I ran Falken Fk451s all around before with 265/35/18 fr and 285/35/18 rear. No problems whatsoever. I've gone thru my rears so I ordered new ones, REO50A pole positions measuring 285/35/18. I had the fronts (falkens) rotated as well by taking off the rim and swapping to the other side. First off I noticed WAY more body roll with alot less responsiveness which I'm guessing is caused by softer sidewalls on the pole positions. I'd be doing 60 and every input of the steering wheel would instantly make car react as expected, but now the car feels really sloppy, swaying madly. To make matters worse, when going around ramps the VDC kicks in which really freaks me out, actually pisses me off cause I spent an **** load on these damn tires.

I used the following tire size calculator:
http://www.miata.net/garage/tirecalc.html

I tried to maintain the same difference in tire size from OEM to new and front to rear.

REAR 245/45/18 -> 285/35/18 so .8" smaller now
FRNT 225/45/18 -> 265/35/18 so .9" smaller now

I know the new tires are alot shorter than OEM but the differences between them (front to rear) are minimal or am I forgetting something.

Did the fact that I have brand new tires at back and 50% tread up front coupled with different tires altogether cause my VDC to go off? Doesn't make sense to me.

BTW, after driving on the Bridgestone Potenza REO50s for a couple days I have to say I prefer the overall feel of the MUCH INFERIOR Falken FK451s. I will admit that the straight line grip is better thou with the Bridgestones. I guess I have to get some sway bars to compensate.

I am having bad luck with my 350 as of late

 

A 14 mm difference should be perfect with VDC.

 

The wider tire like the grab the road a bit , same thing with mine and 275's in the back. When you add a lot of extra width, cars can do some wierd things.

 

You shouldn't be having VDC problems with the sizes you are running. Keep in mind that new tires need to be broken in. They come from the factory coated with a release agent that must be worn off before they are "sticky". They can be quite slippery when new.

 

VDC...what the hell is that?? Oh wait that's right i drive a base model : (

 

If you hardwire the navigation system to VDC will it drive the car for you? That’s what I want to know.

 

Did you get the nismo LSD at least for your base.

 

How many miles on the new tires? They might still need some break-in time.

 

What's the tire pressure if there ofer inflated you get a real floaty feeling.

 

REALLY? Over inflation will cause them to get floaty? I have 39-40 PSI in the rear , the pole positions. I thought getting some more air in them might tighten them up a bit

 

i run 34psi in all 4.

 

No, if anything, back the pressure down to 33-34 PSI (recommended is 35). +1 on breaking them in more. If you're over-inflated, they'll just slip out from under you easier, hence VDC kicking in...

 

Try lowering the air pressure to 34-35. When I first got my RE050A's put on I was disappointed but knew it would take a few hundred miles to break in, There are oils and such in the rubber that needs to be "activated" by driving to really set the compound and it may take two tanks of gas to do it. I'm now very content with my RE050A's.

 

Overinflation will definitely reduce the contact patch and make them even more slippery.

Did you run high pressures in the Falkens?

 

Yes I did, close to 40 PSI, even though they were alot less grippy, they were very predictable. In comparison to the current tires it felt like I had sway bars. On onramps the car shifts that extra little bit which feels as though the *** is gonna go. Leaves me with sorta feeling.

Thanks alot guys for the advice on the pressure, def am lowering to 34 psi. I hope this helps. Will test it out and def give feedback.

Is the sidewall known to be soft on the polepositions?


Oh to add... My sh!tty luck hasn't been stricktly with the Z, I was informed today that I will no longer have a job as my shop is shutting down . Damn that China!!

 

Reading your/this thread, I believe that I may share your experience (but, who knows). My message is not meant as an answer or a solution, but only to provide some information (based upon my personal experience) that may or not be helpful.

My configuration:
2003 Performance Model (and thus VDC).
Stock 18x8" wheels

I did have the "feathering" problem, and Nissan replaced my fronts (Bridgestone Potenza RE040 125/45-18) with new front tires. And, that was with an alignment after my dealership did the Nissan-specified recalibration on their alignment equipment. I waited as long as I could and still remain inside the tire warranty for my Bridgestones (my concern was the problem was not fixed) before replacing my Potenza RE040 fronts. So, my front Bridgestones are fairly new (under 8K miles).

My rears were worn out, so I replaced these with Goodyear Eagle F1 GS-D3 245/45-18" tires. I experienced the same handling you notice with your new tire installation: The very stiff sidewalls on my Bridgestone Potenza RE040 fronts (similar to your Falken Fk451's) running with the soft sidewall flex on the Eagle F1 GS-D3 rears (similar to your new REO50A's) was a little disconcerting. Generally the handling was acceptable, but quick lane changes and even wide and fast directional changes (i.e., highway cloverleafs) was "quirky." And, I even noticed this when driving straight at high speed. I felt as though the backend was too "wiggly."

My thought was that because the Goodyears have a softer sidewall flex than the the Bridgestones, I could correct this by jacking up the psi in the rear Goodyears to 40 psi (I was running 35 psi in the front Bridgestones). This did not work at all, and in fact introduced a new problem (my VDC started acting erractically). Dropping the pressure in the rears so that I was running the same psi in all tires corrected the VDC problem. I suspect that increasing the psi in my softer-sidewalled Goodyears may have slightly increased the overall diameter of this tire, causing a problem with my VDC. Another theory (a complete guess) is that I changed the tire's "surface-contact-area" by doing an "over-inflation." Who knows? I am guessing here.

So at his point I had to know what was going on here. I mounted 245/40-18" Goodyear Eagle F1 GS-D3 (the only size in the F1 GS-D3 series that closely matches OEM 225/45-18") to see what happens when sidewall flex and other tire characteristics are matched with such a great handling car (the Z). And, I do have all four tires with the same psi. The result is absolutely fantastic. Running Goodyear Eagle F1 GS-D3 on all four corners (mine are 245/40-18" fronts and 245/45-18" rears) provides great handling. The "wiggly" rear-end fault I experienced with OEM Bridgestones on the front and the Eagle's on the rears is gone.

Here are my thoughts, based upon my very unscientific sample (my one/single case is hardly statistically valid):

1) When running different brands (or more significantly, different types of tires), you should try to match the tire's characteristics as closely as possible (e.g., sidewall flex, tread design, etc.).

2) You should use the same psi on all four tires.

--Spike

Well... shoot. Sorry to hear that. Many companies have been forced to shift focus because China has a huge available workforce with enormous potential. It is not unlike the Industrial Age that happened in the USA at the Turn of the Century (that would be the last Century, 1900). I think we can expect to see significant changes caused by the influence of a global economy.

 

Thanks for the help on the psi, I dropped it down to 34 and it made a huge difference. The car doesn't feel like as much of a slob when tossing it left to right. I am still experiencing VDC issues on bends/ramps though. VDC kicked in at 80 MPh on a ramp that I've taken at over 90 MPh without a problem on my old balding tires. I have put on close to 500 miles on these tires so they should be good to go. I guess the only thing to do is to change the fronts and hope for the best or just take it easy.

Man that VDC is scary.

 

And... VDC is "fussy." I know what you are saying after experiencing this.

I believe your decison to replace the fronts with tires that exactly match the rears is a wise choice when your car is equipped with VDC. It worked for me (same brand/type tire front to rear).

--Spike

 

I was so focused on the VDC problem you described, I completely missed this statement.

re> "I am still experiencing VDC issues on bends/ramps though. VDC kicked in at 80 MPh on a ramp that I've taken at over 90 MPh without a problem on my old balding tires."

90 mph on a ramp... with balding tires?! Obviously, it wasn't raining, or you would be dead or at least reporting another Z "crash story."

VDC is designed and tested to keep you safe within normal driving range/speed (1-75mph) running OEM stock tires and wheels. Above this speed, you should turn VDC off. VDC was never meant for high-speed driving (80 mph or above).

--Spike

 

When I say ramps, I'm not talking about the 270 deg loops, on the specific ramp I'm talking about I wasn't even pushing the car. I'm not sure what the posted limit is (most cars do about 50-55) but it is a decently long smooth bend.

And yes, no rain. You can bet your a$$ that my crash story will be caused by torrential downpour with gale force winds though.