with my set up i have now i have all three lights on SLIP, TCS, and the tire pressure sensor light. it looks like my old hatch in highschool

 

That is the exact same set up I used for 1.5 years with ZERO problems. Maybe it is the way you drive.

 

As long as your wheels are the same height, you will not have a problem with TCS. It your car has VDC, it might be a different story. But who needs VDC anyway?

 

looks like you have a series of problems going on. I think its all related to one thing that you have done to you car so tell me if im on the money or not. you went and took your stocks off and had some custom rims put on you ride right? this is what went wrong. The jerks who put your new rims on didnt remove your tire presure sensors from your stocks and inserted them into the new rims. the tps sensor are in the little valve that you use to put air into your tire. the 350's come with a custom valve that includes the sensors, so i hope you still have your stocks, for the sensors are still in them. Your other problem wit the tcs and slip are also related to your new fancy rims. because they are more than likely all the same size your on board computer thinks the car is sliding out of control. your stock tires are different sizes from the back vs. the front. front being smaller than the back tires. if your front and back tires are the same size the computer mis reads this as tire slippage. turn your tcs off when you first start you car and this will stop that slip light from coming on and the loss of power as well, but beware. doing this will take away what the tcs is built for wich is to help you keep control of your car if it starts to get away from you on a corner or wet road. reply!

 

i had 245/45 all around on the stock 17" rim. But mine is a base model, no VDC/TCS/etc.
I was running 245/40 all around on the stock 18" rim, no problems either.

 

yeah, most of that sounds true, the rest just makes my eyes hurt. i usually have to turn the tcs off before i go anywhere or it acts up like crazy. hopefully i wont get loose on an offramp any time soon.

 

SCC Tested project Z in some shoot out in a later issue, If I recall correctly, they said it was great on the skid pad, but felt dangerous at track speed. So much so, that they retired it from the competition when it started to rain.

 

I've been considering the "same size" approach for my next set of tires. I have a Touring with 18 X 8 wheels all around with 225/45s on front and 245/45s on the rear.

The tire size calculator at http://www.miata.net/garage/tirecalc.html helps put this in perspective. If I go from the stock 225/45s in the front to a 245/45 size all around it calculates that the diameter changes by 0.7 inches, circumference by 2.2 inches, and revs/mile from 777 to 756. (2.7% "slip")

I gotta believe that's no more significant than tire inflation variations and fluctuations during a daily temperature cycle. I haven't found any specs on the rotation sensors, but can't believe they could be that sensative.

 

TCS and VDC both use the the ABS wheel sensors for tire rotational speed and are quite sensitive.

As a reference, the stock 17s are even closer in size than the 18s with only 1.23" circumference difference between them so it's either really sensitive or the issue is blown out of proportion.

Please let us know how your all four the same experiment goes. Inquiring minds want to know.

Chris

 

Project Z was set up more for autocross than a road course. This means they had their REAR BAR set stiff to rotate the back end. That's why it was so scary at track speeds. Leave the sways stock and you'll be fine at high speeds with the same width tires front and rear. The Z has a staggered stock set-up to make the lawyers happy.

 

take it from a person who is running same all around, it is sensitive. i am running 20" all around so in my case the slip would be more sensitive. yours may not be as sensitive as mine but I do believe you will run into small slip issues when traviling at high speeds. Good luck.

 

What issues do you see with your 20s and at what speed do you start to see it?

 

I've been running the same size all around with no problem. Then again I always have TCS and VDC off. I think the Z is just an inherently unstable car due to poor weight distro, the rear feels much lighter than the front and under moderate braking at high speeds you can feel it break loose. I find the car feels more planted with a full tank of gas. I am going to try slightly taller (18") and wider wheels (9 or 9.5) all around and see how I like it.

 

The Z is unstable?
I don't think I have ever heard anyone call it unstable, at least not on dry pavement. I have not experienced the issues you describe even on harry mountain roads.

Chris

 

I bought the car pre-owned and the previous owner had put on the same size tire all the way around on my '03 Touring. I have NEVER head the VDC, TCS, or ABS act up. Not once! Not an any kind of driving. I was worried I would have issues, but I never have had any. After the first 2 months, I started turning the VDC off in dry weather anyway, but while getting used to the car (came from AWD for 9 years), I left it on and experienced no ill effects.

 

You don't get much better than a 53/47 weight distribution in a front engine rwd design.

 

I found the issue. It wasn't the sway, they said it was the tires.

 

I have an 03 Enthusiast with Kumho Ecstas mounted on the stock 17 inchers. The car feels scary under high speed braking (100mph +). I can feel the rear getting very loose when decelerating from high speeds and have experienced a couple of spins from trail braking. I've driven many sports cars and haven't had this issue under high speed conditions. Maybe my suspension has just loosened up a bit from use? Cause I don't remember this problem when I first purchased the vehicle.

 

But back to the original issue of running the same size all around:

I noticed when looking at the specs while shopping the net for new tires that tread depth for most are 10/32". The "same size" setup I'm considering increases the radius of the fronts by 0.3". I know the handling might be a bit different from the footprint point of view, but from the tire diameter aspect this would be like having very worn stock tires on the back and new stock ones on the front. That shouldn't mess with the sensors; I almost had that scenario when the dealer replaced my fronts for the cupping.

I'm gonna go with the experiment. Worst case is it doesn't behave, I switch back to stock fronts, and I've got two rear spares.

 

well we run a 19x9 all round no problems....just some extra oversteer that was fixed by sway bars