the correct size for the F Sport.
Do I leave the mismatch brands or should I change them all.

 

Welcome to the forum!

Once the tires on the same axle are the same, then you're fine.
And since both axles have all season runflats, you're still fine.
Once the tires on either axle wear to the point of replacement, change all 4. And I say that only because runflats are heavy, expensive, and completely unnecessary on a car like this, so better to go back to all regular tires in whatever brand you want.

 

Are you sure the Turanza EL400 is a run-flat tire? I had those on my 2016 IS 300 when new, and they were not run-flat then.

 

Thank you arentz07 for the correction. It does appear they are not run-flat tires.

 

If you have run flats on the front and non-run flats on the rear then consider all the tires at once when a pair of them are worn out.

 

Sorry to dig up an old thread, but its the only one I could find pertaining to our model/year.

I'm running Michelin PS4S for spring/summer, and my rears are always bald long before the front. At present, the PS4S in the rear are totally bald, while front has 5/32nd evenly on both sides. This is after two seasons.

So basically, I can get 2 seasons from the rears, and 4 from the front, for any given new set of summers.

Thus in theory, I can continue to use the fronts for 2 more years, at which point all 4 will be bald.

Is it safe to just replace the rears? Obviously I would go with the PS4S again. This is for an AWD. I don't track the car or anything, so as far as I can tell, the fronts look great and should provide excellent warm-weather driving, even if the tread is half of new.

 

Short answer - Yes.